gmw.conservation.ca.gov...jun 09, 1994 · i i i i i i i i i i i i i i i i i i i table of contents...

I I I I I I I I I I I I I I I I I I I

GARY S_ R.ASlVIUSSEN & ASSOCIATES, INC. IENWNEERIN(;GFUWGY

1B11 COMMERCENTE~ WF;ST • SAN BERNARDINO. CALIFORNIA 92408 • (909) 888-2422 • FAX (909) 886-6806

SUBSURFACE ENGINEERING GEOLOGY INVESTIGATION

EL RANCHO VERDE COUNTRY CLUB APPROXIMATELY 260 ACRES

RIALTO, CALIFORNIA

June 9, 1994

Project No. 3156.l

Prepared For

Nitto America Co., Ltd. 1950 Sawtelle Blvd., #305

Los Angeles, California 90025


TABLE OF CONTENTS

EXECUTIVE SUMMARY •••. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 3

SITE DESCRIPTION • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7

SITE INVESTIGATION ••••••••••••••••••••••••• , •••• , •••• , , • • • • 8

GENERAL SITE GEOLOGY •••••• , •••• , , ••• , , ••••• , •••• , •••••• , • • 11

SUMMARY OF INFORMATION FROM PREVIOUS INVESTIGATIONS • • • • • • • • • 13 Subsurface Investigations .•.....•...•. , .....•............ , . 13 Magnetometer Traverses •............ , ••...•.•.......•. , . . 16

SUMMARY OF INFORMATION FROM CURRENT INVESTIGATION . , •••••. , • 16 Subsurface Stratigraphy ..........•.............••... , . . . . 16 Faulting and Associated Features , •... , .••.. , •.... , ..... , • . . . 19

Southeast of "Engineer's House" to Southeast End of Site .. , • . . . 19 "Engineer's House" Northwest to Golf Course . • . . . . . . . • . . . . . 22 Golf Course to Northwest of Clubhouse . . • • • . • . . . • . . . . . . . . . 24

GEOMETRY AND GEOMORPHOLOGY OF THE NORTHERN SAN JACINTO FAULT 25

SEISMIC SETTING ••• , ••••• , ••••••••••• , •••• , •••••• , •••••• , • • 27

SEISMIC HISTORY ••••••••••••• , , •••• , ••••• , , •••• , • • • • • • • • • • • 31

SEISMIC ANALYSIS •• , •••••••••••••••• , , ••••• , , •••• , •••••• , . • 34

SLOPE ST ABILITY . I t ••••• I •••• I ••••• I •••••• t •••••• t •••• I t • • • 36

GROUND WATER ..................................... , . .. . . • • .. 37

LIQUEFACTION , •••••• , ••••••••••••••••• , ••••• , , ••• , , •••••• , 39

SUBSIDENCE . . . . . . • • . . . . • . . . . . . . .. . . . . . .. .. . . . . . .. . . .. . . . . . . .. . . 41

FLOODING .... , ....• , .....• , . . .. . . • . . . . . .. . . . .. . .. .. . .. . . . . . . . . . • 42

SEICIIES . t ...... I I •••• I I •••••• t ........................ I • • • • 43

CORRELATION OF SURVEY DATA, TRENCH LOCATIONS AND THE RECOMMENDED RESTRICTED USE ZONE •••••••• , ••••• , • • • 43

CONCLUSIONS , ••••• , , •••• , •••••• , •••• , , ••••••••••••••••• , • 44

RECOMMENDATIONS , ••• , , •••• , • , •••••••••• , •••••• , •••• , • , • • • 47

G.ARY S. RASMUSSEl'-1 & A$SOC:.::1ATX:$

I_

I I I I I I I I I I I I I I I I I I

GARY s_ .RASMUSSEN & ASSOCIA'l'ES, INC./ J.Nl;/NH81.W; (;l!U/,(l(;r

1811 COMMi::.RCENIER WEST • SAN BERNARDINO, CAL.IFORNIA 92408 ... (909) 888-2422 • FAX (909) aaa~oauti

June 9, 1994

Nitto America Co., Ltd. Project No. 3156.1 1950 Sawtelle Blvd., 11305 Los Angeles, California 90025

Attention: Kenneth Sakal

Subject: Subsurface Engineering Geology Investigation of the El Rancho Verde County Club, Approximately 260 Acres, Northeast of Riverside Avenue and Country Club Drive, Rialto, California.

References: Engineering Geology Investigation and Geologic Update, El Rancho Verde Country Club Property, Riverside Avenue and Country Club Drive, Rialto, California, Our Report Dated January 5, 1993, Project No. 3156.

Engineering Geology Investigation of Tentative Tract 11408, Northeast of Riverside Avenue and Southeast of El Rancho Verde Country Club, Rialto, California, Our Report Dated August 25, 1982, Project No. 1825.

Engineering Geology Investigation of Tentative Tract I 0244, Northeast of Riverside Avenue and Immediately Southeast of El Rancho Verde Country Club, Rialto, California, Our Report Dated August 26, 1982, Project No. 1830.

In accordance with your request, we have conducted a subsurface engineering geology

investigation of the El Rancho Verde Country Club located in Rialto, California. This

report will supersede all previous geologic reports of this site by our firm. We

understand that the site will be developed with single-famlly residences in the

southeastern half of the site, a new club house in the northwest-central portion of the

site, and that the existing golf course wlll be redesigned and partially relocated.

The entire site lies within an Alquist-Prlolo Earthquake Fault Zone designated by the

State of California to include traces of suspected active faulting associated with the San

Jacinto fault zone. Three previous subsurface engineering geology investigations by our

firm (Rasmussen, February 29, 1980, August 25, 1982, and August 26, 1982) and a

geologic update (January 5, 1993) were conducted on, or adjacent to, the site. The

purpose of this investigation was to extend the subsurface coverage of the fault zone


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INDEX MAP Gary S. Rasmussen & Associates, Inc.

Nitto America co. - El Rancho Verde Country Club Ria I to, California

Legend

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.·· Fault; dashed where approx., r··· dotted where buried.

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CDMG Base Map: I" = 2000' scale Alquist-Priolo Special Studies Zone Map

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Nitto America Co., Ltd. June 9, 1994

El Rancho Verde Country Club Project No. 3156.1

through the site In order to-provide a recommended restricted use zone for placement

of the new clubhouse and proposed single-family residences. An undated, 200-scale

topographic map, provided by Church Engineering, and undated 200-scale plots of the

trench survey data, also prepared by Church Engineering, were used Jn our investigation.

The approximate location of the site is shown on the index map on page 2.

EXECUTIVE SUMMARY

A subsurface engineering geology investigation of the El Rancho Verde County Club,

located in Rialto, California, was conducted in order to extend the subsurface coverage

of the fault zone from previous Investigations (Rasmussen, February 29, 1980; August 23,

1982; August 26, 1982) through the site in order to provide a recommended restricted use

zone for placement of human occupancy structures. The entire site lies within an

Alquist-Priolo Earthquake Fault Zone designated by the State of California to include

traces of suspected active faulting associated with the San Jacinto fault zone.

Our investigation consisted of background research and review, Including analysis of

vertical and oblique stereoscopic aerial photographs, Including oblique, low sun angle,

stereoscopic aerial photographs flown as part of this investigation, and oblique, infrared

aerial photographs flown by this firm in July of 1982. Pertinent published and

unpublished geologic literature and maps were also reviewed, including reports in our

files on previous investigations conducted on or adjacent to the site. A geologic field

reconnaissance and geologic mapping of the site and surrounding area was conducted on

November 4, 1992.

Subsurface investigations of the site and adjacent areas were conducted in September,

1979 (Rasmussen, February 29, 1980), in July and August of 1982 (Rasmussen, August 25

and 26, 1982), and from September, 1993, through March, 1994 (this investigation).

Faulting where found In the field was flagged and the lath locations surveyed. A total

3



El Rancho Verde Country Club Project No. 3156. l

of 33 trenches totaling 6, 741 feet of exposure were excavated during the different

subsurface investigations which have been performed on or adjacent to the site.

Twenty-three trenches, totaling 3,600 feet of exposure, were excavated during this

investigation. Numerous utilities were encountered during our trenching and caused

substantial delays due to mislocation or lack of Identification by the utility companies

and/or a decrease In the speed of excavation of the trenches due to the utlllty crossings.

The trenches from this subsurface Investigation were backfilled and wheel rolled In

October, 1993, and in March, 1994, but were not compacted.

Previous mapping of the site (Dutcher and Garrett, 1963; Morton, 1974, 1978; Miller,

1979; Morton and Matti, 1987) has shown the northern San Jacinto fault on the site as

a single, straight, northwest-trending trace located at either the base of the Rialto

bench or traversing through the center of the slte, or as several northwest-trending

splays which connect with northwest-trending faults within the San Gabriel Mountains.

Many geologists have postulated that the San Jacinto fault steps northeast In this

vicinity Jn order to transfer motion to the Glen Helen fault and ultimately to the San

Andreas fault. However, the northern San Jacinto fault steps westerly on this site. A

N20E, apparent left-stepping scarp ls located south of the southeast boundary of the

site. This scarp may be a fault which acts to transfer motion northwards from the San

Jacinto fault to the Glen Helen fault or some intermediate fault.

The extreme complexity of the San Jacinto fault on the site and its associated wlde zone

of faulting required the extensive trenching which occurred during our investigations.

Active or potentially active faulting was found in I 3 of the 23 trenches excavated on the

site during this investigation and In 4 of the 6 trenches excavated on the site during two

of our previous subsurface investigations (Rasmussen, August 25 and 26, 1982). The San

Jacinto fault trends almost due north (N5E to NlOW) as lt approaches the southeastern

property line. Approximately 350 feet northwest of the southeast corner of the site, the

fault steps more westerly and is characterized by a series of left-stepping en echelon

4


Nitto America co., Ltd. June 9, 1994


faults trending between NlOW and N12W, which together form an overall trend of N30W.

This zone of en echelon faults is accompanied by a wide zone of faulting and is

characterized by multiple fault scarps.

Faulting at the base of the upper or westernmost scarp along the main trace of the San

Jacinto fault triggered gravity sliding, slope !allure and secondary faulting In the upper

portion of the scarp. These failures are characteristic of the westernmost scarp from

the southeastern corner of the site to just southeast of the "engineer's house". The

fallure planes or secondary faults merge with the main San Jacinto fault at relatively

shallow depths. Displacements to within less than 6 inches of the ground surface were

found In the southeastern portion of the site.

At the "engineer's house" the fault steps westerly to a trend of N52W. A 2 to 4-foot

high, northeast-facing fault scarp is visible from the "engineer's house" northwest for

a distance of approximately 950 feet. The scarp dies out and the fault steps westerly

again to a trend of N65W. Where the scarp dies out, the geometry and appearance of

the main trace of the San Jacinto fault also changes.

Faulting still dips to the northeast but the dips are steeper and the zone narrower than

encountered in the southeast portion of the site. The uppermost Holocene unit is only

offset by a few Inches versus several feet, as observed In trenches In the southeastern

portion of the site. Where the fault enters the existing golf course, only a faint linear

trough ls visible evidence of faulting on aerial photographs flown in 1930. The zone of

faulting increases in width and becomes more diffuse northwest of where the scarp dies

out. The fault appears to offset early to mid~Holocene materials less than 6 Inches and

does not appear to offset any of the younger (late Holocene) overlying units. This

implies that displacement along the San Jacinto fault may be dying out or decreasing

on the golf course.

5

GARY $ RASMUSSEN&, 49-H:.30C:;!A"l'E..:S




The main San Jacinto fault steps west again from a trend of N65W, southeast of the

existing main clubhouse, to a trend of N79W to N81 W, northwest of the clubhouse. The

"hill" occupied by the clubhouse and associated facilities appears to be bounded by an

altered southwest-facing fault scarp. Faulting encountered In a trench located

northwest of the clubhouse office was found associated with this altered scarp. Faulting

has offset early to mid-Holocene materials by about 1 foot. The uppermost subunit in

the early to mid-Holocene unit did not appear to be offset by faulting In this trench.

However, the upper portion of the unit has been altered by grading and placement of

artificial fill and no In-place later Holocene materials were present. Therefore, the

presence or absence of faulting in the most recent materials could not be determined

from this trench. Trenching was not conducted farther northwest on the site.

We have altered and extended the original restricted use zone recommended in our

previous reports (Rasmussen, August 25 and 26, 1982; January 5, 1993) due to the

complexity and width of the northern San Jacinto fault zone on the site. Faulting, where

found in the field, was flagged and the lath locations surveyed by Church Engineering,

Inc. Lath locations from the previous subsurface investigations (Rasmussen, August 25

and 26, 1982) have been Incorporated into Church Engineering, Inc. 's data base. Survey

points and the restricted use zone are shown on Plate 2. Due to the potential hazard of

surface fault rupture, human occupancy structures should not be placed within the

recommended restricted use zone as shown on Plate 2.

The presence of low-angle faults or slope failures observed within the trenches In the

southeastern portions of the site and the steep slopes (20 percent gradient) associated

with the different age terraces on the site, Including the Rialto bench which forms the

southwest boundary of the site, Indicate that there may be a potential for future ground

lurching on the site. The recommended restricted use zone has been extended to Include

the features observed In these trenches and a 50 foot setback from the toe of the Rialto

bench ls also recommended.

6

C.l-.ARY S R.A.SMUSSEN & ASSOCIATES



El Rancho Verde Country Club Project No. 3156.l

The geologic conditions for liquefaction, including severity of earthquake shaking and

shallow ground water, may exist within the northeastern and northwestern portions of

the site. The additional parameters that are necessary for liquefaction should be

evaluated by the project geotechnical engineer.

Lakes or other water containment structures should not be placed within the restricted

use zone due to the hazard of surface fault rupture, unless mitigated by proper

engineering design. Additionally, seiching could occur in either lakes or reservoirs

proposed for the site during prolonged ground shaking.

Due to the potential hazard of tensional ground surface fracturing of geologic materials

on the site in the event of a large earthquake, we recommend that foundations and slabs

of proposed structures be reinforced to resist tensional ground cracking.

SITE DESCRIPTION

The approximately 260-acre site Is located northeast of Riverside Avenue and Country

Club Drive in Rialto, california. The northwestern half of the site consists of the El

Rancho Verde Country Club golf course and associated buildings. The southeastern half

of the site generally consists of open, vacant land with the exception of a small 2 3/ 4-

acre parcel located in the central portion of the southeastern part of the site, which

contains an occupied house ("engineer's house"), barn and horse pasture. A City of

Rialto underground water main ls located just southwest of the house. Other utilities,

including West San Bernardino County Water District water lines and a 5-lnch Southern

calitornia Gas Company gas main, also cross the site.

Old concrete structures such as weir boxes and well housings are located east of the

clubhouse and driving range, and west of a flood control berm. Similar concrete

structures are also located east of the flood control berm and probably tie Into the

7

().ARY S .H.ASMU'SS~N & A~3SOC'";'l.A'T'E~3


Nitto America CO., Ltd. June 9, 1994

Ei Rancho Verde Country Club Project No. 3156.1

concrete structures located west of the berm. Debris consisting of old pipes and

construction materials were scattered throughout much of the area surrounding the

country club, west of the flood control berms. Electrical tie-in facilities are located

east of the driving range. Flood control berms are located on the site and cast of the

site and generally form the northeastern and northwestern site boundaries. West San

Bernardino County Water District wells and pump facilities are located north of the

driving range, northeast of the northeast leg of the golf course, and northeast of the

small levee located in the southeast portion of the site.

Extensive alterations to the natural ground surface have occurred In the southeastern

portion of the site, due both to installation of flood control levees and berms, and

grading and paving of some roads. An irrigation pond is located along the northern

boundary of the site at the extreme northwestern end of the golf course. Existing

vegetation Is composed of willows (in the drainages), rabbit brush, prickly pear,

buckwheat, yucca and assorted grasses. A small abandoned grove of black olive trees are

located adjacent to, and southwest of, the extreme southeastern end of the site. Small

scattered areas of trash and debris are located within the southeastern half of the site

and a small area of recent grading is located just southeast of the access road that leads

to the "engineer's house."

Overall, the site slopes gently to the south-southeast at a gradient of approximately 2

1/2 percent. Scarps associated with the different age terraces on the site and with the

San Jacinto fault slope sharply to the northeast at an average gradient of 20 percent.

Total relief across the site is approximately 145 feet.

SITE INVESTIGATION

A geologic field reconnaissance of the site and surrounding area was conducted on

November 4, 1992. In addition, our Investigation Included review of black and white,

8

0.AR Y 8 B.AS'M USS.l!::t--T & ASSOCIATES



El Rancho Verde Country Club Project No. 3156.I

vertical stereoscopic aerial photographs flown in 1930, 1938, 1953, 1955, 1962, 1965,

1967, 1978, 1980 and 1986; review of color, infrared, verti(',al stereoscopic aerial

photographs flown in 197 4; review of obllque, infrared aerial photographs flown by this

firm In July, 1982; review of oblique low sun-angle stereoscopic aerial photographs flown

by this firm on February 15, 1994; review of pertinent geologic literature and maps,

including reports Jn our flies on nearby projects; and review of significant seismic

Information, including historic seismic activity. The aerial photographs that were used

to create the 200-scale topographic base map were not available and were not used in

this investigation. A list of aerial photographs reviewed and references cited In this

report is included as Enclosure 8.

Subsurface investigations were conducted In September, 1979 (Rasmussen, February 29,

1980); Jn July and August of 1982 (Rasmussen, August 25, 1982; August 26, 1982); and

from September of 1993 through March of 1994 (this investigation) on, or adjacent to,

the site.

Ten trenches (Trenches 1-6), totaling 3,141 feet of exposure, were excavated during our

previous Investigations. The trenches were excavated to a maximum depth of 11 feet

with a John Deere 690 track-mounted backhoe. The trench walls were sloped to increase

thelr overall stability. The trenches were entered, the trench walls were geologically

examined In detail and geologic logs of the trenches were made by a geologist from our

firm. The trench logs from our previous subsurface Investigations (Rasmussen, February

29, 1980; August 25, 1982; August 26, 1982) are Included with this report as Enclosure

2 (Rasmussen, February 29, 1980) and Enclosure 3 (Rasmussen, August 25, 1982; August

26, 1982).

Twenty-three trenches (Trenches 7-26), totalling 3,600 feet of exposure, were excavated

during this Investigation. The northern San Jacinto fault steps westerly on the site and

does not continue northwest as had been previously mapped. The extreme complexity of

the fault on the site and its associated wide zone of faulting required the extensive

9




trenching which occurred during this investigation. The trenches were excavated using

a Cat 225 track-mounted backhoe to a maximum depth of 20 feet, but generally averaged

between B to 12 feet in depth. The trench walls were benched and/or sloped to increase

their overall stability. The trenches were entered and the trench walls were geologically

examined in detail and geologic logs of the trenches were made by a geologist from our

firm. The trench logs from this subsurface investigation have been included as Enclosure

6. Trenching has been conducted from the southeast corner of the site to just northwest

of the clubhouse office. The locations of the trenches are shown on Plate 2. All trench

locations for this investigation were surveyed by Church Engineering,

Evidence of other trenches excavated in a northeast-southwest direction was observed

during our field mapping. Research of City of Rialto and County of San Bernardino

records and discussions with their personnel and the current property owner failed to

reveal who had excavated these trenches. No geologic report was apparently submitted

in conjunction with this trenching by unknown others.

Numerous utilities were encountered during trenching and caused substantial delays due

to mislocatlon by the utility companies and/or a decrease In the speed of excavation due

to the utility crossings. A 14-inch City of Rialto high-pressure water main was

mislocated 20 feet by the City of Rialto Water Department and was encountered In

Trench BA, northwest of the engineer's house. A 4-lnch West San Bernardino County

water main was encountered in Trenches BA and 10. A 2B-lnch abandoned concrete

irrigation pipe was encountered in Trenches BB, 9, I IA, 12, 14, 16 and 23. A 16-inch

abandoned concrete Irrigation pipe was encountered in Trench 19. A decomposed 12-inch

concrete Irrigation pipe was encountered in Trench BB at a depth of approximately 10

feet, A 4-lnch abandoned water main was encountered in Trench l lB and a 10-inch

abandoned concrete pipe was encountered at the northeastern end of Trench 1 lA.

Three-Inch steel irrigation pipes which supply water to the golf course were encountered

in Trenches 12, 23 and 26. A 6-inch Irrigation main for the golf course irrigation system

was encountered ln Trench 23 and ruptured after backfilllng had been partially

10

C.1-..ARY S R.Al:;Mt,J$$l!:::N' & ASSOCIATF~S




completed. An unmarked Pac*Bell trunkllne cable and an unmarked 3/4-inch water

fountain supply pipe were cut by the backhoe In Trench 24. A 5-lnch Southern California

Company gas main was encountered in Trenches 13B, 17 and 19. The trenches were

backfilled and wheel rolled in October, 1993, and March, 1994, but were not compacted.

GENERAL SITE GEOLOGY

The site lies along the northeast boundary of the Perris Block. The Perris Block ls part

of the Peninsular Ranges Geomorphic Province. The Peninsular Ranges Geomorphic

Province extends north to the base of the San Gabriel Mountains and south into Mexico

to the tip of Baja California. The Perris Block is bounded on the northeast by the San

Jacinto fault, on the north by the Cucamonga fault and the San Gabriel Mountains, and

on the southwest by the Elsinore fault and the Santa Ana Mountains.

The site is underlain by fluvial deposits adjacent to the southwest side of Lytle Creek.

Numerous former drainages can be seen on and in the vicinity of the site on the older

aerial photographs, all associated with Lytle Creek which emanates from the San Gabriel

Mountains northwest of the site.

Lytle Creek flows across and deposits upon a large alluvial fan which occupies a

considerable area from Ontario on the southwest, east to Colton and north to the base

of the San Gabriel Mountains. More than 33,000 years ago, uplift of the Perris block

along the San Jacinto fault produced incision along distributary channels of the Lytle

Creek fan (Clarke, 1989). Downcutting resulted in the three largest channels becoming

deep, mid-fan trenches (Clarke, 1989). Continued uplift along the trace of the San

Jacinto fault resulted In complete diversion of the Lytle Creek drainage into the

easternmost channel, beheading the Lytle Creek fan by mid-Holocene time (Clarke, 1989).

Flood control levees near the base of the San Gabriel Mountains have restricted Its flow

to a southeasterly direction since 1938.

11

OARY ~'3 ~~AS.M.USSE.N & ASSC"JClATEt~




Fine-grained alluvial fan deposits of probable late Pleistocene age were encountered

beneath much coarser grained materials in several of the trenches. These materials are

deposits from Cajon Wash. The distal edges of the Lytle and Cajon fans overlapped and

interflngered during the Pleistocene and early Holocene (Clarke, 1989). Alluvium on the

site was entirely deposited by Lytle Creek after the drainage was shifted eastward and

the fan beheaded due to continued incision and uplift along the San Jacinto fault during

the mid-Holocene (Clarke, 1989).

Various benches or terraces are located on, and adjacent to, the site above the currently

active channel of Lytle Creek. Three to five terraces exist on the site but have been

grouped into two general units for purposes of geologic mapping: older terraces of late

Pleistocene age and younger terrace deposits of Holocene age. These terraces represent

stages of uplift and/or flooding and channeling. An even older, higher terrace, the

Rialto Bench, exists immediately west of the site. The alluvial materials underlying this

bench are considered to be late Pleistocene in age (Dutcher and Garrett, 1963; Miller,

1979).

Generally, the on-site alluvial materials become progressively younger towards the active

Lytle Creek channel (from southwest to northeast). Morton and Matti (1990) have

mapped the site as being entirely composed of older alluvium. Dutcher and Garrett

( 1963 l have mapped the site as consisting of both older alluvium (located adjacent to the

San Jacinto fault) and younger alluvium, and Matti and Carson (1991) have mapped the

site as younger and older Holocene alluvial deposits. A geologic index map has been

included as Enclosure 1. A detailed geologic map of the site has been included as Plate

1.

12




SUMMARY OF INFORMATION FROM PREVIOUS INVESTIGATIONS

Subsurface Investigations

Evidence of recent faulting was observed within trenches from our previous Investigation

of the southeastern half of the site (Rasmussen, August 25, 1982; August 26, 1982). The

locations of the trenches from our previous subsurface investigations are shown on Plate

2.

Geologic examination of the trench walls revealed that the on-site alluvial materials

consist of slits, sands and gravels deposited by ancient channels of both Cajon and Lytle

Creeks (Rasmussen, August 25, 1982; August 26, 1982). The alluvial materials within the

western portions of the site at a depth of approximately 11 feet were estimated to be

late Pleistocene in age, as evidenced by the following characteristics: the extreme

deterioration of gnelssic and other metamorphic clasts; the partial cementation of sands

along planes of bedding; the presence of a burled soil (paleosoll; the general darker red

color; the greater lnduration of these sediments compared to the overlying deposit; and

the extent and amount of development of the overlying soil profile. No datable

radiocarbon material was found in any of the six trenches excavated during these

Investigations (Rasmussen, August 25, 1982; August 26, 1982).

As observed within the trenches from our previous subsurface investigations of the site

(Rasmussen, August 25, 1982; August 26, 1982), the character of the sediments changes

drastically and abruptly at the San Jacinto fault, with Holocene-age materials lying

along the northeast side of the fault and generally elevated Pleistocene-age deposits

existing southwest of the fault. The sediments also change color at the fault, with the

light gray sediments representative of Holocene-age alluvium juxtaposed against the

darker reddish Pleistocene-age alluvium. Based on observation of offset of Holocene-age

materials Immediately northeast of the fault, It was our opinion that all of the sediments

trenched during these investigations were sufficiently old enough to reveal evidence of

13




previous fault rupture that would be llkely to re-occur during the life of the proposed

residential structures. The age of the sediments northeast of the main fault trace were

probably not 11,000 years old at a depth of 11 feet, but were estimated to be from

several hundred years old to a few thousand years old.

Approximately 441 feet of trench was excavated during our previous subsurface

investigation of the parcel located adjacent to, and southwest of, the extreme

southeastern end of the site (Rasmussen, February 29, 1980). Two of the trenches

excavated for this investigation are now located on the site (Trenches 1 and 2) and two

are located immediately southwest of the site (Trenches 3 and 4). The trench logs and

unit descriptions are included as Enclosure 2. The trench locations are shown on Plate

2.

Approximately 2, 700 feet of trench was excavated during our previous subsurface

investigations of the southeastern half of the site (Rasmussen, August 25, 1982; August

26, 1982). For purposes of simplifying the logging, the sediments were broken into

fourteen generalized units. Classification of the sediments Into these fourteen units was

based upon alluvial character and composition, not age. The trench logs and unit

descriptions are Included as Enclosure 3. The trench locations are shown on Plate 2,

Evidence of recent faulting was found In four of the six trenches excavated during our

previous Investigations (Rasmussen, August 25, 1982; August 26, 1982). Examination of

Trench 1 revealed a zone of faulting approximately 180 feet In width. The oldest breaks

were observed towards the southwestern portion of the zone; whereas the youngest

breaks (to within several feet of the surface) occurred towards the northeastern portion

of the fault zone. Alluvial materials have been downdropped towards the northeast

relative to the sediments southwest of the faulting (Rasmussen, August 25, 1982; August

26, 1982).

14

C:i.ARY S 'A.ASMUSSEN&. ABt5C:JC::IATE.t-~



El Rancho Verde Country Club Project No. 3156.I

Periodic flooding of Lytle Creek has tended to obscure, modify and erode surface

evidence of faulting on the site. For this reason, previous geologic work has failed to

locate a surface expression of faulting. However, a modified fault scarp can be observed

throughout most of the southeastern portion of the site and northwest of the West San

Bernardino County Water District "engineer's house" In the northern portion of the

southeastern half of the present site. Additional trenches, Trenches 2, 3 and 4, were

placed northwest and southeast of Trench 1 in order to intercept the fault and to better

define Its position, direction and character in the southeastern half of the site

(Rasmussen, August 25, 1982; August 26, 1982).

Evidence within the trenches supporting fault rupture consisted of: offset beds, warping

of beds, rotation of prolate clasts, thick root accumulation, crushed and sheared

materials and differential percolation features (Rasmussen, August 25, 1982; August 26,

1982). Flagged laths were placed at locations along the trenches where the main, active

fault trace was observed. These laths were surveyed so that the exact location of

faulting could be defined and setbacks recommended. The same type and style of offset

In each trench was correlated so that the stake was placed on the main or most recent

movement (active trace of the zone). Setbacks were recommended from the last active

fault trace encountered In Trench 1 (Rasmussen, August 25, 1982; August 26, 1982).

The other trenches were not necessarily long enough to identify all active breaks

associated with the main fault. The main trace of the San Jacinto fault steps or en

echelons between Trenches 1 and 4 (Rasmussen, August 25, 1982; August 26, 1982). The

geomorphology of the area Immediately adjacent to, and southwest of, the "engineer's

house" suggests the existence of such a change. The obvious location of the scarp

coincident with the faulting found in the trenches provided good evidence for continuity

of the fault and Its trend between trenches. Northwest of Trench 4 (Rasmussen, August

25 and August 26, 1982) where the fault crosses younger materials in the golf course,

evidence for faulting becomes more obscure.

15



Magnetometer Tnwerses


Seven magnetometer traverses were measured across or near the southeastern half of

the site during our previous investigations (Rasmussen, February 29, 1980; August 25,

1982; August 26, 1982) at the approximate locations shown on the geologic Index map

(Enclosure 1 ). Magnetometer traverses were measured in a northeast-southwest

direction In order to cross the trend of the major faulting in the area. A Geometrix

Model 846 high precision proton procession magnetometer was used to conduct our

surveys. Magnetic anomalies do not always occur across faults and even when they do

occur, they provide no information as to their state of activity. Therefore, the

existence or absence of active faulting cannot be proven by a magnetic survey such as

was conducted on the site. However, the magnetic data provide additional input for

evaluation of faulting and, in many cases, active faults produce dramatic magnetic

anomalies due to the different types of materials existing on either side of the fault.

