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46 323 14 12
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6 545
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23 1 64
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1210
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2628
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36
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33
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12
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27 25
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10
34
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12
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33
36
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13
30
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28 3025
21
15
17
26
36
28
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13
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31
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22 23
30
28
25
5
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35
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31
26
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22
29
35
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1818
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20
36
34
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25
35
14
36
33
26
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30
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12
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16
10
18
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29
13
3433
28
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10
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5
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1417
34
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21
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26
32
22
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2627
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1110 12
1813141516171818 1314151613 17141516 17
ROCK-FALL HAZARDZION NATIONAL PARK GEOLOGIC-HAZARD STUDY AREA
EXPLANATION
T 38 ST 39 S
37 30'
113 7' 30"
2010
DISCUSSION
USING THIS MAP
MAP LIMITATIONS
SYMBOLSHigh rock-fall hazard: Areas where steep slopes below resistant cliff-forming bedrock units provideacceleration and runout zones littered with abundant rock-fall boulders >1.5 feet in diameter. Suchlarge boulders can damage property and threaten lives. Rock units in high-hazard areas include theShinarump Member of the Chinle Formation, Springdale Sandstone Member of the KayentaFormation, Navajo Sandstone, Lamb Point Tongue Member of the Navajo Sandstone, andQuaternary basalt flows. Where jointed or fractured, these rock units can produce large (>30 feet inlong dimension) angular boulders.Moderate rock-fall hazard: Areas where (1) slopes provide sufficient relief to create an accelerationzone, but where only sparse rock-fall debris is present on slopes or in the runout zone at the base ofthe slope; typically bedrock units in these areas crop out in the slope instead of forming a cappingunit; (2) talus/cliff-retreat deposits form steep slopes due to erosion and previous rock-fall boulders onthose slopes may remobilize; or (3) resistant, cliff-forming bedrock units extend to the canyon floorwith no underlying acceleration zone; rock falls in these areas tend to fall straight down and stopimmediately at the base of the cliff.Low rock-fall hazard: Areas where fine-grained, comparatively soft bedrock units such as mudstoneand shale crop out on steep slopes, or where rock units typical of moderate- or high-hazardcategories crop out in areas of low to moderate relief. Low rock-fall hazard areas typically containsparse rock sources of limited extent.Low probability, high hazard: Canyon bottoms subject to very large low-probability, high-hazard rockfalls. These areas are typically bordered by towering, jointed Navajo Sandstone cliffs. The largest ofthese events (fin collapse/rock avalanche) may involve thousands of cubic yards of material, aretypically sourced high on canyon walls, and have recurrence intervals likely measured in thousandsof years. Runout zones can extend much farther than for the smaller, more frequent rock-fall events.
ByWilliam R. Lund, Tyler R. Knudsen, and David L. Sharrow
HAZARD REDUCTION
Plate 2Utah Geological Survey Special Study 133
Zion National Park Geologic-Hazard Study Area, Washington and Kane Counties, Utah
Camp
Creek
Creek
Horse RanchMountain
Taylor Fork
North
Fork
Middle
Fork
South
LeePass
NaguntMesa
BuckPastureMountain
Creek
Timber
Kolob
CanyonsRoad
ShuntaviButte
GregoryButte
