PHYSI 

DIVISIONS 0 

ALASKA 

0 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 482 
Physiographic Divisions 

of Alaska 

By CLYDE WAHRHAFTIG 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 482 

A classification and brief description with a 

discussion of high-latitude physiographic 

processes 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1965 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

Library of Congress catalog-card No. GS 65-800 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 
CONTENTS 

Abstract------------------------------------------- Introduction ______________________________________ _ 

Acknowledgments _________________________________ _ 

The basis for the classification ______________ ·~---------

Summary of the geologic history of Alaska ____________ _ 

Details of sculpture-physiographic evolution in the last 

million years------------------------------------- Glaciated highlands and mountains ______________ _ Glaciated lowlands _____________________________ _ 

U nglaciated uplands ___________________________ _ 

Unglaciated lowlands ___________________________ _ 

Description of the physiographic divisions ____________ _ Interior Plains _________________________________ _ 

Arctic Coastal Plain _______________________ _ 

Rocky Mountain System _______________________ _ 

Arctic Foothills ____________________________ _ 

Arctic Mountains province __________________ _ 

De Long Mountains ___________________ _ 

Noatak Lowlands ______________________ _ 

Baird Mountains ______________________ _ 

Central and eastern Brooks Range _______ _ 

Ambler-Chandalar Ridge and Lowland section----------------------------~---- Intermontane Plateaus _________________________ _ 

Northern Plateaus province _________________ _ 

Porcupine Plateau _____________________ _ 

Ogilvie Mountains _____________________ _ 

Tintina ValleY--------------------------

Yukon-Tanana Upland _______________ .,. __ 

Northway-Tanacross Lowland ___________ _ 

Yukon Flats section ____________________ _ Rampart Trough ______________________ _ 

Kokrine-Hodzana Highlands ____________ _ 

Western Alaska province ___________________ _ 

Kan:uti Flats __________________________ _ 

Tozitna-Melozitna Lowland _____________ _ 

Indian River Upland.,. __________________ _ 

Pah River· section ______________________ _ 

Koyukuk Flats ________________________ _ 

Kobuk-S'elawik Lowland ____________ · ____ _ 

Selawik Hills _______ - __________________ _ 

Buckland River Lowland _______________ _ Nulato Hills _______ - __________________ _ 

Tanana-Kuskokwim Lowland ___________ _ Nowitna Lowland ______________________ _ 

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Description of the physiographic divisions--Continued 

Intermontane Plateaus--Continued 

Western Alaska province-Continued Kuskokwim Mountains _________________ _ Innoko Lowlands ______________________ _ 

Nushagak-Big River Hille- _____________ _ 

Holitna Lowland _______________________ _ 

Nushagak-Bristol Bay Lowland _________ _ 

Seward Peninsula __________________________ _ 

Bering Shelf ______________________________ _ 

Yukon-Kuskokwim Coastal Lowland _____ _ 

Bering Pia tf orm _______________________ _ 

Ahklun Mountains __ ._ ______________________ _ 

Pacific Mountain System _______________________ _ 

Alaska-Aleutian province ___________________ _ 

Aleutian Islands _______________________ _ 

Aleutian Range ________________________ _ 

Alaska Range (southern part) ___________ _ 

Alaska Range (central and eastern part) __ _ 

Northern Foothills of the Alaska Range __ _ 

Coastal Trough province ___________________ _ 

Cook Iniet-Susitna Lowland ____________ _ 

Broad Pass Depression _________________ _ 

Talkeetna Mountains __________________ _ 

Upper Matanuska Valley _______________ _ 

Clearwater Mountains __________________ _ 

Gulkana Upland _______________________ _ 

Copper River Lowland ______ ~ __________ _ 

Wrangell Mountains ___________________ _ Chatham Trough ______________________ _ 

Kupreanof Lowland _______________ ._ ____ _ 

Pacific Border Ranges province ______________ _ 

Kodiak Mountains _____________________ _ 

Kenai-Chugach Mountains ____ ~ _________ _ 

St. Elias MOU\ntains ____________________ _ 

Fairweather Range ________________ _ 

Gulf of Alaska coastal section ___________ _ 

Chilkat-Baranof Mountains _____________ _ 

Prince of Wales Mountains _____________ _ 

Coast Mountains __________________________ _ 

Boundary Ranges ______________________ _ 

Coastal Foothills ______________________ _ 

References cited ___________________________________ _ 

Index ____________________________________________ _ 

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51 
IV CONTENTS 

ILLUSTRATIONS 

[Plates are 1n pocket] 

PLATE 1. Maps of physiographic divisions of Alaska. 

2. Photographs illustrating minor physiographic features and microrelief in Alaska. 

3. Aerial photographs illustrating the physiography of the Rocky Mountain System and Intermontane Plateaus in 

Alaska. 

4. Topographic maps and aerial photographs illustrating the physiography of the Interior Plains, Rocky Mountain 

System, and Intermontane Plateaus in Alaska. 

