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Glacial Geology and Stratigraphyof Fort Richardson, AlaskaA Review of Available Data on the HydrogeologyLewis E. Hunter, Daniel E. Lawson, Susan R. Bigl, Peggy B. Robinson,and Joel D. Schlagel April 2000

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Abstract: The surficial geology and glacial stratigraphyof Fort Richardson are extremely complex. Recent map-ping by the USGS shows the general distribution of surf-icial deposits, but details on the underlying stratigraphyremain poorly known, leaving a critical gap in the under-standing of ground water conditions below Fort Richard-son. A conceptual model of the subsurface stratigraphywas developed on the basis of results of recent surficialmapping, current knowledge of the glacial history, stud-ies of modern glaciers, and limited subsurface data. Aconfining layer below the southern half of the canton-ment is likely the northern extension of an “older” groundmoraine that crops out further to the south. Below the

cantonment, this moraine is buried below about 15 mof outwash and fan deposits, but it appears to beabsent to the north, where the confined and uncon-fined aquifers are hydraulically connected. The north-ern limit of the “continuous” ground moraine is roughlybelow the cantonment and parts of Operable Unit D.Buried silt horizons in the fan probably create thelocally perched aquifers; however, erosional remnantsof the ground moraine and interfingering of debris flowdeposits along the Elmendorf Moraine are plausiblealternatives. These deposits are composed of finer-grained materials that slow ground water infiltrationand cause water to accumulate.

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Technical ReportERDC/CRREL TR-00-3

Glacial Geology and Stratigraphyof Fort Richardson, AlaskaA Review of Available Data on the HydrogeologyLewis E. Hunter, Daniel E. Lawson, Susan R. Bigl, Peggy B. Robinson,and Joel D. Schlagel April 2000

Prepared for

U.S. ARMY ALASKA

Approved for public release; distribution is unlimited.

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PREFACE

This report was prepared by Dr. Lewis E. Hunter, Dr. Daniel E. Lawson, Susan R. Bigl,Research Physical Scientists; Peggy B. Robinson, Biologist, Geochemical Sciences Divi-sion; and Joel D. Schlagel, Physical Scientist (GIS), RS/GIS Center of Expertise, U.S. ArmyEngineer Research and Development Center, Cold Regions Research and EngineeringLaboratory.

Funding and support for this research was provided by the U.S. Army Alaska, Envi-ronmental Resources Department, Directorate of Public Works, Fort Richardson, Alaska.Technical review was provided by Lawrence Gatto and Charles Collins, both of CRREL.Patricia Weyrick of CRREL is acknowledged for assistance in GIS support. The authorsalso express their thanks to Crystal Fosbrook and Kevin Gardner, Department of PublicWorks, Fort Richardson, Alaska, and Henry Schmoll and Lynn Yehle of USGS, for numer-ous discussions and comments on the text.

The contents of this report are not to be used for advertising or promotional purposes.Citation of brand names does not constitute an official endorsement or approval of theuse of such commercial products.

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CONTENTS

Preface .......................................................................................................................................... iiAcronyms and abbreviations ........................................................................................................ vIntroduction .................................................................................................................................. 1

Physiography ........................................................................................................................... 2Hydrography ............................................................................................................................ 3

Surficial geology .......................................................................................................................... 4Surficial geologic map ............................................................................................................ 5Surficial deposits ..................................................................................................................... 5

Glacial geological history ............................................................................................................ 11Conceptual stratigraphic model ................................................................................................... 13

Post-Rabbit-Creek outwash ..................................................................................................... 16Fort Richardson and Dishno Pond sequences ......................................................................... 16Bootlegger Cove Formation .................................................................................................... 17Mountain View fan .................................................................................................................. 19

Hydrogeology ............................................................................................................................... 20Regional ................................................................................................................................... 20Fort Richardson hydrogeology ................................................................................................ 21Significance to contaminant transport .................................................................................... 29

Conclusions .................................................................................................................................. 33Literature cited ............................................................................................................................. 34Appendix A: Description of map units ........................................................................................ 41Abstract ........................................................................................................................................ 70Plate 1: Surficial geological map of Fort Richardson and vicinity, Alaska (separate pdf file)

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ILLUSTRATIONS

Figure1. General location of Fort Richardson .................................................................................. 22. Physiography of the Anchorage area and Fort Richardson ................................................ 33. Stratigraphic cross section from Fire Island ...................................................................... 44. Major landforms in the Anchorage Lowland ..................................................................... 55. How map unit types relate to a valley glacier .................................................................... 66. Interbedded alluvial sediments as might be produced by periodic discharge

events ............................................................................................................................. 97. Incised fans in flank of Elmendorf Moraine and interfingering of sedimentary

units along the moraine margin ..................................................................................... 108. How a tidewater glacial can advance into the marine environment .................................. 139. Boreholes and ground water monitoring wells .................................................................. 14

10. Conceptual time–stratigraphic model for Fort Richardson below the canton-ment area ........................................................................................................................ 15

11. Conceptual stratigraphic sequence ..................................................................................... 1512. Cross sections along Ship Creek ........................................................................................ 17

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13. Fan such as those along the margin of the Elmendorf Moraine ........................................ 1914. Generalized hydrogeologic cross section from the Chugach Mountains to

Knik Arm ....................................................................................................................... 2015. Ground water maps ............................................................................................................. 2116. 50-MHz radar profile collected along Loop Road ............................................................. 2517. Proposed stratigraphy below the Fort Richardson cantonment ......................................... 2618. Ground water level at Elmendorff Air Force Base in September 1993 ............................. 2619. Ground water level in the lower Ship Creek basin ............................................................ 2720. Comparison of ground water flow patterns ........................................................................ 2821. Operable units on Fort Richardson..................................................................................... 2922. Ground water level at RRFTA ............................................................................................ 3023. Ground water level at RRTSL ............................................................................................ 3124. Ground water level at Poleline Road ................................................................................. 3225. Major water diversions along Ship Creek .......................................................................... 33

TABLES

Table1. Characteristics of surficial deposits ................................................................................... 72. Processes of recharge and discharge in Anchorage lowland ............................................. 83. Identified or suspected contaminants at Fort Richardson, Alaska ..................................... 30

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v

ACRONYMS AND ABBREVIATIONS

asl above sea levelbgs below ground surfaceBP Before PresentCRREL U.S. Army Cold Regions Research

and Engineering LaboratoryDRO Diesel Range OrganicsE&E Ecology and Environment, Inc.ENSR ENSR Consulting and EngineeringERF Eagle River FlatsESE Environmental Science and Engi-

neering, Inc.GIS Geographic Information SystemGPR Ground-Penetrating Radar

OHM OHM Remediation Services Corp.OU Operable UnitPOLLDW Petroleum, Oil and Lubricant

Laboratory Dry WellRRFTA Ruff Road Fire Training AreaRRTSL Roosevelt Road Transmitter Site

LeachfieldS&W Shannon and Wilson, Inc.USACE U.S. Army Corps of EngineersUSAF U.S. Air ForceUSARAK U.S. Army AlaskaUSGS U.S. Geological Survey

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INTRODUCTION

The distribution of surficial deposits acrossFort Richardson is well known, based on morethan 40 years of investigations (e.g., Miller andDobrovolny 1959; Cederstrom et al. 1964; Karl-strom 1964; Schmoll and Dobrovolny 1972a;Reger and Updike 1983, 1989; Yehle and Schmoll1987a,b, 1989; Yehle et al. 1990, 1992; Reger et al.1995; Schmoll et al. 1996). Most of the Fort Rich-ardson cantonment is situated on a large glacioal-luvial fan, which originates at the mouth of theEagle River Valley near the city of Eagle River(Fig. 1, Plate 1). The fan slopes gently to the west–southwest, underlying parts of Elmendorf AirForce Base and downtown Anchorage, and istruncated to the west by sea bluffs along the KnikArm. The fan is composed of outwash depositedby ice-marginal streams and outburst floods thatoccurred when ice-dammed lakes in the EagleRiver Valley drained (Schmoll et al. 1996). Theglacioalluvial fan is bordered on the north by theElmendorf Moraine, a low relief ridge that trendseast to west across the region. The moraineformed about 13,000 14C years ago (Schmoll et al.1972, 1996; Reger et al. 1995). Hummocky end-and ground-moraine deposits mixed with out-wash, estuarine, lacustrine, and bog deposits arefound north and northwest of the ElmendorfMoraine.

Along the southern margin of the fan and fur-ther to the south, several low hills of groundmoraine protrude through younger glacial depos-its of various origins from the most recent glacia-tion of this area (Plate 1). The streamlined hillslocated between the post housing area and GlennHighway are such features (e.g., Birch Hill).These hills are composed of ground moraine (gla-

cial diamicton) that extends underneath the fandeposits and probably below the BootleggerCove Formation, a fine-grained silt deposited inan estuarine environment (e.g., Miller and Dobrov-olny 1959, Reger et al. 1995, Schmoll et al. 1996).The Bootlegger deposits and the ground moraineform an irregular surface upon which youngerglacioalluvial sediments were deposited. Both thefine-grained diamicton of the ground moraine andthe Bootlegger Cove Formation have much lowerhydraulic conductivities than the overlying graveland may confine ground water into multipleaquifers. Older gravel horizons that lie beneaththese deposits form confined aquifers that appearto be hydraulically linked throughout theAnchorage area (Cederstrom et al. 1964).

This report summarizes the results of the ini-tial phase of our hydrogeological study of FortRichardson. Our goal was to synthesize existingsurficial geology and stratigraphy informationrelevant to Fort Richardson, including a review ofthe glacial history of the Anchorage area. Thesedata were then to be integrated into a conceptualstratigraphic model to provide a basis for futureenvironmental studies and to help explainground water behavior below the cantonment.The reason for this work is that the stratigraphicmodels typically used for environmental investi-gations on Fort Richardson are generally over-simplified, potentially leading to a false impres-sion of subsurface conditions. This in turn couldcause unwarranted conclusions to be drawn aboutthe stratigraphy and its influence on ground watermovement, affecting proper management deci-sions, and leading to ineffectual environmentalcleanup efforts and compliance. This report doc-uments the complexity of the stratigraphy on the

Glacial Geology and Stratigraphy of Fort Richardson, AlaskaA Review of Available Data on the Hydrogeology

LEWIS E. HUNTER, DANIEL E. LAWSON, SUSAN R. BIGL, PEGGY B. ROBINSON, AND JOEL D. SCHLAGEL

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basis of data available at the start of the study.Field data collected following this study will bepresented in a subsequent report.

PhysiographyFort Richardson lies in the Cook Inlet–Susitna

Lowland and Kenai–Chugach Mountains physio-graphic provinces of Wahrhaftig (1965) (Fig. 2).The Anchorage Lowland is a roughly triangulararea below 152 m elevation located between theKnik and Turnagain Arms. It is characterized byrolling hills with 15 to 76 m of relief. To the west,the terrain flattens across a broad alluvial plainthat is locally incised by broad, shallow channels.The Anchorage Lowland is characteristic of glaci-ated terrain and contains various landforms,

including hummocky moraine, drumlin fields,and outwash plains. Hills, mostly composed ofglacial drift, lie at the base of the Chugach Moun-tains. These hills are separated by gently slopingalluvial fans formed by streams originating in themountains. Rolling uplands border the ChugachMountains and extend to elevations of 914 m.

The rugged Chugach Mountains rise abruptlyto more than 2000 m along their front, with aflanking region of peaks and ridges generally1000 to 1500 m high. Only the western flank of themountains is contained in Fort Richardson,where elevations reach about 1615 m. The Chu-gach Mountains are cut by a series of northwest-trending U-shaped valleys, including those cur-rently occupied by Ship Creek and Eagle River

Figure 1. General location of Fort Richardson, showing drainages described in the text (white line is border of fort).

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(Fig. 1). Generally sharp-crested ridges separatethe U-shaped valleys, except to the northwest,where they become relatively smooth crested orgently sloping to nearly flat at their crests.

HydrographyFort Richardson lies primarily in the Eagle

River and Ship Creek drainages; only the farsoutheast corner extends into the North ForkCampbell Creek drainage (Fig. 1).

The Eagle River drainage area covers 600 km2

and is 12% glacier-covered (Munter and Allely1992). The Eagle River flows in a well developedmeandering channel, through a large U-shapedvalley for about 32 km from its source in theChugach Mountains. The last 10 km of this reachflows across glaciated lowlands on the north sideof the Elmendorf Moraine (Fig. 1). The modernfloodplain is incised into a paleo-outwash chan-nel. The river straightens just east of Eagle RiverFlats. Here, channel migration has eroded uplandscomposed of stratified glacial sediments. TheEagle River discharges into the Knik Arm at themouth of the Eagle River Flats, a macrotidal salt

marsh (Lawson et al. 1996a,b). Mean annual dis-charge of the Eagle River at a gauging station inthe City of Eagle River is about 15 m3/s; dis-charge peaked in September 1995 at 292 m3/sduring the greater than 500-year flood (Kemperet al. 1995, Brabets 1996).

Ship Creek emerges from the Chugach Moun-tains at the eastern edge of Fort Richardson andflows just south of the cantonment area (Fig. 1).Its channel is incised along the flank of theChugach Mountains but becomes less so in thecenter of Fort Richardson where it crosses an oldalluvial fan. Updike et al. (1984) described ShipCreek as being the most economically importantstream in Alaska because it is used by three pow-erplants, and the Anchorage and Fort Richardsonwater treatment plants, as well as being the pri-mary source of recharge to the Ship Creek aquifer(up to 14 million gal. [53,000 L] per day [Ander-son 1977]). The mean annual discharge of ShipCreek is 16.5 m3/s, with a peak discharge of 181m3/s, which occurred on 27 August 1989 (Brabets1996).

Clunie Creek drains a small lake east of the

Figure 2. Physiography ofthe Anchorage area andFort Richardson. (AfterYehle et al. 1986.)

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Malamute Drop Zone, flowing through a series ofwetlands in an abandoned outwash channel, anddischarges into the salt marshes of the EagleRiver Flats. The old channel is incised into flutedground moraine and represents a meltwaterpathway that was active as Elmendorf ice retreat-ed from the area (Plate 1).

Numerous tributaries including the south andnorth forks of Campbell Creek drain the westernflanks of the Chugach Mountains south of ShipCreek. These eventually flow into Chester Creekwest of the Fort Richardson border. The largerSouth Fork Campbell Creek originates in theChugach Mountains, while the North Fork is fedby a series of unnamed and poorly definedstreamlets that discharge from gullies along themountains.

SURFICIAL GEOLOGY

The geology of Fort Richardson and adjacentlands has been mapped by Miller and Dobrov-

olny (1959), Cederstrom et al. (1964), Schmoll andDobrovolny (1972a) and more recently by Yehleand Schmoll (1987a,b, 1989), Yehle et al. (1990,1992), and Schmoll et al. (1996). Other studies ofthe regional surficial geology have been made byKarlstrom (1964), Reger and Updike (1983, 1989),and Reger et al. (1995). The area is generally cov-ered by deposits of glacial, glacial marine (glacio-estuarine), and glacioalluvial origin, with bed-rock outcrops found on the south and east alongthe Chugach Mountains (Fig. 1; Plate 1). TheseQuaternary-age sediments form a westwardthickening wedge, beginning at the base of theChugach Mountains, and locally reach about 213m.* Below the Fort Richardson cantonment,these sediments are at least 70 to 98 m thick,based on well logs described by Cederstrom et al.(1964).

Because glacial sediments were deposited dur-ing multiple ice advances, they possess a complex

Figure 3. Stratigraphic cross section from Fire Island (after Schmoll and Barnwell 1984) demonstrating thecomplex relationship among glacial sedimentary units.

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* Personal communication with H.R. Schmoll, USGS, 1996.

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Figure 4. Major landforms in the Anchorage Lowland.

stratigraphy (e.g., Fig. 3). This complexity is espe-cially true under the Fort Richardson cantonmentarea, where sedimentary deposits along the southmargin of the Elmendorf Moraine likely inter-finger with alluvial fan sands and gravels. Thesegravels are incised into or truncate ground-moraine deposits, while all of these depositsoverlie older glacial and glacial marine deposits.

Surficial geologic mapWe developed the conceptual stratigraphic

model and interpreted the glacial history of thearea largely on the basis of recent surficial geologicmapping by Yehle and Schmoll (1987a,b, 1989),Yehle et al. (1990, 1992), and Schmoll et al. (1996).These studies provide specific information onsurface morphology and detail how the varioussediments are distributed across Fort Richardson.A geological map of Fort Richardson (Plate 1) wasproduced by incorporating the geological data

from five 1:24,000 topographic quadrangles. Theoriginal Mylar maps were provided to CRREL byH.R. Schmoll and L.A. Yehle, U.S. Geological Sur-vey. A contracted company scanned these mapsand converted raster data to vector data. Poly-gons were developed and labeled at CRREL tocreate an ArcInfo coverage of the surficial geol-ogy for the USARAK’s GIS database of Fort Rich-ardson. The map coverage has been reviewed bySchmoll and Yehle for accuracy and their detailedexplanations of the map symbols are included asAppendix A. Our synthesis of the surficial geol-ogy is presented in the following sections.

Surficial depositsThe most common and spatially extensive

surficial deposits on Fort Richardson are: 1) endmoraine, 2) lateral moraine, 3) ground moraine,4) glacioalluvial, alluvial, and alluvial fan, 5)estuarine, and 6) lacustrine (lake) (Fig. 4 and 5;Tables 1 and 2). Less abundant deposits are thoseof wind, colluvium, and rock glaciers. Wind depos-its in the form of loess (wind blown silt) occur as athin blanket of variable thickness throughout thearea, but they have not been assigned a separatemap unit. Colluvium, a poorly sorted, uncom-pacted, and unstable deposit of silt, sand, andgravel, is found along mountain slopes (solifluc-tion and landslide deposits) and as a veneer oncoastal and stream bluffs. Rock glaciers occuronly in high mountain valleys. They consist ofrock fragments with an ice matrix that allowsthem to flow.

End-moraine depositsThese are ice-marginal sediments deposited

along the termini of glaciers. End morainesdevelop where the glacier remains relatively sta-ble for an extended time. Deposition is polygen-etic, resulting from combined fluvial (proglacialstream), glacial (lodgement, meltout, glacial-tectonic), and gravitational slope processes thatproduce gently arcing ridge complexes at the icemargin (Fig. 5). End moraines are composed ofjuxtaposed sequences of coarse gravel, fine well-sorted sand, dense silt and clay, and diamictons(App. A).

The Elmendorf Moraine is an end morainethat forms a major morphological feature acrossFort Richardson just north of the cantonmentarea. It continues along the north edge of Elmen-dorf Air Force Base and in the Susitna Lowlandacross the Knik Arm (Fig. 1 and 4). Recent studieshave shown that the Elmendorf Moraine corre-lates with ice advances in Turnagain Arm and

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across south-central Alaska. It indicates a majorregional advance between 14,000 and 13,000 14Cyears BP (before present) (Reger et al. 1995). Thereare also several smaller end moraines in the largervalleys of the Chugach Mountains (Schmoll et al.1996).

Lateral-moraine depositsThese deposits develop as narrow, well-defined

ridges and less well-defined ridge segments alongthe sides of glaciers. Lateral moraines are com-posed of sand, gravel, and diamicton, similar toend moraines (Fig. 5; Plate 1). Lateral moraines arefound in the Chugach valleys and along theChugach Mountain front. The latter ridges arealigned in an en-echelon pattern, descendinggradually to the southwest. Older moraine ridgesare generally better developed in the southwest,where they form the principal ridges along thebase of the Chugach Mountains (Schmoll et al.1996). Lateral moraines usually have gentle tomoderate slopes along ridge tops, but steep sides,especially in the downslope direction. Where a

ridge is relatively high on a mountainside, it maydirectly overlie bedrock. In other areas, theyappear laterally gradational with colluvium onthe mountain slopes while overlying other glacialdeposits.

Ground-moraine depositsGround moraines form through a number of

processes believed to operate beneath glaciers,most of which are not fully understood (e.g.,Drewry 1986, Menzies and Shilts 1996). They arespatially extensive and commonly thinner thandeposits of end and lateral moraines (e.g., Fig. 4and 5; Plate 1). Ground moraines may be associatedwith positive-relief landforms, such as flutes anddrumlins. They are generally composed of diam-icton that may exhibit various degrees of sortingand stratification and may contain thin, inter-bedded sand, silt, and gravel horizons. These de-posits are common north of the ElmendorfMoraine, where there are many drumlins and thesurface is locally incised by modern and ancientalluvial channels and are of similar age to the

Figure 5. How map unit types relate to a valley gla-cier. (After Boulton and Eyles 1979.)

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Valley Wall

Colluvium

Kame Terrace

Lateral Moraine

Glacier

Active Lateral Moraine(Ice-Cored)

Morainal Shoal

Glacial Marine Silt

Bedrock

Diamicton (Till)

Glaciofluvial Outwash(Outwash Train)

Debris Flow (Diamicton)

Flute

End Moraine

RecessionalMoraine

Drumlin

Lake/Pond

Ground Moraine

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Table 1. Characteristics of surficial deposits.

Deposit Materials Topography and origin

Alluvial Well bedded and well sorted Smooth, with slopes nearly flat to very gentle; steep scarpsgravels and sands of variable locally separate deposits at different levels; deposits fromthickness (few to tens of meters). active streams and floodplains.Clasts are rounded to well rounded.

Alluvial fan Conically shaped with slopes moderate to gentle, steeper nearthe fan apex.

Colluvial Mainly loose, coarse rubble and Smooth, with slopes generally steep to very steep and gener-rubbly diamicton, locally bouldery. ally unstable; deposits that accumulate on a slope primarily

poorly bedded and sorted through the action of gravity andsecondarily with the aid of water.

Glacioalluvial Features or deposits associated with glacial streams.

Kame Chiefly pebble and cobble gravel and Sharply hilly to hummocky with some local depressions;sand, moderately to well bedded, in slopes moderate to steep; glacioalluvial deposit formedplaces chaotically. by running water within a glacier during early stages of

stagnation and modified during ice meltout.

Kame-terrace Chiefly pebble and cobble gravel and Long, narrow landforms that have smoothly sloping surfacessand, moderately to well bedded and with prominent scarps on their downslope sides; glacioalluvialsorted. deposits formed by water running along the side margin of a

glacier.

Kame-channel Chiefly pebble and cobble gravel and Slightly hummocky in broad, channel-like landforms of lowsand, locally may include some finer relief; glacioalluvial deposits formed in ice-contact channels.materials.

Meltwater- Chiefly gravel and sand, well bedded Smooth with gentle slopes; channel-like deposits formedchannel and sorted; surface may include finer- in areas recently abandoned by glaciers.

grained material with thin organicaccumulations.

Outwash-train Chiefly pebble and cobble gravel and Smooth with gentle slopes except steep at terrace edges;sand, well bedded and sorted. accumulated mainly in front of end moraines, downstream

of meltwater-channel deposits.