Slight anomalies were encountered in the magnetometer traverses of the site. This Is

eSPeclally apparent In Line 1 (Rasmussen, August 25 and 26, 1982) which exhibits an

average increase of about 16 gammas across the fault. Results of the magnetometer

surveys have been plotted and are included as Enclosures 4 and 5. No other significant

anomalies that appear to be related to faulting were found northeast of the main fault

encountered In our trenches.

SUMMARY OF INFORMATION FROM CURRENT INVESTIGATION

Subsurface Stratlmphy

Units exposed ln our subsurface excavations were roughly correlated across the site

during this Investigation. No attempt was made, however, to correlate the units

observed in this investigation with the units noted during our previous subsurface

16




investigations, due to the lapse In time (11 • years) since our previous investigations,

recordation of the units by a different geologist and the use of a different color chart.

No charcoal or other datable materials were encountered in sufficient quantities to allow

a direct determination of the age of the sediments. Ages were assigned to the units

based on density, color, clast size, clast condition and our experience. The ages are

approximate and have not been quantified by absolute or relative age dating. Beds were

grouped into units based on the above characteristics and their stratigraphic relation

ship. Unit "A" covers the largest span of time and contains several facles changes from

fine-grained eolian deposits to coarser grained and bedded alluvial deposits. Unit "A"

is the oldest unit on the site and has been classified as late Pleistocene in age, based on

the following characteristics: the high deterioration of gnelsslc and other metamorphic

clasts; the lesser but significant weathering of granitic clasts; the partial cementation

of sands along bedding planes; the presence of remnant buried soils (paleosols) as

evidenced by the development of ped surfaces with clay films; the general darker red

color; the greater induratlon of these sediments compared to the overlying deposits; the

much higher incidence of fracturing; the higher incidence of tilting and deformation; and

the lack of larger clasts typical of deposits from Lytle Creek. Subunits (e.g. A2, A3, B11

etc.) are not generally correlatable between trenches; the lower case number indicates

the subunit's stratigraphic position within the unit for that particular trench only. A

general description of each unit follows.

Unit "D": late Holocene to present: sllty sand with gravel: variously colored but

usually dark brown or grayish brown in the 2.5Y or lOYR range; loose; massive; porous,

abundant fine to medium pores; abundant organics; bioturbated; roots and rootlets

throughout; clasts are stained same color as unit; minor cobbles; no attempt made to

distinguish soil horizons except where a possible Incipient "B" horizon was present in

Trench 19; near "engineer's house" and on golf course, unit is mixed with or has been

17

CZARY fj RA~li.i:rC.JSt..~EN & ASSOC:1Acf'E..:S




replaced with uncompacted artificial flll (Enclosure 6, Trenches SD, 12, 23, 24 and 26).

Logs are labeled "artificial fill" or "mixed topsoil and fill" where this occurs.

Unit "C": mid- to late Holocene: interbedded cobbly gravel, sandy cobble, sandy gravel

and gravelly sand: variously colored but usually 2.SY 8/1 to SY 7 /2, white to light gray;

loose to medium dense; subangular to subrounded clasts, dominantly granitic in

composition (clasts deposited by Lytle Creek Wash); minor boulders; poorly bedded to

moderately well bedded; channellng common; rare manganese oxide or Iron-oxide staining;

rare to no degraded clasts; generally coarser grained than unit "B".

pnlt "B": early to mid-Holocene: sandy gravel with cobbles, sandy cobble and sandy

gravel: variously colored but usually 2.SY 8/1 to 2.SY 7 /2, white to light gray; medium

dense; manganese oxide and iron-oxide staining common along bedding planes and in

lenses; subangular to subrounded clasts, dominantly granitic In composition ( clasts

deposited dominantly by Lytle Creek Wash); rare boulders; minor degraded clasts - most

maflc in composition; occasionally laminated but generally poorly sorted and poorly

bedded; coarser grained than unit "A" but finer grained than overlying unit.

Unit "A": late Pleistocene: Interbedded and laminated sandy gravel, gravelly sand, sand

and silty sand: variously colored but generally light yellowish brown, (1 OYR in lower

units and 2.5Y In upper units); medium dense to dense; abundant manganese oxide and

iron-oxide staining along bedding planes and coating clasts; minor degraded clasts -

mostly mafic ln composition but rare fe\sic clasts. also; presence of ped surfaces with

thin clay films; finer grained units are usually highly fractured and show abundant

evidence of liquefaction; coarser laminated gravel beds often fine upwards, though some

reverse grading was also observed; coarser units were tilted as much as 43 degrees where

faulted; minor cobbles - generally finer grained and better bedded and sorted than

overlying Holocene units; clasts deposited by Cajon Creek Wash.

18

C.lARY $ "R.ASMUSSl!:N & ASS0(~1A'1'E~S



El Rancho Verde Country Club

Faulting and Associated Features

Southeast of "Engineer's House" to Southeast End of Site

Project No. 3156. l

Trenches 9, 13A and 136, and 19 were excavated across the main trace of the San

Jacinto fault, southeast of the "engineer's house". Trenches 14, 15 and 17 were

excavated across splay faults subparallel to the main trace of the San Jacinto fault in

the southeast portion of the site. Trenches 7, 16 and 21 were excavated in such a

manner as to intercept possible faults associated with the northeast flank of the hill

occupied by the "engineer's house". The trench logs for this investigation have been

included as Enclosure 6. The locations of the trenches are shown on Plate 2.

The San Jacinto fault trends almost due north (N5E to NlOW) as it enters the southeast

corner of the site. Approximately 350 feet northwest of the southeast corner of the site,

the fault steps more westerly and is characterized by a series of left-stepping en echelon

faults trending between NlOW and N12W which together form an overall trend of N30W.

This en echelon stepping of the fault is accompanied by a wide zone of faulting and is

characterized by multiple scarps. Trenches 19 and 13B cross all three scarps associated

with the main trace of the San Jacinto fault near the southeast corner of the site. The

upper or southwesternmost scarp ls the steepest scarp and is characterized by the most

apparent vertical displacement. Movement along the base of the scarp on the main trace

of the San Jacinto fault triggered gravity sliding or slope failure and secondary faulting

in the upper portion of this scarp. Faulting at the top of the slope Is much lower angle

than that at the base (dips of 36 degrees versus 60 degrees at the base). All of these

faults merge at relatively shallow depths.

In Trench 19, faulting associated with the upper two scarps occurred within less than 6

inches of the natural ground surface. Total apparent vertical displacement of the

contact between units "D" and "B" across the upper scarp is approximately 9 3/4 feet;

across the middle scarp it is approximately 5 feet; and none across the lower scarp. The

19

C:l-,A.FlY !.:_;; RA~3Ml.18~JE!'l & ASSOC:IA'T'E~:>



EI Rancho Verde Country Club Project No. 3156.l

contact between units "B" and "A" (Pleistocene-Holocene boundary) was displaced

approximately 11 feet in an apparent vertical sense across the upper scarp; approximate

ly 6 3/ 4 feet across the middle scarp; and approximately I foot across the lower scarp.

Total displacement of the "D"/"B" contact across the entire fault zone in Trench 19 was

approximately 14 3/4 feet and of the "B"/"A" contact was approximately 33 1/2 feet.

It is apparent from the stratigraphic relationships that at least the upper and middle

scarps, and most likely all three scarps, ruptured simultaneously. A minimum of two

rupture events are visible in Trench 19.

Trench l 3B showed similar relations between faulting and stratigraphy as Trench 19 but

had a better defined and larger lower scarp. The "D"/"B" contact was offset in an

apparent vertical sense by approximately 7 l /2 feet across the upper scarp; 8 feet across

the middle scarp; and less than 6 Inches across the lower scarp. A possible remnant

paleosol in unit "B" was offset vertically by more than 4 1/2 feet. A fine sand/silty sand

with gravel unit deposited on top of unit "B" was displaced vertically by 2 feet 3 Inches

across the lower scarp in Trench 13B. Secondary faulting and ground failure was also

associated with the upper scarp in Trench l 3B.

Trench 17 was excavated across the middle and lower scarps. Unit "D" was not offset

by the middle scarp, which appears to be dying out. A sand lense was offset less than

1 foot by a single fault which trended N2W and dipped approximately 77 degrees east.

A narrow fault zone trending approximately N22W and dipping 86 degrees to the east

offset unit "D" in an apparent vertical sense by approximately 1 1/2 to 2 feet across the

lower scarp. A sand layer with minor gravel (possible remnant paleosol) was offset by

approximately 2 feet 2 inches across the same zone.

Trench 15 was excavated across the lower scarp where the scarp begins to die out

southeast of Trench l. Unit "D" was offset vertically less than 6 inches and unit "B" was

only offset by about 1 foot. No faults were found in Trench 1 along the trend of the

20




features observed within Trench 17; therefore, It appears that these faults die out

rapidly to the northwest.

Trench 14 was excavated across the trend of some secondary faults located southwest

of the main trace of the San Jacinto fault, which were Identified In Trenches 1 and 3

during our previous subsurface Investigation (Rasmussen, August 25 and August 26, 1982).

A wide zone of minor faulting was exposed in Trench 14. Unit "D" was generally not

offset, except for a possible fault or channel edge which trended approximately N66W

and displaced unit "D" by less than 1 1/2 feet. Displacements in unit "C" were also less

than 1 1 /2 feet. These faults appear to be secondary faults associated with the en

echelon steps in the San Jacinto fault and die out rapidly.

Trench 9 was excavated across one of the Nl2W-trendlng left steps of the San Jacinto

fault, just southeast of where the fault changes orientation from N30W to N52W. This

compressional step has formed the hill occupied by the "engineer's house". A single fault

scarp Is associated with the main trace of the San Jacinto fault in this area. Unit "D"

ls not offset in this trench; however, the unit is only approximately 1 1/2 feet thick and

has been replaced with artificial fill by the excavation for a 28-inch concrete Irrigation

pipe in the fault zone. Therefore, displacements which may have occurred In unit "D"

are no longer visible due to placement of the pipe and associated fill, and possible

stripping of the unit during excavation. The contact between unit "C" and "B" was offset

vertically by approximately 7 feet in Trench 9.

Trenches 7 and 16 were placed along the northeast flank of the compressional hill

occupied by the engineer's house. No faults were found In Trench 7. Several minor

faults trending N48E to N30E were exposed within Trench 16. Some of the faults were

characterized by apparent down to the southwest, reverse displacements of less than 6

inches in unit "A", indicating that the faults are most likely right-lateral, strike-slip

faults - the compressional hill is located on the "downthrown" side of the faults. Unit

"D" was not displaced by the faults but ls downwarped between the north and south ends

21




of the zone of faulting. Trench 21 was placed less than 100 feet northeast of Trench 16

to intercept any N25E- to N35E-trendlng faults which might have extended northeast

from Trench 16. The N4BE-trending fault was not found on the northeast wall of the

trench and is diSplaced by a N30E-trending fault; therefore, no attempt was made to

follow the trend of this fault by additional trenching to the northeast. No faults were

found in Trench 21. The faults exposed in Trench 16 arc secondary adjustment features

and are not continuous, through-going faults.

"Engineer's House" Northwest to Golf Course

Trenches BA and BB, 10, 11A and 11B were excavated across the main trace of the San

Jacinto fault from just northwest of the "engineer's house" to the point of intersection

of the two legs of the El Rancho Verde golf course, northwest of, and adjacent to the

No. 3 green. The locations of the trenches are shown on Plate 2; the trench logs have

been included as Enclosure 6.

The main trace of the San Jacinto fault steps west again just southeast of the engineer's

house from a trend of N30W to N52W. A two- to four-foot high, northeast-facing,

N52W-trending fault scarp ls visible from the "engineer's house" northwest for a distance

of approximately 950 feet. The scarp dies out to the northwest and the fault steps west

again to a trend of N65W where it was encountered at the southwest end of Trench 1 lB.

The zone of faulting associated with the N52W trend is well confined with a maximum

width of approximately 75 feet.

The total apparent vertical dlSplacement of unit "D" across the zone of active faulting

in Trench BA was about 3 feet. The actual displacement of unit "D" Is difficult to

estimate due to thickening of unit "D" from sloughing of the scarp on the downthrown

side of the fault. The contact between unit "C" and "B'' was offset vertically by about

4 to 5 feet. The total width of the fault zone measured approximately 50 feet in Trench

22




BA. Trench BB was excavated across the north flank of the compressional hill occupied

by the engineer's house. No faults were found in Trench BB.

Trench 10 was excavated across the northeast-facing, N52W-trending scarp less than 150

feet southeast of where the scarp dies out to the northwest. Two zones of faulting were

encountered in Trench 10. A narrow (less than 10-foot wide) N56W-trending zone at the

southwest end of Trench 10 and the main trace of the San Jacinto fuult at 66 feet from

the southwest end of the trench. The main fault zone measured greater than 20 feet in

width. Both zones dipped to the northeast. Together, the entire zone of faulting

measured approximately 75 feet In width. The main trace was associated with the fault

scarp encountered in Trenches BA and 4 (Rasmussen, August 25 and August 26, 19B2J.

A 1- to 2-foot wide crushed zone with prolate clasts accompanied the northeast-dipping

main fault. Unlt "D" was offset vertically less than 2 feet; unit "C" had an apparent

vertical offset of 2 feet, and unit "A" was offset about 8 feet. The narrow fault zone

at the southwest end of Trench 10 had little, if any, geomorphlc expression, did not

offset unit "D" and offset the "C"/"A" contact by less than 2 feet vertically. Some

thickening of unit "D", however, occurred on the downthrown side of this fault zone.

Trench l lA was excavated across the northwest projection of the N52W fault scarp.

Minor fracturing, faulting and liquefaction was visible only in unit "A". Vertical

displacements measured less than 1 inch and were most likely the result of liquefaction,

not primary faulting.

Trench llB was excavated slightly north-northwest of Trench llA. The main trace of

the San Jacinto fault was found at the southwest end of Trench 11 B and trended N65W

to N70W. The narrow fault zone at the southwest end of Trench 10 may have been the

beginning of this west step in the fault.

The geometry and appearance of the main trace of the San Jacinto fault also changes

In Trench llB. The fault is only visible on 1930 aerial photographs as a faint linear

23




trough. The faulting still dips northeast but the dips are steeper and the zone narrower

than encountered in the southeast portion of the site. A small graben present on the

downthrown side of the fault in Trenches 8A, 9, 10, I 3ll, 17 and 19 is absent in Trench

11 B. Unit "D" Is offset only a few inches. Unit "C" has less than 1 foot of apparent

vertical offset; subunit "A" has been offset by 1 I /2 feet along the northeasternmost

trace of the fault, but the total amount of apparent vertical disvlacement of subunits

"A1" and "A2" is not known.

Golf Course to Northwest of Clubhouse

Trenches 23 and 26 were excavated approximately 600~ feet northwest of Trench 11 B

and 400 feet southeast of the main clubhouse. Faults exposed within Trenches 23 and

26 trended from N48W to N67W. The main fault was exposed in Trench 23 on trend with

faulting found in Trench 11 B (N65W). The logs for the trenches have been included as

Enclosure 6 and the trench locations are shown on Plate 2.

Neither unit "D" or ''C" ls offset by faulting in these trenches. Only units "A" and "B"

are offset vertically; the mid- to late Holocene-age unit "C" is not offset. This implies

that the most recent displacement along the main San Jacinto fault is decreasing or

dying out by the time it reaches these trenches. The total width of the zone of faulting

encountered in Trenches 23 and 26 was about 300 feet.

Trench 12 was excavated on the driving range and oriented to encounter any northwest

trending splays from the main trace of the San Jacinto fault. Abundant evidence of

liquefaction was observed in Trench 12 but no faults were found.

Trench 24 was excavated just northwest of the clubhouse office at the north end of

Country Club Drive. The main fault steps west again between Trenches 23 and 24 to a

trend of N79-81 W. The "hill" occupied by the clubhouse and associated facilities appears

24

(J.AR.Y R rtA8MtJSSEl·J,.,,. ARt~c:)..:.:_~lA'l'l::!.,;fj


NI tto America Co., Ltd. June 9, 1994


to be bounded by an altered southwest-facing fault scarp. The main zone of faulting

encountered In Trench 24 was found associated with this altered scarp. Unit "D" was

not offset by faulting in Trench 24. Unit "C" was not present. Subunit "B," was offset

in an apparent vertical sense by about I foot, as was the contact between subunit "B1"

and unit "A" (Pleistocene-Holocene boundary). The most recent displacement on the

fault could not be determined from this trench due to the lack of late Holocene

materials. The fault zone was churned and It appears that faulting was accompanied by

liquefaction along the fault plane. The total width of faulting encountered in Trench 24

measured approximately 270 feet. Trench 24 was the northwesternmost trench

excavated on the site.

GEOMETRY AND GEOMORPHOLOGY OF THE NORTHERN SAN JACINTO FAULT

The site is situated on a series of terraces which form a convex peninsula of land above

the Lytle and Cajon Creek Washes and below the Rialto Bench. The convex teardrop

shape of the site has been controlled by the geometry of the northern San Jacinto fault,

which bisects the site.

Previous mapping (Dutcher and Garrett, 1963; Morton, 1974; Miller, 1979; Morton and

Matti, 1987; Matti and carson, 1991) have shown the northern San Jacinto fault on the

site as a single, straight, northwest-trending trace located either along the base of the

Rialto bench or traversing through the center of the site, or as several splays (see Index

map and Enclosure I), which ultimately connect with northwest-trending faults within

the San Gabriel Mountains (e.g. Lytle Creek fault). Morton and Matti (1990) do not

show the San Jacinto fault on the site on their updated geologic map. Many geologists

have postulated that the San Jaclnto fault steps northeast in this area In order to

transfer motion to the Glen Helen fault and ultimately to the San Andreas fault. The

San Jacinto fault on the site steps west, however. This implies that either the transfer

of motion has occurred southeast of the site or that some other mechanism is utilized

25

C1-AR Y t-·; n.ASMLJA8E.I:-..l' '~· A~·-.>~~~(')(.-:1 A"l'l!:t1




Instead. A N20E, apparent left-stepping scarp is located just south of the southeast

boundary of the site. Th ls scarp may be a fault which acts to transfer motion northwards

from the San Jacinto fault to the Glen Helen fault or some intermediate fault.

A single N32E-trendlng fault trace was exposed in the southwest bank of the wash 200

feet northeast of the northeast site boundary (Plate 2). This fault may be related to the

N20E fault located south of the site and may form part of a left-stepping, northeast

trending transfer structure. No geomorphic expression of this fault was observed in the

field or on the aerial photographs.

A N38W-trending fault exposed In the wash approximately 2,100 feet northeast of the

site was observed by Wessly Reeder, San Bernardino County Geologist (personal

communication, February, 1994). Both his and our observation of this fault suggests it

is active. This fault has not yet been trenched but appears to offset alluvial units of

probable Holocene age (Wessly Reeder and Tom Rockwell, personal communication,

February, 1994). This fault may be either an intermediate step between the San Jaclnto

and Glen Helen faults, or it may be the southern extension of the Glen Helen fault.

If much of the motion of the San Jaclnto fault has been transferred before It reaches the

site, then the rate of activity of the San Jaclnto fault may be decreasing or the fault

may be dying out on the site and may not extend much farther west. Terminating strike

slip faults may change strike abruptly and become normal faults or tensile ruptures (Deng

and Zhang, 1984).

The San Jacinto fault on the site is characterized by a prominent north-northwest

trending, northeast-facing scarp from the southeast corner of the site to approximately

950 feet northwest of the "engineer's house". The fault also changes trend from N30W

to N52W at the "engineer's house". The fault disrupts young, late Holocene deposits and

extends to within 6 inches of the existing ground surface at its southeast end. A large

component of normal, down to the northeast movement is characteristic of this portion

26

Cl-ARY S HASM LTSSE?-..J' &. AS80(~?1A'.Cl:CS




of the San Jacinto fault. Northwest of where the scarp dies out, evidence for the

recency of faulting is much less apparent. The zone of faulting also widens and become

more diffuse and the fault continues to step westerly. The most recent surface rupture

to have occurred on the northern San Jacinto fault on the site may have only extended

to the point where the scarp dies out.

Alternatively, the San Jacinto fault on the site may be stepping westerly due to some

Interaction with, or influence of, either the Fontana ground-water barrier (Barrier "J")

or the Cucamonga fault.

SEISMIC SETTING

The most significant faults to the site from a seismic shaking and ground rupture

standpoint are the faults within the west/northwest-trending San Jacinto fault zone.

The San Jacinto fault, which traverses the site, is generally considered to be the most

active fault in southern California (Allen et al., 1965). The modern topsoil was offset

by the fault in the southeast portion of the site. The San Jacinto fault is generally

characterized by right-lateral, strlke-sllp movement, although there appears to be a

large component of nonnal, down-to-the-northeast motion on the fault on the site.

A N20E-trending possible fault scarp Is located immediately southeast of, and subparallel

to, the southeast boundary of the site. This fault may aid in transferring motion from

the northern San Jacinto fault to the Glen Helen fault. A single N32E-trending fault

trace exposed in the southwest bank of the wash, just 200 feet northeast of the site, may

be a left step of this fault zone.

A N38W-trendlng unnamed fault which may an intermediary step between the San Jacinto

and Glen Helen faults ls located approximately 2,100 feet northeast of the site. This

fault was discovered during a field reconnaissance of the Lytle and Cajon Creek washes

27




by Wessly Reeder, San Bernardino County Geologist (personal communication, February,

1994). The fault has not yet been trenched but appears to offset alluvial units of

probable Holocene age (Wessly Reeder and Tom Rockwell, personal communication,

February, 1994).

Dutcher and Garrett (1963) showed a ground-water barrier (Barrier J) 2 1/4 miles

northwest of the site. Barrier J (Fontana ground-water barrier) is a northeast-trending

feature which may be fault related. Mlcroseismic activity has been attributed to this

suspected fault by Hadley and Combs (1974). Hadley and Combs Indicated that a

composite first-motion plot of microearthquakes In the Fontana area suggests that the

Fontana ground-water barrier represents a left-lateral strike-slip fault. The Fontana

ground-water barrier may truncate the Rialto-Colton fault (Dutcher and Garrett, 1963)

and therefore, may be a younger tectonic feature. Trenching In Holocene-age alluvium

across the mapped location of the Fontana ground-water barrier did not reveal any

evidence of faulting at that location (Rasmussen, August l, 1985).

The Glen Helen fault, located approximately 2 3/ 4 miles north-northeast of the site, ls

a northwest-trending strike-slip fault which ls parallel to, and northeast of, the San

Jacinto fault. The youthful geomorphic appearance of the Glen Helen fault in the

vicinity of Glen Helen Regional Park Indicates that it Is an active fault. In contrast, the

apparent lack of youthful fault geomorphology along the northernmost segment of the

San Jacinto fault as It enters the San Gabriel Mountains suggests that the Glen Helen

fault may represent the active trace of the San Jacinto fault at this location as an en

echelon segment between the San Jacinto and San Andreas faults. The Glen Helen fault

may help transfer motion from the San Jacinto fault to the San Andreas fault.

The Rialto-Colton fault (ground-water barrier) has been mapped approximately 3 miles

southwest of the site. This fault was originally mapped as a ground-water barrier by

Eckis (1934) and named the Rialto-Colton fault. Dutcher and Garrett (1963) enlarged

on Eckis' original work and stated: "Its position is approximately located, largely on

28

c·~ARY s R.AS.'Ml.JSSEN .~ A~:.;;tj(,)(-::I A"rF.t·;




hydrologic evidence but partly on subsurface geologic evidence." The Rialto-Colton fault

disrupts the normal flow of ground water in the area and diverts the flow southeast along

the north side of the fault. The Rialto-Colton fault is considered to be inactive, as

trenching across the fault has shown that It does not offset the upper 5 to 7 feet of

Pleistocene-age alluvium (Rasmussen, January 9, 1981 ).

The active San Andreas fault is located approximately 4 miles northeast of the site. The

location of the main, active trace of the San Andreas fault Is evidenced by vegetation

lineaments, fault scarps, springs, linear ridges, and offset drainages. Although the San

Andreas fault ls characterized overall by right-lateral, strike-slip movement, the San

Bernardino Mountains have been uplifted along !ts trace.

The east-west-trending Sierra Madre-Cucamonga fault ls located approximately 4 1/2

miles northwest of the site (Bortugno and Spittler, 1986; Morton and Matti, 1987, 1990).

The prominent Sierra Madre-Cucamonga fault zone trends along the entire south front

of the San Gabriel Mountains and Is the main fault system along which the mountain

range has been uplifted. The Cucamonga fault zone ls the eastward extension of the

Sierra Madre fault zone which was responsible for the M5.8 Sierra Madre earthquake of

June 28, 1991. The Cucamonga fault zone, which has a significant thrust component, has

been mapped in detail from Lytle Creek westward to San Antonio Canyon (Morton and

Matti, 1987, 1990). The Cucamonga fault is considered to be active from Lytle Creek

to approximately Cucamonga Creek (Matti et al., 1982; Morton and Matti, 1987).

The Cleghorn fault, located approximately 10 miles north of the site, ls a left-lateral

strike-slip fault with a significant dip-slip component. This fault Is considered to be

active by Weldon et al. (1981) as evidenced by scarps, stream offsets and disrupted

terrace remnants. However, Hart et al. (1988) believe that the geomorphic evidence of

Holocene left-lateral, strike-slip displacement reported by Weldon et al. (1981) and

Meisling (1984) ls most likely landslide related, rather than tectonic. According to Hart

et al. (1988), the Cleghorn fault is generally poorly defined and lacks geomorphic

29




evidence of Holocene left-lateral displacement. Weldon et al. (1981) also suggest that

the Cleghorn fault may merge with a previously unnamed northeast-trending fault {Kinley

Creek fault) and that the motion of the Cleghorn fault may be transferred along this

fault to the North Frontal fault system of the San Bernardino Mountains. Both the

Cleghorn and the Kinley Creek faults are considered to be potentially active faults on

the Fault Map of California (Jennings, 1975).

A set of discontinuous south-dipping reverse faults referred to as the North Frontal fault

zone (Bortugno and Spittler, 1986) is located approximately 12 miles north-northeast of

the slte along the northern flank of the San Bernardino Mountains. Several of the

faults place pre-Cenozoic basement rocks over Quaternary alluvium {Dibblee, 1973;

Miller, 1987). Dibblee and Miller also mapped thrusting and folding within Quaternary

alluvium. The youthful fault scarps developed in the alluvial units {Miller, 1987) suggest

that the North Frontal fault zone Is active. Portions of the fault zone are sufficiently

well defined according to fault hazard criteria established by the State of California to

be included within Alquist-Prlolo Earthquake Fault Zones.

The Chino fault, located approximately 23 miles southwest of the site, is considered to

be a potentially active fault, as evidenced by the occurrence of laterally deflected

drainages; low, east-facing, modified fault scarps; offset of Pleistocene-age or younger

alluvium; warping of paleosols; and the occurrence of a strong vegetation lineament

coincident with the suspected trace of the fault within Holocene-age sediments as

observed on aerial photographs taken prior to the construction of Prado Dam (Weber,

1977; Heath et al., 1982). The Chino fault Is considered to be a right-lateral fault which

dips steeply towards the southwest (Durham and Yerkes, 1964). The Chino fault appears

to be part of the Elsinore fault system.

A summary of significant faults and their distances from the site is presented In the

following table:

30

OAR Y S RASMT../:~.38EN & ASSOC~IATES



FAULT

San Jacinto

Transfer fault (N20El

Unnamed fault (N38W)

Fontana Ground-Water Barrier

Glen Helen

San Andreas

Cucamonga

Cleghorn

North Frontal Fault Zone

Chino-Elsinore


DISTANCE (MILES)

on-site

<50 feet

2,100 feet

2 1/4

2 3/4

4

4 1/2

10

12

23

Project No. 3156.1

DIRECTION

Southeast

Northeast

Northwest

North-Northeast

Northeast

Northwest

North

North-Northeast

Southwest

Other active or potentially active faults are located within the general region, but

because of their greater distance from the site and/or lower expected maximum probable

earthquake, they are less important to the site.

SEISMIC HISTORY

The accuracy of locating earthquake epicenters is not always sufficient to determine

which fault they are associated with. Estimates of magnitude and epicenter locations

for earthquakes prior to Implementation of recording instruments were based on

descriptions of the earthquakes by individuals in different areas. Seismic instrumenta

tion did not become available until about 1932, and these earlier instruments were

Imprecise. The earthquake Ioca tions shown on Enclosure 7 are el th er based on

instrument locations or by analysis of isoseismal contouring.

The San Jacinto fault has been the most seismically active fault in southern California

(Allen et al., i965). Between 1899 and 1992, eight earthquakes of M6.0 or greater have

31




occurred somewhere along the San Jacinto fault between the San Gabriel Mountains and

Mexico (Lamar et al., 1973; Kahle et al., 1988).