5. Topographic maps illustrating the physiography of the Pacific Mountain System in Alaska. 

6. Aerial photographs illustrating the physiography of the Pacific Mountain System in Alaska. 

FIGURES 1-6. Map of Alaska showing- Page 

1. Location of 1: 250,000 topographic maps ________________________________________________ ~_____ 4 

2. Mean daily minimum temperatures in January_________________________________________________ 9 

3. Mean daily maximum temperatures in JulY----------------------------·------------------------ 10 

4. Average annual precipitation________________________________________________________________ 11 

5. Extent of existing glaciers, Pleistocene glaciers, and permafrost regions____________________________ 12 

6. Drainage basins of major rivers______________________________________________________________ 19 

TABLE 

Page 

TABLE 1. The geologic time scale----------------'-------------,----------------- 6 
PHYSIOGRAPHIC DIVISIONS OF ALASKA 

BY CLYDE WAHRHAFTIG 

ABSTRACT 

Alaslm occupies the great northwestern peninsula of North 

America, which slopes and. drains westward to the Bering and 

Chul{cbi Seas. Most of the State is mountainous or billy although plains 20-100 miles wide abound. The central part, 

which slopes westward, consists of interspersed plains, plateaus, 

and rounded mountains, extending from beyond the Canadian 

border to the west coast ; this part is bordered on the north 

and south by high rugged ranges which effectively cut off the 

bulk of the peninsula from the Arctic and Pacific Oceans. The 

northern range is the Arctic Mountains province of the Rocky 

Mountain System, dominated by the Brooks Range whose summit altitudes are 6,000-8,000 feet. North of this province are 

the Arctic Foothills, also part of the Rocky Mountain System, 

and the Arctic Coastal Plain, the northwestern extension of 

the Interior Plains. The southern mountain barrier, part of the 

Pacific Mountain System, is a· pair of ridges separated by a 

line of discontinuous depressions, the Coastal Trough province. 

The northern ridge of the pair is the Alaska-Aleutian province ; 

and the southern, the Pacific Border Ranges province. The 

highest peal{S of North America, rising to an altitude of more 

than 20,000 feet, are here; and mountains 8,000-12,000 feet in 

altitude are common. 

'l'he part between the Arctic Mountains and the Pacific 

Mountain ·system is a disordered assemblage of flat plains and 

rolling uplands, surmounted here and there by groups of low 

mountains; the whole region declines in relief and -altitude 

westward. It is divided from east to west into five provinces: 

the Northern Plateaus province, having uplands at altitudes of 

3,000-5,000 feet, formed on Paleozoic and crystalline rocks; 

the Western Alaska province, having uplands at altitudes of 

1,500-3,000 feet, formed on late Mesozoic sedimentary and volcanic rocks ; Seward Peninsula and the Ahklun Mountains, 

two distinctive relatively mountainous provinces; and the Bering Shelf, a nearly featureless plain, which is mostly submerged but has mountainous islands. Southeastern Alaska 

includes parts of the Coast Mountains, Coastal Trough, and 

Pacific Border Ranges ; all are provinces of the Pacific Mountain System. 

By far the largest river is the Yukon, which, together with 

the Kuskokwim and other rivers that flow to the Bering and 

Chul{chi Seas, drains all the Intermontane Plateaus and ·parts 

of the two mountain systems. The Bering-Chukchi-Arctic 

Ocean Divide is in the Arctic Mountains province; and the 

Bering Sea-Pacific Ocean Divide is partly on the crest of the 

Alaska-Aleutian province but for long stretches is in the lowlands of the Coastal Trough where in places it follows eskers. 

Each of the provinces is divided for purposes of description 

into sections, 60 in all; and some of the sections are broken 

into subsections. The general topography, drainage, lakes, 

glaciers, permafrost conditions, and geology of each section are 

briefly described. 

The Rocky Mountain System, Intermontane Plateaus, and 

Pacific Mountain System together constitute the North American Cordillera, one of the major physiographic features of the 

continent. Throughout most of its history the North American 

Cordillera has been the site of geosynclinal sedimentation, 

dominantly miogeosynclinal with interbedded carbonate and 

well-sorted clastic rocks in the Rocky Mountain System and 

northern . part of the Intermontane Plateaus and dominantly 

eugeosynclinal with interbedded volcanic and poorly sorted 

clastic rocks in the Pacific Mountain System and southern part 

of the Intermontane Plateaus. Orogenic activity, accompanied 

by the invasion of immense granitic batholiths in the Pacific 

Mountain System ·and Intermontane Plateaus, has affected the 

North American Cordillera almost continuously since early 

Jurassic time. Near the end of Cretaceous time, orogenic activity reached its climax; and most of Alaska was converted to 

dry land, which has remained ever since. In Cenozoic time 

Alaska has been subjected to faulting, warping, and local folding. These processes formed highlands, whose erosion produced large quantities of poorly consolidated sediments, and 

basins, in which these sediments were deposited and are now 

preserved. Deformation continues and is particularly strong 

along the Pacific Coast. Active volcanoes are in the Aleutian 

Islands, Alaska Peninsula, and Wrangell Mountains. 