(Glacio) Estuarine Chiefly silty clay, silt, and fine sand, Smooth with slopes nearly flat; locally marked by subduedwell bedded and sorted; locally includes hills and irregularities; accumulated in ancestral Cook Inletthin beds of peat and other organic marine environment, coarser facies deposited at glacier tide-material; also locally includes diamic- water margin.ton, coarser sands, and gravels.

(Glacio) Lacustrine Interbedded clay, silt, and sand; well Smooth with gentle slopes, but very steep at valleywardto somewhat poorly sorted. margins; accumulated in freshwater bodies (large lakes to

small ponds) ponded by glacier ice or moraine deposits.

Moraine A mound, ridge, or other accumulation of glacial sedimentproducing a variety of landforms.

End moraine Juxtaposed sequences of deposits from A gently arcing ridge or series of ridge segments depositedpolygenic origins, primarily diamicton at the end (or terminus) of a glacier.(poorly sorted admixtures of silt, sand,and gravel) along with coarse gravel,fine well-sorted sand, dense silt, andclay, moderately to well compacted.

Lateral moraine Sand, gravel, and diamictons. A ridge or ridge segments deposited at the side margin of aglacier. Commonly form gently sloping, sharp-crested ridgesalong the walls of valleys that glaciers formerly occupied.

Ground moraine Diamicton of variable thickness; may Smooth to hummocky, with gentle to moderately gentlecontain thin, interbedded sand, silt, slopes; deposits left behind when glaciers retreat.and gravel horizons, and thin outwashgravel or lake deposits on the surface.

Pond and bog Chiefly peat; includes organic-rich silt, Smooth with very gentle slopes; accumulated in ponds orminor woody horizons, and thin small former lakes or stream channels that filled with organicinterbeds of ash-sized tephra. material.

Rock glacier Mainly angular to some subrounded Moderately hummocky and rough, slopes moderate to veryrock fragments being actively trans- steep; mixture of rock fragments and ice-rich matrix is transi-ported; contains ice-rich matrix; fines tional between a true glacier and a slow-moving landslide.from cobble- and boulder-size frag-ments at surface to more rubbly dia-micton character at depth.

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Elmendorf Moraine. An older ground moraine ofLate Wisconsin age lies at depth south of thecantonment area.* It appears sporadically at thesurface, where it protrudes through youngerglacioestuarine and alluvial fan deposits, andlikely underlies the sediments across much ofFort Richardson.

Glacioalluvial, alluvial, and alluvial fan depositsGlacioalluvial. These are a suite of deposit

types, including kame-channel, meltwater-channel, and outwash-train deposits, consistingof water-laid sediments deposited in front of aglacier (Fig. 5; App. A). Meltwater-channeldeposits are composed of well-bedded and well-sorted sand and gravel, which may include somefiner-grained material that was deposited in ashallow backwater. Thin organic horizons arealso common on the surface of fine-graineddeposits. Thickness is highly variable, often 1 mto a few meters, but in places channel deposits maybe thin and patchy, allowing ground moraine orbedrock to crop out at the channel floor. Stratifiedsand and pebble- to cobble-size gravel form out-wash-train deposits, which accumulated in frontof the Elmendorf Moraine and downstream fromChugach valley glaciers. Most of these latterdeposits now occur mainly in terraces alongformer channels. Kame-channel deposits arecomposed of sand and pebble- to cobble-sizegravel, similar to outwash-train deposits. Somesilt and clay may now fill paleo-topographicdepressions. Thickness is generally at least a fewmeters and the deposits have a hummocky sur-face that may be incised with low relief channels.Kame-channel deposits are common at the transi-tion between high-relief kame and ground-moraine deposits.

Glacioalluvial sediments deposited along gla-

cier margins have a distinctly hummocky mor-phology caused by the meltout of glacier ice,which was buried beneath them (Fig. 5). Thismelting commonly disturbs the overlying sedi-ments and further complicates the stratigraphy.Several types of kame deposits can be recognized;most are generally composed of thin beds of sand,silt, diamicton, and gravel, with varying degreesof bedding and sorting. Irregular hills from melt-out include those near the margin of the Elmen-dorf Moraine, within the Elmendorf Morainenorth of Clunie Creek and at the margin of theAnchorage Lowland downslope of major moun-tain valleys (Plate 1). These deposits are moder-ately loose, but compact in the center of somehills and commonly may merge with end- andlateral-moraine deposits. They are often charac-terized by sharp crests and more rounded hum-mocks, moderate to steeply dipping slopes, andsometimes are truncated by stream channels.

Kame-terrace deposits were formed by waterrunning along the glacier margin. Long, narrowlandforms with smoothly sloping surfacesdevelop. Prominent scarps may remain wheredeposition was in contact with the glacier. Kame-fan deposits, which also form at the glacier mar-gin, range from several to a few tens of meters inthickness. Their topography is generally smooth,and surfaces are relatively moderate, with gentleslopes increasing in steepness towards their icesource.

Alluvial. Both modern and ancient alluvialdeposits are found on Fort Richardson. Theyoccur along present day streams and floodplains(Fig. 1; Plate 1), often incised into older glacioal-luvial and alluvial fan deposits. The deposits arecommonly well-bedded and well-sorted sandsand gravels of variable thickness (a few to tens ofmeters). Clasts are rounded to well rounded.Both modern and ancient stream deposits havenearly flat to gentle slopes. Scarps 1 m to severalmeters high may locally separate deposits from

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* Personal communication with H.R. Schmoll, USGS, 1996.

Table 2. Processes of recharge and discharge in Anchorage Lowland.

Recharge Discharge

Unconfined aquiferStream infiltration (losing reaches) Stream channels (gaining reaches)Rain/snowmelt percolation Seeps/springsDischarge along mountain front

Confined aquiferPercolation from unconfined aquifer Percolation to unconfined aquiferSeeps from fractured bedrock under high hydrostatic headDischarge along mountain front Lateral discharge into unconfined zone

artesian flow to surface or bluffs where confining layer is intersected

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different periods, forming a series of terraces thatrepresent several periods of downcutting.

Alluvial deposits on the east side of theAnchorage Lowland are composed primarily ofwell-bedded and well-sorted sand and gravelderived from local mountain-valley sources. Con-tacts are generally well defined and the morph-ology reflects alternating periods of depositionand incision. Well-developed terraces are com-mon at all levels, with the nested fans emanatingfrom incised channels. These fans formed bothbefore and after the incursion of the Eagle River,while some of the higher-level deposits are prob-ably similar in age to outwash of the Elmendorfand older glacial advances.

Alluvial fan. Fan deposits are common acrossthe area. Important deposits include 1) a large fanemanating from the Eagle River Valley, 2) smallerfans from local valley sources, and 3) fans alongthe edge of the Elmendorf Moraine. Alluvial fansare composed of well stratified and sorted sandand gravel.

The largest of these deposits on Fort Richard-son is the Mountain View fan, which emergesfrom the Chugach Mountains at the south edge ofthe Eagle River Valley (Fig. 4; Plate 1). The Moun-

tain View fan extends from the Chugach Moun-tains to Knik Arm in the area between the Port ofAnchorage and Turnagain Heights and lies belowmost of the Fort Richardson cantonment (Millerand Dobrovolny 1959). This particular fan hasmultiple levels (nested or composite morph-ology), reflecting a complex history of formationby recurrent, sudden breakout discharges froman ancient glacial lake in the Eagle River Valley, ina manner similar to Lake George discharging intothe Knik River (Post and Mayo 1971). The result isa complex assemblage of flood and interflooddeposits (Fig. 6) that reach a thickness of 15 to 18m and are composed of a cobble gravel near thehead of the fan (see Hunter et al. 1997). Furtherwest and downslope, the size of material decreasesfrom gravelly sand to fine sand. A high percent-age of fines (10–15%) is described in borehole logsfrom the cantonment area (USACE 1996b), theamount increasing with depth.* Locally (e.g.,Ruff Road Fire Training Area, E & E 1996), sandand gravel may be interbedded with fine silt andclay.

Also there is a series of small, well-developed

Figure 6. Interbedded alluvial sediments as might be produced by periodic dis-charge events (sand and gravel) and silt deposition in abandoned channels.(After Selly 1976.)

* Personal communication with H.R. Schmoll, USGS, 1996.

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fans along the southern margin of the ElmendorfMoraine (Fig. 4; Plate 1), with their apices in smallchannels cut into the moraine (Fig. 7). The well-preserved fan morphology tells us that they wereactive during the late stages of moraine formation(Plate 1). Because the toes of these fans are nottruncated, they were probably created during latephases of Mountain View fan formation and mayhave developed after the catastrophic dischargesfrom the Eagle River Valley. Elmendorf ice musthave remained close enough to its maximumposition at the terminal moraine to provide sedi-ment and water to the aggrading fans and to keepmeltwater from being diverted into the ancestraldrainages of Six Mile Lake or Eagle River to itsnorth.

Estuarine and glacioestuarine sedimentsEstuarine deposits are formed in present-day

Cook Inlet and its major arms, Knik and Turna-gain, or along similar water bodies of the recentpast (Fig. 2 and 4). Glacioestuarine deposits accu-mulated in an ancestral Cook Inlet that probablydiffered from the present-day inlet in configura-tion because of base level changes and the pres-ence of glaciers.

Modern estuarine deposits are peripheral toCook Inlet, where macrotidal fluctuations of 7–9m intermittently expose recent silty deposits.Older Holocene estuarine deposits occur exten-sively at the upper end of Knik Arm and in EagleRiver Flats (ERF). Estuarine deposits are generallycomposed of well-bedded and sorted silt and finesand, and may locally include thin beds of peat,driftwood, and other organic or windblownmaterial. Deposits of this unit are commonly sev-

eral meters to a few tens of meters thick and con-solidated (e.g., Combellick 1990, 1991, 1994).

Glacioestuarine deposits of late Pleistocene ageaccumulated in an ancestral Cook Inlet that waslarger and deeper than at present, although notrue shorelines have yet been identified.* Theupper limit of marine submergence during thistime may have been as great as 183 to 213 m abovemodern levels (Yehle and Schmoll 1987a, 1988),although Karlstrom (1964) suggests water mayhave been as high as 305 m above present sea level.Deposits that consist of varying combinations ofinterbedded diamicton, stony silt, fine sand, siltand silty clay, and coarse sand–gravel often indi-cate deposition at elevations above present sea level,probably with ice terminating in water nearby.

A major stratigraphic unit considered glacio-estuarine in origin is the Bootlegger Cove Forma-tion (Bootlegger Cove Clay of Miller and Dobro-volny [1959], redesignated as Formation byUpdike et al. [1982]). It was apparently depositedduring a much higher sea level, when ice that cre-ated the Elmendorf moraine advanced into thearea (Reger et al. 1995). The unit is composed ofsilty clay and clayey silt, sometimes interbeddedwith silt, fine to medium sand, and thin diamictonbeds (Updike et al. 1988). Brackish-marine micro-fossils are present throughout much of the forma-tion (Schmidt 1963, Smith 1964), which reaches athickness of 35 m (Updike et al. 1988). This unitoccurs widely throughout the subsurface at eleva-tions typically below about 30 m asl, and underliessurficial deposits exposed in the Elmendorf Mor-

10

Figure 7. Incised fans in flank of Elmendorf Moraineand interfingering of sedimentary units along themoraine margin.

*Personal communication with H.R. Schmoll and L.A. Yehle,USGS, 1996.

Diamicton(Debris Flows)

Glacial Diamicton(Till)

CoarseGravel

Sand & Gravel

Quiet Water SiltMountain View Fan

Dishno Pond Moraine (?)

Elmendorf Moraine

Debris Flow Lobes

Transitional Fan Complex

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aine in bluffs on Knik Arm (Miller and Dobrovol-ny 1959, Cederstrom et al. 1964). The BootleggerCove Formation is exposed principally in thesouthern part of the Anchorage Lowland nearCampbell Creek and along numerous sea andstream bluffs, where it is commonly concealedbeneath other deposits (Plate 1). It is likely that asandy facies of the Bootlegger occurs along theformer basin margin and locally interfingers withdeposits of the Elmendorf Moraine. This is a tran-sitional zone, where coarse clastic sedimentswere contemporaneously deposited adjacent tofans and streams.

Lacustrine and glaciolacustrine depositsLacustrine deposits accumulate in bodies of

water ranging from large lakes to small ponds,and include water bodies closely associated withformer glaciers as well as those formed after theirretreat. Kame-fan deposits are transitional betweenglacioalluvial and glaciolacustrine deposits andare found where ice dams temporarily impound-ed water along the glacier margin. Thicker glaci-olacustrine deposits accumulate in large lakes invalleys blocked by the glacier. Deltas commonlyprograde into the lakes where outwash streamsenter them. Other lacustrine deposits originate inlakes behind moraines or landslides. Depositssimilar in nature also originate in ponds that filltopographic depressions, such as in hummockyground moraine. Bogs form as ponds fill in withorganic material and may accumulate thick lay-ers of peat.

Glaciolacustrine deposits consist of interbed-ded clay, silt, and sand, and may include occa-sional layers of gravel or diamicton. The depositsrange from well to poorly sorted and contacts aregenerally well defined. Surface topography isgenerally smooth, with gentle slopes thatincrease in steepness towards valley margins.The silt and clay are moderately stable, except incontact with colluvium on valley walls, wherethey are susceptible to stream erosion and failure.

Along the Elmendorf Moraine, lake depositsreach thicknesses of 5 to 10 m and may be muchthicker beneath alluvial and peat deposits thatform the floor of the upper part of Eagle RiverValley. Correlative deposits are found in majormountain valleys from Eklutna River south to theEagle River Valley. Older deposits occur alongShip Creek, the lower slopes of Peters Creek, andthe South Fork Eagle River up to an elevation of100 m asl and reach a thickness of about 10 m inthe bluffs of Thunder Bird Creek.

Pond and bog deposits (peat and organic-richsilt, minor woody horizons, and interbeds of ash-sized tephra) are widespread in the ElmendorfMoraine, the floor of Eagle River Valley, andlocally in lateral moraines. Bog deposits mayoverlie silt, clay, marl, or fine-grained sand thatfirst accumulated in small lakes or along streamchannels. These deposits commonly reach 4 m inthickness, but may locally exceed 10 m.

GLACIAL GEOLOGICAL HISTORY

Glacial deposits in the Anchorage area havetraditionally been divided into broad age groupsthat span much of the Quaternary Period (e.g.,Miller and Dobrovolny 1959; Karlstrom 1964;Reger and Updike 1983, 1989; Reger et al. 1995).The earlier studies thought that at least five majorglaciations affected the Cook Inlet region, extend-ing back more than 200 ka BP (Ulery and Updike1983). Their chronological control was derivedfrom relative age dating techniques and minimalconventional radiocarbon data. More recently,Yehle and Schmoll (1987a,b, 1988, 1989), Yehle etal. (1990, 1991, 1992), and Schmoll et al. (1996)have attributed most of the surficial deposits tomultiple advances and retreats of the last glacia-tion (Late Wisconsinan). Rapid changes from gla-cial to marine and terrestrial environments pro-duced abrupt shifts in depositional processes.These rapid changes, taking place as the glaciermargin fluctuated over both the short and longterm, may account for some of the seven or moreglaciations interpreted from the borehole data byTrainer and Waller (1965) and Schmoll and Barn-well (1984).

Below, we review the glacial history of Anchor-age according to Schmoll et al. (1996) and Reger etal. (1995). An understanding of how the glaciersfluctuated and deposited their sediments isrequired for us to develop a conceptual strati-graphic model of the cantonment area. Such anoverarching idea is required to evaluate thehydrogeology of Fort Richardson, so that groundwater flow patterns and contaminant transportcan be evaluated, because detailed geologicaldata on the subsurface are generally not avail-able. So, the conceptual model is therefore basedon knowledge of the glacial history and sedimen-tary processes (Lawson 1979, 1981, 1982, 1988;Boulton 1968, 1970, 1971, 1972, 1975; Powell 1980,1981, 1984a,b; Hunter et al. 1996a,b).

The sequence of events during the last glacia-tion is as follows.

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• Stage 1 corresponds to full glacial conditionsreached prior to 20,000 years BP. Glaciersflowed out of the Chugach and TalkeetnaMountains, where they coalesced and flowedinto the Cook Inlet–Susitna Lowland. Icefilled Knik Arm, overtopping some of theridges along the Chugach Mountains, andflowed into the isostatically depressed CookInlet. Lateral moraine deposits from thistime correspond to the Rabbit CreekMoraines.

• Stage 2 is the retreat from full glacial condi-tions, probably beginning around 18,000 to20,000 14C years BP. A marine transgression(sea inundation) accompanied retreat to anunknown position in Cook Inlet.

• Stage 3 is a stillstand or minor readvance ofthe glaciers, with multiple fluctuations in theice margin that resulted in deposition ofsome of the Fort Richardson moraines.Marine conditions extended to Rabbit Creekand South Fork Campbell Creek about thistime.

• Stage 4 is a retreat of unknown distance,which allowed a marine incursion thatextended north to at least the North ForkCampbell Creek and Chester Creek areas.The lowermost sediments composing theBootlegger Cove Formation were depositedduring this incursion.

• Stage 5 is a readvance that deposited theDishno Pond moraines in the eastern low-land area (Plate 1). Marine conditionsremained in the Campbell Creek and Ches-ter Creek areas, with additional marine sedi-ments deposited to form additional Bootleg-ger sediments.

• Stage 6 corresponds to the final retreat of theice from the Dishno Pond moraines and pro-gressive recession up-valley out of the lowerKnik Arm. Ice-rafted debris in the base of theBootlegger Cove Formation indicates tide-water conditions and glaciers calving ice-bergs into the sea (Schmidt 1963) around14,900 ± 350 14C years BP (Schmoll et al.1972, Reger et al. 1995). Reger et al. (1995)concluded that the Bootlegger Cove Forma-tion was deposited between about 15,000and 13,000 14C years BP. The extent of iceretreat up Knik Arm is not known; however,marine silt equivalent to the BootleggerCove Formation can be found about 60 km

up the Susitna Valley (Reger et al. 1995). Mar-ine submergence during the initial phase ofice retreat was about 140 m above mean sealevel and was probably followed by isostaticuplift shortly after the ice retreated. Coastalprocesses active along the Hillside area andFort Richardson moraine would have erodedthese older morainal sediments up to the levelof submergence.

• Stage 7 is a major readvance of the ice marginaround 13,500–14,000 14C years BP into KnikArm. This advance probably occurred behinda marine shoal that protected most of the gla-cier’s terminus from tidewater conditions(e.g., Post 1975, Mayo 1988) (Fig. 8). The upper-most units of the Bootlegger Cove Formationwere deposited then. These units containsand layers and generally coarsen upwards(Miller and Dobrovolny 1959, Karlstrom 1964,Yehle et al. 1986), apparently recording theincreased proximity of the ice or a shoaling, orboth, during ice advance. Termination of thisadvance constructed the Elmendorf Moraine.Reger et al. (1995) estimate that at the end ofthe Elmendorf advance, land began to emergefrom the sea at about 13,500 14C years BP.Land emergence, ice shove, and glacial tec-tonic uplift of sediments was probably attrib-utable to a combination of high sedimentationrates near the glacier margin and isostaticuplift after the ice receded.

Ice or moraine dams at the mouth of the EagleRiver Valley periodically broke, causing rapiddrainage of lakes impounded in the valley. Suchcatastrophic flooding would cause intense, localscour as water was deflected across the front of theElmendorf Moraine. Recurrence of these eventslikely produced the Mountain View fan that origi-nates at a narrow gap between the Elmendorf Mor-aine and Chugach Mountains near the city of EagleRiver. The fan forms a sand and gravel plain thatextends across the Anchorage Lowland to Knikarm (Fig. 4). As ice began to retreat from theElmendorf Moraine, ancestral channels of theEagle River were reoccupied as new channelsbecame incised, providing lower elevation drain-ages and shorter routes to the Knik Arm.

• Stage 8 represents a rapid retreat of ice fromthe Elmendorf moraine. The hummocky top-ography in the Susitna Valley and upper KnikArm are indicative of ice stagnation anddownwasting. Reger et al. (1995) suggest thatice margin retreat probably reached the

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Palmer area around 9000 14Cyears BP, about the same time aswhen ice retreated to the Turn-again Pass area at the head ofTurnagain Arm. It is not knownwhether or not marine submer-gence accompanied retreat upKnik Arm. Silt and clay depositsfound on the surface north of theElmendorf Moraine may point toa short phase of submergencebeneath the sea or deposition insmall lakes that could have devel-oped in the hummocky glacialdeposits. Numerous stream chan-nels were incised into the Elmen-dorf Moraine, as well as at multi-ple locations farther north. Thesenow-abandoned channels wereactive near the ice margin duringits retreat. Most of the landforms(hummocks, drumlins, flutes,ground moraine, etc.) north ofthe Mountain View fan weredeposited during the advanceand retreat of the Elmendorf ice.

CONCEPTUAL STRATIGRAPHICMODEL

Surficial deposits near the canton-ment area are 70 to 98 m thick (Ceder-strom et al. 1964) and are from the lat-est Wisconsinan glaciation. In theAnchorage Lowland, southwest of thecantonment, deposits reach more than 305 mthick. Diamictons from the maximum extent ofice in the past (more than 120 ka BP) probably liebelow the Bootlegger Cove Formation, DishnoPond moraine, and Mountain View fan deposits,but their extent and locations are not known.Diamictons from these events probably have alow permeability and therefore are confining lay-ers that affect ground water conditions beneaththe cantonment.

Detailed subsurface geological information isgenerally absent, except in a few locations (i.e.,Turnagain Heights and Lynn Ary Park), wheregeotechnical studies have been carried out todetermine the cause of ground failure during the1964 earthquake (e.g., S&W 1964, Lade et al. 1988,Updike et al. 1988) or to investigate ground waterconditions (e.g., Freethy 1976, Anderson 1977,Dearborn 1977, Munter and Allely 1992). There

are also 2281 records in the USARAK’s GIS of soilborings and well logs on Fort Richardson, but only146 reached depths greater than 15 m (Fig. 9). Therecords from these logs contain general informa-tion on engineering properties and material types(e.g., USACE 1996b), but infrequent samplingintervals (2 to 3 m) provide insufficient informa-tion for detailed stratigraphic analyses (all logsdescribed in this report are included in Hunter etal. 1997). This is compounded by a lack of consis-tency in the borehole log descriptions among con-tractors. To achieve a better understanding of thestratigraphy, we must infer subsurface characteris-tics from coastal exposures along the Knik Armand Eagle River, extrapolation from nearby deepwells, limited interpretation of ground-penetrat-ing radar (GPR) profiles, and a reconstruction ofthe glacial history.

A conceptual stratigraphic model for the can-

b. Retreat Phase

Rapid Retreatby Rapid Calving

Initiation ofEarly Retreatbecause of

Climatic Thinningor Changes in

Grounding-LineWater Depth

StableAdvancedPosition

Moraine Shoal(Morainal Bank)

EquilibriumLine

Altitude

a. Advance Phase

StableAdvancedPosition

Beginningof Advance

Early Advancebehind Moraine Shoal

Moraine Shoal(Morainal Bank)

EquilibriumLine

Altitude

Stabilization atRetreat Position

(Shallow Water Depth)

Figure 8. How a tidewater glacier can advance (a) into the marineenvironment as long as a moraine shoal protects it from deep water.Retreat (b) begins when deep water conditions are reestablished and itcontinues until shallow water is reached. (After Mayo 1988.)