KolobArch Langston
Mountain
Creek
La Verkin
WillisCreek
BEAR CANYONTRAP
KO
LO
B
CA
NY
ON
S
BurntMountain
HO P
VA L L E Y
FirepitKnoll
PineValleyPeak
NorthgatePeaks
NorthGuardian
Angel
SouthGuardianAngel
Kolob
Terrac
eRo
ad
Kolob
Terrace
Road
North
Creek
Right
Fork
Left
Fork
Blue
Creek
Goose
Creek
LavaPoint
Kolob
Creek
DeepCr
eek
Coalp
itsWa
sh
Wash
Scoggins
Altar ofSacrifice
The WestTemple
MeridianTower The
Sentinel
MountKinesava
Wash
Hube
r
Creek
Oak
The Watchman
JohnsonMountain FORK
EAST
RIVER
VIRGIN
P A R U N U W E A P
C A N Y O N
BridgeMountain
The EastTemple
MountSpry
CraterHill
TwinBrothers
Mountainof the Sun
The GreatArch
The GreatWhite Throne
LadyMountain
CastleDome
Mount
AngelsLanding
ObservationPoint
Mountainof Mystery
WynopitsMountain
IvinsMountain
Timber
HU
RR
I CA
NE
CL I
FF
S
Death Point
Tucupit Point
Paria Point
Beatty Point
Top
Mountain
Herbs
Po
intLA
NGST
ON
CANYO
N
Currant
Creek
Cane
Creek
POLE
CANYON
L OW
E R
K OL O
B
P L A T E A U
UP P E R
K OL O
B
P L A T E A U
HO
RS
EP A
ST
UR
E
PL A
TE
AU
ZI O
N
CA
NY
ON
O R D E R V I L L E C A N Y O N
TheSubway
GREAT
WEST
CANYON
COUG
A R MO U N TA I N
CourtPatriarchsTheof
CreekBirch
Creek
Pine
Creek
Pine
Creek
Clear
Chec
kerbo
ard
Mes
a
Creek
Clear Creek
Co-op
GIFFORDCANYON
FORK
NORTH
RIVE
R
VIRGIN
ZION-MOUNT CARMEL TU NN EL
TUNNEL
Wash
Terry Wash
Jennin
gs
Wash
Coalpits
TheBishopric
HEAPS
CANYON
ECHO
CANYON
CableMountain
Temple ofSinawava
TELEPHONE
CANYON
IMLAY
CANYON
BULLOCH
GULC
HT H E
N A R R OWS
FORK
NORT
H
RIVER
VIRGIN
WILDCAT
CANYON
RUSSELLGULCH
North
Creek
North
Creek
Zion
Cany
on
Scen
icDr
ive
9
9
The Grotto
Zion CanyonVisitor Center
ZionLodge
Little
Creek
Grapevine
Wash
TOW
E RS
V I R G I NT H E
O F
Abraham Isaac
Jacob
ChurchMesa
PHANTOM VALLEY
CORRAL
HOLLOW
KolobCreek
WeepingRock
Cathedral Mountain
Majestic
Kolob CanyonsVisitor Center
WASH
INGT
ON C
OKA
NE C
O
IRON COWASHINGTON CO
Neag
le R
idge
BullpenMountain
Pocket Mesa
OAK SPRING VALLEY
PINE
VALLEYLEE
VALLEY
CaveKnoll
CAVE
VALLEY
TabernacleDome
Wash
SpringPine
TRAIL
CANYONGrea
theart
Mesa
BEHUNIN
CANYON
Creek
Shunes
Shunesburg Mountain
Wash
Hepworth
Wash
DennettCanyon
Bee HivePeak
HIDDENCANYON
CANYON
MYSTERY
R 12 W R 11 W
T 38 ST 39 S
R 11 W R 10 W
T 40 ST 41 S
T 41 ST 42 S
T 39 ST 40 S
T 41 ST 42 S
T 39 ST 40 S
T 40 ST 40.5 S
T 41 ST 42 S
R 11 W R 10 W
R 10 W
R 12 W R 11 W
R 10 W R 9.5 W R 9.5 W R 9 W
37 27' 30"
37 25'
37 22' 30"
37 20'
37 17' 30"
37 15'
37 12' 30"
37 10' 37 10'
37 12' 30"
37 15'
37 17' 30"
37 20'
37 22' 30"37 22' 30"
37 25'
113 5'
113 2' 30"
113
37 22' 30"
112 57' 30" 112 55'
112 52' 30"
112 52' 30"
112 55'112 57' 30"
113
113 2' 30"113 5'
113 7' 30"
113 10'
113 12' 30"
113 12' 30"
Zion National Park Geologic-Hazard Study Area boundaryZion National Park boundaryCounty boundaryState highwayMinor roadFoot trailExisting park structureArea not studied
This map shows areas of relative rock-fall hazard in the Zion National Park Geologic-Hazard Study Area. Site-specific, rock-fall-hazard investigations should be performed for future development in the study area asrecommended in the table below. Existing park facilities, campgrounds, and high-use trails should be evaluatedas time and funding allow, also as recommended in the table below. A geotechnical consultant should providedesign or site-preparation recommendations as necessary to reduce the rock-fall hazard. These investigationscan resolve uncertainties inherent in generalized hazard mapping and help ensure safety by identifying the needfor rock-fall-resistant design or mitigation.For some areas, site-specific assessment may only require a field geologic evaluation to determine if a rock-fallsource is present. However, if a source is identified, additional work to adequately assess the hazard is needed.Rock-fall sources should be evaluated for the following parameters: rock type, joints and other fractures, beddingplanes, and potential clast size. Slopes below rock sources should be evaluated for slope angle, aspect,substrate, surface roughness, and vegetation. Previous rock-fall deposits should be evaluated for distribution,clast-size range, amount of embedding, and weathering of rock-fall boulders. In addition, evaluation of the runoutzone below a source can be estimated using a simple two-dimensional model, such as the Colorado Rock FallSimulation Program (Jones and others, 2000).The hazard presented by large rock falls in areas designated "low probability, high hazard" is high, but thelikelihood of such an event at any particular location is low. These areas are considered subject only to veryinfrequent events. Site-specific investigations are not recommended for future development in these areas.