Alaska has bedrock structure of great variety and complexity, which is reflected in the number and types of its mountainlands, uplands, and lowlands. Structural trends are predominantly parallel to the Pacific Coast ; they swing from 

northeastward in the southwestern part to eastward in central 

and northern Alaska and southeastward in southeastern 

Alaska. 

For the last 2 or 3 million years, frost climates have prevailed in Alaska, and the geomorphic processes have been predominantly either glacial or periglacial. Most of Alaska north 

of the Pacific coastal belt is underlain by permafrost. The 

firn line today ranges from 3,000 feet on the south coast to 

6,000 feet on the north coast and is 8,000 feet in the eastern 

interior; during the glacial stages of the Pleistocene, it probably averaged 1,000-2,000 feet lower; thus, the Pacific Mountain System, which even today has extensive glaciers and 

mountain icecaps, was covered almost completely by the vast 

cordilleran ice sheet. The Arctic Mountains province, Ahklun 

Mountains, and southern Seward Peninsula were also intensely 

glaciated, whereas, in contrast, most of the Intermontane 

Plateaus, Arctic Foothills, and Arctic Coastal Plain were never 

glaciated. 

Glaciated uplands that were buried by icecaps were eroded 

into blocklike groups of mountains having rounded hummocky 

1 
2 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

summits, isolated by networks of broad steep-sided u-shaped 

valleys and low passes. Ridges and peaks that rose above the 

level of the icecaps are jagged and knifelike. Ranges dominated 

by such ridges have extreme relief, and their valleys head in 

steep-walled glacier-filled cirques. 

Glaciated lowlands are irregular and consist of end and 

ground moraines, drumlins, chaotic assemblages of irregular 

hills and hollows (stagnant ice topography), kames, eskers, 

and glacial-lake plains. Rock-basin and moraine-dammed lakes 

of great size, depth, and beauty are common around the margins of the glaciated lowlands. 

Unglaciated uplands have been sculptured largely by creep 

and solifiuction under an arctic permafrost climate, as the 

abundance of patterned ground, solifiuction sheets and lobes, 

and altiplanation terraces attests. Ridges of the unglaciated 

uplands have broad rounded summits and gentle convex sides 

which are commonly mantled in their lower parts by windborne silt. The uplands are cut by. narrow 1lat-1loored valleys 

which have V-shaped tributary gulches. 

Unglaciated lowlands are generally broad silt plains which 

have meander belts along the wildly meandering axial streams. 

Near the meander belts are fiat plains dotted with thaw lakes 

(in places making up more than 50 percent of. the area) and 

sporadic pingos. Toward the surrounding uplands are rolling 

silt-covered benches pocked by thaw sinks. Near the margins 

of the Pleistocene ice sheets, the lowlands have extensive outwash fans and aprons, commonly trenched by shallow terraced valleys ; the streams are commonly braided. Fields of 

stabilized and active sand dunes are present locally. 

INTRODUCTION 

Alaska, the 49th State of the United States of 

America, occupies the great peninsula at the northwest 

corner of the North American continent and is separated from the conterminous United States by part of 

western Canada. It is one of the last regions of North 

America to be explored, and maps adequate for delimiting its physiographic divisions did not exist before 

the last 20 years. In this paper the State is divided 

. into 12 physiographic provinces and 60 smaller di-

- visions (pl. 1), all but two of which are described 

briefly. 

Almost the entire State of Alaska is included in the 

North American Cordillera, the great mountainous 

backbone of western North America. Mountain-building activity has been recurrent throughout the geologic history of Alaska and has continued to the present time. The great variety of structures produced by 

the mountain-building activity and the differential 

movements of the recent geologic past have combined 

to give the State its extreme topographic diversity. 

Alaska's position at the northwestern corner of North 

America, close to the Eurasian landmass, has caused it 

to play a major part in the biologic, as well as geologic, 

history of the earth. At various times in the geologic 

past Alaska has been connected with Siberia and has 

served as a migration route for plants, animals, and 

men between the Eastern and Western Hemispheres 

(Hopkins, 1959a). 

Although Alaska had long been inhabited by peoples 

of American Indian and Eskimo stock, the first Europeans to see it were Russian explorers under the captainship of Vitus Bering in 1741. The Russians con· 

quered it and explored its southern coastal areas but 

did not penetrate deeply into the interior. It was part 

of the Russian Empire until1867, when it was sold to 

the United States for $7,200,000. Systematic exploration of Alaska by expeditions of the United States 

Government began in 1883 (Brooks, 1906, p. 121-123). 

The first expeditions were sent by the Army and the 

Revenue-Marine Service; they generally had with them 

a geologist who prepared a report on and map of the 

region traversed. About 1898 the task of exploring the 

geology and geography of Alaska, except for the coastline, was taken over almost exclusively by the U.S. 