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tonment of Fort Richardson, based on the LateWisconsinan glacial history of the AnchorageLowland, is shown in Figure 10. Deposits olderthan Wisconsinan age are ignored because theyare poorly documented in the region and morerecent glaciations would have likely modified oreroded them away. Therefore, older diamictondeposits are probably limited and may be onlylocally important in the regional hydrogeology.While the model gives us a theoretical frameworkfor the hydrogeology, it is generalized and doesnot account for the variability in space andthrough time that typifies glacial and glacial–marine environments. Nor does it account for theeffects of erosion and reworking after the sedi-ments were deposited.

The cycles of ice advance and retreat that theregion has experienced would have created acomplex stratigraphy below the cantonment (e.g.,Fig. 3). For our purposes, we assume that a lower

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Figure 9. Boreholes and ground water monitoring wells reaching depths greater than 7.5 m.

boundary equivalent to the late Wisconsinanground moraine (a diamicton equivalent to theRabbit Creek moraines; Plate 1) is located aboveeither pre-Wisconsinan drift or bedrock (Fig. 10).Two diamicton horizons above the Rabbit Creekdeposits correspond to glacial advances that wecall the Fort Richardson and Dishno Pond read-vances. The last advance, which corresponds tothe deposition of the Elmendorf Moraine, did notoverride the cantonment area. Therefore, no diam-icton blanket was deposited across the canton-ment from this advance. Rather, coarse proglacialand ice marginal outwash deposits likely inter-finger with lenses or discontinuous layers of dia-micton generated along the front of the ElmendorfMoraine.

Proglacial stratified silt, sand, and gravel werelikely deposited between the Fort Richardson andDishno Pond events, and on the surface generallysouth of the Elmendorf Moraine (Fig. 10). Ideally,

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Bedrock/ Pre-Wisconsinan Diamicton

Fort R

ichar

dson

Can

tonm

ent

Retreat Advance

Mountain View Fan

Elmendorf Moraine

Bootlegger Cove Formation

Dishno Pond Moraines

Fort Richardson Moraines

Rabbit Creek Moraines

Marine Inundation (?)

Marine Inundation

Silt

San

d

Gra

vel

Dia

mic

ton

Correlative Map UnitsHydrologic UnitsU

ncon

fined

Aqu

ifer

Confining Layerin Anchorage

InhomogeneousConfining Layer

(Leaky)

Inhomogeneous Confining Layer

(Leaky)

Con

fined

Aqu

ifer

Time Stratigraphic Units

Figure 10. Conceptual time–stratigraphic model for Fort Richardsonbelow the cantonment area.

Advance Diamicton

Basal Diamicton

Estuarine Silt Interglacial Phase

Advance Phase

Stillstand Phase

Retreat Phase

Stillstand Phase

Silt

San

d

Gra

vel

Dia

mic

ton

Glacial-Marine StratifiedSand and Gravel

Glacial-Marine StratifiedSand and Gravel

Figure 11. Conceptual stratigraphic sequence.

ice retreat and subsequent read-vance produce a proglacial strati-graphic sequence consisting of agravel that fines upward (decreas-ing millimeter grain size) to thinlylaminated silt, followed by a sandthat grades upward to a gravel (Fig.11). The upward fining in the lowerportion of the sequence records an in-crease in distance from the margin asit retreats. This results in an increasein the percentage of sedimentdeposited from suspension in thesea water (e.g., Dowdeswell andMurray 1990, Cowan and Powell1990). These silt layers, therefore,are the product of deposition whenice was located closer to the head ofKnik Arm. Silt grading upwards togravel in the upper portion of thesequence records the advance of iceinto a marine basin behind amorainal shoal (Post 1975, Mayo1988). Suspension settling was grad-ually replaced by sand and graveldeposition from sediment gravityflows (turbidites and debris flows)generated by failures of the sub-marine moraine as the ice advances.A diamicton (or till) was depositedby the glacier as it overrode the pro-glacial deposits (e.g., Hunter et al.1996b). The thickness of the strata, aswell as the sedimentary sequence,depend on the rate, extent, and dura-tion of retreat and readvance, the

local importance of other sediment sources, andthe length of time that the deposits are exposed tosubglacial and subaerial processes after they weredeposited.

To develop a model of the sedimentary stratig-raphy for Fort Richardson, it is thus critical toknow the extent of the retreat, as well as the ad-vance, of the Fort Richardson, Dishno Pond, andElmendorf glaciations. Unfortunately, this is notwell known. Schmoll et al. (1996) note that estua-rine silt was deposited in the North Fork CampbellCreek and Chester Creek areas following both theFort Richardson and Dishno Pond retreats. Itspresence implies intertidal conditions and marinesubmergence, but the extent of this submergenceup Knik Arm is not known. We assume that thecantonment area was also deglaciated, but proba-bly for a relatively short time.

Bedrock/ Pre-Wisconsinan Diamicton

Fort R

ichar

dson

Can

tonm

ent

Retreat Advance

Mountain View Fan

Elmendorf Moraine

Bootlegger Cove Formation

Dishno Pond Moraines

Fort Richardson Moraines

Rabbit Creek Moraines

Marine Inundation (?)

Marine Inundation

Silt

San

d

Gra

vel

Dia

mic

ton

Correlative Map UnitsHydrologic UnitsU

ncon

fined

Aqu

ifer

Confining Layerin Anchorage

InhomogeneousConfining Layer

(Leaky)

Inhomogeneous Confining Layer

(Leaky)

Con

fined

Aqu

ifer

Time Stratigraphic Units

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What happened between the Rabbit Creek andFort Richardson advances and moraine develop-ment is also unknown. Those deposits are deeplyburied in the Fort Richardson area. The nature andextent of the Fort Richardson moraines suggestthat they probably record a period when the gla-cier terminus was relatively stable. This condition,a stillstand, might have resulted from local chang-es in glacier dynamics as the terminus retreated tothe mouth of Knik Arm (e.g., stillstands are com-mon at points of valley constriction [Warren andHulton 1990]). Therefore, it is probable that thecantonment was not deglaciated between the old-er Rabbit Creek and Fort Richardson stages, andthus subglacial and submarine diamictons weremore or less continuously deposited over this timeinterval.

The best record of glacial activity is associatedwith the advance of ice that built the ElmendorfMoraine (Elmendorf advance). However, therecord of this cycle is not complete below all ofFort Richardson because the Elmendorf advancestopped north of the main cantonment area and,thus, a basal diamicton was only deposited upgla-cier of the Elmendorf Moraine.

During the Elmendorf advance, marine silt ofthe Bootlegger Cove Formation was probablyeroded and recycled into a moraine shoal as the iceadvanced over it. The end of the advance led to theElmendorf Moraine being deposited throughcombined glacial (thrusting, pushing, meltout,lodgement), fluvial (outwash streams), and gravi-tational (debris flows) processes. This produced acomplex internal stratigraphy. Interbedded gla-cioestuarine silts (i.e., Bootlegger Cove Forma-tion), diamictons, gravels, and sands, without aregular lateral or vertical repetitive sequence, isthe result. A local example is the exposed seabluffs at Fire Island near the mouth of Knik Arm(Fig. 3). Any of the fjord bottom sediments in shal-low water near the ice margin were probably erodedby waves and coarsened as a result (similar to thePresumpscot Formation in coastal Maine [Bloom1960]). Close to the Elmendorf Moraine, coarsematerials probably compose a significant propor-tion of the Bootlegger Cove Formation, althoughthis has not been clearly identified.*

The stratigraphy below the cantonment (Fig.10) consists of several major sedimentary units(listed from oldest to youngest) as follows.

Post-Rabbit-Creek outwashThis is a well-stratified, moderate- to well-sorted

sand and gravel above the Rabbit Creek diamictonor bedrock. The unit is assumed to be variable inthickness, up to a few tens of meters thick, but maylocally pinch-out along valley walls. The outwashis unconformably overlain by Fort Richardsondiamicton, but pump tests by Cederstromet al. (1964) demonstrated hydraulic linkage todeposits higher in the sequence. The linkage isprobably related to high hydrostatic pressures atdepth that drive flow through fractures, faults,and local stratigraphic anisotropies in the overly-ing diamicton.

Fort Richardson and Dishno Pond sequencesWell log records described by Cederstrom et al.

(1964) indicate two distinct glacial diamictons bur-ied in the area, while Trainer and Waller (1965) andSchmoll and Barnwell (1984) tell of up to sevenglacial horizons. More than 20 diamicton and 10silt strata were identified in the borehole in TikishlaPark, located about 11 km south of the ElmendorfMoraine (Yehle et al. 1986). However, it is not clearthat these represent more than local variations insedimentary processes and deposition, or move-ments in the ice margin.

For our generalized model (Fig. 10), we acceptthe two-drift theory (Cederstrom et al. 1964)because it agrees nicely (although probably coinci-dentally) with the Fort Richardson and DishnoPond moraines recognized by surficial mappingprograms (e.g., Schmoll et al. 1996). We realize thatthis is an oversimplification, but suggest that it isreasonable for building our conceptual strati-graphic model, given the current constraints inknowledge of the glacial history and stratigraphy.

Deposits of these advances are hydraulicallyconnected, as demonstrated by Cederstrom et al.(1964), and compose the bulk of the confined aqui-fer in the Anchorage Lowland. Despite rapidfacies changes and broad, laterally continuousdiamicton sheets, deposits of these two glacialphases form an extensive aquifer at depth. Thesedimentary sequences are detailed below.

Fort Richardson sequenceA lower diamicton unconformably overlies the

Rabbit Creek outwash. The basal contact is proba-bly erosional, although it should be locally inter-bedded with gravel. This diamicton is probablystratified, with occasional sand and gravel hori-zons. Interbedded gravels and diamictons areexpected where ice-proximal debris flows, gener-* Personal communication with H.R. Schmoll, USGS, 1996.

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ated along the grounding line of the tidewatermargin, would mix with outwash sand and gravel.Diamicton beds decrease in abundance up-section, as the ice margin receded northwards.Higher in the stratigraphic sequence, gravelswould grade to sand and silt. We question wheth-er or not the cantonment area was deglaciatedduring this time, for the Fort Richardson ice mayhave halted its retreat at the mouth of Knik Arm.If there was a limited retreat up Knik Arm, thenthe deposition accompanying it was probablyshort lived and the deposits thin. The uppermostmaterials of the Fort Richardson sequence proba-bly consist of coarsening upward sand and gravelas the ice readvanced into the area, this being theDishno Pond glaciation.

Dishno Pond sequenceThe Dishno Pond advance produced a broad

diamicton (till) sheet that covers much of theAnchorage Lowland (Plate 1). This diamictonunit unconformably overlies the coarseningupward gravel deposited in front of the DishnoPond advancing ice. The diamicton should besimilar to the Fort Richardson diamicton and be afew to tens of meters thick. The upper contact willbe interbedded and gradational into graveldeposited during glacial retreat. This gravelgrades upward in section into a sandy silt and thesilt of the Bootlegger Cove Formation.

Bootlegger Cove FormationThis is a deposit mostly of silt-size material

that covers at least 100 km2 in the AnchorageLowland, where it is an important confining layerin the regional ground water flow system (Ceder-strom et al. 1964, Freethy 1976). The unit is usu-ally 30 to 45 m thick, although locally it mayexceed 90 m (Cederstrom et al. 1964). The Boot-legger Cove Formation exists below ElmendorfAir Force Base (USAF 1994) and is exposedbeneath the Elmendorf Moraine in coastal bluffsof Knik Arm (Miller and Dobrovolny 1959, Ced-erstrom et al. 1964). Boreholes drilled for groundwater investigations near the Fort Richardsonpowerplant revealed a fine-grained silty horizonthat pinched out laterally (Fig. 12) (Freethy 1976,Anderson 1977); however, the northern and east-ern limits of this particular horizon are notknown. If the northeastern margin of the Bootleg-ger Cove Formation extends under the canton-ment area, it is likely to be sandy and to thin fromless than 10 m thick in the south–southwest tononexistent in the north and east. Such a transi-tional sandy phase is likely to be more permeableand hydraulically conductive than the lower por-tions of the Bootlegger Cove Formation commonto the southwest.

Well log and ground water records on FortRichardson attest to the presence of a confininglayer that is sometimes assumed to be the Boot-

a. Longitudinal profile showing the northward pinching of the Bootlegger Cove Formation.(After Freethy 1976.)

Figure 12. Cross sections along Ship Creek.

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Alti

tude

Abo

ve M

ean

Sea

Lev

el (

m)

120

100

80

60

40

Bedrock (Kenai Formation)Till

Sand and Gravel

West East

SGSG SSG

SSG

Clay

SSG

SG

ProjectedRecharge Basin

SG

AK

1843

AK

1331

AK

1845

AK

1846

AK

1847

AK

1851

AK

1848

AK

2681

AK

2682

AK

2683

AK

1044

AK

2684

AK

2128

AK

2127

AK

2123

Water Levels, after RechargeZone of Relative Moisture Change

Water Levels, before RechargeSG

SSG

Sand and GravelSilty Sand and Gravel

Vertical Exaggeration x10

1000 200 300 m

b. Interfingering relationships of strati-graphic units near the Fort Richardsonpowerplant along an east–west transect.(After Freethy 1976.)

c. Interfingering rela-tionships of strati-graphic units near theFort Richardson power-plant along a north–south transect. Grey pat-tern shows moist zonesrecorded with neutronlogs that reflect silt-richhorizons. (After Ander-son 1977.)

Figure 12 (cont’d). Cross-sections along Ship Creek.

0 500 1000 1500 m

AAAAAA

Permeable water-bearing zone

AAAAAASemi-permeable zone (functions as a confining unit in

some places and as a water-bearing unit in others)

Confining zone (generally impermeable -- functions as a ground-water barrier)

Water table (may be under pressure where shallow aquiferis semi-confined)

AAAAAABedrock (Kenai formation)

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

120

90

60

30

Ele

vatio

n (m

)

Datum is Mean Sea Level

Shi

p C

reek

For

t Ric

hard

son

Pow

erpl

ant

Vertical Exaggeration x20

18

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legger Cove Formation, but available data are notconclusive (Hunter et al. 1997). Descriptions ofthe confining layer below the cantonment rangefrom till (wells 1 and 17; Cederstrom et al. 1964) tovariations of silty gravel, clayey gravel, or siltwith sand (e.g., AP-3482, AP-3485) to silt (AP-3468) and clay (AP-3479; USACE 1996b). Themajority of these descriptions suggest that theyare not all fine-grained, estuarine deposits.Clayey gravel, silty sand, or silt with sand couldbe interpreted as a nearshore or ice marginalphase of the Bootlegger Cove Formation, but otherinterpretations are possible, such as diamictonoriginating as ice marginal debris flows or till.Many of the strata are also laterally discontinu-ous and therefore probably not the BootleggerCove Formation. For example, the 9-m confininglayer in well 1 (Cederstrom etal. 1964) at the north side ofthe railroad yard in the can-tonment area does not corre-late laterally with deposits inthe center of the cantonment,where over 42 m of gravel andsand lies below the surface(well AP-3591, USACE1996b). The genesis of thesedeposits needs to be definedby better and more detailedanalyses to determine theirspatial geometry.

Mountain View fanThe uppermost strati-

graphic unit below the can-tonment is the MountainView fan. Its strata are mostlysand and gravel, with a highconcentration (10 to 15%) offines (silt, clay). Interbeddedsilty sand and gravel contain-ing lenses and layers of siltand clay are common. Silt andclay horizons may be raftedblocks transported duringoutburst floods or deposits insmall ephemeral ponds andbackwater areas of aban-doned channels. These fandeposits are commonly on theorder of 15 to 18 m thick in thevicinity of the cantonmentarea (Cederstrom et al. 1964)and are not similar to the

mostly “clean” gravel normally associated withglacial outwash.

The fan’s strata may also interfinger with moreor less continuous horizons of diamicton where itlies near the margin of the Elmendorf Moraine.Glaciers frequently generate debris flows as sedi-ments are released by melting ice during the mo-raine building process. These debris flows couldhave produced diamictons interbedded with siltsdeposited from meltwater, similar to what isfound along the margin of the Matanuska Glaciertoday (Lawson 1979, 1982). More localized layersor lenses of diamicton may also be generated inmeltwater channels incised into the moraine,overall forming a small fan-shaped deposit (Fig.13; map unit eo; Plate 1). Sand and gravel layers

19

Not Drawn to ScaleExtreme Vertical Exaggeration

Incised Gully

Moraine Edge

Flow Deposits

ChannelsDepositional

Lobe

OverbankDeposits

ActiveChannel

LeveedChannel

Inactive Channelsand Fan Lobe

C´C

A

B´

A´

B

Figure 13. Fan such as those along the margin of the Elmendorf Moraine. Thestratigraphy near the apex is composed of interbedded diamicton sheets andincised channel deposits (gravel). Increased meandering near the fan toe producesbroad sand and gravel lenses. (After Galloway and Brown 1973.)

Active ChannelDeposits

Levee Deposits

Active Fan DistChanLob

CD

C

A

B

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develop from the normal flow of water in thesechannels and are interbedded with the debris-flow diamictons (Jopling and MacDonald 1975).Overall, the alternation between debris flowdeposition and stream channel migration pro-duces a complex interbedded sequence of gravelsand diamictons that probably characterizes thenorth cantonment area.

HYDROGEOLOGY

RegionalThe hydrogeology of the Anchorage Lowland

has been extensively studied, as researchers haveexamined various ground water issues (e.g.,Cederstrom et al. 1964, Waller 1964, Barnwell etal. 1972, Freethy 1976, Anderson 1977, Zenoneand Anderson 1978, Dearborn and Schaefer 1981,Munter and Allely 1992). The overall setting isreasonably well known (Fig. 14). Water enters theground water system through runoff along themountain front, percolation of rain and snowmeltacross the region, stream infiltration in losingriver reaches, and seeps from bedrock fractures(Table 2). The water flows down-gradient (from

high hydrostatic head to lower hydrostatic head)in either an unconfined or confined aquifer. Theconfined aquifer often has artesian water; thepotentiometric surface is of higher elevation thanthe base of the confining layer. Regionally,ground water in the Anchorage Lowland flowsroughly from the Chugach Mountains to Knik orTurnagain Arms. It discharges where streambedsintersect the water table (i.e., lower reach of ShipCreek), where the ground water table intersectsthe surface, forming ponds and lakes, or wherethe confining layer is truncated (i.e., coastalbluffs), producing seeps and springs.

The hydrogeology in the Anchorage area hastraditionally been treated as a three-componentsystem, consisting of an upper unconfined and alower confined aquifer, separated by a confininghorizon with low permeability (Cederstrom et al.1964, Freethy 1976, Anderson 1977). The silty clayto clayey silt of the Bootlegger Cove Formation isgenerally thought to be a confining layer becauseof its low hydraulic conductivity (e.g., USAF1994). The Bootlegger Cove Formation extendsacross most of the Anchorage Lowland (Ulreyand Updike 1983), but probably pinches out

20

Knik Arm

Knik Arm City of AnchorageMuldoon

Area

Fort Richardson

Very High Very LowPermeability

Water Table(Unconfined Aquifer)

Potentiometric Surface(Confined Aquifer)

Borehole or Well Where Water Level Was Monitored

Poorly Sorted Glacial Sediment

Sand and Gravel(Principal Confined Aquifer)

Silty Clay and Clay

Consolidated Sedimentsand Metamorphic Bedrock

0 2000 4000 6000 m

200

SeaLevel

150

100

50

–50

–100

Ele

vatio

n (m

)

Figure 14. Generalized hydrogeologic cross section from the Chugach Mountains to Knik Arm. (AfterBarnwell et al. 1972.)

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somewhere below Fort Richardson. Confininglayers appear to exist at the north and southeast-ern sections of the cantonment, but well AP-3591found no confining layer in the center of the can-tonment, where the confined and unconfinedaquifers appear to converge (USACE 1996b).

Sand and gravel of the unconfined and con-fined aquifers are exceptionally permeable andhydraulically conductive. Recharge studies wereconducted by temporarily diverting the flow ofShip Creek into storage basins on Fort Richard-son. The recharge rate was measured at 1.5 × 104

m3/day, while a second test in coarser gravelachieved a recharge rate of 5.3 × 104 m3/day(Anderson 1977, Updike et al. 1984). Anderson(1977) calculated a permeability of 68.6 m/day,while Freethy (1976) proposed a much highervalue of 720 m2/day for transmissivity. Theground water mounded during the second test,equivalent to 9.4 and 4.9 m in the unconfined andconfined aquifers, respectively (Anderson 1977);however, water levels dropped rapidly once theartificial recharge was shut off.

Fort Richardson hydrogeologyThe hydrogeology of Fort Richardson has been

briefly summarized in numerous engineeringreports, but detailed studies are restricted largelyto Freethy (1976), Anderson (1977), and USACE(1996b). Despite these studies, the ground waterconditions below Fort Richardson remain poorlyknown and require further detailed investiga-tions. Detailed subsurface information is generallylacking for the glacial sediments that range from70 to 97 m thick below the cantonment (Ceder-strom et al. 1964).

The shallow, near-surface aquifer occurs in theMountain View fan sediments (Fig. 10 and 12).The water table lies at a depth of 3 to 13 m in sedi-ments that are approximately 18.3 m thick in themain cantonment (Cederstrom et al. 1964, USACE1996b). The water table dips to almost 37 m bgs(below ground surface) at AP-3462, beyond theapparent limit of the confining layer where theconfined and unconfined aquifers converge (Fig.14 and 15a). The confining layer may be the Dish-no Pond or Fort Richardson diamicton or possi-

Figure 15. Ground water maps. (Contours in feet, as originally measured. To convert tometers, multiply by 0.3048.)

a. Top of unconfined aquifer in May 1995. (After USACE 1996b.)

21

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b. Top of unconfined aquifer in August 1995. (After USACE 1996b.)

c. Top of unconfined aquifer in November 1995. (After USACE 1996b.)

Figure 15 (cont’d). Ground water maps.

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d. Potentiometric surface of confined aquifer in May 1995. (After USACE 1996b.)

e. Potentiometric surface of confined aquifer in August 1995. (After USACE 1996b.)

Figure 15 (cont’d).

23

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f. Potentiometric surface of confined aquifer in November 1995. (After USACE 1996b.)

g. Top of confining layer as defined by USACE (1996b).

Figure 15 (cont’d). Ground water maps.

0 200 400 600 800 1000 m

AP-3

AP-3479

AP-3533

AP-3475

AP-3482

AP-3534

AP-3489

AP-3467

AP-3469

AP-3485

AP-3484

AP-3532

AP-3457

Approximate Upper Surfaceof Possible Confining Layer

200

220

240

260

280

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bly the Bootlegger Cove Forma-tion. A deep well drilled at thenorthern edge of the cantonment(well 1; Cederstrom et al. 1964)penetrated about 97 m of unconsol-idated sediment prior to encoun-tering bedrock. The upper 15.2 m,with its base at elevation 83 m asl(above sea level), consisted ofsandy gravel in Mountain View fandeposits. The next 40 m (base at 43m asl) was described by Ceder-strom et al. (1964) as till; however,the properties of this horizon couldalso be attributable to a glacial-marine silt.