The map boundaries between rock-fall-hazard categories are approximate and subject to change as newinformation becomes available. The rock-fall hazard at any particular site may be different than shown becauseof geological variations within a map unit, gradational and approximate map-unit boundaries, and map scale.Small, localized areas of higher or lower rock-fall hazard may exist within any given map area, but theiridentification is precluded because of limitations of the map scale. This map is not intended for use at scaleslarger than the published scale, and is designed for use in general planning and design to indicate the need forsite-specific investigations.
Early recognition and avoiding areas subject to rock fall are the most effective means of reducing rock-fallhazard. However, avoidance may not always be a viable or cost-effective option, especially for existing facilities,and other techniques are available to reduce potential rock-fall damage. These may include, but are not limitedto, rock stabilization, engineered structures, and modification of at-risk structures or facilities. Rock-stabilizationmethods are physical means of reducing the hazard at its source using rock bolts and anchors, steel mesh, orshotcrete on susceptible outcrops. Engineered catchment or deflection structures such as berms or benches canbe placed below source areas, or at-risk structures themselves could be designed to stop, deflect, retard, orretain falling rocks. Conversely, after careful consideration of the hazard, it may be possible to conclude that thelevel of risk is acceptable and that no hazard-reduction measures are required.
37 27' 30"
UTAH GEOLOGICAL SURVEYa division of Utah Department of Natural Resourcesin cooperation withNational Park Service
Approximate meandeclination, 2009
12 9'o
TRUE
NOR
THMA
GNET
IC N
ORTH
Map Location
This geologic-hazard map was funded by the Utah Geological Survey and theU.S. Department of the Interior, National Park Service. The views andconclusions contained in this document are those of the authors and should notbe interpreted as necessarily representing the official policies, either expressedor implied, of the U.S. Government.Although this product represents the work of professional scientists, the UtahDepartment of Natural Resources, Utah Geological Survey, makes no warranty,expressed or implied, regarding its suitability for a particular use. The UtahDepartment of Natural Resources, Utah Geological Survey, shall not be liableunder any circumstances for any direct, indirect, special, incidental, orconsequential damages with respect to claims by users of this product.For use at 1:24,000 scale only. The Utah Geological Survey does notguarantee accuracy or completeness of data.
www.geology.utah.gov
Base map consists of U.S. Department of Agriculture 2006 National AgriculturalImagery Program natural color aerial photography and shaded relief generatedfrom digital elevation data acquired from the Utah Automated GeographicReference Center.
Universal Transverse Mercator Projection, zone 12North American Datum of 1983
REFERENCESBiek, R.F., Willis, G.C., Hylland, M.D., and Doelling, H.H., 2003, Geology of Zion National Park, in Sprinkel, D.A.,
Castleton, J.J., 2009, Rock-fall hazards in Utah: Utah Geological Survey Public Information Series 94, 3 p.Cruden, D.M., and Varnes, D.J., 1996, Landslide types and processes, in Turner A.K., and Schuster, R.L., editors,
Elliott, A.H., and Giraud, R.E., 2009, 2nd damaging Y Mountain rock fall in four years: Utah Geological Survey,
Hylland, M.D., 1995, Fatal Big Cottonwood Canyon rock fall prompts UGS emergency response: Utah Geological
International Code Council, 2009, International building code: Country Club Hills, Illinois, 678 p.Jones, C.L., Higgins, J.D., and Andrew, R.D., 2000, Colorado Rock Fall Simulation Program, version 4.0: Report
Keefer, D.K., 1984, Landslides caused by earthquakes: Geological Society of America Bulletin, v. 95, p. 402-421.Keller, E.A., and Blodgett, R.H., 2006, Natural hazards – Earth’s processes as hazards, disasters, and
Lund, W.R., Knudsen, T.R., and Brown, K.E., 2009, Large rock fall closes highway near Cedar City, Utah: Utah
Varnes, D.J., 1978, Slope movement types and processes, in Schuster, R.L., and Krizek, R.J., editors, Landslides
Chidsey, T.C., Jr., and Anderson, P.B., editors, Geology of Utah’s parks and monuments (second edition):Utah Geological Association Publication 28, p. 106-137.
Landslides – investigation and mitigation: Washington, D.C., National Academy of Sciences, NationalResearch Council, Transportation Research Board Special Report 247, p. 36-75.
Survey Notes, v. 41, no. 3, p. 6-7.