A summary of the dates of these earthquakes, their approximate locations, and their

estimated Richter magnitude is presented in the following table:

DATE LOCATION MAGNITUDE

December 25, 1899 San Jacinto Valley (estimated} 7.1

April 21, 1918 San Jacinto Valley (estimated} 6.8

July 22, 1923 South of Loma Linda (estimated) 6.3

March 25, 1937 Southeast of Anza 6.0

October 21, 1942 Southeast of Borrego 6.5

March 19, 1954 East of Borrego 6.2

April 9, 1968 Borrego Mountain 6.5

November 24, 1987 Superstition Hills 6.6

Since 1899, earthquakes on the San Jacinto fault of Richter magnitude 6.0 or greater

have occurred every 5 to 19 years. The earthquakes In 1899, 1918 and 1923 occurred

along the northern portion of the San Jacinto fault; the earthquake in 1937 occurred

along the middle reach of the San Jacinto fault; and the earthquakes In 1942, 1954, 1968

and 1987 occurred along the southern portion of the San Jacinto fault (Lamar et al., 1973; Kahle et al., 1988).

No slgnlflcant earthquake epicenters can be specifically attributed to the possible

transfer fault (N20E}, the unnamed fault (N38W} or the Glen Helen fault. However, a

distinct northeast shift of a line of northwest-trending earthquake epicenters ls located

southeast of the site, just north of the city of Rialto (Enclosure 7). This shift in the line

of northwest-trending epicenters may correspond with the Glen Helen fault and/or the

unnamed fault of Reeder. The shift in epicenter locations may be evidence which

32



El Rancho Verde Country Club Project No. 3156. I

supports the theory that transfer of the majority of the motion from the San Jacinto

fault to the Glen Helen fault occurs before the San Jacinto fault reaches the site.

No large earthquakes have occurred along the San Andreas fault in the southern

California area In recent time. The last major earthquake along It in this area was the

great earthquake of 1857, which was centered at Fort Tejon, north of Gorman. This

fault has a pattern of almost no movement for long periods of time (131 years, Sieh,

1984), followed by a sudden release of energy. The Fort Tejon earthquake had an

estimated magnitude greater than 8.0, comparable to the 1906 San Francisco earthquake

(Wood, 1955).

Documented evidence for large earthquakes along the Cucamonga fault has only recently

been found. This fault ls part of the Sierra Madre-Cuc.amonga fault system which

ruptured during the M6.4 San Fernando earthquake in 1971. This fault was also

responsible for the M5.8 Sierra Madre earthquake which occurred on June 28, 1991.

Subsurface investigations by this firm have documented evidence of Holocene activity

along the Cucamonga fault (Rasmussen, December 29, 1989; April 18, 1990).

Numerous earthquakes of Richter magnitudes greater than 4.0 have occurred in the area

surrounding the intersection of the Helendale fault and the North Frontal fault zone

along the north side of the San Bernardino Mountains. The locations of these epicenters

are not precise enough to exactly correlate the earthquakes with these two faults. It

ls possible that these earthquakes are related to both faults.

Several earthquakes with estimated magnitudes between 6.0 and 6.5 have been located

along the Chino-Elsinore fault zone between the Santa Ana River and the Gulf of

California during historic time. The closest and most recent of these larger earthquakes

occurred north of Elsinore In 1910. Three earthquakes greater than M6.0 have occurred

along the southern extension of the Chlno-Bsinore fault zone In northern Mexico since

33




1932; however, no earthquakes of this magnitude or greater have been recorded along

the northern end of the fault since 1910 (Lamar et al., 1973).

No significant earthquakes are known to have occurred during historic time along the

unnamed fault, the transfer fault, the Glen Helen fault, the Cleghorn fault, the Chino

portion of the Chino-Elsinore fault zone, or along the Fontana or Rialto-Colton ground

water barriers.

SEISMIC ANALYSIS

Significant earthquakes affecting the site may occur on the San Jacinto, Glen Helen, San

Andreas and/or Cucamonga fault zones during the life of the proposed residential

structures. However, the San Jacinto fault is considered to be the most Important fault

to the site from a seismic shaking and ground rupture standpoint as it traverses the site.

Recurrence intervals for maximum probable earthquakes cannot yet be precisely

determined from a statistical standpoint, because recorded information on seismic

activity does not encompass a sufficient span of time. However, based on the

information available at this time, It is our opinion that a probable earthquake of M7 .0

may occur along the San Jacinto fault. Large earthquakes could occur on other faults

In the general area, but because of their greater distance and/or lower probability of

occurrence, they are less important to the site from a seismic shaking standpoint.

campbell (1981, 1987 and 1989) and Campbell and Borzognla (1993) have presented data

that show a relationship between the distance from a causative fault, the earthquake

magnitude, the subsurface materials and peak horizontal ground accelerations. Based on

peak ground accelerations recorded during the 1989 Loma Prieta (M7.l ), the 1992

Landers (M7.6) and the 1994 Northridge (M6.7) earthquakes, it is our opinion that

Campbell's 1987 attenuation relationship yields the most realistic values. Calculation

34

C.lA.RY ~-:"? 'R .. A.SM'fJSSEN' <'i<. A8SCJC.~IA'T'T-r.~J




of peak ground acceleration using Campbell (1987) for a M7 .0 earthquake occurring on

the San Jacinto fault on the site yiekls a peak ground aeeclcralion of 0.62g. Higher

ground accelerations could occur on the site if the direction of rupture propagation is

towards the site. Increased amplitude, higher frequencies and shorter duration have

been observed In waves recorded at stations in line with the direction of rupture

propagation (Decker, 1994).

This acceleration should not be used as a design value for insertion In the Uniform

Building Code formula; rather, It should be considered as an aid In the evaluation of the

structural design of the human oeeupaney structures to be placed on the site.

The 1992 Landers earthquake sequence has resulted in an Increase in the probability of

a large earthquake on the San Andreas and San Jacinto faults. The Working Group on

the Probabilities of Future Large Earthquakes in Southern California (November, I992)

issued Phase I of a two phase report which analyzes the effects of the Landers-Big Bear

earthquake sequences on the San Andreas fault, the San Jacinto fault and the Mojave

shear zone. Their report concluded that the June 28th earthquakes Increased the stress

toward the fa!lure limit for the San Bernardino Mountain and Coachella Valley segments

of the San Andreas fault and for the San Bernardino Valley and San Jacinto Valley

segments of the San Jacinto fault, thereby advancing the time to failure for both faults.

The 1988 Working Group 30-year probability for a large earthquake to occur along the

San Bernardino Mountain segment only of the San Andreas fault was previously 20

percent, for the Coachella Valley segment of the San Andreas fault It was 40 percent,

for the San Bernardino Valley segment of the San Jacinto fault it was 20 percent, for

the San Jacinto Valley segment of the San Jacinto fault It was IO percent, and for the

Anza segment of the San Jacinto fault it was 30 percent (Working Group on California

Earthquake Probabilities, 1988). If the Coachella and San Bernardino segments can

rupture at the same time, the probability of a large earthquake increases to 30 percent.

The Working Group's Phase I report (1992) was not Intended to replace the 1988

35




Working Group report and does not alter the 30-year probabilities Issued for the San

Andreas and San Jacinto faults in that report. However, as regional earthquake activity

has increased since 1985, and the Landers-Big Bear earthquakes have Increased the stress

towards the failure limit for parts of both the San Andreas and San Jacinto faults, the

chances for large earthquakes to occur in southern California may have slightly

Increased. New findings on the first subcvent in the Big Bear earthquake (Jones et al.,

1993) and the discovery of northwest-trending ground surface rupture along a fault in

the epicentral area by Gary Rasmussen and Wessly Reeder, San Bernardino County

Geologist, may change their models and predictions. The San Bernardino Valley segment

of the San Jacinto fault traverses the site.

The January 17, 1994, M6.7 Northridge earthquake has resulted in an increase in the

static stress on a 20 to 40 kilometer (12 to 25 mile) section of the San Andreas fault

near Palmdale (Simpson et al., 1994). This has resulted in an increase of about l to 3

years of tectonic loading by long-term deep slip on the San Andreas fault (Simpson et

al., 1994). The effect of the Northridge earthquake on the San Jacinto fault or on other

sections of the San Andreas fault has not yet been determined. The largest changes in

static stress resulting from the Northrldge earthquake occurred on faults in the thrust

belts which lie east and west of Northridge (Simpson et al., 1994). This would include

the Sierra Madre-Cucamonga fault zone, which produced the 1971 M6.4 San Fernando

earthquake. The combined effects of the 1992 Landers and 1994 Northridge earthquakes

on major faults in southern California, such as the San Andreas and San Jacinto faults,

has not yet been estimated.

SLOPE STABILITY

Ground lurching occurs when earthquake ground motions are at right angles to a ridge,

cliff, bluff, stream bank, cut slope or artificial embankment (Richter, 1958). Cracks

form parallel to the orientation of the ridge and with continued ground shaking, slumping

36




of material adjacent to the ridge edges may occur. Ground lurching effects were

reported during the Loma Prleta earthquake and were also observed by this firm along

a ridge at the edge of upper Covington Flats in Joshua Tree National Monument after the

Aprll 22, 1992, M6. l Joshua Tree earthquake.

The presence of the low-angle features within trenches l, 9, 13B and 19 and the steep

slopes (20 percent gradient) associated with the different age terraces on the site,

including the Rialto bench which forms the southwest boundary of the site, indicate that

there may be a potential for future ground lurching on the site. The recommended

restricted use zone has been extended to include the features observed in these trenches

and a 50-foot setback from the toe of the Rialto bench is also recommended.

Any artificial cut slopes created during grading higher than 15 feet should be Individually

evaluated for building setbacks from potential ground lurching by the engineering

geologist.

GROUND WATER

Five wells owned by West San Bernardino county Water District are located along the

perimeter of the site and a sixth (well No. 2) is located approximately 860 feet north

northeast of the north-northeast site boundary. Well No. l is the northwesternmost well,

well No. 35 the southeasternmost. The location and numbers of the west San Bernardino

County Water District wells arc shown on Plate 1. The following table gives the

elevations of each well and three recorded water level measurements. Wells are listed

in order from northwest to southeast. All data is from Leon Long, West San Bernardino

County Water District (personal communication, April, 1994).

37

().ARY S f{ASMUSSEl'T ,'Y. A~~~'.:.;;C)C.:'.TATTI:~::>




Well No.

1

34

2

4

5

35

Elevation (feet)

1,470

1,450

1,430

1,398

1,383

1,365

De2th to Ground Water (Elevation) (feet)

3/93 10/93 3/94

123 (1,347) 9 (1,461) 22 (l,448)

116 (1,334) 0 (1,450) 11 (l,439)

213 (1,217) 46 (l,384) 38 (l,392)

133 (l,265) 50 (1,348) 39 (1,359)

130 (l,253) 50 (1,333) 40 (l,343)

176 (1,189) 46 (1,319) 34 (l,331)

A possible ground-water barrier may exist at depth between well Nos. 34 and 2, 2 and

4, and well Nos. 5 and 35. Well Nos. 34 and 2 had a difference in ground-water levels

of 117 feet in March, 1993. Well No. 2 which ls topographically higher than well No. 4

had a ground-water level of 48 feet below that and well No. 4 in March, 1993. Well Nos.

5 and 35 had a difference in ground-water levels of 64 feet on the same date.

None of these possible ground-water barriers appear to be effective at shallow depths

(depths less than 50 feet). No evidence for faulting was observed in the field or on the

aerial photographs reviewed between well Nos. 34, 2 and 4. The possible ground-water

barriers may be the result of older, Inactive faults or may be a result of the subsurface

stratigraphy.

A fault trending N32E, 68SE was exposed ln the wash approximately 200 feet northeast

of the northeast site boundary between well Nos. 5 and 35. No surface evidence for this

fault was found on the site during our field reconnaissance or on the aerial photographs

reviewed. This fault may be inactive but may still act as a ground-water barrier at

depth, or it may be the edge of the fault zone associated with the N20E-trending

transfer structure located just southeast of the site and may be present at depth

between the wells. Alternatively, it may not exist on the site and is a left step of the

38

CJ.ARY ~3 n. A~3M l.1 SSEl·J ,~. A.AHC!C:IA.rrB.--::-_.:;




fault south of the site. The higher rate of change in ground-water levels in well No. 35

suggests there is a ground-water barrier south of it.

Ground water was encountered at a depth of approximately 9 feet at the north end of

the trench on the driving range (T-12) in October of 1993. A "pulse" of high ground

water moved through the wells on the site around October 1, 1993. This "pulse" was the

result of the unusually high precipitation that occurred in the upgradient areas during

the previous spring. Trench 25 was excavated just southeast of trench 12 on February

29, 1994. Ground water was not encountered until a depth of 19 feet. Shallow ground

water encountered in trench 12 in October, 1993, was the result of this "pulse" of ground

water.

The area immediately east of, and lower than, the site within the Lytle Creek channel

was the most northwesternmost reach of an artesian area In the early 1900 's, brought

about by the barrier effects of the San Jacinto fault at depth (Mendenhall, 1905).

Following periods of high precipitation, temporary artesian conditions may occur in and

adjacent to the driving range and West San Bernardino County Water District's well No.

34. Springs were observed in this area In October, 1993.

Some perching of ground water was observed during our previous subsurface Investiga

tions of the southeastern half of the slte (Rasmussen, August 25 nd 26, 1982) within the

northeasternmost trenches. This resulted from the presence of minor to moderate

amounts of clay within the sediments. The amount of ground water was considered

insignificant from a geologic hazard standpoint (Rasmussen, August 25 and 26, 1982).

LIQUEFACTION

Matti and Carson (1991) and the San Bernardino County General Plan Geologic Hazard

overlay map of liquefaction susceptiblllty (San Bernardino County General Plan, 1989)

39

OAR Y S 'FlAS.ML.JS~~EN k . .A.SSOC:IA"I'I:r.:~'.:>



El Rancho Verde Country Club Project No. 3156,l

show that the northeastern portions of the site, northeast of the San Jacinto fault, lie

within a zone of high liquefaction susceptibility. Youd and Perkins (1978) and Youd et al. (1978) listed the parameters for increased liquefaction susceptlb11ity as: 1) high

ground water (less than 33 feet below the surface); 2) sandy sedimentary deposits: 3)

recent age of material; and 4) close proximity to an active fault. The Holocene-age

sediments encountered within the northeastern and northwestern portions of the site

(those areas closest to the active Lytle Creek channel) fall Into at least three of these

geologic parameters.

Thin beds of sandy sediments relatively free of coarse materials were encountered In

many of the trenches from this subsurface Investigation and from our previous subsurface

investigations (Rasmussen, August 25, 1982; August 26, 1982). The lateral extent and

continuity of these sediments is uncertain, but they are not expected to be continuous

for significant distances due to the interfingering and channeling of cobble and boulder

size deposits. Past evidence of liquefaction was observed in trenches T-1 IA and T-llB,

T-12, T-23 and T-24 in Pleistocene-age materials. These deposits are probably too dense

to undergo liquefaction under present conditions.

Because of the large prevalent grain size of the Holocene alluvium, the sediments on-site

are considered to have a low potential for liquefaction from a geologic standpoint during

periods when ground-water levels are less than 33 feet below the surface. water well

records Indicate ground-water depths less than 33 feet below the surface are rare and

occur for relatively short periods of time (usually less than l year) following unusually

high periods of precipitation. The additional parameters required for liquefaction

(density and grain size distribution) should be evaluated by the project geotechnical

engineer to determine the site's final susceptibility to liquefaction.

40

(:;.An.Y S HAt'.-JMl.TE~SEN & ASS()CIA'TF~!-=1




SUBSIDENCE

Project No. 3156.1

Subsidence of the ground surface in the San Bernardino Valley has been documented In

published geologic literature (Fife et al., 1976; Lofgren, 1971; Miller and Singer, 1971 ).

The primary cause of subsidence has been the removal of large quantities of ground

water from the ground-water basin. The maximum subsidence observed in the valley

occurred immediately northeast of the San Jacinto fault, near Loma Linda, and has been

about 1.3 feet from about 1943 to 1969 (Lofgren, 1971 ).

Static ground-water levels adjacent to the site have fluctuated greatly, reaching peaks

in the winter of 1981 with two wells located north of the site flowing at the surface, and

In October of 1993 with springs and a well adjacent to the driving ranch (West San

Bernardino County Water District Well No. 34) flowing at the surface. This Is due, in

part, to the close proximity of the site to the Lytle Creek wash. Current water levels

on the site vary from a depth of 11 feet at the golf course driving range to 34 feet in

the southeastern portion of the site (Leon Long, West San Bernardino County Water

District, personal communication, April, 1994).

Lofgren ( 1971) indicated that less than 0.2 feet of subsidence had occurred in the

vicinity of the site up to about 1970. No evidence of subsidence was observed on the

site, in the field or on the aerial photographs reviewed. Subsidence is not considered

to be a potential hazard to the site unless static ground-water levels are allowed to

decline significantly (greater than 100 feet) in the future from their present levels.

Ground cracking due to subsidence, if it were to occur on the site in the future, would

be expected to occur along major subsurface structural boundaries, such as along the

plane of the San Jacinto fault.

41




FLOODING

Project No. 3156. l

Portions of the site and adjacent areas have been subjected to flooding in the recent

past, especially in 1938 and 1969. Especially prone are the lower lying areas of the site

northeast of Oakdale Avenue and northwest of the country club. Construction of the

flood control levees has at least partially, if not completely, mitigated flood hazards.

The site appears to lie outside of the 100-year flood plain as designated on the San

Bernardino General Plan Flood Hazard overlay map for the Devore and San Bernardino

North quadrangles (San Bernardino County General Plan, 1989). An evaluation of the

potential for flooding of the site and the adequacy of existing flood control devices falls

under the purview of the project engineer.

Seismically induced flooding of the northwestern portion of the site might occur if the

Metropolitan Water District aqueduct, located approximately 2,500 feet northwest and

up-gradient of the site, should catastrophically fail during a large earthquake. The

potential for flooding of the site caused by failure of the aqueduct in the event of a

large earthquake should be addressed by the engineer for the project.

The golf course irrigation pond located at the northwest end of the site could fail during

a large earthquake. We understand that this pond will be replaced with two steel

reservoirs by West San Bernardino County Water District (Leon Long, personal

communication, February, 1994). Ground accelerations of 0.62g are expected on the

site. A seismic analysis should be performed for the proposed reservoirs before their

placement on or adjacent to the site as they could catastrophically fall during a large

earthquake and cause flooding of some portions of the site.

We also understand that lakes are planned for the redesigned golf course. Lakes should

not be placed within the recommended restricted use zone due to the hazard of surface

fault rupture and catastrophic failure of the lakes unless mitigated by proper engineering

design.

42

(JARV ~3 RASMt.J~3~.3EN .~ ASSc:)C.:..'!IA"TE~:3




SE I CHES

Project No. 3156.1

We understand that several lakes are planned for the redesigned golf course. Selchlng

could occur in these lakes during a large earthquake. Seichlng consists of the periodic

oscillation of a body of water which often occurs during, and following, an earthquake.

The potential seiching which may occur in any lakes proposed for the site during strong

ground shaking on the site should be calculated when the location and side and bottom

configurations of the lakes becomes available. The downstream effects which may occur

if one or more of the proposed lakes overflows or ruptures during a large earthquake

should also be evaluated at that time. A comprehensive evaluation of potential

inundation paths resulting from overflow or rupture of any lakes proposed for the site

falls under the purview of the civil engineer for the project.

Potential seiching may also occur in the existing irrigation pond, located at the

northwest end of the site.

CORRELATION OF SURVEY DATA, TRENCH LOCATIONS AND THE RECOMMENDED RESTRICTED USE ZONE

The locations of the recommended restricted use zones that were established during two

of our previous subsurface Investigations (Rasmussen, August 25, 1982; August 26, 1982)

were based on surveyed fault lath locations. Church Engineering used the orlglnal

surveyors (Brown & Mulllns, Inc.) notes from our files to create a survey base map. Only

some of Church's fault lath locations correlated well with those mapped during our

previous investigations. We plotted the lath locations on the 200-scale base map (Plate

1) that were used to establish our original recommended restricted use zone. The lath

locations that we used were copied from the original surveyor's map onto the geologic

field map used for our previous investigations of the site (Rasmussen, August 25, 1982;

43

C~.ARY ::..:; FlA~3'MTJSS1:!'.:;N ~~- AS::...:::;c..:>c::1A~rF...::~.:;




August 26, 1982). Church Engineering has now Incorporated these locations into their

data base.

We have altered and extended the original restricted use zone recommended In our

previous reports (Rasmussen, August 25, 1982; August 26, 1982; January 5, 1993) due to

the complexity and width of the northern San Jacinto fault on the site. Faulting where

found in the field was flagged and the lath locations surveyed by Church Engineering,

Inc. and added to their data base. Survey points and the recommended restricted use

zone are shown on Plate 2.

CONCLUSIONS

Evidence for fault rupture was found In four of the six trenches excavated during two

of our previous subsurface investigations of the southeastern half of the site (Rasmussen,

August 25, 1982; August 26, 1982) and in 13 of 23 trenches excavated during this

subsurface investigation. The northern San Jacinto fault was found to step west on the

site and is characterized by a complex series of left-stepping en echelon faults and

splays accompanied by a wide zone of faulting. Fault rupture was found to be withln 6

inches of the surface in the Holocene sediments In the southeastern portion of the site.

The San Jacinto fault may be dying out on the site or its rate of activity may be

decreasing approximately 950 feet northwest of the "engineer's house". It is our opinion

that the faulting and fracture features observed within the trenches are good evidence

of the main, active traces of the San Jacinto fault zone.

No evidence for faulting was found in the trenches from our previous subsurface

lnvestlgation conducted adjacent to the extreme southeastern portion of the site

(Rasmussen, February 29, 1980).

44




Severe seismic shaking, surface fault rupture and possible ground lurching through the

site should be expected within the next 100 years from an earthquake along the San

Jacinto fault.

The geologic conditions for liquefaction, including severity of earthquake shaking and

shallow ground water, may exist within the northeastern and northwestern portions of

the site. The additional parameters that are necessary for liquefaction (density and

grain size distribution) should be evaluated by the project geotechnical engineer.

Evidence of previous liquefaction of portions of the site was observed in several of our

trenches.

The presence of the low-angle features within trenches !, 9, 13B and 19 and the steep

slopes (20 percent gradient) associated with the different age terraces on the site,

including the Rialto bench which forms the southwest boundary of the site, indicate that

there may be a potential for future ground lurching on the site. The recommended

restricted use zone has been extended to include the features observed in these trenches

and a 50-foot setback from the toe of the Rialto bench is also recommended.

A possible ground-water barrier may exist at depth between well Nos. 34 and 2, 2 and

4. These ground-water barriers may be the result of older, inactive faulting, faults

which do not extend to the surface, or they may be a result of the subsurface

stratigraphy. No evidence for faulting associated with these ground-water barriers was

observed on the site in the field or on the aerial photographs reviewed.

The area immediately east of, and lower than, the site within the Lytle Creek channel

was the most northwesternmost reach of an artesian area in the early 1900 's, brought

about by the barrier effects of the San Jacinto fault at depth (Mendenhall, 1905).

Following periods of high precipitation, temporary artesian conditions may occur in and

adjacent to the driving range and West San Bernardino County Water District's well No.

34.

45




Construction of the flood control levees has at least partially, if not completely,

mitigated flood hazards. The site appears to lie outside of the 100-year flood plain as

designated by the San Bernardino General Plan Flood Hazard overlay map (1989). An

evaluation of the potential for flooding of the northeast portion of the site and the

adequacy of existing flood control devices falls under the purview of the project

engineer.

Seismically induced flooding of the northwestern portion of the site could occur If the

Metropolitan Water District aqueduct, located approximately 2,500 feet northwest and

up-gradient of the site, should catastrophically fail during a large earthquake. The

potential for flooding of the site caused by faBure of the aqueduct in the event of a

large earthquake should be addressed by the engineer for the project.

The golf course irrigation pond located at the northwest end of the site could fall during

a large earthquake. We understand that this pond will be replaced with two steel

reservoirs by West San Bernardino County Water District (Leon Long, personal

communication, February, 1994). Ground accelerations of 0.62g are expected on the

site.

Any lakes planned for the development or golf course should not be placed within the

recommended restricted use zone due to the hazard of surface fault rupture unless

mitigated by proper engineering design.

We understand that several lakes are planned for the redesigned golf course. Seichlng

could occur in these lakes during a large earthquake.

Potential selchlng may also occur in the existing Irrigation pond, located at the

northwest end of the site.

46



El Rancho Verde Country Club Project No. 3156,1

Several utilities cross the San Jacinto fault on the site. These utilities are vulnerable

to breakage and/or deformation due to surface rupture during a large earthquake on the

San Jacinto fault.

Subsidence Is not considered to be a potential hazard to the site unless static ground

water levels are allowed to decline slgnifieantly (greater than 100 feet) in the future

from their present levels. Ground cracking due to subsidence, if it were to occur on the

site Jn the future, would be expected to occur along major subsurface structural

boundaries, such as along the plane of the San Jacinto fault.

The surficial soils have a high erosion potential from both wind and water when not

planted with proper vegetation.

RECOMMENDATIONS

A maximum probable earthquake of M7.0 may occur along the San Jacinto fault, located

on the site; therefore, we recommend that human occupancy structures be designed

accordingly.

Due to the potential hazard of surface fault rupture, human occupancy structures should

not be placed within the recommended restricted use zone as shown on the enclosed 200-

scale map (Plate 2).

Utilities should cross fault traces at a high angle in order to minimize the amount of

damage to utility lines should movement occur along the faults. Shut-off valves for gas

and water mains should be considered on the pressure side of fault zone crossings.

47

,'.}A:RY S .f'-lASMf_TSSEN k . . A~3SOC!AT"'ff:~1




Due to the potential hazard of tensional ground surface fracturing of geologic materials

on the site in the event of a large earthquake, we recommend that foundations and slabs

of proposed structures be reinforced to resist tensional ground cracking.

The potential for flooding of the site caused by failure of the Metropolitan Water

District aqueduct, located 2,500 feet northwest and upgradient of the site, the existing

irrigation pond on the site, the proposed West San Bernardino County Water District

steel reservoirs, or any proposed lakes on the site in the event of a large earthquake

should be addressed by the engineer for the project.

A seismic analysis should be performed for the proposed West San Bernardino County

Water District reservoirs before their placement on or adjacent to the site, as they could

catastrophically fail during a large earthquake and cause flooding of some portions of

the site.

The potential seiching which may occur in any lakes proposed for the site during strong

ground shaking on the site should be calculated when the location and side and bottom

configurations of the lakes becomes available. The downstream effects which may occur

if one or more of the proposed lakes overflows or ruptures during a large earthquake

should also be estimated at that time. A comprehensive evaluation of potential

inundation paths resulting from overflow or rupture of any lakes proposed for the site

falls under the purview of the civil engineer for the project.

An evaluation of the selche potential of the existing irrigation pond should be performed.

The geologic parameters for liquefaction (including shallow ground water and severity

of earthquake shaking) exist on portions of the site. The additional parameters

necessary to result in liquefaction on the site should be evaluated by the project

geotechnical engineer.

48




The maximum inclination of all cut slopes should be 2 horizontal to 1 vertical. Any cut

slopes which could Intercept slope runoff and are greater than 15 feet in height should

be provided with a concrete-lined "V" ditch above the top of the cut slope to protect the

slope from erosion. Any artificial cut slopes created during grading higher than 15 feet

should be Individually evaluated for building setbacks from potential ground lurching by

the engineering geologist.

We recommend a minimum setback for human occupancy structures from the top of

natural steep slopes should be a horizontal distance of at least 10 feet or the horizontal

distance calculated by extending a 2:1 (horizontal to vertical) plane, extending upward

from the toe of the steep slope, whichever is greatest.

Positive drainage of the site should be provided, and water should not be allowed to pond

behind or flow over any cut, fill or natural slopes. Where water Is collected in a common

area and discharged, protection of the native soils should be provided, as the native soils

are moderately to highly susceptible to erosion by running water.

The trench backfill generated dutlng our previous subsurface investigations was not

compacted and the significance of all on-site fill, including the fill generated during this

and previous investigations, with respect to the proposed development should be

addressed by the project geotechnlcal engineer. Evidence of trenching by others was

also observed during our field reconnaissance.

The boundaries of the recommended restricted use zone for human occupancy structures

should be shown on any future grading or development plans for the site. The final

grading plan for the site should be reviewed and approved by an engineering geologist

prior to any grading.

Grading of the site should be evaluated by the engineering geologist by in-grading

inspections.

49




Subdralns may be required beneath any proposed fills placed within the on-site drainages.

The need for subdrains should be evaluated by the engineering geologist during grading.

TSB:GSR/pg

Enclosure l: Enclosure 2: Enclosure 3: Enclosure 4: Enclosure 5: Enclosure 6: Enclosure 7: Enclosure 8:

Geologic Index Map

Respectfully submitted,

GARY S. RASMUSSEN & ASSOCIATES, INC.

Terri S. eehner Senior Staff Geologist

~«7/4-____ Gary S. Rasmussen Engineering Geologist, EG 925

Trench Logs (Rasmussen, February 29, 1980) Trench Logs (Rasmussen, August 25 and 26, 1982) Magnetometer Results (Rasmussen, February 19, 1980) Magnetometer Results (Rasmussen, August 25 and 26, 1992) Trench Logs (this investigation) Earthquake Epicenter Map References

Plate 1: Geologic Map Plate 2: Map Showing Trench Locations and the Recommended Restricted Use Zone

Distribution: Nitto America Co., Ltd. ( 1) The KTGY Group ( 4) Church Engineering, Inc. (1)

NOTI<: Plates l and 2 of Project No. 3156. l have been superseded by Plates l and 2 of Project No. 3156.2

50


ENCLOSURE I GEOLOGIC INDEX MAP

Gary S. Rasmussen & Associates, Inc.

Nitto America Co. - El Rancho Verde Country Club Rialto. California

Base Map: Dutcher and Garrett (1963)

Scale I" - 1/2 mi. Project No. 3156. l

·~····,.