The USACE (1996b) defined thetop of the unconfined aquifer at 52to 55 m asl, at what would be almost 30 m withinthis diamicton. A diamicton was also encoun-tered 4 m below the surface (85 m asl) near the FortRichardson powerplant (well 17; Cederstrom et al.1964). This diamicton was interbedded with sandand gravel down to 17 m depth (61 m asl). Hillsnearby this well site have been mapped as drum-linized ground moraine of Dishno Pond age(Plate 1; App. A). These hills are relict landformsthat project through deposits of the MountainView fan and this may be a lateral extension ofthe diamicton in the powerplant area.

The the two diamicton horizons in wells 1 and17 (Cederstrom et al. 1964) top out at approxi-mately the same elevation (83 to 85 m asl), whichmight suggest that a more or less continuoussheet of diamicton once extended below the can-tonment. However, at the southern edge of therailyard loop, AP-3591 penetrated 46 m of graveldown to 50 m asl (Fig. 9). Although its silt contentincreased at depth, a diamicton was not encoun-tered. We must assume that the confining layerdoes not exist here. Nearby, wells AP-3184 andAP-3470 encounter perched or unconfinedground water at 96 to 98 m asl, respectively. Thisis 12 to 15 m above the diamicton in wells 1 and17. Unfortunately, these wells did not penetratethrough the impermeable confining layer (at AP-3184, drilling was stopped just after groundwater was encountered), and so we cannot deter-mine the thickness of the diamicton or whetherthe lower diamicton extends across the area.

Ground-penetrating radar profiles along Arc-tic Valley Road near here show a strong reflectorbetween 5 and 10 m below the surface thatappears to extend to Davis Highway and Loop

Figure 16. 50-MHz radar profile collected along Loop Road showing ashallow, gently dipping reflector at the interpreted base of MountainView fan.

Road, where a similar reflector dips to a depth of20 m (Fig. 16) (Strasser et al. 1996). The signal isprobably lost below the horizon through attenua-tion in the silty matrix of the confining layer. Theoverlying 10 to 20 m of sediment is sand andgravel of the Mountain View fan. Again, this hori-zon roughly agrees in elevation with the top ofthe diamicton at well 17 and may be the top of aonce-continuous diamicton bed. This stratummay be absent at well AP-3591 because of localdissection during flooding on the fan. Also, pro-glacial streams migrating across the front of theadvancing Elmendorf ice may have eroded anddissecated the sediments. Therefore, the perchedground water zones encountered in wells couldsimply be locally confined by remnants of thediamicton (Fig. 17a). At places where the diamic-ton has been eroded, a gravel aquifer extends togreat depth (e.g., AP-3591). If the diamicton wasactually continuously eroded along the front ofthe moraine, then the location of the dippingwater surface near the Davis Highway and LoopRoad (Fig. 15a) could be its northern limit.

Another plausible alternative is that the diam-icton observed in well 1 formed as a result ofdebris flows from the Elmendorf Moraine. Evi-dence, such as erosional features (clay rip-upclasts) at the base of the diamicton, supports thisconcept, as do observations along modern glaciermargins. The silty deposits may be a transitionalphase of the Bootlegger Cove Formation, with theclay balls being recycled material from marinesilty clay eroded to the north. If this is the case,the diamicton encountered in well 17 is from aseparate source and would either have to dip tothe north and west underneath the cantonment,

0 m

12

24

36Processed Data

Raw Data

0 ns

200

400

600

800

and GravelFluvial Sand

DiamictonSilty Sand and Gravel(Mountain View Fan)

Channel Fill

25

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A B

A B

Perched Water on Top of Diamicton Block That Is an Erosional Remnant

Perched Water on Top of Debris FlowComposed of Diamicton

Fort RichardsonCantonment

Glenn Highway

Elmendorf Moriane (polygenetic mixture of diamicton, sand, and gravel)

Dishno Pond diamicton

Fort Richardson diamicton

Sand and gravel of the Mountain View fan with silt lenses

Older outwash sand and gravel

Fort RichardsonCantonment

Glenn Highway

Not Drawn to Scale

Not Drawn to Scale

a.

b.

26

Figure 17. Proposed stratigra-phy below the Fort Richardsoncantonment. Erosive activity (a)during deposition of the Moun-tain View fan cut through theDishno Pond ground moraineand edges of the Elmendorff Mo-raine. Erosion and deposition (b)associated with the MountainView fan was accompanied bysediment failure along the mar-gin of the Elmendorf Moraine,producing an interstratificationbetween sand and gravel anddiamicton. Wells drilled at site Awould encounter a diamicton atan elevation roughly equivalentto the top of the diamictonencountered in well B.

Figure 18. Ground water level at Elmendorff Air Force Base in September 1993. (Contours in feet, asoriginally measured. To convert to meters, multiply by 0.3048.) (After USAF 1994.)

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Elmendorf Moraine, and Bootlegger Cove For-mation or it has been eroded away. However, adipping horizon like this is not supported by ourinterpretation of the GPR data (Fig. 16).

A more likely alternative is that cantonmentdeposits result from a combination of these twoscenarios, where the diamicton sheet to the southwas eroded by proglacial streams in front of theElmendorf Moraine (Fig. 17b) or dips to thenorth. Stream and fan deposits shed off of themoraine interfinger with gravel deposits in thefan. Blocks of relict diamicton may be locally bur-ied in the gravel sequence, producing a complexarchitecture of interbedded diamicton and siltyoutwash deposits.

The U.S. Army Engineer District, Alaska(USACE 1996b), monitored 43 wells between 1994and 1995, providing the first detailed look atground water conditions in the cantonment areaon Fort Richardson. These data are augmented bysite-specific ground water data related to envi-ronmental investigations (E & E 1996, ESE 1991).

These preliminary data allow us to begin assess-ing ground water movement and contaminanttransport issues.

Ground water maps (Fig. 15a–c) (USACE1996b) and data from recent ground water inves-tigations on Elmendorf Air Force Base (USAF1994) (Fig. 18) allow us to compare these recentresults to the model proposed by Freethy (1976)(Fig. 19). Flow lines on Figure 20 show conver-gent flow in the vicinity of the cantonment area,implying a flow boundary to the north, below thecrest of the Elmendorf Moraine. This pattern wasnot supported by the USACE (1996b) report. Theground water maps produced by the Alaska Dis-trict imply that the surface of the unconfinedaquifer was dipping below the distal edge of themoraine (wells AP-3471 and AP-3472; Fig. 15a–c).This area is, however, located at the outer limit ofthe USACE data and is therefore poorly defined.Figure 20 compares the contrasting flow linesfrom the two models along the north edge of thecantonment. We cannot resolve this discrepancy,

Figure 19. Ground water level in the lower Ship Creek basin as determined by Freethy (1976). (Contours in feet, asoriginally measured. To convert to meters, multiply by 0.3048.)

27

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but it is clearly important to understanding howground water moves and contaminants migrate inthe cantonment area and Operable Unit D (OU D).

The elevation of the water table (unconfinedaquifer) was monitored three times in 1995 andused to contour the water surface below the can-tonment area (Fig. 15). Some interesting changesin the configuration of the water table and associ-ated flow paths took place. Generalized flow pat-terns during each of these periods (May, August,November) were to the northwest, reflectingrecharge from Ship Creek. During relative lowflow (low recharge) conditions in May, thereappears to be a strong divergence in flow near theintersection of the Davis Highway and LoopRoad. The divergence is probably controlled bythe upper topography of a confining layer. Theremay also be flow divergence caused by a zone ofhigh hydraulic conductivity below the MountainView fan deposits in the vicinity just west of LoopRoad. In August, under higher recharge condi-tions, flow lines are still divergent but tend toform broad arcs that are more consistent and sub-parallel, with discharge towards the north justeast of the railyard loop and westerly near LoopRoad.

One problem that we have observed is that thetop of the confining layer, as defined by the Corps

(USACE 1996b), is found at a shallower depththan the unconfined aquifer (Fig. 15a–c, g).Although this appears to be a product of theboundaries chosen for contouring, it introducesserious implications to future modeling, sincethis situation cannot exist in nature. Furtherinvestigation is needed to resolve this issue, espe-cially since it directly affects the modeling of con-taminant transport in OU D (ENSR 1996).

Monitoring of the confining aquifer during thesame period shows a general tendency for north-westerly flow (Fig. 15d–f). Along a line from AP-3479 to the north side of Building 740 (approxi-mately parallel to flow), the gradient of thepotentiometric surface was approximately 0.0155for all measurement periods. The 61- and 76-mcontours almost replicate those proposed byCederstrom et al. (1964). There appears to be onlyminimal seasonal or long-term change in the con-fined aquifer.

Data indicate that along the northwest edge ofthe cantonment, the unconfined aquifer plungesand recharges a deeper aquifer (Fig. 15a). Basedon the ground water data from AP-3471 and AP-3472 (USACE 1996b), it appears likely that at leastsome of this water reenters a confined aquiferand continues flowing to the northwest under-neath the Elmendorf Moraine. More data are

28

Figure 20. Comparison of ground water flow patterns. White flow arrows are inferred from ESE(1991), USAF (1994), USACE (1996b), and E&E (1996). Black flow arrows are from Freethy (1976).

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required however to determine if infact this is happening and how itaffects flow in general.

Significance to contaminant transportBased on the limited preliminary data that are

available, we can begin assessing contaminanttransport in the cantonment area and beneath thedifferent OUs (Fig. 21, Table 3) (USACE 1996a).

Operable Unit AThe Petroleum, Oil, and Lubricant Laboratory

Dry Well (POLLDW), Ruff Road Fire TrainingArea (RRFTA), and Roosevelt Road TransmitterSite Leachfield (RRTSL) are in OU A.

The POLLDW is located in a central part of theMountain View fan deposits, where groundwater is relatively deep, about 61 m below theground surface, or 52 to 55 m asl. Flow vectorsfluctuated from roughly north–northwest to

Figure 21. Operable Units on FortRichardson.

almost westerly during 1995 (USACE 1996b).Mean flow is probably to the northwest, but atpeak discharge the flow is in a north–northwestdirection. In a worst-case scenario, Diesel RangeOrganics (DRO) at the site could be transported tothis deep unconfined aquifer, producing a broadplume at depth. Maximum transport would prob-ably occur during peak ground water discharge,extending the plume to the north–northwest.

Ground water at RRFTA is encountered 46 mbelow the surface where flow is roughly to thewest–northwest (Fig. 22) (E&E 1996). We deter-mined this flow direction on the basis of the siteinvestigation of E&E (1996), but it does not agreewith the surface contours determined from datathat the USACE (1996b) measured. However, on

29

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the basis of the investigation by E&E (1996), flowpaths appear relatively uniform, so that a plumefrom point sources should be long and drawn outalong ground water flow lines.

A similar situation should be expected at theRRTSL, where flow is to the west–southwest and

30

Figure 22. Ground water level at RRFTA as monitored by E&E (1996). (Contours in feet, asoriginally measured. To convert to meters, multiply by 0.3048.)

Table 3. Identified or suspected contaminants at Fort Richardson, Alaska.

Operable unit Source area Contaminants

A Building 986 Petroleum, Oil, POLs, solvents, semi-volatile organics, and metalsand Lubricant Laboratory Dry Well

Roosevelt Road Transmitter Site PCBs, solvents, and metalsLeachfield

Ruff Road Fire Training Area POLs and dioxinsB Poleline Road Disposal Area VOCs, chemical warefare materialsC Eagle River Flats White phosphorusD Building 35-752 PCBs, diesel, alcohols, paint waste, petroleum hydrocarbons,

and dry-cleaning solventsBuilding 700/718 PCBs, POLs, solvents, mineral spirits, alcohols, ethylene

glycol, Stoddard solvent, MEK, cyclohexylamine, PCE, andTCE

Building 704 POLs, chlorinated solvents, alcohols, mineral spirits, paintwaste, and ballast water

Building 726 PCE, TCE, Stoddard solvent and other chlorinated solventsBuilding 796 Battery acid and leadBuilding 955 PCBs, petroleum hydrocarbons, VOCs, semi-VOCs, ethlyene

glycol, metals, and pesticidesBuilding 45-590 Petroleum hydrocarbons and PCEDust Palliative Areas PCBs, petroleum hydrocarbons, and metalsLandfill Former Fire Training Area POLs and VOCsLandfill Grease Pits POLs, solvents, ethylene glycol, paint waste, and pesticidesStormwater Drainage Outfall to Ship Creek Any hazardous substance used at Fort Richardson

MEK = Methyl ethyl ketonePCBs = Polychlorinalted biphenylsPCE = Tetrachloroethylene

POLs = Petroleum, oil, and lubricantsTCE = TrichloroetheneVOCs = Volatile organic compounds

ground water is 24 m below the surface (Fig. 23).However, modeling by E&E (1996) suggests thatDRO-type contaminants are unlikely to migrateinto the ground water at these depths for 90 yearsor more.

AAAAAAAAAAAAAAAA

FormerRoad

AP-3656

AP-3657

AP-3655

AP-3654

AP-3653

N

0 20 40 100 m60 80

Monitoring Well Location

Edge of Trees

Groundwater Contour(15 December 1995)

Groundwater Contour(24 October 1995)

236

240

240

244

244

248

248

252

252

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Figure 23. Ground water level at RRTSL as monitored by E&E (1996). (Contours in feet,as originally measured. To convert to meters, multiply by 0.3048.)

Operable Unit BThe Poleline Road investigation report (ESE

1991, OHM 1994) shows divergent flow belowthis contaminant site (Fig. 24). The area west ofPoleline Road appears to experience south–southwesterly flow, with an increasingly easterlycomponent further to the east. A plume generatedin this area would likely spread out along theflow lines.

Operable Unit C Only limited, very shallow ground water data

are available for ERF (Racine and Cate 1995). Thecontaminant being investigated is elementalwhite phosphorus, which is restricted to the sur-face and near-surface environment. It is relativelyinsoluble and transport appears limited to surfi-cial drainageways and the Eagle River (Lawsonet al. 1996a,b).

Operable Unit DThe numerous OU D sources can be separated

into three general clusters as shown on Figure 21.To the south, the Stormwater Outfall and Build-ing 35-752 overlie deposits of the Ship Creekdrainage. Along this section of Ship Creek,stream waters recharge the aquifer system andthe water table is very shallow (approximately 5m bgs near Building 35-732). Ground water flowlines at these sites trend from west–northwest tonorthwest.

A second group of source areas in the canton-ment lies near the central portion of the MountainView fan deposits, including Buildings 45-590,955, 726, 700/718, 704, and 796. The ground waterflow at Building 955 is similar to that describedfor the POLLDW of OU A. At Building 796,located northeast of most of this group, groundwater is encountered at about 30 m bgs. Groundwater flow ranges from northerly to northwest-erly (Fig. 15a–c). This variability would produce abroad plume if pollutants were to migrate to thisdeep level. The remainder of the group (Build-ings 45-590, 726, 700/718, and 704) are relativelyclose together in an area where the water table isencountered at about 33 m below the surface. Theground water flow lines in this area trend fairlyconsistently to the northwest, which would pro-duce a plume with limited lateral dispersal.

The third group of OU D sources lies at thenorthern edge of the Mountain View fan in thelandfill area (Landfill Grease Pits, LandfillFormer Fire Training Area). These sites are closeto the southern edge of the Elmendorf Moraineand the underlying materials should include aninterfingering of moraine- and fan-related depos-its. The ground water surface in this region wasencountered at a depth of 46 m. These sites are atthe perimeter of the region contoured by theUSACE (1996b) ground water study, whereextrapolation may have resulted in unreliablevalues. The flow directions shown range from

31

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NApproximate Edge of Marsh0 20 40 60 m

Hill

Monitor Well 5278.67 Monitor Well 3

275.77

Monitor Well 2275.09

MonitorWell 1

Monitor Well 4264.92

Appro

ximate

Toe

of H

ill

Gravel R

oad

Reference Monument 1

Bas

elin

e

265

270

275

280

MarshStanding Water Elevation ≈ 89 m

Hill

NApproximate Edge of Marsh

MarshStanding Water Elevation ≈ 89 m

Monitor Well 5277.8

Monitor Well 3275.21

Monitor Well 2274.21

Monitor Well 1

Appro

ximate

Toe

of H

ill

0 20 40 60 m

Gravel R

oad

Reference Monument 1

Bas

elin

e

250

255

260

265

275

280

252.15Monitor Well 4

32

a. September 1991.

b. October 1990.

Figure 24. Ground water level at Poleline Road as monitored by ESE (1991). (Contours infeet, as originally measured. To convert to meters, multiply by 0.3048.)

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westerly in May and August to north–northwestin November. Contaminants reaching the groundwater table in this region would form a broadplume.

CONCLUSIONS

The hydrogeology of Fort Richardson is farmore complicated than that of Anchorage andneighboring Elmendorf Air Force Base. Definingthe boundary conditions is particularly difficult.In both of the other areas, the Bootlegger CoveFormation forms a relatively continuous blanketthat behaves as a flow boundary to the upperunconfined aquifer. Flow across Elmendorf AirForce Base is generally north to south (Fig. 18 and20), with ground water recharge from the Elmen-dorf Moraine and discharge to the lower reachesof Ship Creek. Therefore, both the ElmendorfMoraine and Ship Creek can be treated as flowdivides (north and south, respectively). To theeast, flow circulates counter-clockwise in thevicinity where Ship Creek shifts from a losingstream (where it recharges the aquifer) to a gain-ing stream (where the aquifer discharges into the

stream; Fig. 25). USAF (1994) treats the Bootleg-ger Cove Formation as a boundary to the west,where it reportedly rises below the coastal bluffsand limits westerly flow.

Ground water surface maps currently proposeconflicting models for Fort Richardson (Fig. 20).According to Freethy (1976), the crest of theElmendorf Moraine acts as a flow divide andcauses convergent flow below the northern areaof the cantonment along the front of the moraine.The unconfined aquifer mimics surface topogra-phy and flows from the high elevations along theElmendorf Moraine and the front of the ChugachMountains. Below the cantonment, these topo-graphically driven flows encounter water mov-ing north in response to recharge from ShipCreek. Flow convergence would produce a west-erly flow in the unconfined aquifer and high dis-charge along the front of the Elmendorf Morainetowards Elmendorf Air Force Base. However,because the unconfined aquifer plunges north-ward below the cantonment, this flow insteadprobably recharges the deeper confined aquiferbeyond the eastern limit of the Bootlegger CoveFormation.

Figure 25. Major water diversions along Ship Creek, showing shift from a losing channel onFort Richardson to a gaining channel on Elmendorff Air Force Base. (After Barnwell et al.1972.) 1–The combined capacity of the treatment plants is 64,352 m3/day. During the lowest flowdays nearly every year, they cannot operate at full capacity. 2–Fort Richardson powerplant usesnearly all of the low flow in the stream for cooling and returns warm water to the channel. 3–Elmendorff Air Force Base’s powerplant uses most of the low flow for cooling, then returns it to thechannel. During the low flow months, the stream is supplemented with well water. 4–TheChugach Electric powerplant normally diverts about 11,500 m3/day for cooling water and returnsit to the channel.

2

3

41

0 2 km1

USGS Gaging Station

1

ShipCreek

Dam

1234

ChugachElectric

Powerplant

Fort RichardsonPowerplant and Fish Hatchery

Elmendorf A.F.B.Powerplant and Fish Hatchery

City and MilitaryWater Treatment Plants

11,356 15,142 3,7857,571

3,78511,3567,571Loss

30,283Gain

15,142Gain

7,571Gain

18,927

30,28349,21079,493at Dam56,781 m /day3

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An alternative model is supported by recentground water data (USACE 1996b). Groundwater flow below the southern portion of the can-tonment area agrees with that of Freethy (1976),and the elevation of the potentiometric surfaceagrees with that of Cederstrom et al. (1964). How-ever, ground water measurements below Ammu-nition Area A (AP-3471 and AP-3472) implynorthwesterly flow here, with a limited amountof westerly divergence further to the south. Thesedata would suggest that the confining layerprojects beneath the Elmendorf Moraine. If this istrue, then northwesterly flow of ground watercould transfer contaminants from OU A and OUD underneath the Elmendorf Moraine and to thenorth and west.

The differences between these two models tellus that it is critical to determine whether or notthe Elmendorf Moraine is a flow boundary. Bothmodels are based on limited data that are mostlymarginal to the cantonment. Freethy (1976)looked at the entire Anchorage Lowland, withFort Richardson at the northern limit of his analy-sis. The USACE (1996b) had 13 wells to define theconfining aquifer, but these were located mainlyin the southern part of the cantonment. To resolvethese questions, further studies are needed andadditional measurements of ground water,including new wells, are required to improve ouroverall understanding of ground water flowbelow the Fort Richardson cantonment. The con-fining layer needs to be defined to determine if itis part of the Bootlegger Cove Formation, andtherefore restricted by elevation (or paleobathy-metry), or an extension of the Dishno Pondmoraine. To evaluate potential contaminanttransport pathways, it is critical to determine ifthe sand and gravel of the confined aquiferprojects under the Elmendorf Moraine, therebybeing a northwesterly path to Knik Arm. Byaddressing these questions, we will be better ableto define the flow boundaries required beforeattempting a quantitative ground water flowmodel.

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quadrangle, Alaska. Washington, DC: U.S. Geo-logical Survey, 91-143.Yehle, L.A., H.R. Schmoll, and E. Dobrovolny(1992) Surficial geologic map of the Anchorage A-8SE quadrangle, Alaska. Anchorage, Alaska: U.S.Geological Survey, Open-File Report 92-350.Zenone, C., and G.S. Anderson (1978) Sum-mary appraisals of the Nations groundwater

resources—Alaska. Washington, DC: U.S. Geo-logical Survey.Zenone, C., H.R. Schmoll, and E. Dobrovolny(1974) Geology and ground water for land-useplanning in the Eagle River-Chugiak area, Alaska.U.S. Geological Survey Open-File Report 74-57,scale 1:63,360.

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Additional detail in some other areas was de-rived by Schmoll and Yehle from these airphotosas well.

The geology of the lowland area was includedin previous mapping at smaller scales by Dobro-volny and Miller (1950), Miller and Dobrovolny(1959), and Cederstrom et al. (1964), and at slightlylarger scale but in a more generalized way thatlacked traditional geologic map units by Schmolland Dobrovolny (1972a). Other workers whoreported on surficial geology of the area withoutproviding detailed maps include Karlstrom

APPENDIX A: DESCRIPTION OF MAP UNITS

Figure A1. Index map showing location of surficial geologic maps(circled numbers, listed in text) and selected geomorphic features.

IntroductionThe material in this appendix is a draft report

on the surficial geologic units of Fort Richardsonprepared by H.R. Schmoll and L.A. Yehle of theU.S. Geological Survey. This section contains theirmost recent classification scheme and should beused when referring to the surficial geologic map(Plate 1).