Geological Survey. 

The early exploring parties were searching for routes 

of travel and commerce--navigable rivers and passes 

over the high mountain ranges that border the Pacific 

Ocean. They were in Alaska for the summer only, 

when the swampy lowlands are largely impassable. 

They therefore traveled by boat along the rivers, and 

later by ho~e across plateaus and low mountains. They 

mapped the country topographically as far as it could 

be seen on either side of their route, in part by instrumental observation on the spot and in part by panoramic photographs from which the topography could 

be determined by careful measurements in the office the 

following winter (Bagley, 1917). The narratives of 

their explorations-for example, Spurr's (1900) account of the exploration of southwestern Alaska-are 

stories of high adventure, full of danger and hardship . 

Their discoveries were summarized in two reports of 

the Geological Survey : that by Brooks in 1906 on the 

geography and geology of Alaska and that by P. S. 

Smith in 1939 on the areal geology of Alaska. 

Brooks recognized that Alaska has two great mountain systems and an intermontane plateau region between them, and he saw that these are the northern 

continuations of the mountain ranges of the United 

States and Canada. He also recognized most of the 

subdivisions of the southern mountain system that we 

use today, but the Intermontane Plateaus seemed to be 

a chaotic jumble of hills and lowlands, which he did not 

attempt to classify. 

As late as 1940 most of Alaska was still unmapped, 

topographically and geologically. The application of 

aerial photography to topographic mapping, and particularly the invention of the metrogon le:t:ts which 

permitted horizon-to-horizon photography from a 
IN'FBODUCTlON 3 

single airplane flight, greatly accelerated mapping in 

Alaska. By 1946, in response to wartime needs, a crude 

map of the then territory had been prepared on a scale 

of 1 : 1,000,000, with a contour interval of 1,000 feet. 

Since that time the topographic mapping of Alaska has 

been progressing rapidly under the pr~ams e.f tile 

U.S. Geological Survey, the U.S. Coast. and Geodeti!e 

Survey, and the U.S. Army Map Service. By 19fr(il 

nearly all the State will be covered by topogrnphie·. 

maps of excellent quality having· a. scale of 1 : 25(1},JI)'(!)0l 

and a contour interval of 200 feet (see fig. 1) ; and. tl!te 

greater part of it will be covered also by maps ha::ving. 

a scale of 1 : 63,360 and a contour· interval of 5(!)\ or.· Hl0l 

feet; all maps will be prepared by photogrammettric·. 

methods from vertical or near-vertical aeria:1. plllloto--

graphs. 

Geologic mapping, which is not amenable to accurate 

surveys from the air, has necessarily proceeded much 

more slowly. Nevertheless, in the last 15 years geologic· 

rna ps on a scale of 1 : 250,000 have been made for all 

northern Alaska and much of western Alaska, the 

Brooks Range and southwestern Alaska. 

ACKNOWLEDGMENTS 

This wealth of new geographic and geologic information has made desirable a new classification of the 

State into physiographic divisions. The classification 

in this report was prepared intermittently between 

1949 and 1959; most of the work was done between 

1956 and 1959. The physiographic units and their 

boundaries were determined with the advice and assistance of the following geologists of the U.S. Geological Survey : Robert S. Bickel, Earl Brabb, William 

P. Brosge, Robert L. Detterman, Arthur Grantz, J. M. 

Hoare, David M. Hopkins, E. H. Lathram, Marvin D .. 

Mangus, Don J. Miller, William W. Patton, C. ·L. 

Sainsbury, and John R. Williams. It is hoped that 

the publication of this classification will bring about 

a clearer understanding of the geography of Alaska 

and will stimulate research into the history of the 

formation of the Alaskan landscape. 

In addition to advice and assistance, the geologists 

named above also contributed unpublished information 

on the geology and physiography of Alaska. Arthur H. 

Lachenbruch provided information on the formation 

of ice-wedge polygons. A. R. Tagg and G. W. Holmes 

provided photographs of microrelief features. 

Especial thanks are due Bradford Washburn, Director of the Boston Museum of Science, for permission 

to use his excellent aerial photographs of Alaska. Other 

aerial photographs were provided by the U.S. Navy 

and U.S. Air Force. 

The1 work was; dl<ime nnder the supervision of George 

0. Gates. aan:di. G~ D. Ebe-:rdeill1ll,. and their encouragement 

aJJitdL aJ(ill-wiiee· aJJ!e-. grate::f:wffiy a:eknow ledged. 