:: . ···-·

0

22

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Older alluvium

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Legend (cont.)

Fault; dashed where approx., dotted where concealed, queried where doubtful U upthrown side D down thrown side

Ground-water barrier; queried where physical nature of barrier unknown or uncertain

Magnetometer traverse GSRA - 8/26/82 Project No. 1830

Magnetometer traverse GSRA - 2/29/80 Project No. 1558

// ~ . ./ ~···~--;---·· /.; ....... . . ./--:·· . ' /. '.

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ENCLOSURE 2 TRENCH LOGS (from Project No. 1558)

Gary S. Rasmussen & Associates, Inc. Nitto America Co. • EI Rancho Verde Country Club

Rial to, California Project No. 3156.l

I logged by ELB


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ENCLOSURE 2 TRENCH LOGS (from Project No. 1558)

Gary S. Rasmussen & Associates, Inc . .Nitto America Co. - El Rancho Verde Country Club

Rialto, California Project No. 3156.1


ENCLOSURE 3 TRENCH LOG UNIT DESCRIPTIONS

(from Project Nos. 1825 and 1830) Gary S. Rasmussen & Associates, Inc.

Nitto America Co. - El Rancho Verde Country Club Rialto, califomia

Project No. 3156.1

General Description

I Topsoil - organic materials intermixed with silty sands and occasional gravel, pebbles or cobbles; color: ( lOYR 4/2) to (IOYR 6/2) unless otherwise indicated. Often is gradational into Unit 13.

2 Fill - disturbed alluvium

3 Silty sands - fine grained with clean medium-coarse sand interbeds and occasional interbeds of clay

4 Medium-coarse sands finely laminated, often cross-bedded with occasional interbeds of coarser sands and/or gravels and cobbles

5 Gravels and cobbles with many cobbles greater than 1-foot diameter

6 Gravels and cobbles interbedded with lenses of medium-coarse sands and silty sands with many clasts greater than 1-foot diameter

7 Silty sands with clay (probably representing relic paleosols)

8 Gravels - similar to Unit 5 except finer grained, greater than 50% 1-6" diameter clasts by volume

9 Gravels - (Unit 8) interbedded with lenses of medium-coarse sands and silty sands

10 Fine-medium sands with silt and minor amounts of clay (similar to Unit 7 except with depositional characteristics)

11 Coarse sands, gravels and cobbles, differentially stained with iron oxides along various, more permeable, interbeds

12 Depositional unit which occurs within the eastern portion of the property, broken into four members:

a. Partial aquiclude to ground water, grades from medium-coarse sands near its base ( SGY6/ l) upwards to fine sands with silt and moderate amounts of clay ( 5Y2/ l)

b. Fine to medium sands with occasional coarse sand interbeds, color grades from (lOYR 5/4) at its base upwards to (IOYR 6/6)

c. Fine sands with silt and minor amounts of clay (SY 7 /2)

d. Fine sands with silt (SY S/l)

13 Dark silty sands with minor to moderate amounts of gravel and/or cobbles, especially near its base. Often is gradational into the base of Unit 1. Color: (SY 6/1) to 5Y 4/1 ). Probably contains some wind-blown materials

14 Fine-medium silty sands with gravel and occasional cobbles (similar to unit 4 except with increased silt)


(lOYR 4/1) 1/13 5 - - -6

color indication vertical gradational change lateral gradational change

5Y 2/1 5Y 4/1 5Y 5/1 5Y 5/2 5Y 6/1 5Y 6/4 5Y 7/2 5Y 7/3 5Y 7/4 5Y 7/5 5Y 7/6 5Y 8/1 5Y 8/4

5YR 5/3 5YR 5/6 5GY 6/1 lOY 6/2 lOYR 4/2 lOYR 5/4 lOYR 6/2 lOYR 6/4 lOYR 6/6 10YR7/4 lOYR 8/2

10YR5/4

Sediment Color Designations

Olive black Olive gray Intermediate (5Y 4/1 - 5Y 6/1) Light olive gray Light olive gray Dusky yellow Yellowish gray Intermediate (5Y 7 /2 - 5Y 7 /6) Intermediate (SY 8/4 - 5Y 6/4) Intermediate (5Y 7 /2 - SY 7 /6) Moderate yellow Yellowish gray Grayish yellow

Intermediate (5YR 5/2 - 5YR 5/6) Light olive brown Greenish gray Pale olive Dark yellowish brown Moderate yellowish brown Pale yellowish brown Intermediate (lOYR 5/4 - lOYR 7 /4) Dark yellowish orange Grayish orange Very pale orange

lOYR (Hue) S(Value) 4(Chroma)

Color determination of the sediments observed within the trenches was based upon the Rock Color Chart (Goddard et al., 1980)

I I I I I I I I I I I I I I I I 'I I I

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ENCLOSURE 3 TRENCH LOGS (from Project Nos. 1825 and 1830)

Gary S. Rasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club

Rialto, California Project No. 3156.l

70

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i;;;c:LOSURE 4

CARY S. l\ASMUSSEX & ASSOCIA':'ES, Theodore C. King-Tr. 11408-Rialto, CA.-Project ::o. 1825

Horizontal and Vertical scale 1"=5'

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i ENCLOSURE 3 TRENCH LOGS (from Project Nos. 1825 and 1830)

Gary S.'Rasmusscn & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club

· Rialto, California Project No. 3156.l

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;ENCLOSURE 3 TRENCH LOGS ((mm Project Nos. 1825 and 1830)

Gary S. Ra~mussen & Associates, Inc. Nitto America co: - El Rancho Verde Country Club

~ialto, California Project No. 3156.1 980

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TRENCH LOGS (from Project Nos. 1825 and 1830) : Gary S. Rasmussen & Associates, Inc.

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1'.'Jitto America Co. - El Rancho Verde Country Club Rialto, California

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Rialto, California Project No. 3156. l

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, ENCLOSURE 3 TR~NCH LOGS (from Project Nos. 1825 and 1830)


', Rialto, California Project No. 3156.1

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ENCLOSURE 3 TRENCH LOGS (from Project Nos. 1:825 and 1830)

Gary S. Rasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Couritry Club


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-10 ENCLOSURE 3

TRENCH LOGS (from Project Nos. 1825 and 1830) Gary S. Rasmussen & Associates, Inc.

Nitto America Co. - El Rancho Verde Country Club Rialto, California

Project No. 3156.1

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ENCLOSURE 4

i'-lagnetometer t rilverse 1 continued below

~GNETOMETER TRAVERSES (from Project No. 1558) ' Gary S. Rasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club


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ENCLOSURE 4

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MAGNETOMETER TRAVERSES (Crom Project No. 1558) Gary S. Rasmussen & Associates, Inc.


Project No. 3156.1


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ENCLOSURE 5 MAGNETOMETER TRAVERSES (from Project Nos. 1825 and 1830)

Gary S. Rasmussen & Associates, 1 nc. Nitto America Co. - El Rancho Verde Country Club


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I >.

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u " I c .... (J .... ....

0 ~

(J (J (J c.. "' I 0 r, w .D

l l I

:; c~ w "D

'" (J

l l

I I I I I I I I

f I

.,.,

I I I I

.u

'" '" > ...... " u

l "=<.lpprox. J 50' bv pace method . - '

,,., "' "' " ) " '" '" ·r< .,., (J

"' " u .... .... c <11 .... .... ....

0 0 <11 CJ .....

<11 <11 u (J '" "" ci;i:: > Q!

"' 'O '" (J w

'" (J4-< ..... ~

l i ! n! I

ENCLOSURE 5 MAGNETOMETER TRAVERSES (from Project Nos. 1825 and 1830)


Rialto, California Project No. 3156.I


Trench 7 Logged by TSB Drafted by PAG 70'

5'

0

.-

boulder layer

t;;\ sandy gravel: white (2.5Y 812): ~ dry; mediunl dense; stightty

cemented; mOderately to well sorted; subangular \o sub<ounded, granitic fine to coarse gravel

sandy gravel: yellow (2.SY 7/5); fine- to nwdiun1-grained; n1ediun1 dense; 'Z' silt (possible pedogcnic); subrounded granitic and n1etamorphic clasts (granitics don1inant}; 0)(.idation n\Otlling (reddish yellow, 7.SYR 616); well sorted

ENCLOSURE 6 TRENCH LOGS



50'

I

4 N86E

40'

I

gravelly sand with silt (n1atrix supported clasts): pale yellow (2.5Y 7/-4); dry; medium dense; eolian sandy silt matrix atte(ed by pedOgenic processes; moderately ix>rous; subrounded granitic clasts

gravelly sand with silt {matrix supported clasts); pale yellow {2.SY 7/4); dry; n1edium dense; eolian sandy silt n1atrix altered by pedogenic processes; nlOderatety porous; subrounded granitic clasts

~andy gravel: yellow (2.SY 7/6); fine- to medium-grained; medium dense; 'Z' Silt (possibly pt!dogenic)'; subrounded granitic and ff1etamorphic clasls (granflics dominant); oxidalion nlOtUing (reddish yellow. 7.SYA 616); well sorted

South wall

105'

20'

30'

I

ID'\ sandy gravel: white (2.SY B/2}; \::!) dry; medium dense; slighUy

cemented; moderately to w9'1 sorted; subangular to subrounded, granitic tine to coarse gravel

20'

I

bedding : apparent l,dip 12°E

manganese staining dusky red (10A 3/2)

C\ sandy gravel: light gray o,:;:y (SY 712); dry; loose; subangular

to subrounded graniOc clasts; (young olluvial channel deposits)

IO'

I

80'@

degraded diorllic Clasl

I

I bedding apparent dip S"W

(';;;\ sandy gravel with silt: pale yellow ~ {2.5Y 7/4): p()fOUS; pedogenic silt

n1atrix; subrounded fine to coarse clasls; medium dense; slightly cemented

O'

O'

5'

10'

70'

IO'

15.

I I I I I I I I

Trench BA Logged by TSB Drafted by PAG

5'

IO'

O' IO'

I

® silty sand: light gray (2.5Y 7/2), 0

·

dry) to light yellowish brown (2.5Y 614, damp); fine-grained with brownish yellow (10YR 618) oxkte staining and mottling

20'

I 3"NE apparent dip

sandy gravel: light yellowish brown (~.SY 6/4). ~ry);

30'

I

N38E l!o.. Northwest wall

upper 6-8° compacted from plowing

40' 50'

I I 60' 70'

I rE apparent dip

O'

5'

10'

' 15'

to olive yellow (2.SY 616); dan1p; medium dense, inlerbedded gravelly sand, sandy grav_el an~ ~ble layers· channelized - rare cross bedding; 2 .silt lamin~e· subangular to subrounded granitic (dominant) and metamorphic (15% clasts};weakly cemented; some iron-oxide staining; dark red (lOYA 316) manganese stained when overlain by fine-grained untt

bedding 13°NE apparent dip © silty sand and sandy silt wit~1 ravel:

grayish brown (2.5Y 5/2, dry)' dry; medium dense to loose; generally m sive subangular

I5'

I I I

70' 80'

I I

O'

I I I 10'

I I 15'

lS"E apparent dip

I I Horizontal and Vertical Scale: 1"=5'

apparent dip 3"NE

14" diameter City of Rialto high pressure water main; trends NSSW across trench

orange @ oxide staining

90'

I

sandy gravel with cobbles: while (10YR 8/1): dry; IOose; subangular to subrounded fine to coarse gravel; bedd0<1, generally poorly sorted; young alluvial channel deposits

® sandy gravel: white (10YR 812); dry; n1edium dense; moderately well bedded: subangular to subrounded, fine to coarse gravel; iron-oxide and manganeseoxide staining and nlOllling

IOO'

I

sandy gravel; light yeUowish brown to olive yellow (2.SYA 614 to 616); damp; medium dense; subangu'8r to subrounded fine to coarse gravel with cobble lenses and layers: manganese and iron-oxide staining; slightly cenlented, soote degraded clasts

llO'

I

to subrounded fine to coarse ravel -clasts are dominantly granitic; roots d rootlets throughout; fine matted roolle s concentrated in upper 6-12" (root zone); Sliphlly ix>rous; compacted from pk>wing in u~per 6-8"

dark red manganese stained gravel

I20'

I

silly sand: light gray (2.5Y 7/2),

I30'

I

iron ·OJ<,ide sta1111:rt

--.-.

manganese stained gravel

I40'

·---·


O'

5'

IO'

I5'

Gary S. 'Rasmussen & Associates, Inc. dty) to light y-ilih brown (2.5Y 6/4, damp); fine-grained with t>rownesh yellow (10YR 618) oxide staining and mottling Nitto America Co. - El Rancho Verde Country Club

Rialto, California Project No. 3I56.I

finch SA (continu~d) L ged by TSB i Drafted by PAC '

N38E J!o..

I

170' 180' ~90' 210' 160'

200' I 140'. 150'

I ~ silty clay: brown ( ~ 0'.R 5/3); \.:::;J dan1p; somewhat fissile, hard:

moderately plastic; eroded upper

I I I _,,_ _____ ~I'_ ________________ _:_ ___________________ disturbed zone ----· I

I O'

I 5'

I I 10'

contact; bioturbated lower contact: rare charcoal and son1e burrows

grass root zone

orange iron-oxide stained prolate clasts

t~:::::;:-:--~::=-~--=--=--=--=--=-~==-~=-=-:-:.-:_:::_:::...:.::..:::-:.:::.:::~::~==:~==--~-=-=-.:;-=-::::::::=:-"'==~~==:::::--:::::~~-:::::::_:::::--:::;:~~-::~~~::=:=::-::::::!:~:::::~":~LA~"TH~--,---~-~pe~!ibrb1egougewi1h -·-- --- ----·-· ·-:..--- ·--=-:-- ·~ prolate clasts 0 0. -· ·~ -

I 20° apparent dip

I 15' /' -----'"-NSOW 89NE shears"\ N48W S8NE

I® I I I I I I I I I I

silty sand and sandy silt with gravel: grayish brown (2.SY 512, dry); dry; medium dense to loose; generally massive subangular to subrounded fine to coarse gravel - clasts ate dominantly granitic; roots and rootlets throughout; fine matted rootlets concentrated

. in upper 6-12" (root zone); slightly porous; compacted from plowing in upper 6-8"

210'

5 I beddirlQ apparent dip B"NE

10'

20'

@ silty sand light gray (2.5Y 712). dry) to hght yellowish brown (2.SY 6/4, dan1p); fine-grained with bfownish yellow (1 OYA 618) oxide staining and mottling; tension fractures and faults throughout

bend

v 220'

I

\ /;;'\sandy gravel: white {10YA 8/2): dry; \!;,./ nl0dium dense: moderately wen bedded;

subangular to subrounded, fine to •N56W 73SW <1' apparent vertical offset

coarse gravel; iron-oxtde and manganeseoxide staining and n10ltling

Horizontal and Vertical Scale: 1"=5'

mfilled along planes

230'

I

dark red n1angaoese stained

N44E

N54W 81NE

,.... (across bottom bottom of trench) oxidatKln along fault plane

240'

I

B"NE apparent dip

sandy silt: light gray (1 OYA 7/2); dry to damp; sitt laminae common; dense; some iron-oxide mottling; silt some pinker stained areas; fractured

Ii:\ fine sand with secondary '-Y silt laminae: light grayish

brown (2.5YR 612); damp; dense; highly fractured 250' 260'

I I

sandy gravel: light yellOwish brown lo olive yellow (2.SYR 614 to 616); damp; medium dense; subangu'81 to sub<ounded fine to coarse grevet with cobble lenses and laye!S; mangar"'58 and iron-oxide staining; s~Uy cen1ented; some degraded ciasts

•

cobble layer with orange 1ron-ox1de stain mg

"' .

~N48W 68NE 9" apparent Ver\ical n1edium-grained

gravel

~··

> 1 · apparent vertical offset. prolale clasts

coarse sand with oxide nmltling

dark red nlanganese staining

270'

I 280'

I


5'

10'

15'

20'

284'


15'

20'


Project No. 3156. l


Trench BB Logged by TSB Drafted by PAG

70'

5'

10'

15.

60'

I @ silty sand w'th gray (1 OYA •3/1 g:ave/; very dark

massive· min ), damp; loose· intermix~ wi~~ f~l~bb!os: top;oil may contain Ir , flll areas ash and wood d . obns

moderately 'well and well soned bedded

gra sandy

vef wfth cobbl channeled and es, cross-bedded

@ ~:dl129)~a;ryo~· 1 light gray

to · • oose· subrounded '. subang,ular (young all gran1t1c clasrs·

uv1al channel d , . epos1ts)

@ sandy sill with . f.ght gray (2 5Y minor gravel· dry to damp: m:~~ to SY 7/l ); and rootlets throu um dense; roots

ghout; b1oturbated

Horizontal and Vertical Scale: 1"::5'

50'

I

root zone

®

A N42E

40'

I

sandy gravel with gray (2.SY 7/0 cobbles: light medium dense·-~Y l/2); damp· bedde<l and ~ erately wetl ' s~brounded clas~; £~bangular lo minor rare de · minor rootlets· staining in som9'eaded clasts, oxide' areas

30'

I 20'

I be<lding 8PParent dip •'W

@ sandy gravel with gray (2.sY

7/0 _ ~ cobbles: fight

medium dense· 7/2), damp; subangular-sub poorly bedded; rounded clasts

10'

I

ENCLOSURE 6

Gary S R TRENCH LOGS

O'

N'tt • asmu I o America Co. - :1sen & Associates I Rancho Ve ' nc. Rialto, Califo . rde Country Club

Pr . rn1a oJect No. 3156.1

O'

5'

10'


Trench 8B (continued) Logged by TSB Drafted by PAG bend A.J--"""N'-'1'""5-"'E"---

V bend v

140' @ 130'

10'

15'

20'

sandy silt with minor gravel: light gray (2.5Y 7/0 to SY 7/1 ); dry to dan1p; n1edium dense: roots and roollets throughout; bioturbated

contact

I

N51 E bend V N88E

. 120'

I wood debris 28" OD concrete

irrigation pipe pioce of brown glass

hub cap (edge)

bend v

·-~·

25' large granitic boulder

loose, fine to coarse sand

I piece of wood or large root

laminated ~silt

sand layer

trench trends =N48W l site across trench J

hydrofitl _.----- 12" OD decomposed deposits concrete irrigation pipe,

infilled in cut trench

Horizontal and Vertical Scale: l" = 5'

sandy gravel: light olive brown to light yellowish brown (2.5Y 5/4 -614); damp: dense: poorly bedded; subangular to subrounded clasts

110'

I bloturbated contact

---. o'

.J N42E

70' 100'

I 90'

I 80'

I channel edge, 2rw apparent dip

open burrow with nest material

infillod burrows

~open \"rr~w J . ~ -~-. -_--:.---:::=::---:-==. -:- '\ ~ -- ....___ ---.-:..-.-__.,..... . o,

0

·.o. 10'

®

·o. - •

.J N42E

sandy gravel with cobbles: light gray (2.SY 7/0 - 2.SY 7/2); damp; nl6dium dense; moderately well bedded and sorted: subangular to sub:rounded clasts: minor rootlets: minor rare degraded clasts, oxide staining in some areas 165' 160'

®

I bioturbated contact

15'

20'

sandy gravel with cobbles; light gray (2.SY 7/0 - 2.SY 712); damp; medium dense; moderately well bedded and sorted; subangular to subrounded c/asts; minor rootlets; minor raro degraded clasts, oxide staining in son10 areas

2· OD iron pipe =<N42W

coarse sand layer

..

infilled burrows

150'

I 5° slope: possibly original surface, subsequently buried by additional sandy silt deposits - or overlying sandy silt is bottom of fill

140'

- -.

burrows


15'

20'

10'

15'

20'


Rialto, california Project No. 3156.1


Trench 9 TSB Logged by AG Drafted by P

o~

5'

10'

15'

20'

25'

30'

JO'

I dense growth of poison oak on scarp

© lo (2 SY 7/6), el w · ith eobbles. y d matrix with gravel w se san

sandy dense, coar ? subangular dry; medium enically altered.) some degraded. pores (pedog d gramtoc clasts, tly granitic to subrounde ell bedded, domm~S%) n10derately w n1etamorph1c clasts with some

20'

I

NSW 68SW

le yellow (2.SY 7/4), tine sand. pa d rare gravel, n1mor coars:l~~~Y. lam mated. and massive to upper 6-12 · bedded m cross- and staining oxide n1ottlmg

allow (2 SY 7/6), ravel with cobbles e ~and matrix w1lh © sandy g dense, coars ? subangular

dry, medium enically altered I ome degraded, pores (pedog d granitic c1asts, s tly granitic to subrounde I bedded, dom1nan % n1oderately wel n1ctamorph1C (45 ) clasts w1lh son1e

30'

I

d sandy gravel interbedded sandto"7.ght yellowish hghl obve brown

6141 dry, dense,

brown (2 5Y 5/4 -ded ~and, lan1maled coarse cross-bed ded gravols,

lar to subroun subangu well bedded

. 1 Scale: Vert1ca Horizontal and 1"=5'

N75E ......_ North wall

40'

I

28. concrc_';e 1rr1gatt0t1bypt backhoe broken e (abandoned PIP • no water)

. prolate pebbles

50' 60'

I I

E apparent dip 10aN

. ellow (2.SY 7/6); 'th cobbles. Y d matrix with

d gravel w1 rse san © san Y . dense; coa ? ubangular dry· nl6d1um ically altered.) s degraded,

• nn.-togen ts· some .. pores l~"ded granrtic clas ·. antly granitic to su~~~~~ well bedded; .:~~n (•S%) mode . h some metam clasls wit

70'

10'

root zone

15'

20'

25'

30' N27E BOSE

ENCLOSURE 6

ENCH LOGS Inc TR - Associates, ' Club S Rasmussen & h Verde Country Gary. · _ El Rane o . Nl

·uo America CoR. ·alto California

I ' 3156.1 Project No.

1 Trench 9 (continued)

70'

I

Logged by TSB Drafted by PAG

i 80'

I 5"NE apparent dip

I - ---. _. __ ~·--· --.-

I I I I I I I I I I I I I I I I

15'

20'

25'

30'

15'

20'

25'

30'

140'

b'SW apparent dip

--•

silty sand: possible remnant soil? light yellowtsh brown (2.5Y 614); JX)rous

Horizontal and Vertical Scale: l" - 5'

150'

I

·--

90'

I

160'

I

grey, fine sand ktnse

N75E

100' 110'

I I

170' 180' 190'

I I 15'

20'

25'

30'

1 t"SW apparent dip

\

120' 130' 140'

I I 26"SW apparent dip

15'

20'

25'

@ silty sand and sandy bilt with gravel: grayish brown (2.SY ~2. dry); dry; medium dense to loose: gener0.Jly n1assive· subangulat to subrouncie4 fine to coa~se gravel; clasts are dominantly ·:granitic; roots and rootlets throughout; slightly porous





Trench lO Logged by TSB Drafted by PAC

75' 70'

I

main \race San Jacinto fault

60' I 50·

® silty sand I ~rayish bf:~ ~~~ 5/2Silt with gravel: ense 10 IOO . , dry)· d .

to subround:· generally nla~sNry •. medium are domin ftne to coarse e, subangular

throughou:"'rt~ granitic: roots gr';;"el: clasts in upper 6~ i"'." matted rootlet:" rootlets 2 (root zone)· r concentrated

coarse sand I ' s ightly porous --·---· ayer

LATH ·-5' :.---'-

~

_.:,...- . .--:--- .

D

10'

. -·· ,, .U

@ increase in fi

f,-'<'1-\"hf-.:..:;~~-..X.1 s~lty sand {~~~d and 7"NE apparenl di Solt laminae ), more p than upna an~ cross bedd\nn

20'

0

4"N E apparent d.

dusky red (1 OR 312) op mangan in grave~~' staining

l./Uow unit

•

9"NE L 1· yvr ponKln ol · "•

,. 2· . •- -, '" ,._ro • ~ - Wide crush Olive yellow 12 S~wn to

with prolate las zone S' dry, to 2 SY 61. 614,

103' 100'

.... . . _,,___ "'·-·· . ··-"' coa cemented and diSplaced @ rser in cen\e .' magnesium-nc· h A. sandy gravel· 1· main trace '· dry) · oght yell ·,- ..,:,;~;-·· :::,-:.:;;.;- -~ ::.:::-"'~ :::::" "" ~ site across t and ·n sands and cobble la ded gravelly sa d Pl. niodium ~rO< 50• _ ;;:i~~ dip bedd~~ and warped2 (" Silt \an~\na:.e~~;b channelized~l r~~Ca~~x gravel . ·-- -·~·· .· --- ~.. "-·· ·-"' -·-~ . """~""""' ............. . manyane~e-ome orange iron-oxo " cl.asts; weakly

unil A, stamod when overli\~~ ~taming: dark red y hnc-gHl.incd

Horizontal and V . ert1cal Scale: l" = 5'

I

10'

15'

20'

J N38E Southeast wall

40'

I ~.,~sand . coarse sand: ' . silty sand and bt'own to light 11gtlt yellowish (2.SY 614 gray - 2.SY 712)

root zone

90'

I

30' 20' I 0'

I I 1S'NE apparent dip I 1 ~NE apparent dip

apparent vertical displacenlent 10·

6-a· apparent vertical displacement

7" 12"SW

N56W 66NE .and co:::'s~b~and 12

" app~rent gouge• along la It \ vertical i

N1:7W SSNE tJ ' diSplacemenl

~ f~lts join togethOf 5S'NE ' 1 from bottom of apparen.~ dip

trench r 00 oPPoSite wait

75'

• ,o

50

© IO'

sandy gravel · 811); dry; kJo w_1th cobbk:ls: white fine to se, subangular (10YR S:trat1"f.ie~~e gravel; poorty t~ sdudbrounded

11

• :1~nerally poo ed and a uv1a1 channel ....... - rly sorted· (yo U<'.>"POSllS)' m" ' ung ' tno( boulders

15'

© inter bedded gra sandy gra I vel with cobble . ve and sand

gray (1C!IYR 811

_ ~- ~hite to hgtit Y dense; bedded· 11 ), dry; medium subangular to · pob orly s0<ted su round · 20' ed clasts

ENCLOSURE 6

O'

5'

10'

15.

. Gary S. Ra::ENCH LOGS Nitto America Co. - u~lsen & Associates I . Rancho Ver • nc.

R1a_Ito, Californi de Country Club

Project No. 3156~1


Trench llA Lo~gcd by TSB Dr~fted by PAG

silty sand and sandy· silt with gr av.et grayiStl bl'own {2.5Y 513. Ory): dry, . n10dium dense to ioose; generally massive; subangular to subrounded fine to eoilrse gravel; ctasts are dominantly granioc;

N52E ..,.,_

5'

10'

15'

O'

foots and rootlets throughout, especially in upper 6-8'; slightly ~rous

10' 20'

I I

:f'SW apparent dip

fine sand to silty sand: .. light g(ay (!OYA 7/2) Md pinkish gray (5YR 7/Z) with caddish yellow (7.5YR &'SJ .oxtde mottling; massive to finely laminated and cross bedded; dry; dense; nlOderately fractured {tension fractures)·, roots ak>ng fractures and discolOred pinkish gray

Northwest wall

30'

I

17"\ very fine sand to silty sand: light \0/ gray (SY 712); damp; dense; finely

laminated to massive; brownish; yellow (10YR 6/8) oxide staining; minor clay layers; contorted due to liquefaction

sandy gravel: light yellowish bfown (2.5Y 6/4, dry); lo olive yellow (2.5Y 616); damp; medium dense; interbedded gravelly sand, sandy gravel atid cobble layers; channe\ized - rau~ cross bedding;

C'\ laminated and cross\!::!) bedded graveny sand,

abandoned iron and n1anganese oxide Staining

Z' silt lan1inae; subangular to subrounded granitic (don1inant) and n1etamorphiC (15°) clasts; weakty cen1ented; son1e iron-oxide staining; dark rad (10R 316) n1anganese stained when overlain by fine grained unit

40'

I 50'

I

£.\ sand: light gray l5Y 712) lo white \OI llO't'R 811); fine to medium grained;

son,e ccoss bedding and lamioae; fractured and contorted due to liquefaction

5"SW apparent dip

60'

I 28 • concrete irrigation pipe. trends N01 E

rt:"\ very fine sand to silty sand: light 'OI gray (SY 7/2); damp; deose; finety

laminated to massive; brownish; yelk>w (10YA 6/8) oxide staining; minor clay layers; contorted due to liquefaction


70'

O'

5'

10'


Rialto, California Project No. 3156. I


Trench l IA (contmued) Logged by TSB Draft~d by PAG

70'

O'

5'

10'

140'

O'

5'

10'

15'

Horizontal and Vertical Scale:

80'

I

150'

I

1" = 5'

I

II:'\ remnant srrty \:!I sand bed

90'

I

160'

I

bend v 4• steel (rusted) pipe, trends N79W

N52E

100'

I City of Rialto 14" highpressure water main, N34W (asphalt-wrapped steel pipe)

170'

I

very fine sand to silty sand: light g<ay (5Y 712): damp; dense: finely laminated to massive; brownish; yeaow {l OYA 618) oxide staining; minot day layers; contorted due to lfquefac;:Uon

110'

I

180'

I



120'

I

bedding apparent dip S"SW

N49E I

190' {.\ ·.•

I l!:y I

200'

I

sand; lighl gray (5Y 7/2) 10 white (!OYA &'1); tine lo medium grained;

very fine sand to s•ty sand; light gray (5Y 712); damp; dense; finely laminated to massrte; bfownish; yellow (10YA 618) oxide staining; minor clay layers; contorted d~e to liquefaction

some cross bedding and laminae: rr.c-ltKO<I and conlortO<I due lo liquefaction

Rialto, California Project No. 3156.1 140'

~-:------t-0' . ,__

distorted {liquefied) n1edium sand layer

•

210'

5'

10'

15'

O'

5'

IO'

15'


Trench 1 lA (continued)


210'

O'

220' 230'

I I

N49E

240'

I 1 o· abandoned concrete pipe; broken by backhoe -no water; trends NGOW;

250'

I - • --. --:---- grass root zone

5'

10'

15'

Horizontal and Vertical Scale: l" = 5 •

::)

manganese-oxide

stained

. . coarse. sand with gravel ·'. . " <'.'.\ • ...