The descriptions given here have been derivedby combining the map unit descriptions of the five1:25,000-scale surficial geologic quadrangle mapsthat were used in making the geologic map of FortRichardson and vicinity (plate 1) and that havebeen published or are in preparation in the U.S.Geological Survey open-file report series. Thesemaps are identified by number on Figure A1 andare listed below along with the quadrangle forwhich surficial geology is in preparation.

1. Anchorage B-7 NW(Yehle and Schmoll 1987b)

2. Anchorage B-8 SE/NE(Yehle et al. 1990)

3. Anchorage B-7 SW(Yehle and Schmoll 1989)

4. Anchorage A-8 NE(Schmoll et al. 1996)

5. Anchorage A-7 NW(Schmoll et al., in prep.)

The surficial geology of thesequadrangles was mapped initially atscales of 1:63,360 (northern and east-ern parts) and 1:24,000 (west–centraland southwestern parts) by Schmolland Dobrovolny mainly between 1965and 1971 by interpretation of1:40,0000-scale airphotos taken in 1957and 1:20,000 scale airphotos taken in1962. Field investigations were under-taken by Dobrovolny and Schmoll(1965–1971) and continued intermit-tently by Schmoll (1973–1983) and bySchmoll and Yehle (1984–1995). Theoriginal mapping was changed photo-graphically to 1:25,000 scale by Yehleand Schmoll in 1986–1999 and, exceptin the southeastern part, the moun-tainous parts of the area wereremapped by Yehle from 1:24,000-scale airphotos taken in 1972–1974.

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(1964, 1965), Reger and Updike (1983, 1989), andSchmoll et al. (in press). Bedrock crops out mainlyin the Chugach Mountains, and was not examinedin detail in any of the maps and reports citedabove, but is mapped in parts of the area at1:63,360 scale by Clark and Bartsch (1971). Bed-rock of the entire area is included in the 1:250,000-scale reconnaissance map of Clark (1972) thatserved as the basis for subsequent regional compi-lations at the same scale by Magoon et al. (1976)and Winkler (1992).

The Fort Richardson map area lies athwart theboundary between two physiographic provinces,the Anchorage Lowland and the Chugach Moun-tains. This boundary extends diagonally across themap area from northeast to southwest and ismarked by an abrupt rise of the mountains knownas the Chugach Mountain Front. In the southernpart of the map area, the margin of the lowlandnorthwest of the front consists of a higher-lying,southwest-widening belt of foothills known as theHillside area.

The characteristics of the surficial geologicmaterials delineated by the map units describedhere are based primarily on field observations;they are supported in part by laboratory analyses,especially of grain size, the descriptions of whichfollows the modified Wentworth grade scale

(American Geological Institute 1989). Thicknessestimates are based on unevenly distributed fieldobservations and limited subsurface data; formany deposits, especially in the mountains, dataare lacking and thickness estimates are based inlarge part on geomorphic considerations.

Especially near mapped bedrock or on moun-tain slopes mapped as colluvium, bedrock may bepresent at relatively shallow depth. Elsewhere,however, bedrock lies at considerable depth. In thedescriptions that follow, “bedrock” refers to themetamorphic rocks of map unit bo. The term “olderbedrock” is used only selectively to avoid ambigu-ity with the term “younger bedrock,” which isused for the Tertiary continental rocks of map unitby.

The units described here may be overlain by asmuch as 1 m of organic and windblown (includingvolcanic) materials that thicken locally and gradeinto map unit p. In the urbanized parts of the maparea, much of this mantle has been removed orotherwise modified. Where the mapped deposithas also been significantly altered, in some placesthe landform destroyed, a suffix u is added to themap-unit designator. Slope information is derivedfrom or based on geomorphic analogy to estimatespresented in Schmoll and Dobrovolny (1972b),whose slope categories are used (Fig. A2). Stan-

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a° v =

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24° Slope: Steep Slopes (45%)

14° Slope: Moderate Slopes (25%)

8.5° Slope: Gentle to Moderately Gentle Slopes (15%)

Figure A2. Slope categories used in these descriptions. (After Schmoll and Dobrovolny 1972b.)

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dard age designations are omitted from map sym-bols because all units except bedrock are of Qua-ternary age. The correlation of map units is shownon Figure A3.

Surficial depositsSurficial deposits underlie the surface of the

Anchorage Lowland and extend to depths of tensto at least 100 m (mainly west of the map area). Theyconsist mostly of Pleistocene-age glacial drift that

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represents a sequence of several glaciations. Someof these deposits are found in stratigraphicsequences exposed in bluffs along Knik Arm andlocally in exposures along streams and in roadcuts.Except for the uppermost one or two, most of thedeposits in these sequences cannot be directlyrelated to the deposits mapped at the surface. Thedeposits at the surface occur in well-defined land-forms and include extensive areas of moraine andrelated glacioalluvial, glaciolacustrine, and glacio-

Figure A3. Generalized stratigraphy exposed in bluffs along Knik Arm.

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estuarine deposits. Glacial deposits are commonalso within and on the walls of major mountain val-leys, and quite prevalent, but thinner, along theChugach Mountain Front; higher on the moun-tains, glacial deposits are more widely scattered.Colluvial deposits of Holocene and late Pleistoceneage form an extensive veneer on especially thelower slopes of the Chugach Mountains. Othernonglacial deposits are more restricted in arealextent, although some are widely distributed. Theyinclude pond, peat, estuarine, alluvial, and anthro-pogenic deposits and are mostly Holocene in age.

Deposits in stratigraphic sequences Deposits in stratigraphic sequence, undi-

vided—Deposits that crop out in bluffsalong Knik Arm and are too narrow inmap area to show individually; portrayedgraphically in Figure A4. Individual unitsshown on that figure that are not other-wise shown on the map are describedhere, as are other deposits that occur onlyin stratigraphic sequence and that areshown on the map.

Diamicton deposits. These are poorly sortedmixtures of gravel, sand, silt, and minor clay-sized material that locally includes widely scat-tered boulders; they are commonly massive, withminor bedding locally. Mainly of glacial origin,they are equivalent to ground-moraine deposits.

kd Knik diamicton (late Pleistocene)—Includes interbeds of silt, sand, and gravel;crudely bedded in some places. Thicknessat least 10 m. May be partly glacioestua-rine in origin. Probably equivalent in ageto Dishno Pond deposits, but may includeolder late Pleistocene deposits.

od Older diamicton deposits (Pleistocene)—Somewhat more oxidized and compactthan most deposits of ground moraine atthe surface. Thickness at least 10 m. Possi-bly equivalent in age to deposits olderthan those of the Rabbit Creek moraine.

Glacioalluvial deposits. These are chiefly pebbleand cobble gravel with some interbedded sand;they are well bedded and sorted.

eoa Advance outwash deposits related toElmendorf Moraine (late Pleistocene)—Thickness about 10 m. Deposited as theglacier advanced into glacioestuarinewater or just prior to the time when the

glacier terminus was farther to the north-east.

doa Advance outwash deposits related to Dish-no Pond moraines (late Pleistocene)—Thickness 2 to 6 m, base of unit not exposedin places.

og Older deposits (Pleistocene)—Moderatelyogx oxidized to yellowish gray in most places.

Thickness about 8 to 15 m; base of unit notexposed. Relationship to glacial depositsnot evident. In places more strongly oxi-dized to yellowish-orange, possibly but notnecessarily indicating deposits of substan-tially greater age.

oe Older glacioestuarine deposits (late Pleis-tocene)—Interbedded diamicton, variablypebbly to cobbly silty clay and clayey silt,silt, and fine to medium sand. Beddingcommonly fairly even but strongly contort-ed locally. Thickness 10 to 14 m; base of unitnot exposed. Probably deposited in glacio-estuarine water that occupied ancestralCook Inlet prior to glacier advances repre-sented by Dishno Pond or earlier late Pleis-tocene moraines.

oei Deposits that are somewhat indurated(Pleistocene)—Well-bedded silt and clay lo-cally and intermittently exposed belowmean sea level. Bedding gently warped atone place.

pi Interglacial pond deposits (Pleistocene)—Chiefly silt and clay with some fine sand;commonly include marl and intermixedand interbedded organic material (peat,twigs, and wood, commonly compressed)whose age is beyond the range of the radio-carbon-dating method. As much as a fewmeters thick, overlain and underlain byglacial deposits. Exposed in a few roadcutsalong Glenn Highway, at two places alongEagle River, and in one Knik Arm bluff.

Moraine depositsThese are subdivided primarily according to

type of moraine (end, lateral, and several types ofground moraine) and subordinately according tocorrelations mainly with named end and lateralmoraines that extend along the Chugach Moun-tain Front where their typical localities occur.Holocene-age moraines correlated generally withsimilarly situated moraines in the southeasternpart of the Municipality of Anchorage, althoughnot with the specifically named moraines there.The till that composes most moraine deposits is

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chiefly a diamicton, consisting of massive, unsortedto poorly sorted mixtures of gravel, sand, silt, andrelatively minor amounts of clay; in places it mayconsist of poorly sorted silty sandy gravel; itincludes large boulders; locally it may includebeds of gravel and sand. These deposits are gener-ally moderately to well compacted.

End-moraine deposits. These are formed at theterminal areas of glaciers where the glacier frontwas relatively stationary. Contacts are welldefined. Topography is irregularly hilly, in placesbeing formed in well-defined gently arcing ridgecomplexes; slopes are gentle to moderate in smallareas on some hill and ridge tops and in interven-ing swales, and are steep on hill and ridge sides.Except for the large Elmendorf Moraine in the An-chorage Lowland, deposits are restricted to smallmoraines in mountain valleys, most of which arecorrelated with varying degrees of certainty withnamed typical deposits in lateral moraines alongthe Chugach Mountain Front.

ame Deposits of Alaskan moraines (Holocene)—Mark terminal position of former small gla-ciers in heads of a few valleys tributary toShip Creek in southeastern part of maparea. Thickness probably 10 m or less.

eme Deposits of main phase of Elmendorfemeu Moraine (late Pleistocene)—Mark limit of

last significant readvance of large glacier inKnik Arm sector of Anchorage Lowland.Thickness probably 10 to 20 m in largeElmendorf Moraine complex (a formallynamed geographic feature) that alsoincludes map units emh and ekh; may includegravel and sand near southern margin ofcomplex. Probably less than 10 m thick insmall moraines in largest Wolverine Valleyand in upper part of Snowhawk Valley.emeu are deposits modified by urbaniza-tion or other anthropogenic activity.

emy Deposits of younger phase of ElmendorfMoraine—Occur in prominent ridge thatmarks a slight readvance of the glacier andthat extends beyond the deposits of themain phase west of the map area.

dme Deposits of Dishno Pond moraines (latedmeu Pleistocene)—Mark limits of readvances

during general recession of glaciers fromup-valley sources in mountain valleys.Thickness 10 m or more in Eagle River Val-ley and South Fork Valley, probably lessthan 10 m in Chester and Wolverine Val-leys. dmeu are deposits modified by urban-

ization or other anthropogenic activity. fme Deposits of Fort Richardson moraines (late

Pleistocene)—Thickness may be as muchas 10 m in remnant of major moraine inShip Creek Valley in southeasternmostpart of map area, less than 10 m in Chesterand Wolverine Valleys, where mark minortermini of glaciers.

rme Deposits of Rabbit Creek moraines (latePleistocene)—Thickness may be as muchas 10 m in major moraine in Ship CreekValley in southeasternmost part of maparea, less than 10 m in valleys of Wolverineand South Fork Campbell Creeks wheremark principal termini of glaciers.

lme Deposits of Little Rabbit Creek moraines(Pleistocene)—Probably more oxidizedthan younger end-moraine deposits.Thickness less than 1 m. Occur as rem-nants down-valley from better developedRabbit Creek moraines in Wolverine Val-leys.

Lateral-moraine deposits. These occur in narrow,well-defined ridges, as well as in less well-defined ridge segments, that mark side marginsof former glaciers. Ridges descend gradually inaltitude southwestward along the ChugachMountain Front and are arranged en echelon;successively older groups of moraine ridges aregenerally better developed to the southwest. Theapproximate altitudinal ranges are given for eachmajor lateral-moraine group; older morainedeposits are very poorly represented along thefront by lateral moraines, if at all. These are locallypresent on the sides of several mountain valleys,descending down-valley. Contacts are generallywell defined, except being gradational commonlywith colluvium on the upslope sides and locallywith other glacial deposits. Topography is mod-erately irregular; slopes are gentle to moderate onsmall areas on some ridge tops, and are steep onridge sides, especially the downslope side. Bed-rock may occur locally at shallow depths where aridge is relatively high on the mountainside.These are more stable than other deposits onmountainsides, but some instability can beexpected on steeper slopes.aml Deposits of Alaskan moraines (Ho-

locene)—Thickness probably less than 10m. Single occurrence in head of valley trib-utary to Snowhawk Valley.

eml Deposits of Elmendorf moraines (latePleistocene)—Thickness several to about

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10 m. Occur discontinuously from LittlePeters Creek (300 m) to Eagle River (260 m),where merge with end-moraine and kamedeposits to form prominent ElmendorfMoraine complex; also present in valleytributary to Snowhawk Valley and in larg-est Wolverine Valley.

dml Deposits of Dishno Pond moraines (latePleistocene)—Thickness probably 1 m toseveral meters, but as much as 15 m wherebetter developed near Ship Creek. Extenddiscontinuously from Parks Creek (390 m)to south of Ship Creek (190 m); moderatelywell developed along Eagle River and itsSouth Fork Valleys; single small occurrencein largest Wolverine Valley.

fml Deposits of Fort Richardson moraines (latePleistocene)—Thickness probably severalmeters, except 10 to 15 m where betterdeveloped south of Chester Creek. Extenddiscontinuously from near Carol Creek(500 m); quite continuous southwest ofEagle River Valley, widening to form a welldeveloped complex of ridges in the Hill-side area (350 m). Also present extensivelybut discontinuously along sides of severalmountain valleys.

rml Deposits of Rabbit Creek moraines (latePleistocene)—Thickness ranges from sev-eral meters in the northeastern to at least 10m in the southwestern ends of the distribu-tion. Discontinuous from near Carol Creek(580 m) to South Fork Campbell Creek,where well developed (440 m).

lml Deposits of Little Rabbit Creek moraines(Pleistocene)—May be more oxidized thanyounger lateral-moraine deposits. Thick-ness probably a few to several meters.Extend quite discontinuously southwest-ward from near South Fork CampbellCreek (500 m); occur also at one locality inChester Creek Valley.

sml Deposits of Ski Bowl moraines (Pleisto-cene)—Probably more compacted and oxi-dized than younger lateral-moraine depos-its. Thickness probably several meters.Contacts more gradational and topog-raphy more subdued than those of young-er deposits. Occur along Chugach Moun-tain Front in small saddle between frontand Ship Creek Valley (typical area) and asscattered remnants farther up Ship CreekValley and in Snowhawk Valley.

gml Deposits of Glen Alps moraines (Pleis-

tocene)—Probably well compacted and oxi-dized. Thickness poorly known, probably afew to several meters. Contacts gradation-al. Topography includes remnant ridgesand patches of hummocky ground; slopesmoderate to steep. Occur high on slopes ofNorth Fork Campbell Creek Valley and inmountain pass north of Ship Creek.

Ground-moraine deposits. These are formedmostly beneath glaciers; they are generally thinnerand found in landforms commonly more subduedthan the well-developed ridges and hills of end- andlateral-moraine deposits. Where ground-morainedeposits are extensively developed, those in sever-al distinctive types of landform are mapped sepa-rately. They occur in the Anchorage Lowlandmainly north of the Elmendorf Moraine; south of itmost ground-moraine deposits are concealed byyounger deposits or modified by the action of gla-cioestuarine water, or both. Occurrences along theChugach Mountain Front and within mountainvalleys are more widely scattered and restricted inarea.

amg Deposits of Alaskan moraines (Holo-cene)—Thickness poorly known, probablyseveral meters. Occur only in a few moun-tain valley heads in southeastern part ofmap area.

amb Deposits that thinly mantle bedrock—Simi-lar to other ground-moraine deposits butmay be only a few meters thick. Bedrockmay be present at surface locally. Single oc-currence in valley head tributary to Snow-hawk Valley.

emg Deposits of the Elmendorf Moraine (lateemgu Pleistocene)—Thickness several to about 12

m, except only a few meters in mountainvalleys. May include older ground-moraine deposits at depth. Contacts gener-ally well defined but may be gradationalwith other ground-moraine deposits. Top-ography generally smooth to very gentlyhummocky, slopes gentle to moderatelygentle. Widespread north of the Elmendorf(end) Moraine complex. Single occurrencesin largest Wolverine Valley and in valleytributary to Snowhawk Valley. emgu aredeposits modified by urbanization.

emh Deposits with high relief—Thicknessemhu may be greater than in other ground-

moraine deposits, perhaps 15 to 20 m. Top-ography more boldly hummocky to hilly

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and slopes steeper. Occur in associationwith end-moraine deposits as part ofElmendorf Moraine complex, but notformed in the well-developed ridges char-acteristic of those deposits. emhu, depositsmodified by urbanization or other anthro-pogenic activity.

emd Deposits in well-developed drumlins—Thickness may be as much as 15 to 20 m.Occur in elongate hills with moderatelysteep side slopes that merge laterally intolow-relief terrain of other deposits, com-monly other ground moraine. Best devel-oped northeast and southwest of EagleRiver Flats.

emf Deposits in fluted terrain—Similar to otherground-moraine deposits but formed inhills more elongate and of lower relief thandrumlins with which they are associated.Limited to a few occurrences near LakeClunie.

emk Deposits that include some kame depos-emku its—May include gravel and sand either in

extensive areas that are not readily distin-guishable from ground moraine or locallyin areas too small to map separately. Occurmainly north and south of Peters Creek inassociation with kame fields and at a fewlocalities farther southwest. emku aredeposits modified by urbanization or otheranthropogenic activity.

emm Deposits modified by glacial lake water—Similar to other ground-moraine depositsbut surface of deposits appears to havebeen winnowed and include better-sortedsilt, sand, and gravel. Single occurrencealong Eagle River about 3 km east of GlennHighway.

emb Deposits that thinly mantle bedrock—Simi-lar to other ground-moraine deposits butmay be only a few meters thick. Bedrockmay be present at ground surface locally.Occur locally along lower part of and adja-cent to Chugach Mountain Front and atone place in valley tributary to SnowhawkValley.

dmg Deposits of Dishno Pond moraines (latedmgu Pleistocene)—Thickness probably several

to 10 m. Contacts generally well defined,may be gradational with colluvium. Top-ography smooth to gently hummocky,slopes gentle to moderate. Occur mainlynear Dishno Pond (typical area), in EagleRiver Valley, and northward along the

Chugach Mountain Front. dmgu are depos-its modified by urbanization or otheranthropogenic activity.

dmf Deposits in fluted terrain—Similar to otherground-moraine deposits but occur in well-developed, long, relatively narrow ridgesseveral meters high, parallel to direction ofice flow, and separated by channel-like de-pressions. Occur only in Eagle River Valleyjust east of Eagle River community.

dmo Deposits overridden by later (Elmendorf)glacier ice—Probably similar to flutedground-moraine deposits but occur in verysubdued ridges. Present only down-valleyfrom fluted terrain.

dmk Deposits that include some kame deposits—More likely to include gravel and sand thanother ground-moraine deposits. Restrictedto a few localities near Dishno Pond.

dmm Deposits modified by glacial lake water—Thickness possibly a few meters in an irreg-ularly thick mantle of somewhat bettersorted, more gravelly diamicton that formsa lag accumulation seemingly originatedby the winnowing action of glacial lake wa-ter. Probably gradational at depth mostly tounmodified glacial diamicton. Occur at afew places in Eagle River Valley alongnorth side of river opposite mouth of SouthFork Valley.

dmb Deposits that thinly mantle bedrock—Similarto other ground-moraine deposits but onlya few meters thick. Bedrock may be presentlocally at ground surface. Single occurrencenear mouth of South Fork Valley.

fmg Deposits of Fort Richardson moraines (latePleistocene)—Thickness probably a few toseveral meters. Contacts well definedexcept gradational with bedrock andlateral-moraine and colluvial deposits.Topography generally smooth, slopes mod-erate. Occur mainly in South Fork (EagleRiver) Valley and locally downslope fromlateral moraines along Chugach MountainFront; occur also in Wolverine Valleys insouthern part of map area.

fmb Deposits that thinly mantle bedrock—Thickness probably a few meters or less.Bedrock outcrops present locally; mayinclude some admixed rubble. Occur at afew scattered localities along ChugachMountain Front and in upper part of NorthFork Campbell Creek Valley.

rmg Deposits of Rabbit Creek moraines (late

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Pleistocene)—Thickness probably a fewmeters. Contacts gradational with lateral-moraine and colluvial deposits. Topogra-phy smooth, slopes gentle to moderate.Occur extensively in valleys of ChesterCreek and the north and south forks ofCampbell Creek, and at widely scatteredlocalities along the Chugach MountainFront.

rmb Deposits that thinly mantle bedrock—Thickness about 1 m to a few meters. Bed-rock outcrops commonly present; includeadmixed rubble. Contacts well definedexcept gradational with bedrock. Topogra-phy smooth, slopes gentle. A few occur-rences along Chugach Mountain Front.

lmg Deposits of Little Rabbit Creek moraines(Pleistocene)—May be more oxidized thanyounger deposits. Thickness probablyonly a few meters. Contacts gradational.Topography smooth, slopes gentle tomoderate. Occur in Ship Creek Valley andin a few places along Chugach MountainFront south of North Fork CampbellCreek.

lmb Deposits that thinly mantle bedrock—Thickness may be about 1 m. Some bed-rock outcrops present; include admixedrubble. Occur at several places alongChugach Mountain Front southward fromthe north side of Ship Creek.

smg Deposits of Ski Bowl moraines (Pleis-tocene)—Probably more oxidized thanyounger deposits. Thickness a few to sev-eral meters. Contacts gradational. Topog-raphy smooth, slopes moderate. Occur inbroad areas where mountain valleysemerge along the Chugach MountainFront, at scattered localities on mountainridges (especially south of MeadowCreek), and at one locality in Ship CreekValley.

smb Deposits that thinly mantle bedrock—Thickness possibly 1 m to a few meters.Small bedrock outcrops common; admixedwith or containing mostly rubble, espe-cially in small map-unit areas. Topogra-phy smooth, slopes gentle to moderate.Occur at scattered localities along EagleRiver Valley and south of there near thenorthwestern ends of mountain interfluveridges, especially where Ship Creek Valleyemerges at the Chugach Mountain Front.

gmg Deposits of Glen Alps moraines (Pleis-

tocene)—Probably more oxidized thanyounger deposits. Thickness probably a fewmeters. Contacts gradational. Topographysmooth, slopes gentle to moderate, locallysteeper. Occur in Chester Creek Valley.

gmb Deposits that thinly mantle bedrock—Themore common mode of occurrence for GlenAlps deposits. Thickness quite variable,probably a few meters or less. Bedrock out-crops common; admixed with or consistingmostly of rubble. Topography somewhatmore irregular than in areas of other groundmoraine, slopes locally steep. Occur high onslopes of Ship Creek Valley and on moun-tain interfluve ridge between North andSouth Forks of Campbell Creek.

mmg Deposits of Mount Magnificent moraines(Pleistocene)—Probably more oxidized andcompacted than older deposits; clayeymatrix common locally. Thickness com-monly a few meters, perhaps thicker wheremore extensive. Contacts fairly well definedto gradational. Topography smooth toslightly irregular, slopes mainly gentle.Occur on high-level glacially planed bed-rock surfaces between Little Peters andMeadow Creeks (typical area) and at a fewsmaller localities on interfluve ridges adja-cent to Ship Creek and North Fork Camp-bell Creek Valleys.

mmb Deposits that include mainly bedrock rub-ble—Thickness probably 1 m or little more;in many places may consist only of widelyscattered erratics; bedrock outcrops com-mon. Contacts gradational. Topographyfairly smooth, slopes gentle, somewhatsteeper near contacts. Occur at scattered lo-calities high on mountain ridges near Carol,Ship, and North Fork Campbell Creeks.

omb Older deposits that include mainly bedrockrubble (Pleistocene)—Thickness less than 1m; in many places consist of rubble withwidely scattered erratics; bedrock outcropscommon. Contacts fairly well defined. To-pography smooth, slopes gentle to nearlyflat. Occur high on interfluve ridges nearSouth Fork Eagle River Valley and Snow-hawk Valley, near McHugh Peak, and onsummit of Flattop Mountain. Altitudinallysimilar to deposits on summit of MountSusitna (west side of Cook Inlet Basin).