THE B&SIS~ FOR THE; CLASSIFICATION 

Tb Ji>;liDl'pose· of a:. ph.ysiographic classification of a 

regiE>n as; tar~ amrdl <!tiiversified. as Alaska is to divide it 

into a:Fea:s; tmtr wFe~ so. homogeneous topographically and 

distinet; :tirem, the rureas around them that the physical 

a::p~peruFa:nce• of tih~ region can be easily apprehended 

and! d~seribed .. 'Fhe· boundaries· of the physiographic 

d'i!visii01il'Si are tlrerefore drawn where the topography 

chlrunges; i·~. eb:ruFacter. The physical divisions must be 

stmh.. tla!rutt 01il~ ~an describe them accurately in short, 

gelile:rr.wli statements. If the units are too large, they 

cannot be described in general terms without doing 

viel'ence· to~ th:e, facts about their parts; and if they are 

too• smaH,,major relations of topography, geology, and 

drainruge' ca;nnot be described because the units do not 

irrelude· them .. 

ALthough the basis for selecting the units is largely 

topogra:phical, a major use of the classification is to 

deduce' the history of the topography in order to understand why there are mountains in one place and valleys 

m' a;nother. Such a history is necessarily geologic, and 

the· geologic structure must be considered in determining which areas shall be designated physiographic 

units. For example, the Upper Matanuska Valley and 

the Broad Pass Depression are shown as physiographic 

units because they are structurally controlled troughs, 

although many valleys that are just as wide are not 

considered physiographic units because they bear no 

relation to the structure. 

· The terminology follows the scheme used for the 

physical divisions of the conterminous United States 

by Fenneman and others ( 1946), in which the great 

·physiographic features of North America were broken 

into major divisions, each major division, into provinces, and each province into sections. In addition, in 

the classification of Alaska, some division of sections 

into subsections has been necessary. As far as possible, 

the boundary lines were drawn to correspond with 

those of Bostock ( 1948) for the Canadian Cordillera so 

that the physiographic units would match across the 

international boundary. Bostock's names were used for 

the units unless Alaskan names had already appeared 

in the literature or seemed more appropriate. Bostock's 

grouping in.to units corresponding to provinces and 

major divisions could not be adhered to in all details. 

The major divisions and their boundaries are shown 

on plate 1. These in turn have been divided into 12 

·provinces, which ~reshown on plate 1. The provinces 

have been divided into 60 sections, whose descriptions 

begin on page 18. The number in parentheses follow-
GULF OF 

.P A C 

F I ·c 

AL UTIAN 

<f1 o<:,o RAT 0 

KISKA ISLANDS 

~ 

FIGURE 1.-Location of 1:250,000 topographic maps. 
SUMMARY OF THE GEOLOGIC HISTORY OF ALASKA 5 

ing the title of each province or section or the first mention in the text of each subsection corresponds to the 

numbering of that area on plate 1. 

The descriptions of the individual provinces and sections include: a brief sketch of the topography; some 

salient features of the drainage; statements on the 

lakes, glaciers, and permafrost; and a condensed ac-· 

count of the geology as it affects physiographic development. These statements are based on the literature 

de~ling with· the geology and geography of Alaska, 

chiefly publications of the U.S. Geological Survey; on 

topographic maps and aerial photographs; and to 

a very large extent, especially for the geology, on unpublished information given freely by my colleagues 

of the Geological Survey and listed on plate 1. 

Two sections shown on plate 1, the Old Crow Plain 

( 8) and the Duke Depression (50), are not described 

in text. These lie largely in Canada and have very 

small prongs that extend into Alaska. Descriptions for 

these areas were given by Bostock (1948, p. 76, 96-97). 

SUMMARY OF THE GEOLOGIC HISTORY OF ALASKA 

Alaska has already been indicated to be a region of 

intense orogenic (mountain-building) activity. Any 

understanding of its present topography depends, 

therefore, on some knowledge of its geologic history. 

A brief account of the geologic history is given in this 

section and summarized in table 1. 

Most of Alaska has been studied geologically only in 

an exploratory manner. In his cross-country travels 

the geological explorer attempted to interpret, on the 

basis of a single traverse, the geology for many miles 

on either side. Only in recent years has there been 

much geologic mapping that attempted to cover uniformly the geology of a large area. Despite the speed 

at which the early Alaskan geologists worked, the 

extrapolations they had to make from rock outcrops 

near at hand to mountains miles away, and the lack of 

accurate maps on which to plot their observations, few 

of their interpretations of the geology have been found 

to be in serious error. Nevertheless, our knowledge of 

the geologic history of the State is still fragmentary 

and hypothetical. The most recent general summary 

of the geology of Alaska, on which this brief account 

is based, is that of Miller and others ( 1959). The 

geology of Alaska, at the same scale as plate 1, is shown 

on the map by Dutro and Payne ( 1957). 

The oldest rock unit in Alaska is the schist of the 

Yukon-Tanana Upland and the Alaska Range-called 

the Birch Creek Schist from. outcrops along Birch 

Creek. This schist was originally sand and mud deposited in ancient seas and is thought to have been 

tightly folded and metamorphosed in early Precambrian time. 