Silty sand o.

/;;'I coarse sand with gravel: white (10YR 8/1); \:)J n1ediun1 dense; massive and contorted;

interbedded with subunits A.z and ~

very fine sand to silty sand: light gray (SY 7/2); dan1p; dense; finely laminated to massive; brownish; yellow (10YR 618) oxtde staining; minor clay layers; contorted due to liquefaction

258'

5'

10'

15'

20'





Trench llB

O'

Logged by TSB Drafted by PAC

10'

I carbon 14 2

10'

15"NE apparent dip sample @

5'

10'

15'

®

70'

5'

10'

15'

75°NE apparent dip

56"NE apparent dip

@ silty sand: light gray (1 OYR 7/1), dry) to light brownish gray (1 OYA 6/2, moist) with brownish yellow (1 OYA 618) oxide staining; finely laminated where sandier to massive; minor coarse sand and gravel; medium dense; moist

silly sand/sandy silt: natural (dry); grayisf1 brown (2.SY 513). n1edium dense to loose; generally n1assive; n1inor bioturbation; organics; slightly porous; roots and rootlets lhroughout; n1inor subangular to subrounded fine to coarse gravel

80'

I

cross bedded and lan1inated coarse sand with silt larninae

f'i:\ sand: tight gray (SY 7/2) 10 white '-JI (10YA 811); fine to n10dium grained;

some cross bedding and laminae; frac~ lured and contorted due lo liqucfact\on

6" apparent vertical offset 41/z' apparent

vertical offset

30' main trace San Jacinto fault l

LATH

100'

I

very fine sand to sandy silt white (1 OYA 811 l to light gray (SY 7/2); dense; damp; finely larninated and cross bedded; browniSh yellow ( 1 OYR 1!111) oxide staining; contorted due to liquefaction

106'

40'

l

O'

5'

10'

15'

N41E ...... Nor~hwest wall

! 50'

I

•

60'

I WSBCWD abandoned (dry) 4' steel water line. trends N51W

70'

grass----:=:- =- ~ \~;.-,~"'--.--.-__ br_u_sh-j_ O,

\\2/ . .

•. Qractation_al· change·

IA\ very fine sand to silty sand: light GI gray (SY 712); damp; dense; finely

laminated to massive; brownish; yellow (10YR 6/8) oxide staining; minor clay layers; contorted due to liquefaction


5'

10'

cross- bedding and laminae increase

15'




Trench 12 Logged by TSB Drafted by PAG

O'

5'

IO'

15'

10'

I

Silty sand layer

sandy gravel with cobbles and boukiers; iron- and manganese-oxide stained

® silty sand and sandy silt with gravel: grayish brown (2.SY 51'3, dry); dry; medium dense to loose; generally massive; subangutar to subrounded fine to coarse gravel; clasts ate dominantly granitic; roots and rootlets throughout, especially in upper &-a·; slightly porous

Horizontal and Vertical Scale: l" - 5'

grass root zone (sod), compacted

boulder cut by backhoe

20'

I ~ laminated gravelly \:..:J sandlsandy gravel

sandy gravel with cobbles; manganese- and iron-oxide stained; poorly to moderately bedded; OOgraded Ol9lan1orphic and dioritic clasts

I N26E )!..

Northwest wall

30'

I

coarse Ian nated and cross-bedded sand

boulders (fen oul after wall c~ned)

40'

I

fine laminated sand and sitty sand

50'

I

m1erbedded laminated and manganese- and iron-oxide stained sandy gravel and gravelly sand with minor cobbkts

ti:'\ sandy gravel with ~ cobbtes; iron and

manganese-oxide stained

60' 70'

I clay layer

coarse sand Jense

(A"\ fine lan1inated silty sand \:::J and fine sand; cross-bedded

light gray (10YR 7/2) to pinkish gray (5YA 7/2); contorted and liquefied


O'

5'

10'

15'



I I I I I I I I I I I I I I I I I

Trench 12 (continued)

70'

O'

-' "

10'

15' -.... . ·.:--.:~.


fine laminated

80'

I

sand and silty sand

Horizontal and Vertical Scale: 1"=5'

90'

I

·-.

~SW apparent dip I coarse sand layer

100'

I

liquefaction feature in fine sand

N26E

110'

I

I'::'\. sandy gravel; v:::;J oxide staining

3· steel irrigatk>n pipe (golf coarse), trends N83E

cross bedded and contorted fine laminated sand coarse sand layers

with oxide mottling

120'

I pink manganese- . stained coarse grave1

silty sand with clay; greenish gray

~ liquefaction

130'

I reddish brown clayey sand

I fine sand layers


140'

5'

10'

15'

.. 20'

G S Rasmussen & Associates, Inc. ary_ • Co El Rancho Verde Country Club Nitto Amenca · - .

Rialto, califorma Project No. 3156.1


Trench 12 (continued l Logged by TSB Drafted by PAG

140'

10'

15'

20'

24 • abandoned eoncrete irrigation pipe

150'

I

channel edge apparent dip 2G"NE

~ brown fine sand and 'OJ silty sand with minor

gravel; orange iron and pink manganese staining

210'

10'

20'

25'

reddish brown clayey sand

220'

I

pink manganese s1aining

I Horizontal and Vertical Scale: l" = 5'

grayish brown silty sand

topsoil: yetlOwish brown

160'

I

230'

I

·o

236'

170'

I

10'

15'

20'

N26E

1; of water in bottom of trench - lower sides caving; water still flowing in, 2:00 p.m., 10/6/93

180'

I 190' 200' 210'

I

3• steel kogation pipe -

I

golf course spnnklet system trends •N68E reddish brown

clayey sand {o\d fill line

gravelly sand wr..h cobbles. tight gray

Of sod line}

··°-

coarse cross-bedded sanci and laminated with warse, n'\Odera.tely

well sorted dark yellowish brown gravel

gravel; light gray

ENCLOSURE 6 TRENCH l.OGS

Gary S. Rasmussen & Associates, Inc. Nitto America Co. - El Ran~ho "'.erde Country

Rialto, Cahforma Project No. 3156.l

10'

15'

20'

Club


Trench 13A Logged by TSB .Draftediby PAG

70'

5'

10'

15'

140'

5'

10'

15'

bedding apparent dip S"E

Horizontal & Vertical Scale: 1 It ; 5'

60' 50'

I I

©

_- N86E

40'

I

ex~r~nlely weathered and oxidized clast, fissile texture, held together

South wall

by siliceous grains only © interbedded cobbly gravel and gravel, sandy gravelly sand: light

gray (2.5Y 7/2), dry to da . subangular to sub n1p, loose; rounded clast · moderately well bedd . .

5•

granitic; n1inor lan1ina:c1· don1inantly

laminated sandy gravel with eobbles

l~inated sandy gravel with cobbk!s

•'

30'

I 20'

I

bedding apparent dip 3"E

10'

o.,ooc:>·"' o·O· •°' .....

I

·•

~oarse sand, laminated interbedded with fine- ' to coarse gravel

O'

5'

10'

bedding apparent dip s"E

(2.SY 7/2 to SY 713)

17'\. lamtnated sand v::.J gravelly Y gravel lnterbedded with . sand, coarse sand and hght yeuowish brown eobble layers· (2.S_Y 7/2) and pale Y~:R5~4), light gray · lanunaled, inlerbedded and I 213). dry to damp; htghty weathered schtstose some cross bedding; clasts; subangular with and coarse maric minor manganese-oxid some _subrounded clasts; e coating on some clasts

. . .. . - '° . . • . . . .. a.=

n1edium to coarse gravel, well sorted, with nlinor cobbles: ltght yeUowish brown (2.5Y 614)." subangular to subrounded clasts

bcdrling apparent dip 5"E

ENCLOSUl~E 6 TRENCH LOGS

70'

5'

10'

15'

. Gary S. Rasmussen & A 1 Nitto America Co _ El R ssoc ates, Inc. · ancho Verde c Rialto c l'f . ountry Club , a 1 orma

Project No. 3156.1

I Trench 13A (continued) Logged by TSB Drafted by PAG

I I I

170'

® silty sand with gravel and cobbles: light brownish gray to dark grayish brown (2.5Y 6/2 [dry] to 2.5Y 4/2 !wet]); 'A' horizon

160'

I

4 N86E

150' 140'

I 5'

• • • . ....

I • oo 0 •...•• ,. .••.••.

I I I I I I I I I I I I I I

10'

15'

© interbedded bbly gravel, sandy gravel and gravelly sand: light gray (2.5Y 7/2), dry lo darnp; loose; subangular to subrounded clasts; n1oderately well bedded; dominantly granitic; Olinor laminae

Horizontal & Vertical Scale: 1" = 5 •

laminated sandy gravel interbedded with gravelly sand, coarse sand and cobble layers: light yellowish brown (10YR 6/4], light gray (2.SY 712] and pale yellow (SY 213); dry to damp; lan1inated, interbedded and son1e cross bedding; highly weathered schistose and coarse mafic ctasts; subangular with some subrounded c~ts; minor manganese-oxide coaling on some ciasts


10'

15'



I I I I I I I I I I

I I I I I I I I

Trench 13B Logged by TSB Drafted by PAG

70'

bedding apparent dip 30°W

15'

20'

(main fault), n1ay con1e all the way to surface, nlinimum of 6" from surface

soil offset 1 •

60'

I ©

.o

50'

. . I silly sand w1t11 gravel and cobbles: liqt1l brownish gray to dark grayisll brown (2.5Y 612 (c\ryj lo 2.5Y 4/2 [welj); 'A' riorizon

main fault: N11E 40°SE prolate clasts

\

bedding apparent dip 3°E

bedding -------appare~l dip 11 °W -------- fault:

faults merge at base of trench, total apparent vertical displacement

of NB contact -sY:r:' total apparent vertical displacement

of BID contact -4·

lnterbedded sandy gravel with cobbleS, sandy cobbles, gravelly sand and sand: light gray (2.5Y 7/2.); loOSe to medium dense; dry to dan1p; subangular to subrounded clasts; poor to moderate bedding: minor laminae; n1inor bOulders

Horizontal & Vertical Scale: 1" = 5'

-N07"E, 40SE

;tt N75E South wall

30• ® 20' 10' ©

I iOterbedded sandy gravel with I I interbeddcd cobbly gravel, sandy cobb'8s, sandy cobb'8s, gravelty gravel and gravelly sand: light sand and sand: ltght gray (2.SY gray (2.5Y 7/2), dry to dan1p; loose; 7/2); loose to medium dense; dry subangular to subrounded clasts; to dan1p; subanguiar to subrounded laminated gravelty moderately well bedded; dominantly

O' 40'

I ~--------------::-----------r minor laminae; minor bOulders • ~~~~~~~~~~~~~~~~~~~=c\aS~~ts~;=poo~~r~lo~mod~:•~ra~l~e~bod~~d~ing~;~:::-~~~~~~~san~d~,~c~h~a~n~ne~liz~·~e~d~~~g~r~a~ni~ti:c;~rn~in~o~r:l~af:rn~in~a~e~~~~~~~~ O'

\ bedding apparent dip 15°W

be ding apparent dip 1°E

CaCO, coaled tension fracture

possible tension fradure

fault plane: N11W 31NE, a· apparent vertieal offset at contact between units

coarse sand layers

·o. ~ •

' laminated sandy gravel ~terbedded with graveUy sand, coarse s~d and cobble layers: lighl yellowiSh brown (l~YR 614), lighl gray (2.SY 7/2) and pale yel~ (5Y 213); dry IO damp; laminated, inlerbedded Bnd some cross bedding; highly weathered schistose and coarse mane claSts; subangular with iome subrounded clasts; n1ioor manganese-oxide coating on son1e clasts

chann~ deposit with cObbles


5'

10'



ITrench 13B (continued) Logged by TSB

I Drafted by PAG

I I I I I I I I I I I I I

20'

25'

30'

140'

silty sand with gravel and cobbles: hgl1t brownish gray to dark grayish brown (2.5Y 612 [dry[ to 2.5Y 412 (wotJ); 'A' horizon

0

silty sand grades into or is mixed with top so41

.•

,©. .?

1---0:::.- . ' --. ..

, I·

~~3BSo:_,_

gravel

(;;"'\ paleosol: fine sand to silty sand, ~ pale yellow (2.5Y 7/4) to light yellowish

brown (2.SY 614), moderately porous; n1edium dense to dense; n1inor roots and rootlets; rare laminae in fine sand lenses· otherwise n1assive; n1inor gravel '

130'

I

I ENCLOSURE 6 TRENCH LOGS

?

120' 110'

portiOns of opposite wall of trench used to trace k'.>wer units where buried by slough on south wall

100'

total apparent vertical displacement across zone of unit D =8'

I I coarse sandy gravel I with cobbles

CObbty graver

®

possible tensional fractures, no apparent displacement in paleosol

infilling in ter.sk111a1 fracture, dOes not appear to be displaced paleosol: silty sand with gravel.

fault: light yellowish bcown (2.5Y 614), NOSE SSNW, very porous, abundant rootlets;

=-3%' apparent / I prolate clasts, ./more s~t and gravel, denser than P,

vonical offset ,,,-/' ..______ _ ______,/

181. silty sand with gravel (slope wash), < 1 • rootlet zone at top

buried 'A' hOrizon

laminated sandy gravel interbedded with gravelly sand, coarse sand and cobble layers: light yellowish brown (10YR 6/4), light gray (2.5.Y 7/2) and pale yellow (SY 213); dry to damp; ~minated, 1nterbedded and some cross bedding; highly weathered schistose and coarse n'\afic c~ts: subangular with some subcounded clasts; nunor n\anganese-oxide coating on some clasts

170' 160'

I I granitic boulder pink, highly w~thered

medi m sand lense

80'

I So. Cal. Gas Co. gas line, rusted steel (iron) pipe; trends =due north (NO"E);

70'

NOT MARKED \

coarse sand and fine gravel layer l ren1nant P, '?}

fault:

/./ prolate clasts along plane

0i, interbedded sandy gravel with ~ cobbles, sandy cobbles, gravelly

sand and sand: light gray (2.5Y 7/2); loose to medium dense; dry to damp; subangular to subrounded cl~ts; poor to moderate bedding; nllnor laminae; n1inor boulders

recently buried soil 'B' horizon

buried soils

150'

I bou,lder

..

15'

•

20'

(.;"\ paleosol (P ,): silty sand, '-!:.Y slightly greener than 2.5Y 6/4

(light yellowish brown) dry, porous; rootlet casts; small pores; minor coarse gravel and few cobbles; dense

140' fine sand to silty sand with gravel: light gray (2.SY 712)

20' .. .. 20'

• •

25' 25'

I Nitto

Gary S. Rasmussen & Associates, Inc. America Co. - El Rancho Verde Country Club

Rialto, California 30'

fine sand with silt lower 3-4 • siltier, possibly remnant 'B' horizon, buried soil altered/ eroded by sk>pe wash dePosits, light yellowish bfown (2.SY 614)

cobbly gravel with sand

@ I 30'

Project No. 3156.1

I I Horizontal & Vertical Scale: l" = 5 •

paleOsot fine sand to silty sand, pale yellow (2.SY 7/4) to light yellowish bfown 12.5Y 6'4), nlOderately porous; medium dense to dense; mtnOJ roots and rooUets; rare laminae in fine sand tenses; otherwiSe n-1assive; n1inor gravel

gneissic boulder

granitic boulder lan1inatod sa'ndy coarse gravel


Trench 14 Logged by TSil Drafted by PAC

o·

5'

10'

15'

70'

10'

iriiE:lrbedded sandy gravel wiltl cobbles, sandy cobbles, gravelly sand and sand: light gray (2.5Y 712); loose to medium dense; dry to danlp; subangular to subrounded clasts; JX>or to n1oderate bedding; n1inor lan1inae; n1inor boulders

10'

I bedding: apparent dip ft'W

sandy gravel with cobbles to cobbly gravel; dark yellowish brown (lOYR 4/4 - 4/6, n10ist), medium dense; most; son1e bedding; subangular 10 subrounded clasts, multiple lithologies, don1inanlly granitic or gneissic; occasional schistose or coarse n1afic clasts are highly weathered and oxidized (older alluviun1)

\ 80'

I

,;..- N77E south wall

20' 30'

I I

90' 100'

I I

bend N75E v

40' 50' 70'

I I

IO'

151'.

N75E bend N78E

v 110' 120' 140'

I I o·

5'

IO'

• ~ •• 9-_ <:,\ c°o ~ .G 0 ("\ !" .~ 9 •· 9 0: ···.·<? .• · •• o. ·- Q • q .... ., ..... , c:i,,. S~dy cobbles With gravel . I do'stur•-· zone·. rau1ted ")•oCJ.a~on? •. oo-~o v. •<>o. ~- •. D·O'•'O"'' .. , .,...._.

with prolate clasts and warped \. C'\ coarse lanitnatoo fine to mediunl bedding, 6"-10" apparent verti-

bodding ~ sand wilti gravel lasninated sand cat displacement on each trace -apparent dip 4"W \ dies out rapidly upward,

possible fault: N50W 81SW, ""'N46W 85SW site across trencll

qravel iaver

c-14 sample

15' eroded out by ratn, cannol 10" apparent correlate units across, vertical offset horizontal and vertical displacen10nl not known

Horizontal and Vertical Scale: I" = 5'


Gary s. Rasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club



Trench !'4 (continued) Logged by TSB Drafted by Pl\G

140'

O'-bedding bedding

150'

I 160'

I bedding apparent dip l5°W

be~ding

apparent dip 14"W

apparent dip 16"W apparent dip 1 O"W lATH

5'

10'

andesite(?) boulder with quartz/plage dike

210'

lan1inated fine to n1edium sand with n1inor gravel; cross-bedded; white to lighl gray (2.SY 7/2 -

..

812. dry to danlp); loose; tan1inated fine sand, coarse sand and fine ---------1 gravel; dry to dan1p (eolian)

218'

clay: brown (10YR 5/3, moist); finely laminated; slightly plastic; n1inor silt; breaks apart along lan1inae

Horizontal and Vertical Scale: l" 5'

A N78E

bedding

170' laminated fine to I mediun1 sand with minor gravel

bedding apparent dip 1.S"E apparent dip 4W

o· - •·

@ sandy gravel with cobbles to cobbly gravel: dark yellowish brown (1 OYA 4/4 - 4/6, n10ist), n1ediun1 dense; most; some bedding; subangular to subrounded clasts, multiple lithologtes, dominantly granitic or gneissic; occask>nal schistose or coarse mafic clasts are highly weathered and oxidized (older alluvium)

silt in fine sand: light gray (2.5Y 7/2); moist; finely lan1inaled

180'

I

difficult to see on other waJI as bench has destroyed contact between upper gravel and underlying fine to coarse sand unit

1 !JO'

I

@ silty sand with gravel: very dark grayish brown to

200' dark brown (10YR 312 - 313);

I IOOse; moist; organic rich: rootlets throughout; n1inor cobbles (topsoil 'A' horizon)

210'

sand: light yellowish brown

sandy gravel with cobbles: right gray to light olive brown, (2.5Y 7/2 to 2.SY 514, moist); loose to medium dense; moist: bedded; subangular to subrounded clasts - domin(Ultly gneissic or granitic

to light olive brown (2.SY 6/4-5/4, n1oist); laminated and crossbedded fine to coarse sand; medium dense; moist (eolian)

in composition; no degraded clasts; minor roots and rootlets; fining upward sequences


O'

Gary S. Rasmussen & Associates Inc Nitto l\merica Co. - El Rancho Verde Count~y Club

Rialto, california Project No. 3156.l



75'

O'

5'

10'

very little oxide staining

147'

70'

I

difficult to see on opposite wall due to caving

140'

I

60'

I

130'

manganeseoxide stained

coarse sand and fine gravel layer

I laminated sandy gravel bedding apparent dip 7.5°E

10'

burrow

fine gravel pocket

medium

15' ® sandy cobbles with gravel. willl larninated sandy gravel layers: light brownish gray to light yellowish brown (2.SY 612 - 6/4, moist); dense coarse sand - boulder size / clasts, dominantly graniliC/gneissic in / composition: subangu/ar to subrounded ctasts; dark yellowish brown (l OYA 4/6) and yo11owisl1 rod (5YA 5/8) iron-oxide staining; dusky rod (lOYA 3/3) manganese oxide staining from ::.60-147'

possible fault: N02W apparent vertical displacen1ont ::s.6"

Horizontal & Vertical Scale: l" = 5 •

.J N66E Southwest wall

120'

I

fci::1lt: ""'NOSW (site across trench) apparent dip 35-61"E

40'

I

2'9· granitic boulder


30'

I

llO'

I

infiHed remnant burrow, infilled with sand: olive gray (SY 4/2, dry)

silty coarse gravel with sand and minor cobbles

100'

I

Possible fault difficult to pick up on other side of trench

sandy cobbles with gravel: light olive brown (2.SY 5/4, moist}; loose to medium dense: greater percentage of cobbles than underlying unit: very litUe oxide staining; subangular to subrouncted clasts - dominantly granitic/gneissic in composition

90'

I laminated coarse sand layer

silty sand layer

80'

I 75'

infillod wilh sand (SY 4/2): moist

O'

5'

10'

5'

silty sand layer

heavy oxidation and rnanganoseoxidc staining

fault: across portion of bottom of trench, apparent dip 74°W



10'


Project No. 3156.1


Trench 16 Logged PY TSB Drafted~ by PAG

10'

15'

20'

25'

70'

@ laminatod sandy gravel

Horizontal & Vertical Scale:

60' 50'

I I

@ silly sand with gray (10YA 3/l~·ravel: very dark ~assive; minor , damp; loose; mtermixcd with f~~bbles: topsoil

28" abandon d irrigation pi

9. concrete

brok pe, on by backhoe· exposed at surface,

bedding apparent dip S"E

1" = 5'

40'

I

bedding apparenl dip 2"E

A N69E Southwest wall

30' 20'

I I bedding apparent dip 1 G°E

bedding apparent dip 8oE

10'

I

unit@?

laminated light brown~ravolly sand

I. 1sll gra 1 1ght yellow· h Y

0

(2.SY 612 is brown - 6/4)

ENCLOSURE 6

Gary S TRENCH LOGS

O'

5'

10'

Nitto Americ~ Rasmussen & A Co. - El Ra h ssociates, Inc R" nc o Verd c · ta.Ito, Califor . e ountry Club

Project No. 31;~~1



140'

15'


130'

I

LATH

o"<Souo~ . . .. -· .

20'

I fault: ""N35W apparent dip 83°E, apparent reverse motion =2Yz-6"

t fault -""N31E (site across trench) apparent dip 79"E, prolate clasts, apparent reverse n1otion .,,3y2•

-------------- laminated @ sandy gravel

Horizontal and Vertical Scale: I" = 5 •

120'

I channel odgo

I fault: ,,,.35E apparent d'ip 62E, apparent reverse n1olion ~2-4"

110'

I

.; N69E

deconlposed diorittc cobble

laminated sandy

100'

I iron-oxide stained

gravel bed prolate clasts

apparent normal rootion, apparent dip 32"E (site across trench) maximum apparent offset s· prolate clasts

coarse gravel layer

0

fault: ""'N48E 85E prolate dasts, apparent reverse

90'

I LATH

.--·

decomposed granitiC cobble

n10tion ""'4'5", not visible on oPposite wall of trench; n1ay be displaced by adjacent N30E-trending fautt

166'

20'

25'

160'

I laminated sandy gravel

tA) laminated sand: \81 5Y 5/3 (moist),

5Y 7/3 (dry), oxide-stained in places

80'

I

- 0

bedding

150'

I

70'

-'4

@

140'

bedding apparenl dip S"W


15'

20'

25'

15'

20'

25'

. Gary S. Rasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club

Rialto, California Project Nb. 3156.l


Trench 17 Logged by ;rsB Drafted by' PAG

i 65'

5'

sandy gravel with silt; 1an1inated


60'

l 50'

I silty sand with gravel and cobbles: light brownish gray to dark grayist1 brown (2.5Y 612 (Ory) to 2.5Y 4/2 (wet]); 'A' horizon

A

Nitto Gary S. Rasmussen & Associates, Inc. America Co. - El Rancho Verde Country Club

Rialto, California

B

D

Project No. 3156.1

Horizontal and Vertical Scale: I" - 5 •

MAIN FAULT N22W 86NE

total apparent vertieal offset ""2'10"

total apparent vertical offset ... 1·5·

total apparont vorUcal offset ""'l '4 •

40'

I

10'

15'

30'

I

101' t;:;\ silty sand with gravel and \!:::..) cobbles: Hght brownish

gray to dark grayish brown (2.SY 612 (OryJ to 2.SY 4/2

(well); 'A' noriZon \

• •

90'

I laminated sandy gravel with cobbles

•.

o .

laminated gravelly sand

20'

I

...

wat~ coarse sand layer

80'

I 5andy cobbles

cross-b&dd0d medium sand la~er

raun

10'

I

conlact? no prorate clasts

7· apparent vertical offset

70'

I

fault zono of prolate clasts N22W BSNE, topsoil D offset 16" ;tpparenl vertical d1sptacen1enl

O'

5'

10'

15'

65' gravel layer 5'

lAn1

15'

sttndy layor with minor gravol: lighl gray (2.5Y 7/2, dry) to light olive brown {2.5Y 5/4, n1oist); possible rcn1nant pa/eo~ol


Trench 18. Logged by TSB Drafted by PAG

70'

5'

IO'

15' bedding apparent dip 4°W


60' 50'

I

sandy cobbles {channel deposit in unit Ai

126'

gravelly sand lense

cobbfy sandy graver; poorly bedded

5'

..

10'

15'

I

120'

I

<6" thick laminated eolian sand layer

juniper roots

coarse sand with gravel and minor cobbles

bedding apparent dip 1"W

40'

I

110'

I

I i

..ti N83W South wall

cobbly gravel layer with sand

laminated coarse sand/ firn1 gravel layer

sandy gravel: light gray (2.5Y 712., dry) to yollowish brown (2.SY 6/4, moist); loose: Jarninated witt1 n1inor cross-bedding; sandy cobblo-cobbty gravel layers and looses; subangular to subrounded clasts, don1inantly graniticfgneissic in con1position, minor degraded clasts; rare boulders

30' 20' IO' O'

I I I I

D

"' © 0 -.