Kame and kame-terrace depositsKame deposits and kame-terrace deposits are

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both glacioalluvial in origin and closely associ-ated with glacier ice. Kame deposits are formedby running water within a glacier during the ear-ly stages of stagnation when large amounts ofglacier ice were still present. They occur in fieldsof locally prominent landforms that includeirregular hills and areas of sharply hummockyterrain. Kame fields are especially well devel-oped in the margins of the Anchorage Lowlanddown-valley from major mountain valleys,where copious quantities of water drained fromthe valleys into the glacier. Some kames of espe-cially high relief are mapped separately, but thesignificance of differences in relief is not evident.Eskers (similarly formed deposits in long, com-monly sinuous ridges) of substantial size havenot been recognized, but several small esker-likeridges are included in kame deposits. Kame-terrace deposits were formed by running wateroutside the margin of a glacier and occur in long,narrow landforms that have smoothly slopingsurfaces with prominent scarps on their ice-proximal (downslope) sides that developedwhen the adjacent glacier melted.

Kame deposits (late Pleistocene). These arechiefly pebble and cobble gravel and sand, mod-erately to well bedded, in places chaotically; theyare generally well sorted; they include some silt,and, especially in the cores of hills, diamicton;locally, they may include large boulders. They aremoderately loose, but compact in the cores ofsome hills. Contacts are generally well defined,merging with end- and lateral-moraine deposits.Topography is sharply hilly to hummocky, withsome local depressions; slopes are moderate tosteep, except being gentle to nearly flat in minorchannels, on depression floors, and on some hill-tops.

ek Deposits of the Elmendorf Moraine—Ineku landforms of moderate to low relief.

Thickness several to a few tens of meters.Widely distributed within areas of groundmoraine. eku are deposits modified byurbanization.

ekh Deposits that exhibit high relief—In land-ekhu forms of broader shape than most kames,

and locally with steeper side slopes. Thick-ness possibly several tens of meters; local-ly may include larger cores of diamictonthan smaller kames. Associated mainlywith end-moraine deposits. ekhu aredeposits modified by urbanization.

ekg Deposits near Gwenn Lake—In landforms

of fairly high relief. Thickness possibly afew tens of meters. Formed by ancestralEagle River as part of a glacioalluvial trainthat extended from glacial Lake Eagle (inEagle River Valley), through Fossil Creekchannel, and into the Otter-Sixmile chan-nel; in this sector the stream entered themargin of the glacier and deposits wereemplaced beneath it.

ekl Deposits of low relief—Occur in fairlybroad areas with moderately irregular top-ography that lie at intermediate levelsbetween higher-lying kames and channelscut below them; may be pitted outwashdeposits. Thickness perhaps only a fewmeters. Occur mainly southwest, locallynortheast, of Peters Creek Valley in areasof kames and ground moraine. May gradeto some deposits mapped farther south-west as kame-channel deposits.

ekb Deposits that thinly mantle older bedrock—Similar to other kame deposits but may beonly a few meters thick; bedrock may beexposed locally. Occur only near Upperand Lower Fire Lakes.

ekby Deposits that thinly mantle younger bed-rock—Similar to other kame deposits butmay be only 1 m to a few meters thick; bed-rock exposed locally; some apparent bed-rock that includes thin coal beds insteadmay be detached blocks of rock that wereshoved by glacier ice. Occur only near andnorth of Eagle River community.

dk Deposits of Dishno Pond moraines—Indku landforms of moderately high relief. Thick-

ness several to a few tens of meters. Occurprincipally in prominent kame field southof Ship Creek, locally farther northeast.dku are deposits modified by urbanizationor other anthropogenic activity.

dkh Deposits that exhibit high relief—Probablythicker than other kame deposits, andtopography more bold. Occur mainly inkame field south of Ship Creek; singleoccurrence east of Eagle River community.

dkb Deposits that thinly mantle older bed-rock—Thickness may be only a few meters;bedrock may be exposed locally. A fewoccurrences along base of Chugach Moun-tain Front southwest of Eagle River.

fk Deposits of Fort Richardson moraines—fku Thickness probably a few to a few tens of

meters. Occur mainly in a prominent kamefield that dominates the Hillside area

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downslope from lateral moraines and thatextends southwestward along the Chu-gach Mountain Front from north of Ches-ter Creek. fku are deposits modified byurbanization.

fkh Deposits that exhibit high relief—Probablythicker than other kame deposits. Contactsgradational with them. Occur locally withinprominent kame field in Hillside area,mainly south of North Fork CampbellCreek.

rk Deposits of Rabbit Creek moraines—Thickness probably several meters. Occurnear Carol Creek.

Kame-terrace deposits (late Pleistocene). These arechiefly pebble and cobble gravel and sand, mod-erately to well bedded and sorted; locally, theymay include boulders. They are moderatelyloose, with contacts being generally well defined.Topography is smooth, with slopes being gentleexcept in the steep scarp at the edges of the terraces.

ekt Deposits of the Elmendorf Moraine—Thickness may be a few to as much as sev-eral tens of meters. Occur near Little PetersCreek where the valley intersects theChugach Mountain Front.

ektr Roosevelt Road deposits—Younger depos-ektru its that occur in three levels as part of gla-

cioalluvial train formed when ancestralEagle River extended from glacial LakeEagle (in Eagle River Valley), through Fos-sil Creek channel, and into Otter-Sixmilechannel. Equivalent to deposits in someterrace levels in Fossil Creek channel;highest level deposits possibly equivalentto low-level Tuomi Lake deposits. ektru aredeposits modified by urbanization orother anthropogenic activity.

ektt Tuomi Lake deposits—Occur in two lev-els that were part of same glacioalluvialtrain as Roosevelt Road deposits. Occuronly south of Sixmile Lake.

dkt Deposits of Dishno Pond moraines—Thick-dktu ness probably a few to several meters.

Occur in two levels north of Ship Creek.dktu are deposits modified by urban-ization.

fkt Deposits of Fort Richardson moraines—Thickness probably a few to several meters.Occur in Hillside area in a single dissectedterrace near North Fork Campbell Creek.

Other glacioalluvial and related alluvial depositsThese are dominantly gravel and sand, subdi-

vided into 1) kame-channel, 2) meltwater-chan-nel, 3) outwash-train, and 4) alluvial deposits.The first three categories constitute glacioalluvialdeposits that formed in areas outside of glaciersor recently abandoned by them. Alluvial depositsformed farther away from glaciers and after theyhad a direct influence on deposition. Streams inwhich they formed commonly led to deltas westof the map area that were marginal to ancestralCook Inlet. These deposits are listed togetherbecause they follow one another sequentially orgrade from one to another to form nearly a con-tinuum both in space and time. The glacioalluvialdeposits are named from the associated glacialdeposits, whereas the alluvial deposits are namedseparately.

Kame-channel deposits (late Pleistocene). Theseare chiefly pebble and cobble gravel and sand.Locally, they may include some finer materials,and may include pitted outwash or meltwater-channel deposits, or both. Thickness is probablyat least a few meters. Contacts are well defined.Topography is slightly hummocky in broad,channel-like landforms of generally low reliefthat commonly lie at levels intermediate betweenkame and ground-moraine deposits of higherrelief and lower-lying meltwater channels withgently sloping smooth surfaces; slopes are typi-cally gentle but locally are steeper where hum-mocks are well developed.

ekc Deposits of the Elmendorf Moraine—Occur extensively northeast of the EagleRiver Flats. May grade into depositsmapped as ekl farther northeast.

dkc Deposits of Dishno Pond moraines—Occurlocally in kame field southwest of ShipCreek.

fkc Deposits of Fort Richardson moraines—Afew occurrences in the Hillside area nearSouth Fork Campbell Creek.

Meltwater-channel deposits. These are chieflygravel and sand, well bedded and sorted; at thesurface they may include some finer-grainedmaterial with thin organic accumulations. Thick-ness is probably 1 m to a few meters except asnoted. In places, channel deposits may be verythin or absent and ground-moraine deposits orbedrock may lie at shallow depth or floor thechannel. Peat deposits may be present locally,especially in smaller channels. Contacts are well

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defined. Topography is smooth and slopes aregentle.

ec Deposits of the Elmendorf Moraine (latePleistocene)—Occur in narrow channelsalong the Chugach Mountain Front and inbroader channels commonly well incisedbelow the level of ground moraine on theAnchorage Lowland. Generally older thandeposits mapped separately in the follow-ing units, but in northern part of map areaincludes some younger deposits as well.

ecc Clunie Creek glacioalluvial deposits—eccu Thickness may be a few tens of meters,

more commonly about 10 m; probablythinner in narrower channels. Occur main-ly in major channels cut well below, andthus younger than, channel depositsmapped as ec; best developed near LakeClunie and in the valley of Clunie Creek,the typical locality, where deposits occurat three levels. May grade northeast, how-ever, into channel deposits mapped as ec.Formed when the glacier had retreatedsubstantially northeast. eccu are depositsmodified by urbanization.

ecs Sixmile Lake alluvial deposits—Occur inthree levels near Sixmile Lake, the typicallocality. Formed when ancestral EagleRiver last occupied the Otter-Sixmilechannel; may be equivalent in part toyoungest Fossil Creek or oldest ClunieCreek deposits.

ecf Fossil Creek glacioalluvial deposits—Occurecfu in a series of well-formed terrace levels

within the prominent, single channel ofFossil Creek (the typical locality) that is cutas much as 50 m lower than the surface ofthe Elmendorf Moraine as well as the adja-cent Mountain View alluvial fan. Gradedto various levels of Gwenn Lake kame andRoosevelt Road kame-terrace deposits;formed when ancestral Eagle River wasfirst able to cut through the ElmendorfMoraine rather than having to flow moresouthwestwardly around it. ecfu aredeposits modified by urbanization.

dc Deposits of Dishno Pond moraines (latedcu Pleistocene)—Occur in narrow channels

extending along the Chugach MountainFront from the vicinity of Meadow Creekin the northeast and descending south-westward to near Chester Creek on theAnchorage Lowland; occur locally on the

flanks of Eagle River Valley. dcu are depos-its modified by urbanization.

dcm Deposits overridden by glacier ice—Maybe relatively thin or include mainly diamic-ton, or both. Merge laterally with morainedeposits that have been overridden by gla-cier ice (map unit dmo) Occur only east ofEagle River community.

dcl Lower-level deposits—Occur in a fewplaces near Chester Creek and alongGlenn Highway north of Ship Creek; far-ther northeast not differentiated from mapunit dc.

fc Deposits of Fort Richardson moraines (latePleistocene)—Occur in numerous narrowchannels mainly extending from near Car-ol Creek southwestward along ChugachMountain Front into Hillside area; foundlocally in a valley tributary to South ForkCampbell Creek.

fcl Lower-level deposits—Occur mainlybetween Chester Creek and South ForkCampbell Creek at altitudes substantiallylower than those of other channel depos-its; may grade to Klatt Road deposits.

rc Deposits of Rabbit Creek moraines (latePleistocene)—Occur mainly in relativelyshort, narrow channels near the upperboundary of the Hillside area south ofSouth Fork Campbell Creek; found alsoalong the Chugach Mountain Front inwidely scattered localities from CarolCreek to south of Ship Creek.

lc Deposits of Little Rabbit Creek moraines(Pleistocene)—May be somewhat more ox-idized than younger channel deposits.Occur in isolated localities along ChugachMountain Front near Ship Creek Valleyand south of Chester Creek.

sc Deposits of Ski Bowl moraines (Pleisto-cene)—Probably more oxidized thanyounger channel deposits. Occur in sever-al isolated places on mountain interfluveridges.

gc Deposits of Glen Alps moraines (Pleisto-cene)—Probably more oxidized thanyounger channel deposits. Occur at a fewlocalities high on mountain interfluveridges north of Chester Creek Valley andnear North Fork Campbell Creek Valley.

mc Deposits of Mount Magnificent moraines(Pleistocene)—More oxidized than young-er channel deposits. May include muchbedrock rubble. Occur in the typical area

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north of Meadow Creek and on a fewprominent topographic saddles high onmountain interfluve ridges in southernpart of map area.

oc Older deposits (Pleistocene)—Gravel andsand of these deposits may be less wellsorted, thinner, and probably more oxi-dized than other channel deposits; mayinclude much bedrock rubble and smallbedrock outcrops. Tentatively identified ata few places on high ridges near MountGordon Lyon and near benchmark Rusty.

Outwash-train deposits. These are chiefly peb-ble and cobble gravel and sand, well bedded andwell sorted, that accumulated mainly out in frontof the Elmendorf Moraine and downstream fromvalley glaciers in mountain valleys. They are nowfound mainly in terraces and channels. Contactsare well defined. Topography is smooth andslopes are gentle, except where they becomesteep at terrace edges.

eo Deposits related to Elmendorf moraineseou (late Pleistocene)—Thickness several to a

few tens of meters in fan-like remnantsthat extend south from front of the Elmen-dorf Moraine complex and that probablywere once more extensive. Some depositsappear to emerge from within morainecomplex, probably reflecting fluctuationsof the glacier front. Small occurrences inlargest Wolverine and Chester Creek Val-leys likely to be only a few meters thick.eou are deposits modified by urbanizationor other anthropogenic activity.

ch Cheney Lake deposits—Thickness at leastchu 10 m. Occur as remnants in channel now

occupied by Cheney Lake, where principaldeposit largely removed by excavation,and as a few terrace remnants nearby. Pos-sibly an extension of outwash from Elmen-dorf Moraine (map unit eo). chu are depos-its modified by urbanization.

ps Patterson Street deposits—Thickness maypsu be as much as 10 m. Occur in channel rem-

nants that extend discontinuously fromGlenn Highway south of Ship Creek toNorth Fork Campbell Creek. Probablyoutwash from Elmendorf Moraine (dis-continuously traceable to map unit eo). psuare deposits modified by urbanization.

eoy Deposits of the younger phase of theeoyu Elmendorf Moraine—Probably thinner

than main-phase deposits and at lowerlevel. Possibly coeval with Mountain Viewalluvial-fan deposits with which theyappear to merge. Occur only near westedge of map area. eoyu are deposits modi-fied by urbanization or other anthropo-genic activity.

ecb Bluff Road deposits—Thickness probablyonly a few meters, but underlain by Moun-tain View deposits from which they maynot be distinguished readily. Occur as fill-ing of shallow channel that emanated fromyounger phase of the Elmendorf Moraineand that was incised across MountainView alluvial-fan deposits. Underlie partof runways and housing area on Elmen-dorf Air Force Base.

do Deposits related to Dishno Pond moraines(late Pleistocene)—Thickness probably afew meters. Occur in low terraces in ShipCreek and Chester Creek Valleys.

fo Deposits related to Fort Richardson mor-aines (late Pleistocene)—Thickness at leasta few meters in Ship Creek and SnowhawkValleys where they form major terrace andmay grade to (but are no longer in contactwith) glacial lake delta deposits, map unitfgd. Probably thinner in Chester Creek Val-ley and other small valleys to the south.

ro Deposits related to Rabbit Creek moraines(late Pleistocene)—Thickness probably afew to several meters in Ship Creek Valleyadjacent to major end moraines; probablythinner in Wolverine Valleys.

lo Deposits related to Little Rabbit Creekmoraines (Pleistocene)—May be some-what more oxidized than younger out-wash-train deposits. Thickness probably 1m to a few meters. Mapped at two placesin largest Wolverine Valley; in smallerWolverine Valleys included with kame-fandeposits into which they grade, map unitlkf.

Alluvial deposits of Eagle River source (late Pleis-tocene). These are dominantly gravel and sand,well bedded and well sorted, that occur at severallevels but are found mainly in a major channeland a large alluvial fan. They formed when waterof glacial Lake Eagle (in Eagle River Valley),dammed by the Elmendorf glacier, broke out andflowed southwestward around the ice as anancestral Eagle River, truncating outwash depos-its that emanated directly from the glacier. Such a

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breakout process probably occurred repeatedly,resulting in a complex of deposits. Althoughcommonly referred to as “Naptowne outwash,”these deposits are not outwash in the strict sense.Contacts are well defined. Topography is smooth,with slopes being gentle to very gentle.

mvf Mountain View alluvial-fan deposits—mvfu Chiefly cobble gravel near apex of fan;

grade southwestward to finer grainedgravel and sand; mainly sand at distal endwest of map area. Thickness 10 m or more.Occur in broad, low-gradient alluvial fanthat heads at south edge of the broad EagleRiver Valley where it emerges from theChugach Mountains and that extendssouthwestward to downtown Anchorage.Named from community of MountainView at west edge of map area. Complexnature of fan indicated by presence of sev-eral levels near head of fan separated bysmall scarps, although these levels havenot been correlated directly with twohigher-level remnants mapped fartherdown the fan, mainly south of Ship Creek.In that vicinity the fan has been dissectedby ancestral Ship Creek and subsequentdeposition has partly filled some of theresulting channels. mvfu are deposits mod-ified by urbanization or other anthropo-genic activity.

mvi Deposits at intermediate level—Occur in aremnant slightly higher than main part offan; extend southwestward from south ofShip Creek to south of Glenn Highway.

mvh Deposits at highest level—Occur in rem-mvhu nants substantially higher than main fan;

extend discontinuously from north of ShipCreek to Middle Fork Chester Creek. mvhuare deposits modified by urbanization.

nc Nunaka Valley channel deposits—Thick-ncu ness at least 10 m. Occupy major channel

that lies at higher altitude than, and to thesoutheast of, Mountain View fan. Extendfrom Ship Creek to South Fork ChesterCreek. Probably represent earlier episodeof drainage from glacial Lake Eagle; alter-natively, could be derived largely fromShip Creek. ncu are deposits modified byurbanization.

ncc Checkmate boulder-rich deposits—Occurnccu in smaller channel that branches off major

channel and lies southeast of it and that isnow occupied by underfit South Fork

Chester Creek. Erosion in this channel wasless deep than in major channel and wasnot followed by significant deposition ofgravel and sand. Instead, deposits arefiner-grained or more poorly sorted andnumerous boulders are present on groundsurface. May represent lag concentratefrom erosion of earlier glacioestuarine ormoraine deposits, or both, or may haveformed as debris flow developed duringrapid erosion of those deposits. Peat depos-its may have accumulated at surface inplaces, but most of these have beenremoved during urbanization. nccu aredeposits further modified by urbaniza-tion.

Alluvial deposits of local mountain-valley source.These are chiefly gravel and sand, well beddedand well sorted. Contacts are well defined exceptas noted. They occur mainly in large alluvial fans,in terrace remnants at higher levels, and in chan-nels that are cut below the level of fans or extendfrom them. They formed both before and after theincursion of the Eagle River; some high-leveldeposits probably correlate with outwash fromElmendorf glacier.

The Ship Creek deposits are subdivided intodeposits at six levels: three cut below level ofMountain View fan in two different channels, oneat about fan level, and two at levels higher thanthat of the Mountain View fan farther up ShipCreek near the Chugach Mountain Front. Thick-ness is probably several to 10 m.

scl Lower-level deposits (Holocene)—Extendsclu along present course of Ship Creek from

Chugach Mountain Front nearly to itsmouth, mainly in extensive low terracethat gradually becomes higher to the west.sclu are deposits modified by urbaniza-tion.

scc Chester Creek deposits (early Holocene?sccu and late Pleistocene)—Occur in channel

developed by ancestral Ship Creek when itflowed southwestward from its presentnorthernmost reach and formed channelnow occupied by lower course of ChesterCreek. sccu are deposits modified by ur-banization.

sch Chester Creek deposits at higher levelschu (late Pleistocene)—Occur mainly in broadschp channel cut slightly below level of Moun-schpu tain View fan when ancestral Ship Creek

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first flowed southwestward through valleynow occupied by lower course of ChesterCreek; there, deposits now found in terraceremnants. schu are deposits modified byurbanization. schp are deposits overlain bypeat about 1 m thick of mainly Holoceneage; schpu are areas that have been drainedand most peat removed during urbaniza-tion.

scf Alluvial-fan deposits (late Pleistocene)—scfu Thickness may be more than 10 m. Occur in

prominent fan that extends along ShipCreek from Chugach Mountain Front toGlenn Highway. Fan appears graded tovarious levels of Nunaka Valley and Moun-tain View deposits. scfu are deposits exca-vated in conjunction with regional urban-ization.

sct Terrace deposits (late Pleistocene)—Occursctu near head of Ship Creek alluvial fan in rem-

nants of small, higher-level alluvial fan, orof fan-delta graded to level of glacioestua-rine water in which Muldoon Road depos-its accumulated. sctu are deposits excavat-ed in conjunction with regional urbaniza-tion.

scth Highest-level deposits (late Pleistocene)—Occur near head of Ship Creek alluvial fanin remnants of probable fan-delta graded tolevel of glacioestuarine water in whichAbbott Road deposits accumulated.

Deposits of North Fork Campbell Creek (late Pleis-tocene). These are subdivided into deposits at threelevels. Thickness is probably a few meters, exceptas noted.

nfl Lower-level deposits—Occur in channelson both sides of main alluvial fan of NorthFork Campbell Creek that were not neces-sarily occupied contemporaneously.

nf Main alluvial-fan deposits—Thicknessprobably several to 10 m. Occur in promi-nent fans along North Fork Campbell andChester Creeks where they have descendedfrom Hillside area; mapped also in low ter-race remnants farther up North ForkCampbell Creek Valley.

nfh Higher-level deposits—Occur mainly innfhf higher part of alluvial fan of Chester Creek;

also in single high-terrace remnant alongNorth Fork Campbell Creek. nfhf are proba-bly sand and silt with peat at surface; occurin single channel north of Chester Creek.