Survey, Survey Notes, v. 27, no. 3, p. 13.
prepared for the Colorado Department of Transportation, 127 p.
catastrophes: Upper Saddle River, New Jersey, Pearson Prentice Hall, 395 p.
Geological Survey, Survey Notes, v. 41, no. 3, p. 8-9.
– analysis and control: Washington, D.C., National Academy of Sciences, National Research Council,Transportation Research Board Special Report 176, p. 12-33.
1 0 10.5 MILE1000 0 1000 2000 3000 4000 5000 6000 7000 FEET
1 0 10.5 KILOMETER
SCALE 1:24,000
Recommended Requirements for Site-Specific InvestigationsRelated to Rock-Fall Hazards to Protect Life and Safety
High, Moderate
FamilyDwellings andCampgrounds
Buildings and OtherStructures That
Represent aLow Hazard
to Human Life inthe Event of Failure
All OtherBuildings and
Structures ExceptThose Listed in
Groups I, III, andIV
Buildings andOther
Structures Designated as
EssentialFacilities
Buildings and OtherStructures That
Represent a SubstantialHazard to Human Lifein the Event of Failure
HazardPotential
LowNone
I II III IV
No2
No2 YesYesYesYesYesYes
No NoNoNoNo
Occupancy Category1
1Modified from International Code Council (2009). 2Property damage possible, but little threat to life safety.
YesYes
Rock fall is a natural mass-wasting process that involves the dislodging and downslope movement of individualrocks and small rock masses (Varnes, 1978; Cruden and Varnes, 1996). Rock falls pose a safety threat becausea falling or rolling boulder can cause significant damage to property, roadways, and vehicles as well as injury oreven loss of life (see, for example, Hylland, 1995; Keller and Blodgett, 2006; Elliot and Giraud, 2009; Lund andothers, 2009). Rock-fall hazards exist where a source of rock is present above slopes steep enough to allowrapid downslope movement of dislodged rocks by falling, rolling, and bouncing.Rock-fall hazard is based on a number of factors including geology, topography, and climate. Rock-fall sourcesinclude bedrock outcrops or boulders on steep mountainsides or near the edges of escarpments such as cliffs,bluffs, and terraces. Talus cones and scree-covered slopes are indicators of a high rock-fall hazard, but otherless obvious areas may also be vulnerable.Rock falls are initiated by freeze/thaw action, rainfall, weathering and erosion of the rock and/or surroundingmaterial, and root growth. Rock fall is also the most common type of mass movement caused by earthquakes.Keefer (1984) indicates that earthquakes as small as magnitude (M) 4.0 can trigger rock falls. All nine of Utah'shistorical earthquakes of M 5 or greater have caused rock falls. Sources of earthquake ground shaking thatmight produce rock falls in the Zion National Park Geologic-Hazard Study Area include a large earthquake on theHurricane fault west of the study area, or a moderate earthquake (< M 6.5) within the study area itself (IvanWong, URS Corporation, written communication, 2008).Slope modification, such as cuts for roads and building pads or clearing of slope vegetation for development, canincrease or create a local rock-fall hazard. However, in many cases a specific triggering event is not apparent.Although not well documented, rock falls in Utah appear to occur more frequently during spring and summermonths. This is likely due to spring snowmelt, summer cloudburst storms, and large daily temperature variations(Castleton, 2009).Rock fall is the most common mass-movement type in the Zion National Park Geologic-Hazard Study Area. Thecombination of steep slopes capped by well-jointed, resistant bedrock formations provides ample opportunity togenerate rock falls. Bedrock units particularly susceptible to rock fall in the study area include the ShinarumpMember of the Chinle Formation; Springdale Member of the Kayenta Formation; Lamb Point Tongue Member ofthe Navajo Sandstone; other ledge- and cliff-forming strata in the Moenkopi, Moenave, and Kayenta Formations;and the massive, pervasively jointed, cliff-forming Navajo Sandstone. Rock falls are particularly prevalent andhazardous where softer, more easily eroded bedrock units crop out on slopes below stronger, more resistantbedrock formations. Erosion of the underlying soft units and subsequent undercutting of the more resistantbedrock formations triggers many rock falls.Talus deposits blanket steep to moderate slopes throughout the study area. These deposits are derived fromupslope ledges and cliffs and consist chiefly of accumulations of poorly sorted, coarse, angular blocks of varioussizes. The boulders in talus deposits may exceed 30 feet in long dimension (Biek and others, 2003). Thewidespread distribution of talus and the direct relation of talus deposits to the rock-fall process attest to thewidespread extent of the rock-fall hazard in the study area.For additional information about the rock-fall hazard in the Zion National Park Geologic-Hazard Study Area, referto the Rock-Fall Hazard chapter in this report.
_