5'

10'

juniper root © topsoil: silty sand with gravel. grayish brown {2.5Y 5/2., dry} to dark grayish brown (2.5Y 4/2, moist); loose to medium dense; many fine pores; fine rootlets throughout;

100'

I

sandy gravel: light gray {2.SY 7/2, dry) to yellowish brown (2.SY 614, n1oist); Joose; laminated with minor cross-bedding; sandy cobble-cobbly gravel layers and lenses; subangular to subrounded clasts, dominantly graniti~gneissic in composition, minor degraded clasts; rare boulders

minor cobbles; clasts are subangular to subrounded and stained; organics

cobble lense with boulder

90' 80'

I I decon1posed mafic cobble

juniper roots

70'

cross-bedded coarse sand lonso

C'\ cobbly, sandy gravel: light gray ~ (2.5Y 712. dry) to white (2.5Y 812.

dry); loose; poorly bedded; channeling common; subangular to subrouridod granitic/ gneissic clasts; rare boulders; nitnor laminated sand-gravel layers

silty sand with minor graver; light olive brown (2. 5Y 5/4): n1oist; medium dense to loose; bioturbatod


5'

15'





10'

15'

20'

25'

70'

®

60'

I

silty sand with gravel: light yellowish brown (2.SY 612, dry) to light olive brown (2.5Y 5/4, damp); loose; dry to damp; n1inor cobbles; massive; very fine pores; abundant fine rootlets and roots; 4-e· root zone at top; organic rich: incipient ·s· horizon at base in some areas

poorly sorted, massive sandy gravels (1 OYA 5/6. damp, to 10YA 614, dry)

fine to coarse laminated sand layer

fault

I interbedded sandy cobbles with gravel and laminated and cross-bedded sandy gravel: light gray (2.5Y 7/2, dry) sandy gravel and pale yellow (2.5Y 7/4, dry) sandy cobbles; dry to damp; medium dense; well-bedded where finer grained and poorly sorted; poorly bedded and subangular to subrounded clasts, don1inant1y gneissic/granitic in litllology


®

50'

I sandy gravel with cobbles: white (2.5Y 812, dry) to pale yellow (2.5Y 7/4, dry); medium dense to loose; dry to damp; generally poorly bedded and moderately well sorted; occasional n10dium to coarse sand layers and fine gravel layers; subangular to subrounded clasts, don1inant1y gneissic/granitic lithology

.t!11 N87W

40'

I

fault =-N05E 54SE (along fault plane) 8-9' apparent vertical displacen1ent of contact between unils A and B

possible incipient ·s· horizon

5" gas main (So. Cal. Gas)

bedding apparent dip r:f


sn1a11 prolate pebbles and shearing along fault planes

30'

I

fault: N06W 46E (fault plane) to

20'

I IO' O'

I -----:---t-" O'

•

N 16W (site across trench, but only approximate as opposite

wall has been dug out :;:>,j~~~~~~~~~~~~~~~~~~~~~~~~~£~~~f~~~7 by excavator : 5'

fault. ~NS2E 36E low-angle normal (gravity failure?)

bedding appamnt dip 3Yi°W

mediun1 to coarse cross-bedded sand

slightly laminated, poorly sorted sandy gravel

poorly bedded sandy gravel with cobbJes: pale yellow (2.5Y 7/4)



10'

15'


Project No. 3156.I


Trench 19 (continued) Logged by TSB Drafted by PAC

25'

30'

35'

140'

•

130'

I

zone of moisture: relic paloosol

120'

I (;;'\_ sandy gravel with cobbles: white (2.SY 812, ~ dry) to pale yellow (2.SY 7/4, dry); mediun1

dense to loose; dry to danlp: generally poorly bedded and moderately well sorted; occasional medium to coarse sand layers and fine gravel layers; subangular to subrounded clasts, don1inantly gneissic/granitic lilhology

poorly sorted, fine sandy gravel layer in unit B

lan1mated sandy gravel with cobbles

fault: I f.'. ,,..N26E 70SE, ~ mterbedded sandy cobbles with gravel and ""'1' apparent lan1mated and cross-bedded sandy gravel: vertical displacement light gray (2 SY 7/2, dry) sandy gravel and

pale yellow (2.SY 7/4, dry) sandy cobblos; dry to dan1p; mediun1 dense; wet/-bedded where finer grained and poorly sorted; poorly bedded and subangular to subrounded clasts dominantly gneissic/granitic in lilllology '

®

®

Horizontal and Vertical Scale: I" = 5 •

110'

I

zone of moisture -co..'l.rse sand tense with gravel

16" OD concrete pipe {abandoned)

N87W

faul!: N10W, apparent dip 74E

100'

I (site across trench and across portion of bottom of trench); 2-4 • I hick zone of prolate clasts

split and rotated cobble

O•

©. bedding laminated apparent dip ftW sandy gravel

181'

25'

35'

6%-7' apparent verttcar displacement of Um! A

170'

I possible fault: sense of displacement maybe upon east, dlff1eult to correlale units across begin to

Jose bedding

sandy gravel with cobbles: while {2.5Y 812, dry) to pale yellow (2.SY 7/4, dry}; medium dense to loose; dry to damp; generally poorly bedded and n1oderately well sorted; occasional n1ediun1 to coarse sand layers and fine gravel layers; subangular to subrounded clasts, dominantly gneissie/qranitic lithology

on opposite wall -N30W 83NE

slightly yellower in color

90' 80' 70'

I 10YA 6/4 (dry) 10YR 5/6 (moist)

poorly sorted massrve sandy gravels: light yellowish brown 10 yellowish brown ( 1 OYA 6/4 - 516)

I relic pafeosol

n1ediun1 coarso graver (channel deposit)

I possible fault or channel edge? N20W 58NE - plane

pC>Orly sorted, massive sandy gravels: yellowish brown to light yellowish brown (10YA 5/6, damp, to 10YR 6/4, dry)

15'

20'

25'

160' 150' 140'

I coarse sand layer in unit 'B'

I poorly sorted, fine sandy gravel layer in unit B

medium sand k!nse

~ possible fracture or fault o( roots

fault: N17W 86NE, prolate clast zone 2-3" wide, ,,.., • apparenl vertical ortsct

unit discoloration more diffuse

poorly sorted fine sandy gravel layer in unit 'B'


0

25'

30'

35'





43'

5'

10'

15'

Trench 20

40'

I

(';;\ silty sand with gravel. \;;;) vory dark grayish brown to

dark brown (1 OYA 3/2 - 3/3). loose. nlo1st, orgarnc rich, rootlets throughout, minor cobbles (topsoll 'A' horizon)

© sandy gravel with cobbles: Hglll olive brown (2.5Y

30'

I

5/4); moist 17'\ sandy gravel with cobbles: \!:,) light yellowish brown

(2.SY 6/4); dry: dense; larninated and poorly sorted

Trench 21

45'

O'

5'

10'

@ silty sand with gravel: very dark gray (lOYA 311); damp; loose; massive; minor cobbles: topsoil intermixed with fill

0

0

@/ sandy gravel with cobbles: white to light gray (2.SY 612-712); damp: modiun1 dense to loose; poorly bedded; n1oderately well sorted; minor oxide staining

40'

I


N67E

20'

2· diameter

root _l

bedding apparent dip 6°E

I moister but may be part of unit

A N65W

30'

I

0

strong iron-oxide and manganese-oxide staining along beds

IO'

I

20'

I ' ..

sandy gravel with cobbJes: paJe yellow (1 OYA 713); bedded and laminated; moderately well sorted; inlerboddod sandy cobbte ~yers wtlh gravel and laminated sandy gravel layers slrongly stained by orange iron oxido and rod manganese oxide

O'

O'

5' 5'

10' IO'

15'

20'

10' O'

I O'

"®. ·o. :..._:

5'

10'

N86E ,.. Trench 22

2I' IO' O'

I

l~~~~to:p:s:o·~· ~;:-~:::::::--:::::::::::--:-:::::~~==~-.~~~·;;:::~.-~:::;.~-~~~ _:.....-- -- ~ - __,-~-:- · . (;:;\'silty s~d~ dark bioWn-. I - .\£/.t2.5\' 4/2,. moist to 2.5Y

5/2; dry); .,mOi$! (fiil) I

·@ silty 'SMdlsandy. silt .:...... .

. ~ht 'j;:~~-~7~~~. )~-::.~'.-. ,_.;·.-=-. -;.:-.:;_.~.;:~:;-'.:;. _-;.' ~-;::: .. Q-:.-;'.;;:-:;-.;;0--=·~:.;-;;7~ ~ t:.: Q· O.:·o~·o" ·@eo'?.:o:(Yo')J.o.-.A~<::>-~~o.~~80·o<-<S -~·~a··. ·. o: ~Q B -,nterbedded sandy graver~.o;)o?;. .. ·q·v- ·

·d•o .. o ··.~ • 0 00 0 •. ~ O..;.·O ~.·~·~":;Md sandy cobbles with graves.~• ..... ;-"*·cY .o;:io-o- •• light gray (2.5Y 712) ~o; ·.• .0 0 < •• ..,""! ..... d.o.c1.o • .. ~ .. ,o. o.cs.• .. d.o.C)'.i..~~:; .,_ 0 0. ·•o ·· ·• 'O o•O•. "d • • • .g. q' • .,. • ·• ~· • • •

o o e1~0~ •

. --• I silty sand/sandy silt:. . _. /":"\ . _ •

'-.!light gray (2._SY.614); .• · 'OI: - · : · · . he~vy. a<aoge 1rqn-ox1de ~ -· • _ .

• staining;,l~l.nat~~ T·. ~o, D·."·. 'o .----:- • • • () • • 'Cl c .o ~ ... '"·• ·o '. 0 ....., .. ac:• eJ·o·

000.,•"".o-.D"'·"' o f:l•·c:t~· o•.e>· ·o '• ,o, .• .•. · .. o. .,· "'"o'o"a·

o. d p0·~00 ° 0 :o.•

·t>/ot:? • \ ·o. • o "' ;,, , . o, • ~. ,,,0 · .. ·

• Q ·o t:J ., ••

ot:>,,;~ .... (:I., ••• D . ;, :

t:\ gravellW sand interbedded with \CJ sandy gravel: light olive brown

to light yellowish brown (2.5Y 5/4-6/4); manganese-oxide and iron-oxide staining; minor cobbles



O'

5'

IO"

15'

20'


Project No. 3I56.l



5'

10'

15'

10'

15.

20'

70'

140'

Horizontal and Vertical Scale:

60'

I

--· ___ .D

bedding apparent dip 26"'1N

manganese-oxide stained gravel bed

1" = 5'

130'

I

i N22E N~rthwest wall

' 40' 50' 30' 20' IO' O'

I l I I I pocket of heavy dark red n1anganese-

cQncentrated ~ --' roots - -~ o zone of '~~---:-------:-------:==--==:-::=::::-----::~o~xK!;e~s;ta.i·~n:in;g=:;----:::-=~~~:.----:?~~~~-:=-=-"----. -----------J--0'

\ -.

._....:_:.-, ~ - 0 •

- .q·

________ -,-------:----:--,----:--:-.-----\-- .....-- - ~ - . o ·A ·sittr sand with·graver and - • _:__.__ --...-·- -· -·

0

~ .-; -·

0

o • · 0 . ~ ~~i~or:co"bbles:. veiy ~il~k 'grayish • _-bro~_ (2;5'1'. ~2); n1oist; loose'; 5'

•

Nl6E

© sandy gravel wilh minor cobbles: light yellowish brown (2.5Y 6/4, moist) to light gray (2.SY 7/2); 'loose; moist; bedded

120'

I

-1 fault: N74W

•

sand: medium to coarse-grained; pale brown to light yellowish brown (1 OYA 613 - 614); moist; loose; coarsely laminated bedding, apparent dips 12-26°W

bend v

j apparent dip 66SW

fault: N81W, apparent dip 76SW

17'\ ci:rarse laminated sand interbedded ~ with sandy gravel: light gray 10

pate yellow {2.SY 7/2 - 7/3); tense within fine to coarse sand unit

@ sand: fine- to coorse-grained; pate yellow 12.5y 7/4); fractured and faulted' generally massive; dense;' damp

100'

I

apparent dip SO°E

fractures

m.a!>s1ve: abu~dant _Orgai1fcs 0

@ gravelly sand interbedded with sandy gravel with cobbles with manganeseoxide staining: hght olive brown (2.SY 514); moist: medium dense; bedded; poorly sorted {cobbles and gr~vels in a coarse sand matrix); mmor degraded clasts

10'

abundant pine tree roots

Nl3E bend v )e.

90'

I

fracture: apparent dip 39'W apparent dip 46'"W

N22E

6" steel irrigation main N41W

80'

I

sand: medium to coarse-grained; pale brown lo light yellowish brown (1 OYR 613 - 6/4); n1oist; loose; coarsely lan1inaled

sandy gravel: light yellowish brown (2.5Y 6/4) to light gray (2.SY 7/2)

·-·...,......:... .


70'

5'

10'

15'


Rialto, California Project No. 3156.l


Trench 23 (continued) Logged by TSB Drafted by PAG

140'

IO'

15'

20'

fault: N58-63W, Nl2W

apparent dip 65NE, I 1 + • apparent

sandy gravel wiUl cobbles

vertical displacement


©

@

Nl6E Southeast wall

160' 170'

I I

@ N68W

Nl6E lllo.. Northwest wall

170' 160' @ zone of I silty sand with gravel and concentrated minor cobbles: lil!ery dark grayisll roots brown {2.5Y 312); moist; loose;

LATH

IO'

gravelly sand interbedded with sandy gravel with cobbles with manganeseoxtde staining: light olive brown (2.5Y 514); moist; medium dense; bedded; poorly sorted (cobbles and gravels in a coarse sand matrix); minor degraded clasts

180'

I

massive; abundant organics

laminated fine to coarse sand with minor gravel: pale yellow I (2.5Y 7/4); damp; medium den~e

190'

I

150'

I

200'

I

140'

LATH

{;;\fine to \3' coarse sand


210'

10'

15'

20'

10'

15'

20'




Trench 23 (continued) Logged by TSB Drafted by PAC

210'

10'

15'

20'

laminated nne to coarse sand with minor gravel: pale yellow {2.5Y 7/4); damp; medium dense

220'

I 3• Iron irrigation pipe, ... N46W

Horizontal and Vertical Scale: 1" = 5'

230'

ll--i:=I LAlH

© sandy gravel with cobbles: 24 2 • light gray (2.SY 712)

concentrated roo zone

. -~ ._. ·-·-·.



10'

15'


Project No. 3156.1

I Trench 24A Logged by TSB Drafted by PAG


O'

10'

5'

15'

N45E .......

70'

manganese-oxide staining .

15'

sandy gravel with cobbles: white to hghl gray {2.SY 8/1 to 7/2), dry; nl0d1un1 dense; poorly bedded; well sorted; subangular to subrounded clasts; n1inor degraded clasts; moderate nlflnganese and iron-oxide staining

10'

I

massive fine to medium sand: light yellowish brown (2.SY 6/4); moderatety dense

20'

I

relict paleosol? very pale brown (10YR 7/41

30'

I

N56E "nz Northwest wall

40'

reddish brown staining, I both sK1es of trench

churned zone

fault zone: N81-87W,

60'

I

bedding

bend v

..... 0 ,;.. oo•••o••

70'

10'

15'

apparent dip: GOW @ fault: ~N35W

apparent dip 84°NE on northwest wall and 72°SW on southeast wall al least 4' apparent vertical

possible fault apparent dip 2Yz'W \

bedding apparent dip ~

apparent dip 52"SW I (site across trench)

® at bottom of

offset and 4' wide "churned• zone. followed across trench bottonl -faulting and ltquefaction

trench but not exposed in trench wall sandy gravel with cobbles: white

lo lighl gray (2.SY 811 to 7/2), dry; medium dense; poorly bedded;

sandy gravel with cobbles: light gray, dry, to tight yellowish brOW'1 dan1p {2.SY 7/2 - 6/4); dense; dry to damp; poorly sorted and moderately bedded; subangular to subrounded clasts; minor cobble layers;

bend N43E bend v

N38E .,,,,,_ bend v

N30E well sorted; subangular to subrounded clasts; minor degraded clasts; moderate n1anganese and iron-oxide staining

v 80'

I iron-oxide

.. ... ·-· .. - ,· ....

A ' • cJ •o• o• • ··o;o •

t apparent dip 32"W

fault: N54W apparent dip 77"NE across boltom of trench, =4' apparent vertical offset, prolate clasts

1· apparent vertical offset

90' 100' llO'

I I

.• :o·~~.,,~-~ ·- .. ~- ·. . ......___

fault: N84W, fault N76E, apparent dip 66"SW apparent dip 71°5[

~ total offset @: 13" total offset @: 11 •

prolate pebbles and graYel

strike folJowod across t1ench botton1 ®

@

I

iron-oxide stained cJntact

fault: =NS9W apparent dip 49SW (site across !ranch) apparent reverse displacen10nt: 6"

I

fautt N78W apparent dip 63SW

(site across trench) < 1 • apparent vertical offset

mterbedded siH, laminated silty sand, s<t.nd and gravelly sand; light gray and very pale brown (10YA 712 - 713 and 7/4); mterbedded laminatecr fine to coarse sand and fine to coarse gravel; subangular to subrounded clasts; dense, dry to damp; minor oxide staintng; minor sandy silt beds; minor degraded clasts; fining upward sequence

l19'

5'




I Horizontal and Vertical Scale: I" = 5'


Tre,nch 24B Logged by TSB Drrlfted by PAG

Trench 24C

®

180'

cart patn

silty sand: dark grayish brown (2.SY 412, dry} to very dark grayish brown (2.5Y 3/2, moist); loose, massive; minor gravel and cobbles - sonH:t degraded; artificial fill and topsoil, n'rixed

J Nl 6E

170'

I

......c_N24E - ------

Southwest wall

165' 160' 150'

bedding I apparent dip 0-3°N I

5'

10' n1ed1um to coarse sand lense

fine san lense

15'

sandy gra'lel with cobbles: white 10 lighl gray (2.5Y 811 to 7/2), dry; n1edium dense; poorly bedded; well

possible fault with prorate clasts or channel edge

sorted; subangular to subrounrted clasts; n1oderata n1anganese and iron-oxide staining

bend ~NOBE

-.

fault ~NSBW (site across trench) apparent dip 72°NE total apparent vertical displacement ot unit A approx. 2Y2 ', fault plane ts not well defined

v Southeast wall

manganese-oxide stained beds

bedding

140'

I

apparent dip 23°W

©

fault or fracture inftlled with gravel al lop

sandy gravel with cobbles: light gray. dry;. to lighl yellowish brown, damp (2.5Y 7/2 - 6/4); dense; dry to damp; poorly sorted and nlOderatety bedde<t; subangu!a! to subrounded clasts; n1inor cooble layers;

130' ,"2. water line

I to water fountain

@

bedding apparent dip t'N

interbedded sitt. tan1inated silty sand, sand and gravelly sand; light gray and

Pac•aeu cable

~ery pale brown (10YR 7/2 - 7/3 and 7/4); mterbedded lanlinated fine to coarse sand and fine to coarse gravel; subangular to subrounded clasts; dense, dry to damp; minor oxide staining; minor sandy silt beds; minor degraded cJasts; fining upward sequence

silty sand: dark grayish brown

119'

5'

10'

~15'

(2.5Y 4/2, dry) to very dark grayish br_own (2.5Y 312, moist); loose, massive; nl1~or. gr~vel and cobb'8s - some degraded; art1fic1al fill and topsoil, mixed

bend ~ N03W v 200' South wan· 190' 180' 220' 210'

I I I l 245' 240' 230'

manganese-pxide staining

O' I iron-oxide staining

l

bedding manganese-ox~e stained. poorly sorted gravel Jense

apparent dip 13"N

\an1matW coarse sand w1t11 gravel:uml in A very pale ttrown ooY11 7/3)

Horizontal and Vertical Scale: 1·· = 5•

poorly sorted grave!

large bOulder ' . . 1nterbedded silt, lan1inated silly sand,

@ sand and gravelly sand; ligtll gray and very ~le Drown (lOYA 712 - 713 and 7/4); intert>edded Jan1inated fine lo coarse sand and fine 10 coarse gravel; subangular to subrounded clasls; dense, dry to dan1p; minor OKide staining: O\iClOC sandy silt beds: R\iOOf degraded c:lasts; fining upward sequence

iron-01'.ide staining

manganese-oxide staining

O'

cart path

10'



Rialto, CB!ifornia Project No. 3156. I

I I I

Trench 24C (continued) Logged by TSB Drafted by PAC

O'

310'

bedding apparent dip 6"N

300'

I 290' 280'

bedding l I

apparent dip 19"S graver lense I ·-· -· ,___,___ -,---r- -- . ~ -. -· - ~

I I I I I I I I I I I I I I

5'

10' pale brown rine sand layer iron-oxide n10Uled

interbedded silt, lan1inated silty sand. sand and gravelly sand; light gray and very pale brown (tOYR 7/2 - 7/3 and 7/4), interbedded lan1inated fine to coarse sand and fine to coarse gravel; subangular to subrOunded casts: oonse. dry to darnp; mm oxide slaining; minor sandy silt beds; minor degraded clasts; fining upward sequence



possible warped bedding


Project No. 3156.I

I Horizontal and Vertical Scale: l" ~ 5 •

wide zone (2-3") of prolate grains and shearing, but little dispracemenl

5'

10'

'o foll ~.

fault N53W, apparent dip: 75"S poorly sortod apparent vertical manganese-oxide displacement: a· I stained gravel lens•

® silty sand: dark &ray1sh brown O 12.SY 4/2, dry) to very dark grayish

351'

brown (2.SY 3/2, n-ioisl); loose, massrve; n1inor gravel and cobbles - some degraded; artiftcial fill and topsoil, mixed

cobbly gravel with sand

340'

I

d' N28E Southwest wall

-.--

degraded clast in fill

n1anganese-oxide staining along bedding

270'

I

manganese-oxide stained gravel lense

260'

l asphalt (little subgrade)

iron-oxide slaining

250'

I n1anganese-oxide stai ing

bedding apparent dip 2"N

245'

Iii"\ sandy gravel with cobbles: while \!:31 to li~ht gray (2.SY 8/1 to 7/2), dry;

medium dense; pQOrly bedded; well sorted; subangular to subrounded clasts: nlOderate manganese and i"on-oxde stani"lg

n1anganese-oxide stained poorly sorted graver lense '

sa~dy gravel with cobbles: light gray, dry, to bgh~ yellowish brown, dan1p (2.5Y 7/2 _ 6/4); dense, dry lo damp; poorly sorted and moderately bedded; subangular lo subrounded clasts· minor cobble layers; '

silty sand with gravel lense within Unil B light yellowish brown (2.5Y 6/4)

330' 320'

I channel

fine sand with gravel lense

interbedded sill. laminated silty sand, sand and gravelly sand; light gray and

l

very pale brown_ (10YR 7/2 - 713 and 7/4); mterbodded larn1nated fine to coarse sand and fine to coarse gravel; subangular to subrounded clasts; dense. dry to dan1p; n1inor oxide staining; minor sandy silt beds, minor degraded clasts; fining upward sequence ,

fault. N7BW (site across tronch) apparent dip: 48SW apparent total vertical displacement 1Yz" does not offset

310'

overlying channel deposit

O'

5'

10'

O'

5'

10'



O'

O' silty sand with gravel: dark grayish brown (2.5Y 4/2); loose; damp; topsoil

10'

I

N28E ""-

© sandy gravel with cobbles: light gray (SY 7/2, damp);

21'