Deposits of South Fork Campbell Creek. These aresubdivided into deposits at five levels. Thicknessis probably several meters, except as noted.

sfs Southern lower-level deposits (Holocene?sfsu and late Pleistocene)—Occur in channel

that carried South Fork water at one ormore times after deposition of main fan.Channel now contains underfit NorthFork Little Campbell Creek, developedfrom underflow of South Fork CampbellCreek, which currently flows only about 1m below the level of this channel. There isdanger that at times of high water it couldreoccupy this channel, perhaps on a long-term basis, and thereby flood at least somepart of the channel area. sfsu are depositsmodified by urbanization.

sfn Northern lower-level deposits (late Pleis-sfnu tocene)—Occupy channel and smaller

alluvial fan that could have carried someSouth Fork and probably all North ForkCampbell Creek waters northward into acombined ancestral Ship Creek and EagleRiver. sfnu are deposits modified byurbanization.

sf Deposits of main alluvial fan (late Pleis-tocene)—Thickness probably 10 m or more.Occupy prominent alluvial fan lying mainlyon south side of South Fork; extend up-valley from apex of fan as low-level terracedeposits.

sft Terrace deposits (late Pleistocene)—Occuronly in scattered terrace remnants at inter-mediate levels in upper South Fork Valley.

sfth Highest-level deposits (late Pleistocene)—Occur only in scattered terrace remnantsat high levels in upper South Fork Valley.

Alluvial deposits of the lower Hillside area (latePleistocene). These are the deposits of two princi-pal southwest-trending channel and terrace sys-tems that lead to deltas (west of the map area)that formed marginal to ancestral Cook Inlet.Thickness is probably a few to several meters.Contacts are well defined. Topography is smooth,with slopes being gentle to very gentle.

sh Spring Hill deposits—Occupy channel sys-shu tem that extends from near apex of main

alluvial fan of South Fork Campbell Creekand that splits into a more deeply incisedchannel to the southwest and a shallower

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channel to the northwest. Also occur invalley of South Fork Campbell Creek inintermediate-level terrace; remnants higherthan deposits of main alluvial fan and low-er than deposits of main terrace. shu aredeposits modified by urbanization.

The Klatt Road deposits are subdivided intodeposits at the following three levels.

kcl Lower-level deposits—Occur mainly inkclu terraces at levels higher than Spring Hill

deposits and in channels graded thereto;mapped also in a channel that probablycarried water from North Fork CampbellCreek toward the southwest. kclu aredeposits modified by urbanization.

kc Main-level deposits—Occupy major chan-nel system extending southwestwardfrom South Fork Campbell Creek.

kch Higher-level deposits—Occur in terracekchu remnants at levels higher than the main

channel and in shallow channels graded tothose levels. kchu are deposits modified byurbanization.

Glaciolacustrine, lacustrine, and related depositsThese deposits are subdivided into five types

that accumulated in bodies of water ranging fromlarge lakes to small ponds. Some were closelyassociated with glaciers, whereas others formedafter retreat of the glaciers: 1) Kame-fan depositsare transitional in origin between glacioalluvialand glaciolacustrine deposits. Like kame-terracedeposits, they were deposited along the margin ofa glacier, but their (commonly) small source val-leys were generally perpendicular to and blockedby the glacier. In part the blockage may have re-sulted in small ice-dammed lakes, but many de-posits seem to have more the character of deltasor alluvial fans. This implies that lakes, if any,were short-lived, and that drainage probably wasable to enter the glacier and form the extensivekame fields associated with lateral moraines. 2)Glaciolacustrine deposits accumulated whenmore permanent lakes did form in commonlylarge valleys blocked by the glacier. The principallakes thus formed in this map area, their namesderived from the valleys in which they werelocated, are glacial Lake Eagle (Schmoll et al., inpress) and glacial Lake Ship, named here. 3) Del-taic deposits formed locally where streamsentered such lakes. 4) Some deposits formed inlakes when glaciers were no longer present in

major valleys but where moraines or landslidesblocked the valley. 5) Ponds formed in many un-drained depressions on the uneven surface ofmoraines or areas formerly occupied by glacio-estuarine water. As the ponds filled, mainly withorganic material, they became bogs that no longercontained open water and are now sites of thickpeat accumulation.

Kame-fan deposits. These are chiefly gravel andsand, well to poorly bedded and sorted, and mayinclude beds of fine sand, silt, clay, and diamicton.Thickness is probably several to a few tens ofmeters. Contacts are fairly well defined, exceptwhere they are commonly gradational with collu-vium. Topography is generally smooth, withslopes being moderately gentle to moderate, andlocally steep at ice-proximal margins.

ekf Deposits related to the Elmendorf Moraine(late Pleistocene)—Occur at a few localitiesalong the Chugach Mountain Front nearCarol Creek.

dkf Deposits related to Dishno Pond morainesdkfu (late Pleistocene)—Occur commonly at two

levels along Chugach Mountain Front nearShip Creek and north of Eagle River Valley,and locally along south side of that valleynear mouth of South Fork Valley. dkfu aredeposits modified by urbanization.

fkf Deposits related to Fort Richardsonmoraines (late Pleistocene)—Occur nearmouths of all but the largest mountain val-leys along Chugach Mountain Front fromLittle Peters Creek southwestward to SouthFork Campbell Creek, and at a few placesalong the sides of valleys of Little PetersCreek, Eagle River, and its South Fork.

rkf Deposits related to Rabbit Creek moraines(late Pleistocene)—Occur locally in valleysof Eagle River and South Fork CampbellCreek.

lkf Deposits related to Little Rabbit Creek mor-aines (Pleistocene)—May be somewhatmore oxidized than younger deposits.Occur prominently in Ship Creek andSnowhawk Valleys, and in the two morenortherly Wolverine Valleys where theyextend up-valley to include outwash depos-its; also found locally in Chester Creek Valley.

skf Deposits related to Ski Bowl moraines(Pleistocene)—Probably more oxidizedthan younger deposits. Occur prominentlyin Ship Creek and nearby Snowhawk Val-leys (the typical area) and locally near

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Mount Gordon Lyon and in northernmostWolverine Valley.

gkf Deposits related to Glen Alps moraines(Pleistocene)—More oxidized than young-er deposits. Single occurrence in northern-most Wolverine Valley.

Glacial-lake delta deposits (late Pleistocene). Theseare chiefly gravel and sand, generally well bed-ded and sorted; they may include thin beds of, orbe underlain by, finer-grained glaciolacustrinedeposits. Thickness is probably 10 m or less. Con-tacts are generally well defined, but gradationalto glacioalluvial deposits up-valley. Topographyis generally smooth, with slopes being gentle, ex-cept for moderate to steep slopes at small scarpson the down-valley sides.

egd Deposits related to the Elmendorf mo-raine—Occur in Eagle River Valley inprominent landform at mouth of SouthFork and farther downstream on bothsides of Eagle River.

dgd Deposits related to Dishno Pondmoraines—Occur in valley of South ForkEagle River and near mouth of SnowhawkValley.

fgd Deposits related to Fort Richardson mo-raines—Occur as part of major terrace inShip Creek Valley and where tributariesentered glacial Lake Ship.

rgd Deposits related to Rabbit Creek mo-raines—Occur along the sides of ShipCreek Valley where tributaries enteredglacial Lake Ship.

Glaciolacustrine deposits. These are interbeddedclay, silt, and sand; they may include some graveland diamicton in varying proportions; they arewell to somewhat poorly sorted. Contacts are rel-atively well defined. Topography is generallysmooth, and slopes gentle, except for being verysteep at valleyward margins. These deposits aremoderately stable except near the contact withvalley-wall colluvium, where they are susceptibleto stream erosion, earthflowage, or other land-slide processes.

egl Deposits related to the Elmendorf Moraine(late Pleistocene)—Mainly deposits of gla-cial Lake Eagle. Thickness 5 to 10 m; maybe much thicker beneath alluvial and peatdeposits that form the floor of the innerEagle River Valley, but mapped only mar-ginal thereto.

dgl Deposits related to Dishno Pond moraines(late Pleistocene)—Thickness probablyabout 10 m. Occur 1) in valley of South ForkEagle River (laid down in an arm of glacialLake Eagle) and 2) along south side of ShipCreek Valley near Chugach Mountain Front(laid down in a low level of glacial LakeShip).

fgl Deposits related to Fort Richardsonmoraines (late Pleistocene)—Thickness 10m or more. Best developed and probablythickest in valley of Ship Creek where laiddown in intermediate levels of glacial LakeShip; distinguished from Rabbit Creekdeposits only on altitudinal basis. Occuralso in valleys of Meadow and North ForkCampbell Creeks near Chugach MountainFront.

rgl Deposits related to Rabbit Creek moraines(late Pleistocene)—Thickness 10 m or morein Ship Creek Valley where laid down inhigh levels of glacial Lake Ship; distin-guished from Fort Richardson depositsonly on altitudinal basis. Probably less than10 m thick in valley of Meadow Creek.

sgl Deposits related to Ski Bowl moraines(Pleistocene)—May be more oxidized thanyounger deposits. Thickness probably afew to several meters. Occur only in high-level tundra flat north of Ship Creek neararea of typical Ski Bowl deposits.

Lacustrine and related deltaic deposits. The con-tacts of these are generally well defined. The sur-face is smooth to slightly irregular; general slope isless than 1%.

lyd Young deltaic deposits in Eagle River Valley(Holocene and late Pleistocene)—Chieflygravel and sand; may include some beds ofsilt. Thickness may be as much as 10 m.Occur only in Eagle River Valley nearmouth of South Fork.

ly Young lacustrine deposits in Eagle RiverValley (Holocene and late Pleistocene)—Chiefly interbedded silt and clay, blue-gray; include some beds of fine sand andfine tephra. Thickness probably 10 m orless, base of unit not exposed. Occur only atlow levels of inner Eagle River Valley, laiddown in a late stage of glacial Lake Eagle orin a subsequent lake blocked by moraine orlandslide deposits; may underlie alluviumon valley floor.

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pf Deposits in Fire Creek Valley (Holocene)—Deposits not exposed; genesis and charac-ter mainly inferential. Probably silt, clay,and fine sand; may include thin tephrabeds and peat near surface. Deposits alter-natively could be either 1) estuarine, formedin a narrow inlet of Knik Arm, or 2) mainlyfine-grained alluvium of Fire Creek. Thick-ness probably several to a few tens ofmeters. Contacts gradational to fine-grainedalluvium of present Fire Creek. Poorlydrained.

p Pond and bog deposits (Holocene andpu late Pleistocene)—Chiefly peat (mosses,ppfu sedges, and other organic material in vari-

ous stages of decomposition); include silt,organic-rich silt, minor woody horizons,and a few thin interbeds of mainly ash-sized tephra. At depth also may includeclay, marl, or fine to medium sand. Accu-mulated mainly in former small lakes or informer stream channels that are now bogs.Soft and moist. Thickness commonly asmuch as 4 m, locally as much as 10 m; adja-cent mapped deposits extend beneaththese deposits. Contacts well defined, butdeposits may grade laterally to the similarbut much thinner mantle that overliesadjacent deposits. Surface smooth; slopesless than 1%. Poorly drained. Widespreadoccurrences within Elmendorf Moraineand on the floor of Eagle River Valley;common locally in areas of lateral mo-raines and associated channels. Scatteredoccurrences elsewhere in Anchorage Low-land; most peat there, however, probablydid not begin accumulating in ponds, and ismapped with underlying alluvial depositsin map units schp, evp, and wsp. pu is peatpartially or totally removed during urban-ization; ppfu is an area that probably con-tained permafrost.

Glaciolacustrine or glacioestuarine deposits(late Pleistocene)

These deposits accumulated either 1) in lakesmarginal to glacier ice or in narrow valleys mar-ginal to former glaciers when the valleys wereblocked by moraine remnants or alluvial fans ofmountain-origin streams, 2) in the margins ofglacioestuarine waters as they rose, followingwithdrawal of glacier ice, or 3) in a high-level,basin-wide glacial lake of the type envisioned byKarlstrom (1964).

ev Early View deposits—Dominantly silt andevpf silty clay, locally may include fine sand.evu Thickness probably a few to several

meters. If glacioestuarine, equivalent topart of Bootlegger Cove Formation. Con-tacts generally well defined. Topographysmooth, slopes nearly flat. Occur in broad,channel-like area now occupied by anorth-flowing reach of South Fork ChesterCreek, commonly downslope from adja-cent Muldoon Road deposits. evpf is anarea containing permafrost; evu are depos-its modified by urbanization.

evp Deposits with peat at surface—Peat about 1m thick in a few central areas that are appar-ently less well drained than surroundingareas.

evc Coarse-grained deposits—Probably con-evcu tain higher proportion of sand (and per-

haps some gravel) than remainder of de-posits to which they are mainly marginal.Also mapped south of North Fork LittleCampbell Creek where finer-graineddeposits are lacking and identity is basedmainly on geomorphic relationship toadjacent, higher-lying Muldoon Roaddeposits; here, less likely to be of lacus-trine origin. evcu are deposits modified byurbanization.

br Birch Road deposits—Fine sand and silt,finely bedded and well sorted, especiallywhere typically developed south of maparea; here may be coarser-grained or morepoorly sorted, or both, and may includesand, gravel, and diamicton, especiallynear map unit fk. Topography fairlysmooth to slightly hummocky, slopes gen-tle. Occur principally in narrow belt thatwidens southwestward from South ForkChester Creek and that lies between about140 and 200 m in altitude. Possibly depos-ited in a local glacier-dammed lake or in abasin-wide glacial lake.

Glacioestuarine deposits or moraine andkame deposits modified in a glacioestuarineenvironment (late Pleistocene)

These occur in relatively prominent hills inAnchorage Lowland south of Elmendorf Mo-raine. Formed either as ground moraine and as-sociated kames and subsequently modified bywave and tide action in a glacioestuarine envi-ronment, or by redeposition of glacial deposits

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that formed near the glacier-glacioestuaryboundary and that slumped subaqueously. Mostlikely some combination of these processes wasinvolved in producing the deposits, but the rela-tive importance of each is uncertain and mighthave varied both within the same deposit andamong the deposits included here.rj Russian Jack deposits—Mainly diamicton;rju especially at depth may be ground mor-

aine equivalent to Dishno Pond, Fort Rich-ardson, or older lateral moraines; nearersurface includes some interbedded silt,fine sand, and sand and gravel both inwell defined beds and as obscurely bed-ded, discontinuous horizons. Thickness asmuch as 25 m. Contacts fairly well definedbut may be gradational with MuldoonRoad deposits in many places. Occur inwell-defined hills of smooth topographywith gently to moderately gently slopingtops and moderately to steeply slopingsides. Although some hills appear drum-linoid in form, others owe their presentconfiguration to erosion that producedadjacent channels. Widespread betweenShip Creek and North Fork Little Camp-bell Creek. rju are deposits modified byurbanization.

Modified kame deposits. These are mainly graveland sand, well to moderately poorly bedded andsorted; they include some interbedded fine sandand silt. Diamicton may be dominant in the coresof hills and also may occur at the surface of thehills. Contacts are well defined. Topography iscommonly sharply hilly, with slopes being gener-ally moderate to steep.

dkm Deposits related to Dishno Pond mo-raines—Occur near South Fork ChesterCreek at southwestern end of DishnoPond kame field where it was encroachedupon by glacioestuarine water; hills moresubdued than those in unmodified part ofkame field.

fkm Deposits related to Fort Richardson mo-raines—Extend discontinuously from SouthFork Chester Creek to south of South ForkCampbell Creek where lowest-lying hillsof Fort Richardson kame field are moresubdued than but identifiable separatelyfrom hills composed of glacioestuarinedeposits.

bp Boniface Parkway deposits—Extend dis-bpu continuously from south of Ship Creek to

South Fork Campbell Creek. Associatedwith Russian Jack deposits and may repre-sent more gravelly phase of those depositsor perhaps are remnants of a once continu-ous esker system originally part of DishnoPond moraine complex. Occur also nearNorth Fork Campbell Creek in small hillsthat may be modified kames and thus sim-ilar to deposits mapped as fkm. bpu are de-posits modified by urbanization.

or O’Malley Road deposits—Mainly in iso-lated hills that could represent either moregravelly phase of glacioestuarine depositsor partly buried kames that were initiallypart of Fort Richardson or Rabbit Creekmoraine complexes. Occur only near andsouth of North Fork Little CampbellCreek.

Estuarine and glacioestuarine depositsThese are estuarine deposits formed in

present-day Cook Inlet and its major arms, KnikArm and Turnagain Arm, or in similar bodies ofwater of the recent past with similar configura-tion and tide characteristics. Glacioestuarine de-posits accumulated in an ancestral Cook Inletthat probably differed from the present-day inletin configuration, in level with respect to thepresent land surface, and in its association withglacier ice. Over time, however, the ancestral inletevolved to that of the present day with generallygradual changes in level and configuration.

Modern estuarine deposits (latest Holocene).These are deposits that are at least partly still inthe transport mode in that they are or have beenuntil very recently reworked by the modern estu-ary. They have been mapped around the marginsof Knik Arm. Intertidal deposits are chiefly siltand fine sand; they are somewhat coarser nearlevees of major tide channels. They are well bed-ded and sorted, being loose and water saturated.Thickness is less than 1 m to a few meters, proba-bly underlain by several meters of older intertidaldeposits. Contacts may vary in location with eachtide as well as from season to season and year toyear. The surface is generally smooth, but incised1 m to a few meters by numerous channels thatmay have steep margins. Slopes are otherwisenearly flat to gentle, commonly less than 1%.These deposits are best developed where adja-cent land is not bounded by bluffs.

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il Deposits of the lower intertidal zone—Insome places include driftwood and gravelin a shoreward-most part of deposit wherethey form discontinuous storm beach.Reworked twice daily when covered by wa-ter at high tides; exposed a low tides.Deposits extend into area mapped as waterwhere they are exposed at low tides. Upperboundary may be a few meters above meanhigh water.

iu Deposits of the upper intertidal zone—Locally more sandy and gravelly thanlower-zone deposits, especially in upper-most parts of zone, which are covered bywater only at times of exceptionally hightides coupled with major storms. Containsome driftwood and fine gravel as well asfiner organic and windblown material. Sur-face marked by standing water in some ar-eas where drainage is very poor.

ib Beach deposits—Chiefly sand with somegravel, well bedded and sorted; locallydriftwood laden near base of bluffs. Encom-pass the lower and upper intertidal zonesalong base of bluffs in northern part of maparea; elsewhere not shown separately frommap unit s but shown on Figure A3. Nearshoreward end of Eagle River Flats, formbelt between upper and lower intertidalzones.

Older estuarine deposits (Holocene). These areonly rarely flooded by present day high tides.They are more firm than modern estuarine depos-its. Contacts are well defined, except indefinite inthe part adjacent to younger deposits. Topographyis smooth, locally incised by channels of smallstreams; slopes are nearly flat.

io Intertidal deposits—Chiefly silt, fine sandysilt, and fine sand, well bedded and sorted;may include some thin beds of peat, drift-wood, and other organic material, andwindblown material. Thickness commonlyseveral meters to possibly a few tens ofmeters. Occur extensively in Eagle RiverFlats and locally near mouth of Fire Creek.

ibo Beach deposits—Chiefly sand with somegravel. Thickness probably a few meters.Occur locally marginal to south side ofEagle River Flats.

Glacioestuarine deposits (late Pleistocene). Theseaccumulated in a variety of environments inancestral Cook Inlet. Several different water levels

are inferred from deposits at recognizably differ-ent, somewhat terrace-like levels; however, noshorelines have been recognized definitively. Theland/water interface probably fluctuated repeat-edly as glacier fronts withdrew and then read-vanced and as world-wide sea level fluctuated,and also as the land surface responded to regionalglacioisostatic and tectonic effects. Inlet waterwas at least partly in contact with glacier ice, asreflected in both the volume and the variety ofmaterial types, especially in their relative coarse-ness and poor sorting. These deposits consist ofvarying combinations of interbedded diamicton,stony silt, fine sand, silt, clayey silt, and silty clay,with coarser sand and gravel present locally.Contacts are generally well defined; contactsbetween adjacent glacioestuarine deposits arelocated only approximately, but deposits areprobably not in gradational contact. Topographyis commonly smooth but marked locally by smallsubdued hills or minor surface irregularities;slopes are very gentle to moderate

bc Bootlegger Cove Formation—(Bootleggerbcu Cove Clay of Miller and Dobrovolny

[1959]; redesignated as Formation inUpdike et al. [1982]). Silty clay and clayeysilt with minor interbedded silt, fine sand,fine to medium sand, and thin beds ofdiamicton, and with scattered pebbles andcobbles in widely varying concentrations.Brackish-marine microfossils are presentthroughout much of the formation(Schmidt 1963, Smith 1964); mollusk shellsin one horizon have an uncalibrated radio-carbon age of about 14,000 years (Schmollet al. 1972). Thickness as much as 35 m(Updike et al. 1988), quite variable becauseof irregular lower and upper contacts(Trainer and Waller 1965). Principaldeposit of ancestral Cook Inlet during andimmediately following withdrawal of gla-cier ice. Occurs widely in subsurfaceunderlying deposits mapped at the sur-face from north of the Elmendorf Morainesouth to bluffs near Turnagain Arm. Sensi-tive zones within formation responsiblefor catastrophic landsliding along bluffswest of map area during large-magnitudeearthquakes such as that of 1964 (Hansen1965). Present knowledge of distributionand age of formation well summarized byReger et al. (1995). Shown mainly withinmap unit s (Fig. 4). bcu is a concealedoccurrence at Glenn Highway–Boniface

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Parkway interchange that was exposedalong Glenn Highway during construc-tion.

ws Winchester Street deposits—Chiefly medi-wsu um to fine sand with some interbedded

silt. Thickness probably a few to severalmeters. May represent marginal facies ofestuary that had less contact with glacierice than older and higher-level estuariesrepresented by Muldoon Road and AbbottRoad deposits. Occur mainly betweenChester Creek and North Fork LittleCampbell Creek near west edge of maparea. wsu are deposits modified by urban-ization.

wsc Coarse-grained deposits—Dominantlywscu sand and gravel. A few terrace-like occur-

rences mainly adjacent to hills of MuldoonRoad and Russian Jack deposits. wscu aredeposits modified by urbanization.

wsp Deposits with peat at surface—Maywspu include finer-grained material than else-

where within these deposits. Peat com-monly more than 1 m thick. BootleggerCove Formation may be present at shallowdepth. wspu is peat removed duringurbanization; permafrost subsequentlyreported.

mr Muldoon Road deposits—Chiefly fine sandmru and silt; locally include interbedded diam-

icton or may consist mainly of crudelybedded fine-sandy diamicton. Thicknessprobably several meters. Interpreted as re-working of ground moraine as inlet waterencroached upon areas abandoned by gla-cier ice. Widespread between Ship Creekand South Fork Little Campbell Creek,commonly lower than about 110 m in alti-tude in lower terrain surrounding hills ofRussian Jack deposits into which they maygrade or onto which they may lap. mru aredeposits modified by urbanization.

ar Abbott Road deposits—Chiefly diamicton,aru crudely bedded to massive, with some

interbedded silt and fine sand; coarsersand and gravel may be present locally. Inbelt about 1 to 2 km wide along AbbottRoad, contain high proportion of rubble innear-surface exposures, possibly the resultof a landslide emplaced either on glacierice or directly in estuarine water shortlyafter ice withdrew. Thickness several toabout 10 m. Alternately may representground moraine only somewhat modified

by encroaching estuarine water as icemelted and ice front receded. Extend in arelatively narrow belt from North ForkCampbell Creek to south edge of map areaat an altitude between about 110 and 140m, just downslope from Birch Road depos-its. aru are deposits modified by urbaniza-tion.