773-592 0-66-2 

Apparently most, if not all, of Alaska was under 

water during much of the Paleozoic Era, for thick deposits of this age are found throughout the State. The 

Paleozoic rocks of the Brooks Range consist largely 

of limestone, sandstone, and shale, or of their metamorphic equivalents. In the central part of Alaska, 

the rocks also consist largely of limestone, sandstone, 

and shale; chert, volcanic rock, and graywacke as old 

as Ordovician in age are interbedded with the other 

rocks. In southern and southeastern Alaska, graywacke 

and volcanic rock-the rocks of orogenic belts-are 

common throughout the Paleozoic sequence, interbedded with great thicknesses of limestone, slate, schist, 

and nonmarine red beds. 

Even in the early Paleozoic rocks there are fragmentary records of mountain-building activity, for 

angular unconformities exist between rocks of Ordovician, Silurian, and Devonian age in southeastern 

Alaska and similar unconformities in central and 

northern Alaska record a period of mountain building 

at the beginning of Devonian time. Whatever the 

nature of these orogenies, they have had practically no 

effect on the present topography of Alaska. 

In Mississippian time extensive submarine volcanic 

eruptions occurred in various parts of Alaska, and 

during part of the Permian and Triassic most of 

Alaska south of the Yukon River was a great submarine volcanic field. The ancient basalt flows of this 

age constitute the greenstone formations common in 

Alaska ; the most famous of these is the Nikolai Greenstone of the Kennicott Copper district. After the eruption of the greenstone, more limestone and shale were 

deposited over the sea floor. 

A new period of orogenic activity began in Jurassic 

time. ·It was heralded by the eruption, in southern 

Alaska, of andesite flows and tuffs. These were intruded in mid-Jurassic time by an enormous granitic 

batholith that stretched from the Talkeetna. Mountains 

through the southern Alaska Range to the Aleutian 

Range. From this time on, parts of Alaska were 

rapidly uplifted to form mountains, from which sediments were eroded and deposited in adjacent basins 

that were as rapidly subsiding. These sediments became 

the great thicknesses of graywacke, argillite, and ·conglomerate that make up great parts of the mountain 

ranges of southern and central Alaska. Not only were 

the blocks of land uplifted and depressed, but they 

were also squeezed together and slid over and past each 

other; therefore, throughout large parts of Alaska the 

consolidated bedrock is tightly folded, broken by 

numerous faults, and slightly metamorphosed. The 

deforma.tion was not continuous but was probably of. a 

pulsating nature. Periods of rapid change alternated 
6 

Time of beginning, in 

years before present 1 

8,700 years 

About 2 million 

About 63 million 

About 135 .million 

About 230 million 

About 345 million 

About 600 million 

Oldest age determined from rocks 

Era 

Cenozoic 

Mesozoic 

Paleozoic 

by radioactivity: Precambrian 

3300 million 

:P.iEI:n3i£0GRAPmC DIVISIONS OF ALASKA 

''l'!A.1H<E :t..-Geologic time 8cale 

Period 

I . Recent 

'Qtia:ter- ' 

nary ! 

Pleisto-

.cene 

Tertiary 

Cretaceous 

Jurassic 

Triassic 

Permian 

~ 0 Pennsylvanian ~ ~ 

s:l 

0 

.a 

~ Mississippian 

0 

Devonian 

Silurian 

Ordovician 

Cambrian 

Precambrian 

I 

l 

·Typical fossils 

Civilli'zed man . 

·Mammoth,, ;gii8.1lllt beav-er. 

Various khids of horses, 

camels, saber-toothed 

tigers, and other mam- mals. In sea, mollusks (clams and 

snails) and echinoderms (sea urchins and 

sand dollars). 

Age of dinosaurs on land; in sea, age of 

complicated nautiluslike animals called 

ammonites. 

Small dinosaurs, 

amphibians. 

Amphibians, clubmoss 

and fern forests on land. Trilobites, 

early corals, and 

primitive fishes in sea. 

Most primitive fishes. 

First forests on land. 

Chiefly trilobites and 

brachiopods (lampshells). 

Earliest trilobites. 

No fossil record. 

Ev.ents in Alaska and. elsewllere 

Retreat of the glaciers; :rise ef sea to 

present level. 

Growth of vast ice sheets and glaciers; 2 

cold climates; growth .of mountains to 

their present height. 

Most of Alaska probably· dry land. Accumulation of gravels in many low areas. Accumulation of coal in swamps 

to form Nenana, Matanuska, and Bering River coal fields. A period of 

waning mountain-building activity ex- cept in the Aleutians and the Gulf of 

Alaska coastal belt. 

Period of culmination of great mountainbuilding period in Alaska. Intrusion 

of Coast Range batholith and other 

batholiths. Accumulation of vast thick- nesses of sand, shale, and impure 

sandy muds in basins where KenaiChugach Mountains, Kuskokwim 

Mountains, and Nulato Hills now stand, as well as north of Brooks Range. 

Folding and thrusting of rocks of 

Brooks Range and elsewhere. 