5' 5'

~~~~~%g~~~~~q~§)~~~~~~~~~~~-l=- possible remnant

10'

15'

20' ground waler al 19'

2/29194


© inlerbedded gravelty sand and sanely gravel; light gray to light yellowish brown 12.5Y 712 - &'4)

buried soil or silty sand layer

10'

15'

20'




I 5'e

I I 10'

I I I I I O'

I I 5'

I 10'

I I I

50'

I bedding apparent dip 12"N

n1oisture zone and churning from tree roots, n1akes boundaries difficult to define

D

4 N31E

40'

I

.. . . . . ...

30' 20'

I I abundant roots

-•· ... - .

10'

I

•

sandy gravel with cobbles: finer grained than overlying materials

. -·· fractures, \ bedding

·bedding apparent dip S"N

sandy gravel with cobbles: manganese-oxide s1ained fault or fracture,

bedding apparent dip 3°N

degraded cobble no displacen1ent apparent dip 40"N

titted laminated fine sand and fine gravel: reddish yellow (7.SYA 516, n1oist); heavy manganese-oxide staining; medium dense; moist degraded clasts. reverse and normal grading

fault: N67W apparent dip: 80"N, does not appear to offset overlying unit; narrow, (< 1 • wide) minor gougo zone; no clay

140' © 130' 120' © sandy gravel with cobbles: I I sandy gravel with cobbles: ~-~wm~ ~--mw~ medium dense to loose; dry to minor iron-oxide stained; minor damp; lan1inated; minor iron- OOulders: medium dense; moist;

110'

I

light olive brown (2.5Y 514); ""'N48W, 90, does nol appear to offset overlying unit ·minor iron-oxide stained; minor

boulders; n1ediun1 dense; n'lOist; subangular to subrounded clasts; minor boulders; minor degraded clasts

degraded cobble (granitic) in fill

silty sand with gravel and n1inor cobbles: very dark grayish brown (2.SY 312); moist; loose; massive; abundant organics

intermixed lop ii 100' and artiftcial fill

I concrete pipe buried in fill

90'

I

coarse sand: pale brown to brownish yellow {1 OYA 613 - 6/6, moist); moist; medium dense; coarsely lam.inated; minor gravel; rare cobbles - many degraded

80'

I oxide staining; subangular to subangular to subrounded clasts·, subrounded clasts minor boulders; minor degraded clasts ____ ,_-.,--;-.,--~~ •

1~~---,.---,--l.;--c-._._, ·-·--~~--~~=-~=~'":--: .. -:-_ --:-----:-~~~ ·-·

• . ·.

degraded mafic clasts

• .-

28" concrete pipe, ..,N10W

.. • . -· fi\I •

manganese-oxide and iron-oxide stained sandy gravel with sitt and cobbles: b<own (7.5YR 514): possible paleosol in IOwer contact

coarser and less mottled, lighl yelklwish b<own (2.5Y 6/4)

• •

.•

bedding apparent dip 8"'N

degraded boulder

(4"\ molt$ed sandy silt and fine sand; ~ light yeflowish brown ( 1 OYA 4/6,

mois() to hght brown (7.SYA 6/4); dense; moist, iron-oxide mottled; JM>SSible liquefaction, nlinor coarse sand and fine gravel

interfmgering contact


O'

O'

channel edge

5'

10'

70'

5'

10'


I Horizontal and Vertical Scale: l" • 5'


Project No. 3156.1

-

+'

+ +•

+

+ • +

'+

+

+ +' -t

+ f + :+ -l1 ~

-

T

"· ' .. +,. ~·+++ +- ...

N

- -

,+

,+ "'!"-+ +-+-+

+ + +

+ + +

+ . ' :

+

-

+ + + +

+

+

+

:

+

+

+ +

+

- -

+, + +

+, +

+ +

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ENCLOSURE 8 REFERENCES

Gary S. Rasmussen & Associates, Inc. Nitto America Co., Ltd.- El Rancho Verde Country Club


Allen, C.R., Saint Amand, P., Richter, C.F., and Nordquist, J.M., 1965, Relationship between seismicity and geologic structure in the southern California region: Seismological Society of America Bulletin, v. 55, no. 4, p. 753-797.

Becker, A.M., 1994, Directivity in strong ground motion, Abstract in Large earthquakes in Metropolitan areas: preparedness, consequences, and response: Earthquake Engineering Research Institute Annual Meeting, April 7-9, 1994, Pasadena, California.

Bortugno, E.J., and Spittler, T.E., (Compilers), 1986, Geologic map of the San Bernardino Quadrangle: California Division of Mines and Geology, Regional Geologic Map Series, Map No. 3A, Scale 1:250,000.

Campbell, K.W., 1981, Near-source attenuation of peak horizontal acceleration: Bulletin of the Seismological Society of America, v. 71, p. 2039-2070.

Campbell, K.W., 1987, Predicting strong ground motion in Utah, in Assessment of regional earthquake hazards and risk along the Wasatch fault, Gori, P.L. and Hays, W.W. (eds): U.S. Geological Survey Open-File Report 87-585.

Campbell, K.W., 1989, Empirical prediction of near-source ground motion for the Diablo Canyon power plant site, San Luis Obispo County, California: U.S. Geological Survey OpenFile Report 89-484.

Campbell, K.W., and Borzorgnia, Y., 1993, Near-source attentuation of peak horizontal acceleration from worldwide accelerograms recorded from 1957 to 1993: Fifth U.S. National Conference on Earthquake Engineering, Chicago, Illinois, July 10-14, 1994 (In press).

Clarke, A.O., 1989, Neotectonlcs and stream piracy on the Lytle Creek alluvial fan, southern California: California Geographical Society, v. 29, p. 21-42.

Deng, Q. and Zhang, P ., 1984, Research on the geometry of shear fracture zones: Journal of Geophysical Research, v. 89, no. B7, p. 5699-5710.

Durham, D.L., and Yerkes, R.F., 1964, Geology and oil resources of the eastern Puente Hills area, southern California: U.S. Geological Survey Professional Paper 420-B.

Dutcher, L.C., and Garrett, A.A., 1963, Geologic and hydrologic features of the San Bernardino area, California, with special reference to underflow across the San Jacinto fault: U.S. Geological Survey Water Supply Paper 1419.

i


Eckis, Rollin, 1934, Geology and ground-water storage capacity of valley fill, South Coastal Basin investigation: California Department of Water Resources Bulletin 45.

Fairchild Camera, 1930, Black and white aerial photographs, Flight C190, photograph numbers 77, 78, 91 and 92, Scale: 1" =approx. 1,660'.

Fife, D.L., Rodgers, D.A., Chase, G. W., Chapman, R.H., and Sprotte, E.C., 1976, Geologic hazards in southwestern San Bernardino County, California: California Division of Mines and Geology Special Report 113. ·

Hadley, D. and Combs, J., 1974, Microearthquake distribution and mechanisms of faulting in the Fontana-San Bernardino area of southern California: Bulletin of the Seismological Society of America, v. 64, no. 5, p. 1477-1499.

Heath, E.G., Jensen, D.E., and Lukesh, D.W., 1982, Style and age of deformation on the Chino fault: Geological Society of America Meeting, Cordilleran Section, 78th Annual Meeting, Neotectonics in Southern California, April 19-21, 1982, Anaheim, California.

Jones, L.E., Hough, S.E., and Helmberger, D.B., 1993, Rupture process of the June 28, 1992, Big Bear earthquake: Geophysical Research Letters, v. 20, no. 18, p. 1907-1910.

Kahle, J.E., Wills, C.J., Hart, E.W., Treiman, J.A., Greenwood, R.B., and Kaumeyer, R.S., 1988, Surface rupture, Superstition Hills earthquake of November 23 and 24, 1987, Imperial County, California: preliminary report: California Geology, v. 41, no. 4, p. 75-84.

Lamar, D.L., Merifield, P.M., and Proctor, R.J., 1973, Earthquake recurrence intervals on major faults in southern California, in Moran, D.E., and others, eds., 1973, Geology, selsmlcity and environmental impact: Association of Engineering Geologists Special Publication, p. 265-276.

Lofgren, B.E., 1971, Estimated subsidence in the Chino-Riverside-Bunker Hill-Yucaipa areas in southern California for a postulated water level lowering, 1965-2015: U.S. Geological Survey Open-file Report, Water Resources Division.

Matti, J.C. and Carson, S.E., 1991, Liquefaction susceptibility in the San Bernardino Valley and vicinity, southern California - A regional evaluation: U.S. Geological Survey Bulletin 1898.

Matti, J.C., Tinsley, J.C., Morton, D.M., and McFadden, L.D., 1982, Holocene faulting history as recorded by alluvial stratigraphy within the Cucamonga fault zone: A preliminary view: Guidebook, Field Trip Number 12, 78th Annual Meeting of the Cordilleran Section of the Geological Society of America.

Mendenhall, W.C., 1905, The hydrology of the San Bernardino Valley, California: U.S. Geological Survey Water Supply Paper 142.

Miller, F.K., 1979, Geologic map of the San Bernardino North Quadrangle, California: U.S. Geological Survey Open-File Report 79-770, Scale 1:24,000.

ii


Miller, R.E., and Singer, J.A., 1971, Subsidence in the Bunker Hill-San Timoteo area, southern California: U.S. Geological Survey Open-file report.

Morton, D.M., 197 4, Geologic, fault and major landslide and slope stability maps, in Fife, D.L., et al., 1976, Geologic hazards in southwestern San Bernardino County, California, California Division of Mines and Geology Special Report 113.

Morton, D.M., and Matti, J.C., 1987, The Cucamonga fault zone: Geologic setting and Quaternary history, in Morton, D.M., and Yerkes, R.F., eds., 1987, Recent reverse faulting in the Transverse Ranges, California: U.S. Geological Survey Professional Paper 1339.

Morton, D.M., and Matti, J.C., 1990, Geologic map of the Devore 7.5-minute quadrangle, San Bernardino County, California; U.S. Geological Survey Open-File Report 90-695.

Rasmussen, G.S., July, 1982, Color, infrared, oblique aerial photographs.

Ramussen, G.S., February 15, 1994, Low-sun angle, oblique aerial photographs, photograph numbers 1-24.

Rasmussen, Gary S. & Associates, Inc., February 29, 1980, Engineering geology investigation of approximately 5 acres, northeast of Tract No. 8612 and Tentative Tract Nos. 9147 and 9148, west of Sycamore Avenue, Rialto, California, Project No. 1558.

Rasmussen, Gary S. & Associates, Inc., January 9, 1981, Subsurface engineering geology investigation of an 8.74-Acre Site (Plaza Rialto), southeast of the intersection of Merrill Avenue and Riverside Avenue, TlS, R5W, a portion of Section 14, SBB&M , Rialto, California, Project No. 1 700.

Rasmussen, Gary S. & Associates, Inc., August 1, 1985, Subsurface engineering geology investigation, northwest portion of Section 30, TlN, R5W, SBB&M, Fontana, California, Project No. 2160.1

Rasmussen, Gary S. & Associates, Inc., December 29, 1989, Subsurface engineering geology and geotechnical feasibility investigation, proposed Oak Summit Development, north of the northern terminus of Etiwanda Avenue, portion of Sections 8, 16, 17 and 18, TlN, R6W, SBB&M, Rancho Cucamonga area, Callfornia, Project No. 2739.

Rasmussen, Gary S. & Associates, Inc., April 18, 1990, Subsurface engineering geology and geotechnical feasibility investigation, 160-acre proposed residential development, portion of Section 16, TlN, R6W, SBB&M, Rancho Cucamonga area, San Bernardino County, California, Project No. 2837.

Richter, C.F., 1958, Elementary Seismology, W.H. Freeman & Co., 768p.

San Bernardino County, 1974, Color infrared aerial photographs, photograph numbers 220-222, Scale: l" : approx. 2,450'.

San Bernardino County Flood Control District, 1938, Black and white aerial photographs, Flight No. W-75, J-2, photograph numbers 12 and 13, Scale: l": approx. 1,000'.

iii

0-AR,Y s FiASM (_JSSEN ,!\.'., ASSC:)c.:;r A'I'EH


San Bernardino County Flood Control District, 1938, Black and white aerial photographs, Flight No. W-75, J-3, photograph numbers 7-9, Scale: I" ; approx. 1,000'.

San Bernardino County Flood Control District, 1955, Black and white aerial photographs, Flight No. F34, 5, photograph numbers 28-30, Scale: l" ; approx. 1,200'.

San Bernardino County Flood Control District, 1962, Black and white aerial photographs, Flight No. C-26, photograph numbers 27 and 28, Scale: I" ; approx. 1,000'.

San Bernardino County Flood Control District, 1965, Black and white aerial photographs, Flight No. C-140, photograph numbers 52 and 114, Scale: l" ; approx. 2,000'.

San Bernardino County Flood Control District, 1966, Black and white aerial photographs, Flight No. C-144, I, photograph numbers 7-10, Scale: I"; approx. 500'.

San Bernardino County Flood Control District, April 17, 1967, Black and white aerial photographs, Flight No. C-132, photograph numbers 12-19, Scale: 1"; approx. 1,000'.

San Bernardino County Flood Control District, January 21, 1978, Black and white aerial photographs, photograph numbers 148-152, Scale: I"; approx. 2,000'.

San Bernardino County Flood Control District, February 25, 1986, Black and white aerial photographs, photograph numbers 149-151, Scale: I" ; approx. 2,000'.

San Bernardino County General Plan, 1989, Hazard overlay maps with amendments through December, 1993.

Sieh, K.E., 1984, Lateral offsets and revised dates of large earthquakes at Pallett Creek, California: Journal of Geophysical Research, v. 89, p. 7641-7670.

Simpson, R.W., Harris, R.A., and Reasenberg, P.A., 1994, Stress changes caused by the 1994 Northridge earthquake, in Program for Northridge Abstracts, 89th Annual Meeting of the Seismological Society of America, April 5-7, 1994, Pasadena, California.

United States Department of Agriculture, 1938, Black and white aerial photographs, Flight No. AXL 60, photograph numbers 88-91, Scale: I"; approx. 1,700'.

United States Department of Agriculture, 1953, Black and white aerial photographs, Flight No. AXL 31K, photograph numbers 106-108 and 139-142, Scale: l"; approx. 1,700'.

United States Department of Agriculture, 1953, Black and white aerial photographs, Flight No. AXL 34K, photograph numbers 42 and 43, Scale: l" ; approx. 1, 700'.

Weber, F.H., Jr., 1977, Seismic hazards related to geologic factors, Elsinore and Chino fault zones, northwestern Riverside County, California, Final Technical Report: California Division of Mines and Geology Open-file report 77-4-LA.

Wood, H.O., 1955, The 1857 earthquake in California: Seismological Society of America Bulletin, v. 45, p. 47-67.

iv

C"1-ARY S RASMV::S~';EN c~- ASSOC'.lA"I'E::_-;


Working Group on California Earthquake Probabilities, 1988, Probabilities of large earthquakes occurring in California on the San Andreas fault: U.S. Geological Survey Open-File Report 88-398, 62p.

Working Group on the Probabilities of Future Large Earthquakes in Southern California, 1992, Future Seismic Hazards in Southern california, Phase I: Implications of the 1992 Landers earthquake sequence: California Division of Mines and Geology.

Youd, T.L., and Perkins, D.M., 1978, Mapping liquefaction-induced ground failure potential: Journal of the Geotechnical Engineering Division, p. 433-446.

Youd, T.L., Tinsley, J.C., Perkins, D.M., King, E.J., and Preston, R.F., 1978, Liquefaction potential map of San Fernando Valley, California: Proceedings 2nd International Conference on Microzonation, San Francisco, p. 267-278.

v

C_}ARY S f-'-ASMUSSEN & AS~?OC~IA'.!.'E~-:'>

STATE OF CALIFORNIA -THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY BAY AREA REGIONAL OFFICE 185 Berry Street. Suite 3600 San Francisco, CA 94107 Phone (415) 904-7707

ATSS 539· 7707 Fa. (415) 904-7715

wessly A. Reeder, County Geologist Building and Safety Division county of San Bernardino 385 North Arrowhead Avenue San Bernardino, CA 92415-0181

Dear Wes:

PETE WILSON, Governor

•.

October 4, 1994

We are placing on open file the following report, reviewed and approved by the County of San Bernardino in compliance with the Alquist-Priolo Earthquake Fault Zoning Act (formerly the AlquistPriolo Special Studies Zones Act) :

Engineering geology investigation and geologic update, El Rancho country Club property, Riverside Avenue and Country Club Drive, Rialto, CA; by Gary S. Rasmussen & Assoc.; 1/5/93 with subsurface investigation of 6/9/94 and response of 8/9/94.

It was nice talking to you yesterday the San Jacinto and related faults. your chart at a later date.

and getting your imput on I will get back to you on

EWH:ra cc :AP filev

Sincerely,

EARL W. HART, CEG 935 Senior Geologist &

Program Manager

,f? F J-.. 'J er & COUNTY OF SAN BERNARDINO

BUILDING AND SAFETY DEPARTMENT ( _ _J';_ij/{ __ ) ENVIRONMENTAL

·····························f~,~~'?iDIN"O\ ~···•MIAINIAIGIEMIEINITIGIRIOIUP·-385 North Arrowhead Avenue • San Bernardino, CA 92415-01B1 • (909) 387-8311 1~---.·-.·.,,.·•• ···· ... I \'~"''.</; ·~ ( \ ·?lf! FRED NORTON, C. B. O.

r1 ,, .. 1

September 30, 1994 Fax No. (909! 387-4301 --;;:-..:::;/

Director

Earl W. Hart California Department of Conservation Division of Mines and Geology 185 Berry Street, Suite 3600 San Francisco, California 94107

Dear Mr. Hart:

Pursuant to Section 3603(t) of the Alquist-Priolo Earthquake Fault Zoning Act, and on behalf of the City of Rialto, the following fault-rupture hazard report and subsequent response reports prepared by Gary S. Rasmussen & Associates, Inc. are being forwarded to you.

I. Engineering Geology Investigation and Geologic Update, El Rancho Verde Country Club Property, Riverside Avenue and Country Club Drive, Rialto, California, Dated January 5, 1993, Project No. 3156.

2. Subsurface Engineering Geology Investigation, Lil Rancho Verde Country Club, Approximately 260 Acres, Rialto, California, Dated June 9, 1994, Project No. 3156.1.

3. Response to San Bernardino County Review of Subsurface Engineering Geology Investigation, El Rancho Verde Country Club, Rialto, California, Dated August 9, 1994, Project No. 3156.2.

In addition, I have enclosed copies of my three reviews dated June 8, 1993, July 14, 1994 and Seplember 7, 1994.

Sincerely,

;J~, WESSL YA. REEDER, County Geologist Building and Safety Division Department or Architecture, Building and Engineering Public Works Group (909) 387-4240

WAR:ljg

cc: Donn Mon~ag, City of Rialto ,, 11 ,Ii' 1' 1

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COUNTY OF SAN BERNAROINO ENVIRONMENTAL

MANAGEMENT GROUP

3" - •forth Arrowh'"d Avenue • Son Bernerdlno. CA 92415-0181 • 1909) 387-8311 Fu No. 19091 387-4301

September 7, 1994

Donn Montag, Principal Planner City of Rial to Planning Department 150 South Palm Avenue Rialto, California 92376

FRED NORTON, C. B. 0. Director

SUBJECT: REVIEW OF RESPONSE REPORT, FAULT-RUPTURE HAZARD INVESTIGATION, EL RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.2.

In accordance with your request, I have reviewed the following report prepared by Gary S. Rasmussen & Associates, Inc. dated August 9, 1994.

Response to San Bernardino County Review of Subsurface Engineering Geology Investigation of EI Rancho Verde Country Club, Rialto, California, Project No. 3156.2.

The report is the third submittal for this project. The first report is covered by my review dated June 8, 1993 and the second report is covered by my review dated July 14, 1994. The third report provides additional information and clarification with respect to the recently completed fault investigation.

The report indicates that many of my previous concerns can be attributed to drafting errors on the map plates and trench logs. These drafting errors apparently included fractures that were incorrectly labeled as faults. The report indicates that these drafting errors have now been corrected and the restricted use zone has been revised.

Based upon the additional information provided in the response report, it is my opinion that the subsurface investigation meets the minimum requiremel)ts of the Alqu_ist_-l'riolo Earthquake Fault Zoning Act for evaluating the hazard-of surface fault rupture.

Although it has not been unequivocally demonstrated that all Holocene-age faulting is ' confined to the recommended restricted use zone, additional faulting (if it exists) is \ probably minor as it has no apparent geomorphic expression in a surface that is

1

estimated to be approximately 2000 years old. I

DONN MONTAG SUBJECT: REVIEW OF RESPONSE REPORT, FAULT-RUPTURE HAZARD

INVESTIGATION, EL RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.2.

PAGE2

There appears to be a potential forextensive ground fracturing. This potential may be greatest in the area northeast of the San Jacinto fault. Speci_~J_f()~.!19JJ.tion~ sbould be requi~~d and should be designed by both the structural and geotechnical engineerii"w)tfr

. input from the geologist. Post-tensioned.slabs may be a possible mitigation method for ground fra.cturing. According to the report, open fissures are expected to be less than .· two inches in width. I

The report recommends that the geologist review and approve the final development plan as well as all grading plans. In addition, the geologist should stamp and sign grading plans.

The newly revised restricted use zones are shown on Plate 2 of the response report (August 9, 1994). These zones should be shown on the final development plan and on any required conditional development plan or specific plan. No human occupancy structures should be placed within the recommended restricted use zones.

A geotechnical investigation should be required prior to grading plan approval. The soils engineer should address all existing fill, including fill associated with the fault trenches. The geotechnical investigation should also address the potential for liquefaction as identified in the geology report.

Upon receipt of additional copies, a copy of each of the three submitted reports will be forwarded to the State for filing.

Sincerely,

WESSL Y A. REEDER County Geologist Building and Safety Public Works Group (909) 3 87-4240

WAR:Ijg

-BlJtLDING AND SAFETY DEPARTMENT 'f;;jj!/_ __

\,;; "'"'" - l

COUNTY OF SAN BERNARDINO ENVIRONMENTAL

MANAGEMENT GROUP ,_ - - .1_~ ,. ' l • 'I, L _',- '}.~• '~~,111111 .. 111111111111111111111111 ... 385 North Arrowheod Avonuo • Son Bornordlno, CA 92415-0181 • (909) 387-8311

Fa• No. (909) 387-4301 \~~ .... ~! FREO NORTON, C. B. 0. ~ Director

July 14, 1994

Donn Montag, Principal Planner City of Rialto Planning Department 150 South Palm Avenue Rialto, California 92376

SUBJECT: REVIE'V OF FAULT-RUPTURE HAZARD INVESTIGATION, EL RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.l.

In accordance with your request, I have reviewed the following report prepared by Gary S. Rasmussen & Associates, Inc. dated June 9, 1994:

Subsurface Engineering Geology Investigation, El Rancho Verde Country Club, Approximately 260 Acres, Rialto, California, Project No. 3156.J.

The report is the second submittal for this project. The first report is covered by my review dated June 8, 1993. Both reports have been reviewed with respect to conformance with our Fault-Rupture Hazard Investigation and Report Standards. The principal recommendation in my previous review was for more trenching. In addition, it was recommended that Plate 1 of the report clearly show the relationship between trenches, trench coverage, restricted use zones and the proposed development.

Since my previous review, additional trenches have been excavated on the site. The submitted report includes the results of the additional trenching. The new report is intended to replace the previous report. The fault zone was found to be more complex than initially thought and the recommended restricted use zone previously recommended, has been extensively modified.

Considering the unusual character and complexity of the faulting, the youthfulness of much of the alluvium and the spacing of the trenches, it is my opinion that the submitted report does not fully satisfy the recommendations contained in my previous review and does not meet our Fault-Rupture Hazard Investigation and Repott Standards.

·"·::'. :...':!";. . ~- ' . ·: t

-· DONN MONTAG, PRINCIPAL PLANNER SUBJECT: REVIEW OF FAULT·RUPTURE HAZARD INVESTIGATION, EL

RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.1. PAGE2

The following items need to be addressed:

I. Plate 2 of the report must clearly show the relationship between trench coverage, restricted use zones and the proposed development. In Holocene.age alluvium, a 5 degree "factor of safety" should be used in establishing what is covered by the trenches. This is especially imperative on this site where complex oblique splays and en echelon faulting occurs.

It is important to note, that unless it can be demonstrated unequivocally that an extensive and undisturbed Pleistocene·age geomorphic surface exists, then geomorphology should not be used in lieu of trenching within the Alquist·Priolo zone.

2. Plate 2 of the report shows various fault splays that apparently veer away from the main fault zone. These fault splays would project outside of the restricted use zone into buildahle areas. No trenches were placed to show that these subsidiary faults terminate within 1he

. restricted use zone.

3. The report documents a potentially active fault approximately 200 feet northeast of the site. The fault trends towards the site beneath young alluvium at S32°W. If extrapolated, this fault would project imo a designated buildable area. No trenches were placed to show that this fault does not project on to the site.

4. Our policy dictates a minimum fifty.foot setback from active faults. There are faults exposed in trenches 14, 15 and 16 that are less than fifty feet within the restricted use zone. The restricted use zone should be adjusted accordingly.

5. Trench 21 is approximately forty.five feet long and eight feet deep. Since this trench alone is being used to show that a northeasHrending fault zone terminates, it may not be deep enough or long enough. In addition, this trench appears to have been one of the few trenches that was not surveyed. Its location should be verified.

6. The report acknowledges that previous published mapping places a major splay of the San Jacinto fault at the bluff located along the west boundary of 1he site. Since no trenches were placed down the slope of the bluff on this site, the report should document in greater detail the evidence that supports the non·fault and erosional character of this feature. Several geologists believe that the bluff is a modified fault scarp and it is included within the Alquist·Priolo Earthquake Fault Zone.

DONN MONTAG, PRINCIPAL PLANNER SUBJECT: REVIEW OF FAULT-RUPTURE HAZARD INVESTIGATION, EL

RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.1. PAGE3

7. The report recommends that foundations and slabs be "reinforced to resist tensional ground cracking". The consultant should specify the maximum width of ground cracking that is expected. It may not be

- feasible to design foundations and slabs to resist large open ground fissures.

8. The report relies on evaluating geomorphology to establish the extent of active faulting. The geologic map (Plate !) apparently shows the fault~ as dashed whete there is geomorphic expression and dotted where they ate buried. It is somewhat unclear however, as the map shows some faults as exposed in young alluvium (as well as fill), but buried in older materials. I would expect the opposite relationship.

9. Unit B is shown as historic in trench 8B, but is offset by faulting in other trenches. This may be a drafting error or the unit designations may not be contemporaneous. -

10. Plate I of the first report submined (dated January 5, 1993) shows two main traces of the San Jacinto fault. The nonheastern-most trace is shown as continuing N34 °W for approximately 500 feet beyond trench 4 (excavated in 1982). Beyond that point, the fault is shown as questioned. No new trenches were placed across this mapped trace where it was shown as approximately located. The extreme northeast end of Trench 11 A may intersect the questioned portion of the previously mapped fault; however, if the fault trends N33°W instead of N34°W, it would miss trench! IA.

The investigation may have established the extent of ground rupture associated with the most recently active strands of the San Jacinto fault. However, the extent of Holocene age faulting on site has probably not been established. Admittedly, an evaluation of all Holocene faulting on site may not be feasible and a risk analysis for the proposed development may be necessary.

Sincerely,

WESSLY A. REEDER, County Geologist Building and Safety Department Environmental Management Group (909) 387-4240

WAR:ljg

cc: Rasmussen & Associates Geology File

.......

• COUNTY OF SAN BERNARDINO

BUILDING AND SAFETY DEPARTMENT _ \".,i}f_ j ENVIRONMENTAL \ ,:: ,,.;~6· MANAGEMENT GROUP 1 Mt; ~ru;.,~I!t .. O ,. ............ .

385 North Arrowhoad Avenue • Sen Bernardino. CA 92415-0181 • (909) 387·8311 Fu No. (9091 387-4301

·~ FRED NORTON. C, B. 0.

June 8, 1993

Donn Montag, Principal Planner City of Rfalto Planning Department 150 South Palm Avenue Rialto, California 92376

Oitec:tor

SUBJECT: REVIEW OF FAULT-RUPTURE HAZARD INVESTIGATION, EL RANCHO VERDE, RIALTO, COUNTY REVIEW NO. 572.

In accordance with your request, I have reviewed the following report prepared by Gary S. Rasmussen & Associates, Inc., dated January 5, 1993:

Engineering Geology Investigation and Geologic Update, El Rancho Verde Country Club Property, Riverside Avenue and Country Club Drive, Rialto, California.

The submitted report represents a geologic update and compilation of previous subsurface data. The previous data includes information from a fault-rupture hazard investigation conducted in 1982 for the southeast portion of the site (formally Tentative Tracts 10244 and 11408). The report and an addendum from the previous investigation were reviewed and approved by Floyd Williams for the City of Rialto in May of 1983. The "updated" site is now more than twice the size of the tracts originally investigated.

The updated report was reviewed with respect to fault-rupture hazard report standards as adopted by the San Bernardino County Building and Safety Department. A copy of the standard procedure is enclosed for your information.

The entire site is located within an Alquist-Priolo Special Studies Zone. However, the entire site is not covered by the limited number of trenches previously excavated. The northwest portion of the site is approximately a mile from the closest trench. The trench cannot provide coverage at that distance. Subsurface data should not be extrapolated more than 600 feet beyond a trench without additional surface or subsurface information.

Plate 1 of the report should not only show the boundary of the recommended restricted use zone, but the limits of the area investigated. Although no human occupancy structures are currently proposed in the northwest portion of the site, the report should clarify what is buildable ground and what needs additional investigation should structures be proposed. Typically, we require a 5 degree factor of safety for subsurface coverage from the ends of trenches.

-~- .

DONN MONTAG SUBJECT: REVIEW OF FAULT-RUPTURE HAZARD INVESTIGATION, EL RANCHO

VERDE, RIALTO PAGE2

The report indicates that the "not-a-part" portion on the site belonging to the West San Bernardino County Water District will require additional trenching if it becomes part of the project. Supporting documents within the Specific Plan/EIR suggest that this "not-a-part" parcel is now a part of the project and therefore will require trenching. If the recommended 500 to 700 foot long additional trenching encounters faulting, then the existing adjacent restricted use zones may have to be modified.

Recommendations Prior to Report Approval.

0

0

0

(;2y,

Plate 1 of the report should show the area that is covered by the previous trenches. The plate should clearly show the relationship between previous trenches, trench coverage, restricted use zones and the proposed development. The restricted use zone should not be extended more than 600 feet beyond trench 4 without additional trenching. Plate 1 currently extends this zone more than 2,000 feet.

The formally "not-a-part" parcel has apparently been incorporated into the project. Additional trenching is recommended by the consultant and should be completed prior to report resubmittal.

The report states that all other applicable recommendations from the previous reports be adhered to. These additional recommendations should be included in a resubmitted report.

WESSLY A. REEDER County Geologist Building and Safety Department Environmental Management Group (909) 387-4 240

WAR:ljg

Enclosure

cc: Gary S. Rasmussen & Associates, Inc.

• ·-NO. A- ISSUE:

REV BY: W. REEDER PAGE

EFFECTIVE 11/8/84 REVISED 1 OF 2 1/28/94

~-'1..-1 v APPROVEO, FRED NOFrroN. C.B.O .. OIRECTOR ~S~U~B-J-EC-T~~~~~~~~~~~~~~~~~~--J

County of San B&rnerdino Environmental Management Group

BUILDING AND SAFETY DEPARTMENT STANDARD PROCEDURE

FAULT-RUPTURE HAZARD INVESTIGATION AND REPORT STANDARDS

The Alquist-Priolo Earthquake Fault zoning Act (formerly the Alquist-Priolo Special Studies Zones Act) allows counties to establish policies and criteria that are more restrictive than the Act. This includes setting specific investigation and report standards. Generally, fault-rupture hazard investigations and associated reports need to follow the guidelines outlined in Division of Mines and Geology Note 49 entitled "Guidelines for Evaluating the Hazard of surface Fault Rupture" and Appendix c of Division of Mines and Geology Special Publication 42 entitled "Fault-Rupture Hazard Zones in California". In addition, other guidelines and requirements are included in Sections 85.020410 and 85.020415 of the county Development Code.

The policies outlined in this standard procedure are intended to clarify our requirements and augment the State guidelines.

1. Trenches and/or other exposures in Quaternary alluvium must provide subsurface coverage for that portion of the project proposed within the Alquist-Priolo Earthquake Fault Zone or when approved by the County Geologist, for individual building pads within the Alquist-Priolo Earthquake. Fault Zone. Trenching may not be necessary if development is not proposed within the Alquist-Priolo Earthquake Fault zone.

2. In determining the amount of subsurface coverage provided by widely spaced trenches and/or other exposures in Holocene alluvium, a 5 degree "factor of safety" will be used based on the overall trend of the principal faulting. Subsurface data (trench coverage or fault location) should not be extrapolated more than 600 feet beyond a trench without additional surface or subsurface information. Where en echelon faulting or other complex structure is suspected, 600 feet may not be sufficient.

3. The county Geologist shall be notified at least two days in advance as to where and when trenching will take place. Failure to notify the County Geologist could result in the need to re-excavate trenches.

4. Trenches excavated in Holocene-age alluvium must be a minimum depth of 10 feet. In pre-Holocene materials, trenches must be excavated to a reasonable depth to adequately expose faulting.

5. For non-critical facilities, a minimum 50-foot setback for human occupancy structures from active faulting is required per the Development Code. Greater setbacks may be appropriate from poorly defined faulting or complex faulting such as low angle and thrust faulting. In certain situations, somewhat lesser setbacks may be appropriate from well defined active faultin ex osed in re-Holoce mate ·

11·114't-4e7 Flin;. 11191

•

A-146 Page 2 of 2

6. If active faulting is suspected within 50 feet beyond the end of a trench, a 50-foot setback from the end of the trench will be considered appropriate,

7. A potentially active fault is a Quaternary fault with unknown Holocene activity. For purposes of establishing minimum building setbacks, a potentially active fault shall be treated the same as an active fault. If it can be demonstrated that no surface ground rupture has occurred along a fault during all of the Holocene, the fault should be designated as "not active". There are no minimum building setbacks for faults designated as not active. However, the potential for sympathetic movement along the fault must be addressed.

s. Principal faulting encountered in the trenches should be staked. Fault laths should be surveyed or tied to a recoverable monument. Trench locations can be tied to a recoverable point. Building setback lines must be tied to a surveyed point.