Alluvial depositsThese are subdivided into deposits formed by

streams 1) along their normal courses and foundat or near stream level, as well as in terraces wellabove stream level, and 2) in alluvial fans at oneor more levels.

Alluvium along streams. These deposits arechiefly gravel and sand formed in present-daystreams, ancestral streams, and some olderstreams no longer present that lack any directassociation with glaciers; they include some fine-grained deposits. Generally, they are well beddedand sorted, with clasts commonly rounded towell rounded. Thickness is variable, probably afew to several meters; it may be 10 m or more inlarge valleys and in large alluvial fans. Contactsare well defined. Topography is smooth, withslopes being nearly flat to very gentle, andsteeper on alluvial-fan deposits. Steep scarps 1 mto several meters high separate deposits at differ-ent levels between adjacent map units and locallywithin map units.

aa Alluvium in active floodplains (latestHolocene)—Gravel and sand transportedintermittently and deposited temporarilyin bars that commonly change their posi-tion along braided and single channels.Vegetation cover generally absent or justbeginning to develop in areas that havenot been affected directly by the stream fora few years. Area subject to continuingerosion and flooding; in places streammay encroach upon areas adjacent to areaof map unit. Mapped mainly along EagleRiver and locally along Ship Creek.

al Alluvial deposits along modern streamsalu and in lowest terraces (Holocene)—Chiefly

gravel and sand except in the Eagle RiverValley up-valley from South Fork conflu-ence where sand is more common andoverlies lacustrine silt and clay at depthsof about 7 m. Generally less than a fewmeters above stream level. Include somematerial of active floodplains still partly intransport mode in areas too small to map

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separately. Mapped mainly along majorstreams; occur also along small streams inareas too narrow to map separately. alu aredeposits modified by urbanization.

alf Fine-grained deposits along some minoralfu streams—Chiefly silt and fine sand; may

include some peat deposits near surface.Occur mainly along parts of Mink and FireCreeks and the Otter-Sixmile channel, andlocally where small low-gradient streamscross low-lying areas. alfu are depositsmodified by urbanization.

at Older alluvial deposits in terraces (Holo-cene)—Chiefly gravel and sand, commonlyseveral meters above stream level. Occurlocally along Clunie Creek and Eagle River.

ath Deposits in higher terraces (Holocene andlate Pleistocene)—Still older alluviumoccurring in local remnants about 10 mabove Meadow Creek and at least 5 mabove the lower reaches of Eagle River.

alo Older alluvial deposits in channels (Holo-cene and late Pleistocene)—Chiefly graveland sand in channels abandoned bystream that formed them and that are nowoccupied, if at all, by underfit streams.Thickness probably only 1 m to a fewmeters. Mapped only in a few places alongtributaries to Ship Creek and in the Hill-side area between North and South Forksof Campbell Creek.

Alluvial-fan deposits. These formed near themouths of large streams and where small tribu-tary streams enter larger streams that have lowergradients. They are graded to or just above mod-ern stream levels. Slopes are moderately gentle tomoderate, steeper near the heads of fans.

af Coarse-grained deposits (Holocene)—afu Chiefly gravel and sand; dominantly gravel

in large fan near mouth of Peters Creekand possibly in large fan near mouth ofClunie Creek and where Eagle River entersEagle River Flats; in moderate to small fanscommon in many valleys may be some-what less well sorted than other alluvium,and locally include silt and diamicton bedsresulting from minor mudflows. afu aredeposits modified by urbanization.

aff Fine-grained deposits (Holocene)—Chieflyfine sand and silt; locally may includecoarser sand and some gravel. Occur mar-ginal to intertidal deposits, in and adjacent

to low-lying, nearly flat channels, and in afew other localities where minor streamscross areas of substantially lower slopethan areas just upstream.

afo Older alluvial-fan deposits, undividedafou (Holocene and late Pleistocene)—Gravel

and sand, possibly admixed with somefiner-grained material and thin diamictonbeds. Deposits typically less well sortedand more steeply sloping than those inother alluvial units. Occur commonly asremnants associated with younger alluvialfans, but graded to levels well above mod-ern streams. Near mouth of Clunie Creekrepresent slightly older part of main fan.Common on lower parts of mountain-valley walls and present at a few placesalong Chugach Mountain Front. afou aredeposits modified by urbanization.

afp Deposits along Peters Creek—Chieflyafpu gravel with some sand. May be fan delta

graded to a level above present sea level,and possibly latest Pleistocene in age; alter-natively, might have extended substan-tially farther northwest into Knik Arm,and be graded to near present sea level buteroded to present distribution. Slopes veryto moderately gentle, gradually increasingto steep near head of fan. Much materialremoved as major source of gravel andsand, especially near toe of fan. afpu aredeposits modified by urbanization.

Colluvial depositsThe term colluvial deposits (colluvium), as used

here, includes those deposits that occur on slopesand that have accumulated primarily through theaction of gravity and, secondarily, through theaction of running water. Colluvium is broadlysubdivided into 1) deposits that have accumulat-ed particle by particle over a long period of time,and 2) those deposits that have moved en masse.Among those in category 1 are deposits on moun-tain slopes, deposits derived mainly from mor-aines, and deposits on bluffs along streams andalong Knik Arm. Those in category 2 include bothslow-moving solifluction deposits as well as avariety of landslide deposits, most of which havebeen emplaced rapidly. Most colluvial depositsare relatively poorly sorted and many are notwell compacted; because of their location onslopes, they are subject to instability especiallywhen excavated.

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c Colluvial deposits on mountain slopes(Holocene and Pleistocene)—Mainly apron-like deposits of loose, sandy to rubblydiamicton derived directly from weather-ing of bedrock upslope; include some sheet-wash deposits. Thickness probably lessthan 1 m to several meters, thicker on lowerparts of slopes. Contacts gradational. Top-ography smooth, surface gently concave,slopes generally steep to very steep, butusually not in excess of 70%. Commonlyveneered by thin, low vegetation. Someinstability likely. Occur on mountain slopesin a belt downslope from mapped bedrock.

ct Talus deposits (Holocene)—Cone-shaped toapronlike deposits on valley walls withinrugged mountains. Mainly loose, coarserubble, and rubbly diamicton deriveddirectly from weathering of bedrock up-slope. Thickness variable, generally thick-est in middle to lower parts of cones andaprons, probably several to a few tens ofmeters, thinning gradually upward towardsapexes and more abruptly downward neartoes. Contacts generally gradational, to bed-rock at apex and to other mapped units attoe; individual cones commonly have well-defined boundaries, however. Talus depos-its too small to map separately are includedin bedrock map unit. Topography smooth,slopes steep to very steep, as much as 100%near apex, rarely less than 35% near toe.Commonly free of even low vegetation andsubject to continuing deposition from ups-lope, including rockfalls and debris-ladensnow avalanches; slopes generally unsta-ble. Occur locally on highest and in associa-tion with steepest mountain slopes.

ca Colluvial and alluvial deposits (Holo-cene)—Areas of colluvium and alluviumtoo small to map separately. Chiefly moder-ately loose, sandy to rubbly diamicton,poorly sorted sand and gravel, and someorganic debris. Thickness probably a fewmeters. Contacts generally gradational.Topography irregularly gullied, slopessteep to very steep, generally rangingbetween 35 and 70%. Commonly coveredby at least low vegetation, but vegetationmay be lacking in some gullies where activedeposition is occurring. Some instability ofslopes likely. Occur in small valleys andgullies in mountains, especially near headsof small valleys.

cg Mixed colluvial and glacial deposits (Holo-cene and Pleistocene)—Diamicton; mayinclude chiefly gravelly to rubbly sand,with some silt and clay; locally bouldery.Derived from both bedrock and glacialdeposits, either of which may be present inareas too small to map separately. Poorlybedded and sorted. Loosely to moderatelycompacted in most places. Thickness a fewto several meters. Contacts gradational.Slopes smooth to slightly irregular, steepto very steep. Common along middleslopes of most major mountain valleysand along Chugach Mountain Front whereglaciers formerly abutted the slope butfew identifiable glacial deposits arepresent at the surface.

cm Colluvial deposits derived mainly frommoraines (Holocene and Pleistocene)—Diamicton similar to that of adjacent up-slope moraines, but less compact. Includeminor amounts of better-sorted sand, silt,and gravel that occur in irregular beds andthat may have been derived from better-sorted glacial deposits and moved partlywith the aid of running water. Commonlya few meters thick. Contacts generally gra-dational, especially upslope. Slopes gener-ally moderate and moderately stable.Commonly associated with lateral mor-aines along the Chugach Mountain Frontand in a few places in mountain valleys.

cw Colluvial deposits on walls of inlet andcwu stream bluffs (Holocene and late Pleis-

tocene)—Loose accumulations that arederived from adjacent, upslope surficialdeposits and that form a veneer on bluffsafter active erosion has ceased. Chieflydiamicton, consisting of pebbly silt andsand with some clay, cobbles, and boul-ders, and a variable amount of organicmaterial. Massive to poorly bedded; poorlysorted. Generally a few meters thick, thin-ner at the upslope part; usually thickerdownslope. Contacts generally welldefined. Slopes steep to precipitous.Although stabilized locally by vegetation,subject to instability because of renewederosion and accompanying mass-wastingprocesses. Occur commonly along bluffsdeveloped in surficial deposits along KnikArm and along valley walls of majorstreams where they cross the AnchorageLowland. Locally present on scarps bor-

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dering deeper and wider channels withinthe lowland and within lateral morainesalong the Chugach Mountain Front, alonginner valleys cut lower than the floors ofmajor mountain valleys, and in some nar-row gullies cut into mountain-valleywalls, notably along the south side ofNorth Fork Campbell Creek. cwu aredeposits modified or completely removedduring urbanization.

cwb Deposits that conceal Bootlegger Cove For-cwbu mation (Holocene)—That formation itself

likely to be present behind lower part ofbluff. Possibly subject to development oflarge landslides especially during greatearthquakes such as the 1964 Alaska earth-quake. Occur only along Ship Creek nearwest edge of map area. cwbu are depositsmainly removed in conjunction withurbanization.

cwf Fine-grained deposits—Chiefly silt, clay,and fine sand; massive to poorly bedded,poorly sorted. Thickness probably a fewmeters. Slopes irregularly moderate tosteep and particularly subject to instabil-ity. Occur along walls of inner valleyswithin mountains adjacent to lacustrinedeposits, and locally along Knik Armnortheast of Eagle Bay where fine-grainedmaterials, possibly the Bootlegger CoveFormation, are present in bluffs behindthis colluvial veneer.

cs Solifluction deposits (Holocene and Pleis-tocene)—Chiefly loose, organic-rich, sandyto rubbly diamicton, commonly lackingclasts larger than pebble size. Derivedmostly from weathering of frost-shatteredbedrock directly upslope, seasonally mov-ing very slowly down broad mountainslopes either with the aid of interstitial orunderlying ice (solifluction in a strictsense) or of water derived largely fromsnowmelt. Thickness probably 1 m to afew meters. Contacts gradational to 1)very thinly concealed bedrock, 2) othercolluvium, and 3) thicker accumulationsof material that has moved downslope bylandsliding; include some landslidedeposits too small to map separately. Top-ography generally fairly smooth, but withmany minor irregularities, especially inthe form of small lobes with flatter uppersurfaces and steeper fronts. Slopes steep tomoderately steep. Generally unstable.

Occur at scattered localities on mountainslopes, especially on middle and lowerslopes.

cl Landslide deposits, undivided (Holoceneand late Pleistocene)—Include a wide vari-ety of materials, chiefly diamicton, withlesser gravelly silt and sand, and relativelyminor amounts of clay and organic mater-ial; locally include rubble and some largemasses of bedrock. Earthflow deposits toosmall to map separately present locally.Massive; nonsorted to poorly sorted. Rela-tively loose. Thickness probably severalmeters to possibly several tens of meters lo-cally in large landslides. Contacts moder-ately well to poorly defined. Topography ir-regular to hummocky, slopes moderate tosteep. Queried deposits alternately may berock-glacier, moraine, or other colluvialdeposits, or even in-place bedrock. Occur inmany places on mountain slopes, and local-ly in mountain valleys associated with glaci-olacustrine and lacustrine deposits, on inletand stream bluffs associated with wall col-luvium, and on a few hills within theElmendorf Moraine.

clb Older landslide deposits involving Boot-legger Cove Formation (Holocene)—Proba-bly gravel, sand, silt, and clay partly mixedto form poorly compacted diamicton. Occurlocally along south side of lower Ship CreekValley near west edge of map area.

cld Landslide deposits related to Dishno Pondmoraines (late Pleistocene)—Identity post-ulated largely on basis of landforms similarto but more subdued than adjacent lateralmoraines and kames, the lateral continuityof which is lacking in area of these depos-its. Mainly diamicton, gravel, and sand.Occur downslope from Chugach Moun-tain Front south of Ship Creek.

clm Deposits possibly modified in a glacioestu-arine environment—Landforms even moresubdued in this lower-lying area may havebeen reworked subaqueously shortly fol-lowing deposition.

clg Landslide deposits involving glacioestua-rine deposits (Holocene and late Pleisto-cene)—Identity postulated largely on basisof irregularly lumpy, crudely lobate topog-raphy in areas of channels adjacent to high-er-lying glacioestuarine deposits. Occursouth of South Fork Chester Creek andnortheast of alluvial fan of South Fork

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Campbell Creek.cle Landslide deposits resulting from earth-

flows (Holocene and late Pleistocene)—Similar to other landslide deposits withinthe mountains, but interpreted on thebasis of landform to have been emplacedin a probably more fluid state and there-fore may include a higher proportion offiner-grained material. Contacts generallywell defined. Mainly in long, narrowoccurrences in gullies and small valleyswithin Chugach Mountains.

Rock glaciers and rock-glacier depositsRock glaciers may be regarded as transitional

between true glaciers and a kind of active, slow-moving landslide, and their deposits are likewisetransitional between ground-moraine and collu-vial deposits.

rg Active rock glaciers (latest Holocene)—Accumulations of mainly angular to somesubrounded rock fragments still activelybeing transported, derived from upslopetalus deposits or directly from bedrock.Contain ice-rich matrix and move veryslowly downslope. Surface generally lacksvegetation, dominated by cobble- andboulder-size fragments. At depth, sub-stantially more fine-grained material maybe present to form coarse, rubbly, massive,and poorly sorted diamicton; at greaterdepth, dominantly clear glacier ice may bepresent, as reported in some rock glaciers(Moore and Friedman 1991). Thicknessseveral to a few tens of meters. Contactsgenerally well defined except gradationalto talus at upslope margin. Surface moder-ately hummocky and rough; slopes gener-ally moderate but steep to very steepalong Front and some side margins.Unstable because of continuing very slowmovement and potential for melting ofice-rich matrix. Occur mainly at heads ofvalleys near Tikishla and TemptationPeaks in southeastern part of map area.

rd Rock-glacier deposits (late Holocene)—Similar to material of active rock glaciers,but may contain less interstitial ice or less(perhaps no) clear ice at depth. Movementprobably has ceased and these deposits aresometimes termed inactive rock glaciers;however, distinction between the twoforms may be difficult to make, or a rock

glacier may be alternately active and inac-tive over a period of years. Some vegeta-tion covers surface. Generally more stablethan active rock glaciers, but some insta-bility likely, especially if excavated,because of loose nature of material andlikelihood that some interstitial ice may bepresent and that some massive clear icemay be present at depth. Occur in south-eastern part of map area down-valley fromrock glaciers, and in some nearby valleysthat no longer contain active rock glaciersat their heads.

rds Deposits of valley-side source (Holo-cene)—Similar to other rock-glacier depos-its but appear to have headed in andderived from colluvial deposits along theside of long, narrow valleys. Probably donot have, and may never have had, clear-ice cores of any significant thickness.Appear to have originated as coalescedlobate rock glaciers. Occur prominently asmajor valley fills in Snowhawk and NorthFork Campbell Creek Valleys.

rdo Older rock-glacier deposits (Holoceneand late Pleistocene)—Similar to youngerrock-glacier deposits but with somewhatmore subdued surface that is more com-pletely covered by low vegetation. Surfacesomewhat resembles that of ground mor-aine, but is more finely hummocky ratherthan smooth, reflecting presence of angu-lar to subangular cobble- and boulder-sizefragments just beneath vegetation cover.Not moving as an active rock glacier andunlikely to contain glacier ice, althoughpermafrost likely to be present locally.Occur in several small valleys in south-eastern part of map area, commonly in val-leys at altitudes lower than the valleyscontaining younger rock-glacier depositsor active rock glaciers.

Anthropogenic deposits (latest Holocene)f Engineered fill—Chiefly compacted peb-

ble gravel, in many places underlain bymore poorly sorted sandy to silty gravel,both emplaced to engineering specifica-tions. Includes some areas where a moreheterogeneous assemblage of materialmay have been emplaced without utilizingengineering specifications; in a few placesincludes land areas extensively modifiedby earth-moving or rock-quarrying equip-

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ment. Thickness as much as severalmeters. Contacts well defined, but widthshown on map may be exaggerated toaccommodate linear base-map symbolsprovided for roads and railroads. Mappedmainly along Glenn Highway and theAlaska Railroad, at some airfield runways,and along some streets within the urban-ized area, especially where they cross low-lying places. Minor fill for roads not shown.

BedrockBedrock is not shown in detail here. It is subdi-

vided into two units, younger bedrock and olderbedrock. Younger bedrock comprises sedimen-tary rocks of Tertiary age and is confined to a fewoutcrops in the margins of the Anchorage Low-land. Older bedrock includes rocks of bothChugach and Peninsula tectonostratigraphic ter-ranes (Coney and Jones 1985, Jones et al. 1987,Silberling et al. 1994) and consists of variablymetamorphosed sedimentary and igneous rocks.It is exposed only in the Chugach Mountains andin narrow canyons where major streams areincised in the Hillside area and just northwest ofthe mountain Front. Where mapped on mountainslopes, bedrock may be concealed by thin col-luvium.

by Younger bedrock (Tertiary)—Continentalrocks, mainly sandstone, siltstone, clay-stone, and minor coal of the Kenai Group(Calderwood and Fackler 1972). TyonekFormation (Wolfe and Tanai 1980) isexposed locally along lower course of theEagle River where two fossil-plant locali-ties have been examined by Schaff (1964)and by Wolfe et al. (1966). It is likely thatthis is the formation present at scatteredroadcut localities within about 2 km of theChugach Mountain Front in the vicinity ofthe community of Eagle River, and north-ward along the Glenn Highway (Dobrov-olny and Miller 1950, Schmoll et al. 1971,Zenone et al. 1974). Similar rocks mayoccur in poor exposures along the GlennHighway about 3 km south of the Eagle

River. Several meters exposed at a fewplaces along the Eagle River, but only 1 mor a few meters in roadcuts. Kenai Grouppresent at depth beneath surficial depositsthroughout most of the Anchorage Low-land, where thickness of surficial depositsmay be as much as 100 m. About 15 kmsouthwest of the Eagle River, however,Sterling Formation (overlying the Tyonek)has been tentatively identified (Stricker etal. 1988) in a drill hole (Yehle et al. 1986),and this formation probably constitutespart of the total thickness of Kenai Grouprocks southwest of the Eagle River.

bo Older bedrock (Tertiary to Permian)—Predominantly rocks of the Chugach ter-rane: McHugh Complex occupies most ofthe mountainous area; Valdez Groupoccurs near South Fork Eagle River andon part of the ridge between it and ShipCreek Valley. Rocks of the Peninsula ter-rane crop out in the margins of theAnchorage Lowland and may occur onridges near Parks and Little Peters Creeksas well. The two terranes are separated bythe Border Ranges fault (MacKevett andPlafker 1974) which, however, is mainlyor perhaps entirely concealed beneathsurficial deposits within the map area.McHugh Complex (Clark 1973) consistsprincipally of a metaclastic sequence in-cluding variably metamorphosed gray-wacke, argillite, phyllite, and conglomer-atic graywacke; locally consists of a meta-volcanic sequence including greenstone,metachert, cherty argillite, and argillite.Valdez Group includes principally meta-graywacke, metasiltstone, and argillite;felsic to intermediate hypabyssal intru-sive rocks are present in and west of thecanyon near the mouth of the South ForkEagle River. Peninsula terrane rocks con-sist mainly of metasedimentary and meta-volcanic rocks including metasandstone,metachert, siliceous argillite, marble, andgreenstone (descriptions and distributionfrom Clark 1972 and Winkler 1992).

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April 2000 Technical Report

Glacial Geology and Stratigraphy of Fort Richardson, Alaska:A Review of Available Data on the Hydrogeology

Lewis E. Hunter, Daniel E. Lawson, Susan R. Bigl,Peggy B. Robinson, and Joel D. Schlagel

U.S. Army Engineer and Research Development CenterCold Regions Research and Engineering Laboratory72 Lyme Road Technical Report TR-00-3Hanover, New Hampshire 03755-1290

U.S. Army AlaskaFort Richardson, Alaska

The surficial geology and glacial stratigraphy of Fort Richardson are extremely complex. Recent mapping by the USGSshows the general distribution of surficial deposits, but details on the underlying stratigraphy remain poorly known, leav-ing a critical gap in the understanding of ground water conditions below Fort Richardson. A conceptual model of the sub-surface stratigraphy was developed on the basis of results of recent surficial mapping, current knowledge of the glacialhistory, studies of modern glaciers, and limited subsurface data. A confining layer below the southern half of the canton-ment is likely the northern extension of an “older” ground moraine that crops out further to the south. Below the canton-ment, this moraine is buried below about 15 m of outwash and fan deposits, but it appears to be absent to the north, wherethe confined and unconfined aquifers are hydraulically connected. The northern limit of the “continuous” ground moraineis roughly below the cantonment and parts of Operable Unit D. Buried silt horizons in the fan probably create the locallyperched aquifers; however, erosional remnants of the ground moraine and interfingering of debris flow deposits along theElmendorf Moraine are plausible alternatives. These deposits are composed of finer-grained materials that slow groundwater infiltration and cause water to accumulate.

Anchorage, AlaskaElmendorf Moraine

Glacial stratigraphy Quaternary geologyMountain view fan

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Plate 1. Surficial Geology Map of Fort Richardson and Vicinity, Alaska.(separate pdf file)

click here