Period of growing mountain-building ac- tivit)' in Alaska. Volcanic deposits in 

the Talkeetna Mountains and intrusion 

of the Talkeetna batholith. Sand and 

shale in Cook Inlet. 

End of period of outflow of submarine 

lavas over much of southern Alaska. 

Early part of period of outflow of submarine lavas over much of southern 

Alaska. 

Submarine lavas and dark sedimentary 

rocks in southern Alaska. 

Chert in central Alaska. Limestone in 

northern Alaska. 

Sandstone and shale in northern Alaska; 

limestone and other sedimentary rocks 

deposited in central and southern 

Alaska. Apparently a period of moun- tain-building in Alaska, in which the 

mountains may have trended northeast or north. 

In southeastern Alaska accumulation of 

pure limestone in reefs associated with 

volcanic rocks. 

Little record in Alaska. Limestone in 

Seward Peninsula. 

Little record in Alaska. 

Formation of Birch Creek Schist of central 

Alaska (Fairbanks area, Yukon-Tanana 

Upland, and Alaska Range). 

• Date of Pleistocene-Recent boundary is based on Charlesworth (1957, v. 2, p. 

1525-1526); date of boundary between Tertiary and Quaternary is based on Leakey 

and others (1961) and on J. F. Evernden and G. H. Curtis, quoted in Hay (1963); 

other dates from Kulp (1961). · 

2 It has been determined that ice advanced and then melted away at least 4 times 

in Central United States and probably also in Alaska. The last such advance and 

the one that left the clearest mark on the topography Is called the Wisconsin 

Glaciation. 
SUMMARY OF THE GEOLOGIC HISTORY OF ALASKA 

with periods of relative stability, and a block that was 

uplifted at one time might be depressed at another. 

Orogenic activity reached its climax in late Early 

and Late Cretaceous time. At that time, the rocks were 

tightly folded and had a cleavage; and great batholiths 

were intruded in the Alaska Range, in the Interior 

Plateaus, in the Kodiak and Chugach Mountains, and 

throughout southeastern Alaska and adjacent British 

Columbia. The Paleozoic rocks of the Brooks Range 

were thrust northward and folded into great flat folds 

overturned to the north. By the end of Cretaceous 

time, most of Alaska was dry land-a segment of the 

great mountain belt that borders the Pacific Ocean on 

the east, north, and west. The part of that belt in 

North America is called the North American Cordillera. In Alaska the structures produced· by this 

orogeny are great arcuate belts roughly parallel to the 

shore of the Gulf of Alaska, and structural trends are 

generally northwestward in southeastern Alaska, 

roughly due west throughout most of central and 

northern Alaska, and southwestward in western and 

southwestern Alaska. 

The structures characteristic of the North American 

Cordillera in Alaska have their counterparts farther 

south in Canada and the conterminous United States. 

Thus the bedded rocks of the Pacific Mountain System 

consist largely of great thicknesses of tightly folded 

graywacke, argillite, conglomerate, and basalt and 

andesite flows and tuffs. Rocks of the Rocky Mountain 

System are mainly limestone, quartzite, slate, and shale 

that were folded and thrust northward or eastward, 

away from the Pacific. The greatest intrusive and 

volcanic activity has been in the Pacific Mountain 

System, which contains an almost continuous belt of 

granitic batholiths from Mexico to the Aleutian Islands 

as well as a chain of active and recently active volcanoes. The evidence of igneous activity decreases· 

·across the cordillera away from the Pacific, and relatively little igneous activity occurred in the north front 

of the Brooks Range. 

...... : .. Orogenic activity continued in the North American 

~;·dordillera throughout the Tertiary. The beit immediately adjacent to the Pacific Ocean has been the most 

active. Tertiary rocks along the coast of the Gulf of 

Alaska have been tightly folded, thrust, and raised to 

great heights. The great chain of volcanoes in the 

Aleutians suggests the presence of magma at depth. 

Both the Aleutians and the Gulf of Alaska coast have 

experienced many strong earthquakes in recent years. 

In the remainder of Alaska, the orogenic activity of 

Cenozoic time was much less intense than that of the 

Cretaceous. It has consisted mainly of block faulting 

and, in late· Cenozoic time, of broad gentle warping 

and uplift. In the Alaska Range and elsewhere, bodies 

of coarse poorly consolidated conglomerate and sandstone which are folded and faulted indicate at least one 

period of intensive mountain building in central 

Alaska in Tertiary time. 

· Cenozoic time (the last 60 million years) has probably been largely an era of erosion in Alaska, interspersed at times by local depression of the ground 

surface which caused continental sediments to accumulate in basinlike areas of relatively small extent. It is 

the period of the formation of the physiography of 

Alaska. It is much more difficult to reconstruct the history of the formation of this landscape than it is to 

unravel the history of the rocks on which it is formed, 

even though the landscape is younger than the rocks. 