9. Fault location and/or building setbacks must be shown on a plat contained within the report and on the grading plan and composite development plan. The direction (azimuth) and setback distance of the building setback line must be specified.

10. Trench logs should be completed on each trench, The logs must be a reasonable graphic representation of the subsurface conditions encountered in the trenches, show the topographic profile and be 11t an undistorted scale no smaller than 1 inch equals 10 feet. Trench logs should show distances along trench, depth and direction of trench and/or identify which trench wall was logged. The strike and dip of faulting and prominent fracturing should be shown.

11. The determined or estimated age of faulted and unfaulted materials exposed in the trenches should be discussed in the written report.

12. Conclusions based solely on geophysical investigation methods are unacceptable. Geophysical methods alone never prove the absence of a fault nor do they identify the recency of activity.

13. It is the responsibility of the applicant to verify that a development lies outside of the Alquist-Priolo Earthquake Fault Zone in cases where the exact boundary of the zone with respect to proposed structures, is in question.

.•


GARY S. RAS"MUSSEN & ASSOCIATES, ING./ ENGTNFERINGGHU.Ol;Y

1811 COMMERCf.NTER WEST • SAN BERNARDINO, CALIFORNIA 92408 • (909) 888-2422 • FAX (909) 888-6806

RESPONSE TO SAN BERNARDINO COUNTY REVIEW OF SUBSURFACE ENGINEERING GEOLOGY

INVESTIGATION EL RANCHO VERDE COUNTRY CLUB

RIALTO, CALIFORNIA.

August 9, 1994

Project No. 3156.2

Prepared For

NITTO America Co., Ltd. 1950 Sawtelle Boulevard, Suite 305

Los Angeles, California 90025


GARY s_ RASMUSSEN & ASSOCIATES, INC_/ J.:St;/,';l'FRJS1'<'/cl)/.()(;r

11.:1; 1 COMMCRCENl'E~ WE:'.ST • SAN BERNARDINO, CAl,.JFORNlA 9240FJ • (909) 886-2422 • f-AX {909} IJ80-fJBOf3

August 9, 1994

NITTO America Co., Ltd. Project No. 3156.2 1950 Sawtelle Boulevard, Suite 305 Los Angeles, callfornia 90025

Attention:

Subject:

Kenneth Sakal

Response to San Bernardino County Review of Subsurface Engineering Geology Investigation of El Rancho Verde Country Club, Rialto, California.

References: Review of Fault-Rupture Hazard Investigation, El Rancho Verde, Rialto, County Review No. 572,l, Prepared by the Geology Section of the San Bernardino County Bulldlng and Safety Department, Letter Dated July 14, 1994.

Subsurface engineering geology investigation of the El Rancho Verde Country Club, approximately 260 acres, northeast of Riverside Avenue and Country Club Drive, Rialto, California, Our Report dated June 9, 1994, Project No. 3156.1.

Engineering geology Investigation and geologic update, El Rancho Verde Country Club property, Riverside Avenue and Country Club Drive, Rialto, California, Our Report Dated January 5, 1993, Project No. 3156.

Engineering geology investigation of Tentative Tract 10244, northeast of Riverside Avenue and Immediately southeast of El Rancho Verde Country Club, Rialto, california, Our Report Dated August 26, 1982, Project No. 1830.

Engineering geology investigation of Tentative Tract I 1408, northeast of Riverside Avenue and southeast of El Rancho Verde Country Club, Rialto, California, Our Report Dated August 25, 1982, Project No. 1825.

Engineering Geology Investigation of Approximately 5 Acres, Northeast of Tract 8612 and Tentative Tract Nos. 9147 and 9148, Rialto, California, Our Report Dated February 29, 1980, Project No. 1558.

This letter responds to the questions and concerns of our referenced subsurface

engineering geology investigation of the El Rancho Verde Country Club (Rasmussen, June

9, 1994) raised by the City of Rialto through the San Bernardino County review letter

of July 14, 1992. This letter addresses the County's questions in the order in which they

arc presented in their review. Our response to each of the County's iterns is preceded


NITTO America Co., Ltd. August 9, 1994


by a summary of the County's concern. References cited In this response are

documented Jn the referenced reports.

RESPONSE TO REVIEW

l. Plate 2 of the report must clearly show the relationship between trench coverage, restricted use zones and the proposed development, incorporating a 5 degree "factor of safety" in Holocene-age alluvium.

Plate 2 of our referenced subsurface Investigation (Rasmussen, June 9, 1994) showed the

locations of trenches excavated for our current subsurface investigation and the

locations of trenches excavated for our previous subsurface investigations (Rasmussen,

February 29, 1980; August 25, 1982; August 26, 1982). Our recommended restricted use

zone for human occupancy structures ls based on subsurface coverage provided by

trenches placed on and In the immediate vicinity of the site for our current and previous

investigations. Fault-Rupture Hazard Investigation and Report Standards No. A-146,

issued by the County, requires a 5 degree "factor of safety" based on the overall trend

of principal faulting In alluvial materials of Holocene age, Trenches l and 5 of our

previous investigations (Rasmussen, August 25, 1982; August 26, 1982) and Trench 12 of

our current investigation provide a 5 degree "factor of safety" that includes all of the

site.

The extent of active faulting on the site and the location of our recommended restricted

use zone for human occupancy structures ls based on subsurface coverage provided by

our trenches, supplemented by site geomorphology and review of aerial photographs.

Based on subsurface trenching, geomorphology, aerial photograph review and geologic

field reconnaissance, no evidence for active faulting was observed outside of the

recommended restricted use zone on the site. The 5 degree factor of safety associated

with our trenches on the site, in conjunction with site geomorphology, is considered to

provide adequate control of active faulting traversing the site. It should be pointed out

2




that the youngest geomorph!c surface on the site Is the one immediately east of the San

Jacinto fault in the southern portion of the site (Qyal). This surface is estimated to be

about 2,000 years old and has been offset by faulting. Because this unit is extensively

faulted and shows abundant geomorphic expression of faulting, it can be used as

supplemental evidence for the lack of active faulting In areas between trenches. The

trenches corroborate that faulting in this area ls young enough and large enough to

result in geomorphic expression wherever active faulting has occurred.

2. Various fault splays are shown that veer away from the main fault zone. These fault splays would project outslde of the recommended restricted use zone lnto buildable areas. No trenches were placed to show that these subsidiary faults terminate within the restricted use zone.

Our subsurface investigation (Rasmussen, June 9, 1994) showed several faults trending

in a more northerly dlrection than the main zone of the San Jacinto fault. This faulting

does not depict all of the faults identified in the southeastern portion of the site. The

faulting shown on Plates I and 2 of our subsurface investigation is a generalized

representatlon of en echelon faulting and Riedel shearing Identified in the southeastern

portion of the site. For simplicity, only those faults associated with prominent fault

scarps are shown on our geologlc and trench location maps and then in a diagrammatic

manner to make the fault zone clearer to the non-geologist.

En echelon faulting was observed in Trenches 14, 15 and 17 (Rasmussen, June 9, 1994).

However, the northwest projection of faulting observed in these trenches was not

observed in Trench I of our previous subsurface Investigations (Rasmussen, August 25,

1982; August 26, 1982). In addition, secondary features resulting from severe seismic

shaking were incorrectly labelled as faults in our subsurface report (Rasmussen, June 9,

1994). The trench logs showing these corrected features for Trenches 14 amd 15 are

included as Enclosure 1 of this letter. En echelon faulting observed in Trench 1 of our

previous subsurface investigation and Trench 9 of our current investigation was

3


NITTO America Co., Ltd. August 9, I 994


associated with east-facing fault scarps. However, no evidence for the northerly

continuation of this faulting was observed in either Trench 16 or Trench 8Il of our

current investigation. The northwest-trending fault Identified in Trench 14 of our

current Investigation did not rupture alluvial sediments in Trench 2 of our previous

subsurface investigation (Rasmussen, February 29, 1980). The approximate location of

this fault is based on review of stereoscopic aerial photographs southeast of Trench 14.

The trench location map Included as Plate 2 of this letter correctly shows the southeast

extension of this fault as an aerial photograph lineament.

The width of our recommended restricted use zone ls greater in the southeastern portion

of the site, reflecting the presence of more northerly trending en echelon fault splays.

Due to a drafting error, the northern and southern projections of these faults were

shown as buried beneath alluvium of Holocene age in our report. Active faulting

associated with these en echelon fault splays is considered to die out to the north and

south and ls considered to be entirely contained within our recommended restricted use

zone. This is characteristic of "Riedel shears" in alluvium (see reponse to Item 10 ). The

corrected fault locations are shown on the revised geologic and trench location maps

Included as Plates 1 and 2. Because only a small percentage of geologists and even

fewer engineers understand "Riedel shears", the faults depicted on Plates 1 and 2 are

intended to be more diagrammatic of the fault traces encountered as opposed to the

actual en echelon traces encountered in the trenches and observed in the field. The

diagrammatic depiction makes the trend of the recommended restricted use zone easier

to understand. As documented In the trench logs, depiction of actual fault traces found

would make the map unreadable.

3. A potentially active fault, trending approximately N32E, Is shown located approximately 200 feet northeast of the site. If extrapolated to the southwest, this fault would project into a designated buildable area. No trenches were placed to show that this fault does not project onto the site.

4

I_




Our referenced subsurface investigation {Rasmussen, June 9, 1994) documented the

presence of a northeast-trending fault within alluvial materials northeast of the site.

Our report indicated that no evidence for active faulting associated with this fault or

the southward projection of this fault onto the site was observed in tlie field or on the

aerial photographs reviewed. The location of this northeast-trending fault is shown on

Plates 1 and 2 of this letter. This fault is considered to be an en echelon step of a

northeast-trending fault identified approximately 30 feet southeast of the site

(Rasmussen, June 9, 1994). Due to the proximity of this northeast-trending, en echelon

faulting, the extreme southeastern margin of the site Is included within a recommended

restricted use zone for human occupancy structures {Plate 2).

If this fault is not an en echelon step of the fault immediately south of the site, one

would expect to sec geomorphic or other evidence of a continuation of this fault onto

the site as can be seen by offset of this same surface by the northeast-trending fault

immediately south of the site. This is the same surface that Is estimated to be about

2,000 years old. Both the northwest-trending faulting on site and the northeast-trending

fault off site to the south offset this surface and have geomorphic expression.

Therefore, a continuation of this fault onto the site should have been equally obvious.

4. County Standard No. A-146 requires a minimum 50-foot setback from active faults. Faults exposed in Trenches 14, 15 and 16 are shown less than 50 feet within the recommended restricted use. zone.

Trenches 14 and 15 of our current subsurface Investigation encountered evidence for

northwest-trending faulting. The setback from faulting In Trench 14 is 50 feet from the

main fault trace. The additional fracturing and minor offset southwest of the main fault

Is secondary but are still included within the setback zone. The lower unit of the main

fault cannot be correlated across the fault. It can be correlated across the other

fractures and offsets farther southwest as minor displacements indicative of secondary

failures.

5




Similarly the last obvious fault zone to the northeast ls flagged on our trench log 15 at

approximately Station 114. The 50-foot setback is measured from this clearly offset

feature. Also, there was a subtle fault scarp associated with this zone of faulting that

ended at this location. A secondary shaking feature was observed approximately I 0 feet

farther to the northeast. This secondary feature was mislabelled as a possible fault on

the original trench log. This secondary feature is Included in the setback zone. The

corrected trench logs for Trenches 14 and 15 are included as Enclosure l.

The northwesterly setback line from faulting in Trench 16 was inadvertently measured

from the wrong fault. The setback line has been adjusted accordingly on the enclosed

Plate 2.

5. Trench 21 Is approximately 45 feet long and 8 feet deep. This trench may not be deep enough or long enough. In addition, this trench does not appear to have been surveyed.

Trench 21 was placed to Intercept northeast~trending faulting observed within Trench

16. Trench 21 Is located topographically at approximately the same elevation as Trench

16. Most alluvial materials exposed within Trench 21 correlate stratigraphically with

the oldest alluvial materials exposed within Trench 16. The approximate 8-foot depth

of Trench 21 exposes alluvial materials sufficiently old enough to show the faulting

exposed in Trench 16, if it existed. ln fact, the trench logs indicate the lowest portion

of Trench 21 exposes Unit A, the oldest unit found in this area and older than exposed

in the bottom of Trench 16. However, no evidence for faulting was observed within

Trench 21, indicating that the faulting exposed within Trench 16 rapidly dies out to the

northeast and does not offset older alluvial materials in Trench 21.

The location of Trench 21 was measured by tape and Brunton compass from Trench 16

and Is Q!ili' 50 feet from the surveyed location of the end of Trench 21. The location of

Trench 21 and the boundaries of the recommended restricted use zone in the immcdla tc

6




vicinity of Trench 16 are based on surveyed laths associated with Trench 16. The

approximate location of Trench 21, as shown on Plate 2 of this letter, is considered to

be accurate and in conformance with County Standard No. A-146.

6. A major splay of the San Jacinto fault has been shown on previously published geologic maps located at the bluff along the west boundary of the site. Since no trenches traverse the bluff, the report should document the non-fault character of this feature.

Our current subsurface investigation (Rasmussen, June 9, 1994) identified a northeast

facing escarpment associated with the Rialto Bench coincident with the southwest

boundary of the site. Due to the steep inclination of this escarpment and the proximity

of this feature to existing residential structures located off site (many of whom had

yards and even fences that encroached onto the site), no attempt to place a trench

across this feature was conducted associated with our current investigation on the site.

A trench was placed across this feature approximately 150 feet southwest of the site

during a previous subsurface investigation conducted by our firm (Trench 4, Rasmussen,

February 29, 1980). This trench was Inadvertently left off of our June, 1994, map. It

Is shown on the enclosed Plate 2. No evidence for faulting was observed associated with

this escarpment within that trench. In addition, our current investigation found no

evidence for active faulting associated with this escarpment In the field or on the aerial

photographs reviewed. No evidence for a significant ground-water barrier associated

with this escarpment was observed in the depth-to-ground-water data in the vicinity of

the site (Rasmussen, June 9, 1994).

Due to the relatively large topographic change associated with this escarpment

(approximately 40 feet), a significant fault would be expected associated with this

feature if it were tectonic in origin. No evidence for faulting or even any fracturing

was observed in Trenches 1, 5 and 6 of our previous subsurface investigations on the site

(Rasmussen, August 25, 1982; August 26, 1982) or in Trench 4 of our 1980 investigation.

7




Jn contrast, the main trace of the San Jacinto fault, as exposed In our trenches on the

site, displays significant amounts of faulting and fracturing within a zone up to 250 feet

wide. This northeast-facing escarpment is considered to be an erosional feature

associated with former channels of Lytle Creek. Another erosional escarpment ls crossed

by Trench I (August, 1982) and Trench 20 (this investigation), which suggests this is a

common type of feature in the area.

Oue to the steep inclination of this escarpment and its proximity to the San Jacinto

fault, a potential may exist for ground lurching associated with the escarpment.

Therefore, the southwestern portion of the site is included within a recommended

restricted use zone for human occupancy structures. The recommended restricted use

zone includes the northeast-facing escarpment and a 50-foot setback from the toe of the

escarpment as shown on Plate 2 of this letter.

7. Quantify the amount of tensional cracking expected (maximum width of cracking) so that foundations and slabs can be adequately designed.

Trenches placed on the site associated with our Investigations displayed evidence for

numerous tensional fractures within the alluvial materials (Rasmussen, June 9, 1994;

August 26, 1982; August 25, 1982; February 29, 1980 ). These fractures displayed no

evidence for offset of the geologic units. This fracturing is considered to be the

response of the .soil to compressional and dilational effects of large earthquake waves.

Ground responses similar to those which produced the fracturing should be expected in

the future. Concrete has significant strength only in compression. Therefore, to lessen

future damage to any structures on the site, foundations and slabs should be designed to

also resist the tensional forces that may propagate through the soil as the result of

large, nearby earthquakes. We are primarily concerned with a differential ground

response caused by the seismic waves, i.e. one portion of the footing (slab) undergoing

compression at the same time as another portion of the footing (slab) is undergoing

tension. The actual amount of tensional cracking will vary, depending on many factors,

8

I I I I I I I I I I I I I I I I I 1. I



including, but not limited to, strength of the soil, the friction between the soil and the

footing, the confining force on the soil (mass and area of the structure), moisture

content, density, frequency and amplitude of the seismic waves and the natural period

of the soil column with respect to the period of the seismic waves. We don't expect

offset, per se, on any of these fractures or we would include them in the recommended

restricted use zone for human occupancy structures. However, fracturing less than 2

inches in width may occur associated with tensional cracking on the site. Due to the

pervasiveness of these features exposed in our trenches on the site, we recommend the

strengthening of footings for human occupancy structures to accommodate the

compressional and tensional effects of seismic waves resulting in ground cracking less

than 2 inches, such as the use of post-tensioned slabs. The actual design of foundations

and slabs to resist tensional fracturing falls under the purview of the project structural

and geotechnical engineers.

8. The report relies heavily on evaluating geomorphology to establish the extent of active faulting. The geologic map (Plate 1) apparently shows the faults as dashed where there is geomorphic expression and dotted where they are buried. However, the map suggests some faults are exposed in young a"!Iuvium and fill, but buried beneath older alluvial materials. The opposite relationship would be expected.

The extent of active faulting on the site was determined from trenches placed on the

site associated with our present and previous investigations. Geomorphology was

utilized as secondary evidence to support the presence or absence of faulting on the site.

Where evidence for active faulting was encountered in trenches on the site, site

geomorphology provided additional evidence for the projection of this faulting in the

form of east- to northeast-facing fault scarps, aligned drainages, offset alluvial

materials and offset geomorphic surfaces. Several trenches placed across the site,

especially Trench 1 of our previous investigations (Rasmussen, August 26, 1982; August

25, 1982), found no evidence for active faulting in the northeast and southwest portions

of the site. Geologic field reconnaissance and review of stereoscopic aerial photographs

also found no evidence for active faulting in these portions of the site. Our subsurface

9




Investigation (Rasmussen, June 9, 1994) relies first and foremost on our subsurface

coverage of the site. Geomorphlc evidence was used to extrapolate and complement our

subsurface coverage, but was not used as a replacement for subsurface coverage.

As indicated in response to question 2, faulting shown on the plates In our referenced

report and in this letter represent generalized locations of faulting on the site.

Extensive en echelon faulting was observed in trenches placed in the southeastern

portion of the site. For simplicity, only diagrammatic fault splays are shown on Plates

1 and 2. Due to drafting errors, a few aerial photograph lineaments were shown depicted

as approximately located faults and some faults were shown as "approximately located"

rather than buried. These errors are corrected on Plates 1 and 2, included with this

letter.

9. Unit B is shown as historic In Trench BB, but Is offset by faulting in other trenches. This may be a drafting error or the unit designations may not be contemporaneous.

Our referenced subsurface investigation (Rasmussen, June 9, 1994) described Unit B as

a sandy gravel of early to mid-Holocene age. Due to a drafting error, Unit B is shown

overlying historic fill in the vicinity of Station 130 of Trench SB (Rasmussen, June 9,

1994; Enclosure 5). A revised log of Trench BB, showing the corrected contact, is

included as Enclosure 1 of this letter.

10. Plate l of the Rasmussen report dated January 5, 1993, showed two traces of the San Jacinto fault. The northeasternmost trace is shown continuing N34W approximately 500 feet beyond Trench 4 (Rasmussen, August 25, 19B2). No trenches were placed across this mapped trace where it is shown as approximately located associated with the current investigation. The extreme northeast end of Trench i I A may intersect the questioned portion of the previously mapped fault. However, if the fault trends N33W Instead of N34W, it would miss Trench 1 lA.

10




The fault encountered in Trench 4 of our engineering geology investigation (Rasmussen,

January 5, 1993) is an en echelon fault feature. This fault is considered to be a Riedel

shear equivalent to an R-1 shear or a Sigma-1 shear. This relationship can be clearly

seen when comparing the strike of faulting measured in Trenches 4, 8 and I 0 with the

actual surface strike of faulting and by the surface trace of the fault scarp. This fault

splay ls similar to en echelon faulting observed in the southeast portion of the site. No

evidence for active faulting associated with this en echelon feature was observed in the

field, on the aerial photographs reviewed or exposed in Trench 11 A (Rasmussen, January

5, 1993; June 9, 1994). Based on the obvious Riedel shear en echelon style of faulting

documented in these trenches, Trench i lA would easily intersect any continuation of

faulting. Trenches BA and SB would show any additional width and direction of faulting

from the northeast. In addition, a fault scarp is located coincident with faulting found

in the trenches. The width of our recommended restricted use zone in the Immediate

vicinity of this feature is based on the subsurface location of faulting associated with

en echelon faulting observed on the site and is considered to be conservative.

Concluding Remarks

The current plans for development of the site indicate all of the human occupancy

structures will be placed southwest of the San Jacinto fault, except for the clubhouse.

Because of the extensive faulting found on and adjacent to the site, we recommend that

the final development plans, including the location of the clubhouse, be reviewed and

approved by the engineering geologist. The grading plan also should be reviewed and

approved by the engineering geologist as recommended in our June 9, 1994, report. All

the recommendations in that report remain valid and should be adhered to, except where

superseded by this letter. Plates l and 2 of our June 9, 1994, report are superseded by

the enclosed Plates I and 2, as are trench logs 8B, 14 and 15.

11




we trust that this letter responds adequately to the questions and concerns expressed

by the City of Rialto. Please contact us if you have any further questions.

FFJ:GSR/pg

Enclosure 1:

Plate 1: Plate 2:

Distribution:

Respectfully submitted,

GARY S. RASMUSSEN & "}SSOCIATE~ INC.

L / i' -1··)· ;/ I _/. I . ·. ',,.,, ;-·-; !~ "t-~·~. ·i. L .J ,/ ( ··•·-.. ' , . /~·(. ("{ ._ .I / ,

Frank F. Jordan, Jr. / Registered Geologist, RG 5984/

,//41/4t~-Gary S. Rasmussen Engineering Geologist, EG 925

Trench Logs for Trenches BB, 14 and 15

200-Scale Geologic Map 200-Scale Trench Location Map

NITTO America Co., Ltd. (1) KTGY Group (4) Church Engineering, Inc. (1)

12


Trench 80 Logged by TS Drafted by p~~~

70'

5'

10'

15'

0

\

GO'

I

n1oderato1 . and J Y well bedded we l sorted sand

gravel witn cobb y ct1annclcd les, and cross-bedded

t,::'\ sandy grav~I I ~ (SY 7/2) d igt1I gray to ' ry, Joosa suhrounded , subangu/ar (younl) alluv1"I gran1t1c clasts

"' chan 1 ·

@ sandy silt with l1ghl gray (2.SY ";;or graver dry 10 aan1p n o to SY 7/1) and rootlets, lhr~~~~nl dense, ~oots

out, b1oturba!ed

llorizont· l . ,. and Verlic<il S . C<i/c: I" r'

"

ne nenosrts)

50 1

I

©

J N42E

40'

I

sandy gravel with gray (2.SY 7/0 cobbles light rnoct

1uni d - 2.5Y 712)' da ense· m • mp·

bedded and sort odcrately well ' subrounded clas~sd; s~bangular to minor rare deg , n11nor rootlets staining in son1radect clasrs, oxide'

e areas

l

30' 20'

I I bedding apparent dip 4 '"W

@ sandy gravel wit gray (2.5Y 7/0 -h11J:bbtes: lighc n'ledium dense· ); damp; subangular-subrpoorly bedded· ounded' crasts'

j 0.

I

.~N~l.OSUHE 6

Gary S R lll:NCll LOGS Nitto /\meri~,.,· asmusscn & I\ •. . Co. - El Ran ssocrntcs, lnc.

I"· I , cho Verde 'Id to C J'f . Countr"

I' . ' a I ornia , roJcct No. 3156. 2

O'

o•

5'

10'

Club



l.oi;i;ed by TS ll Orn fled by !'1\C hl'll!J

v bend bend v V :\88E

140' @

130' 120'

IO'-

15'

20'

25'

sanrJy silt with minor gravel light gray {2.SY 7/0 to 5Y 711); dry to dan1p; n1ediun1 denso; roots and rootlets throughout; bioturbated

I

I wood debris I

I

contact

deposits

I loril.ontal and Vertical Scale: I" = 5'

28' OD concrete

concrete irrigation pipe, infirtod in cut troncr1

I wood debris

I \

s;;:indy gravol: light olive brown to Jigt1t yonowisll brown (2.SY 5/4 -614); dan1p: dense: roorly bedded; subangular to subroundcd clasts

bend v

II O'

I

degraded clasl

coarse sand layer

.J N421~-

100' 90'

I I open burrow with infillod

sandy graver: light gray

oxidized strong brown {7.SYR 416)

well sorted sandy gravel with cobbles, oxide staining

(SY 7/2); dry; loose: subangular to subrounded granitic clasts; (young alluvial channel doposits)

sandy silt with minor gravel: lighl gray {2.SY 7/0 to SY 7/1);

sandy graval with cobbles: light gray {2.SY 7/0 - 2.SY 7/2); damp: mediurn dense; n1odera1ety wen bedded am~ sor1ed; subangular lo subrounded clasts; n1inor rootlets; minor rare degraded clasts, oxide staining in son1e areas

dry to damp; n1odium dense; roots and rootlets throughout; bioturbaled

165'

15'

20'

160'

I bioturbated contact

sandy gravel with cobbles: hgt1t gray (2.5Y 7/0 - 2.SY 7/2); dan1p: 1nodium donso: nlOdcraloly well l>oddod and !'>Ortod, suhan9ular lo subroundod clasts: n1inor rootlots, nunor raro degraded clasts. oxide staining in SOfne areas

2· OD iron pipe =-N42W

coarse s<i.nd layer

N42E

I infiJJed burrows

silty sand with gravel: very dark gray {10YR 3/1); dan1p; loose; niassive: mtnor cobbles: topsoil intermixed with fill; fill areas may con1ain trash and wood debris

150'

I 5" slope: rossibly original surface, subsequently buried by <i.dditional s<i.ndy silt deposits - or overlying sandy r.ilt is bottom of fill

\\ \' . I -ihri.llod burrows

--

ENCl.OSUHE 6 TllENCll LOGS

IO'

15'

20'

140'

10'

15.

20'

Gary S. Hasmussen & Associates, Inc. Nitto America Co. - El Rancho Verde Country Club

Rialto, California i'roject No. 3156. 2


5'

10'

15'

IO'

70'

Oakdale Avenue: < 1 • thick asphalt with <2" subgrade and often no sutigrade

80'

I 90'

I

A :'(771~

sou th w;li I

100'

I

bend \/

N75"-'E~-

110'

I

bend

v 120'

I laminated fine sand with medium gravel, waTped and displaced (2.5Y 7/2)

70'

N78E

130' 140'

I sand: light yellowish brown to ohve brown (2.SY 6/4 - 514, nlOist); medium dense to loose where coarser, nlOist; n1assive but grades westward into two larninated units; rare roots. rare charco {fluvial sand bar and/or r

.. coarse sand 1aycr 0 0

o Cobble l'yers sand layer

\

n1edium laminated

Qravel layer

J - 0 • 6 ('; ,_,• '_J ., o '-' Q ... '"'•::i • • ·0 o .'·. _() •,, • .o r.. ·.o Q 0~ 0 . ;?, •.'. ~ sandy cobbles wilh gravel · • ;,-'i r- ,.., cc_, Q .-_, '2 () Q 'l.J a I disturbed zone: faulled

1 •,_, ) • .... ~) <-- ,- :· ... CJ~- "' . ,~ / . ..,., ' . \D. 0

·• D

0

. {.\ "'"'" """"'"'"" lone to medium :~·d:'.·~~-~~l:p~~.~~~.~~- c-14 sample

hoddinlJ I ~ ~.uid ...,.11

1l gietvcl lanunated sand cal displacenlent on each trace -appareut c11p 4'W dies out rapidly upward,

P"~•'>tlllfJ faun N~W e.1 SW ,,.N46W 85SW site across lrench

c<irfE!!attt umt5 acH1s.s.

/!(H(./'IJOt;11 iilH1 \/(:rt1cnl

1 o· apparent vort1ca1 offset


10'

151',

O'

5'

IO'


Rialto, California Project No. 3156.2·

I lorizontal and \l('rtit:al Seal,~: I" " '.'"1'


Trench l4 (continued)

Logged by TS!l Drafted by 1'1\(;

l 40'

o·-bedding bedding

l 50'

I bedding apparen1 d1r t 5"W

beCd1ng apparent chp 1 .fw

apparent dip 16"W apparent dip 1 O"W

5'

10'

andesite(?) OOukier with quartz/plage dike

210'

_-. .. .. •

bedding I apparent dip 2"E

fault

lan1inated fine to n1edium sand with minor gravel: cross-bedded; white to light gray (2.5Y 7/2 -

N30W 60-75NE, minin1um apparent vertical displacen1enl of 1·- 1Y2'

8/2, dry to dan1p); loose; laminated fine sand, coarse sand and fine ---------' gravel: dry to damp (eolian)

218'

clay: brown (1 OYA 5/3, n1oisl); finely lan1inated; slighUy plastic; n1inor silt; breaks apart along laminae

l lorizo11t<1I and Vertical Seale: I"

4 N78E

@

170'

secondary silt and clay layers

sandy gravel with cobbles to cobbly gravel: dark yellowish brown (10YR 4/4 - 4/6, n10isl), mediunl dense; most; son1e bedding: subangular to subrounded clasts. multiple lithOlogies, dominantly granitic or gneissic; occasional sct1istose or coarse n1aric clasts are nighly weathered and oxidized (older alluviun1)

silt in fine sand: light gray {2.SY 7/2); n1oist; finely lan1inated

180'

I

-N25W aasw -N09E 78NW '-----..,.----'

secondary features; erOded out by rain water; warping and 1 • -4 • apparent · vertical displacement

secondary feature: -N14E 72NW 8" apparent vertical displacement

difficult lo see on other watl as bench has destroyed contact between upper' gravel and underlying fine to coarse sand unit

HJO'

I

@ silty sand with gravel. very dark gr ay1sh Drown to

200' darkbrown(10YR3/2-3/3): 210'

I loose, n1oist. organic rich roollots llirougt1out, n11no; cobbles (topsoil 'A' horizon)

-N02W 815 (site across trench) =-4 • apparent vertical offset

sandy gravel with cobbles: light oray to light olive brown, (2.SY 7/2 to 2.SY 5/4, moist); loOse to medium dense· moist; bedded; subangular to subro~nde<i clasts - dominanlly gneissic or granitic

•

sand: light yellowish brown lo light olive brown (2.SY 614-514, n1oisl); laminated and crossbedde<l fine to coarse sand; n1ediurn dense; moisl (eolian)

in comPosition; no degrac:led clasts: minor roots and rootlets; fining upward sequences

ENCLOSUllE 6 THENCll LOGS

Gary S. Hasmussen & Associates, Inc.

o·

Nitto America Co. - El llancho Verde Country Club llialto, California

Project No. 3156.2

I I I I I I I I I I I

Trench 15 Logged by TSlJ

75'

O'

5'

10'

Drafted by PAC

70'

I

possible fau/1?

very little oxide staining

147'

difficult to see on opposite wall due to caving

140'

I mangancseoxide stained bedding

GO'

I

I prolate clasts, possibly 1 + foot of vertical displacement, :..N25W, difficult to correlate units across feature

coarse sand and fine gravel layer

50'

I

thick 1' matt ot roots

130'

l laminated sandy gravel bedding apparent dip 7.S"E

n1edium to coarse sand (pateosol)

burrow apparent dip 12"E jun1bled zone of cobbles

I 5'

I I 10'

I 15'

I I lorizontal & Vertical Scale: I" = 5'

I

40'

I

bedding

...,#_ N66E Southwest wall

sandy cobbles

@

30'

I

apparent dip 4-6'\V

sa~dy grav~I: light olive brown (2.SY 514, moist); medium dense: laminated coarse sand to coarse gravel with minor cobbles· sub~~g~lar to subrounded clasls, domin~tly granitic in composition; generally dips between 4-6'1 westerly - grades into gravelly sand to the west and becomes more massive

120'

I orange ironoxide staining

LATH

-.-·-·-

110'

I

·-bedding apparen! dip 2'6E

100'

I

20' l O'

I I roar lone upper 2-6"

\

@

topsoil: illy sand wilh cobbles and gravel: very dark brown (10YR '212, nloist); high organic content; 2-6" rootrel zone at top: rootlets throughout; formed on young alluvium

sandy cobblos with gravel: light olive brown (2.SY 5/4, moist); loose to n1edium dense: greater percentage or cobbles than undertying unit; very litOe oxide staining; subangular to subrounded clasts - dominanlty granitie/gneissic in composition

O'

90' 80' 75'

I lan1ina1ed coarse sand layer

silty sand layer

I infilled with sand {SY 4/2}; moist

O'

5'

10'

5'

silty sand layer

ENCLOSUnE 6 THENCH LOGS


10'

Nitto America Co. - El Hancho Verde Country Club Rialto, California

Project No. 3156.2

OVERSIZED -·-·. -. -

... . - ..... - . ·-

DOCUMENT HAS -· ·-·

BEEN PULLED AND SCANNED WITH THE MAP

FILE. ·-·-·--._

·~

. . •· ..

- . .

.. . . . . . . . . . . . . . . -~ .

. . '. . .

gmw.conservation.ca.gov...jun 09, 1994 · i i i i i i i i i i i i i i i i i i i table of contents...

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