The advantage to a geologist of a sequence of sedimentary rocks is that the rocks themselves contain the 

record of the history of their deposition, stacked in 

order like the pages of a book. The landscape, however, does not generally retain the record of its formation. The record of erosion is like messages on a blackboard, for each stage of the erosional process destroys 

most of the product of the stage before it, and to work 

out the successive stages we must rely on undestroyed 

relics of the old topographies, which are hard to find 

and even harder to interpret. 

. Many hypotheses have been proposed for the evolution of the drainage of Alaska and for the distribution 

of its mountains and lowlands. Information on the 

later geologic history of Alaska is as yet insufficient to 

eliminate any but a few of these hypotheses or to give 

a history of the development of drainage that explains 

all known features. Therefore, no account is given 

here of the development of the major physiographic 

features or of the development of the drainage. 

Certain facts of the physiography of Alaska, however, must be taken into account in formulating any 

history of its physiographic development. Although 

the mountain systems broadly parallel the major belts 

of internal structure of the cordillera, there are significant local differences, particularly in southwestern 

Alaska, where the north front of the Pacific Mountain 

System trends diagonally across several structural 

belts. The Western Alaska province of the Intermontane Plateaus is underlain largely by folded and 

faulted marine and continental sedimentary rocks of 

Cretaceous age. The Northern Plateaus province, on 

the other hand, is underlain chiefly by metamorphic 

rocks of Paleozoic and Precambrian age, including the 

oldest rocks in Alaska, and by large granitoid batholiths. There is no break in the structure of the under-
8 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

lying rocks at the boundaries of this province with the 

mountain system to the north and south. Many of the 

lowlands are underlain, beneath a thin cover of soft 

Tertiary or Quaternary sedimentary deposits, by the 

same kinds of rock-crystalline or partly metamorphosed-that make up the mountains that surround 

them. It seems, therefore, that the present topography 

neither can be explained as being an immediate product 

of the niain period of rock deformation and igneous 

activity in the North American Cordillera, nor can it 

be explained entirely by differential erosion of the 

rocks deformed in that period. Folding and faulting 

of more recent age, probably during late Tertiary or 

Quaternary time, were at least partly responsible for 

the topography. 

The drainage similarly shows many anomalies. The 

major drainage divides do not generally coincide with 

major mountain axes but lie for long distances in lowlands to the north or south of them; and a large number of rivers cross mountain ranges through deep 

canyons from one lowland to another, even though the 

lowlands join around the ends of these ranges. 

DETAILS OF SCULPTURE-PHYSIOGRAPHIC EVOLUTION IN THE LAST MILLION YEARS 

Although the drainage and the larger physiographic 

features of Alaska may have originated far back in the 

Tertiary and possibly even earlier, the erosion and deposition that was responsible for the detailed form of 

mountainsides and valley floors has probably taken 

place throughout Quaternary time, when the present 

climate in Alaska was being established. Quaternary 

climatic patterns are unusual in the history of the earth 

in that extreme cold prevails in the polar regions. Much 

work has been done in Alaska and elsewhere on the 

erosional processes prevailing in these cold climates, 

and we have · some idea about how the details of 

topography were formed. 

The Quaternary has been a period when vast sheets 

of ice, compacted from snow, covered large parts of 

North America, Europe, Asia, Patagonia, and Antarctica and pack ice covered the polar seas. Several periods 

of growth of these ice sheets, accompanied by cooler 

and wetter conditions around the world, have alternated with periods having climates similar to, or even 

warmer and drier than, those of today. We know that 

much, though not all, of Alaska was covered with ice 

during the Pleistocene glacial advances; large parts 

are still ice covered. Furthermore, north of the southern coastal areas, Alaska is a region of permafrostthat is, a region where large areas of the ground a few 

feet below the surface are frozen the year around. A 

climate in which glaciers or permafrost can form is 

called a frost climate and is generally characterized by 

an average annual temperature that i~ below freezing. 

Figures 2, 3, and 4 indicate in a general way the 

climate of Alaska by showing the average January 

minimum and July maximum temperatures and the 

annual precipitation. 

The layer of permafrost has profoundly affected the 

weathering and erosion of the rocks and produced a 

characteristic topography over much of interior and 

northern Alaska. Figure 5 shows the extent of the 

permafrost areas and the extent of Pleistocene and 

modern glaciation in Alaska. 

In addition to its direct effect in the formation of 

glaciers and permafrost, the arctic and subarctic climate of Alaska has an indirect effect on the processes 

of erosion by its control on vegetation. Much of Alaska 

is above or beyond timberline and is covered by a dense 

mat of low bushes, herbs, grasses, and moss; parts are 

so high and cold that they are barren rock deserts. The 

distribution of the major types of vegetation in Alaska 

is given by Sigafoos (1958), and some of the climatic 

factors controlling the distribution of vegetation are 

discussed by Hopkins ( 1959c). 

The physiographic sections of Alaska that are shown 

on plate 1 can be conveniently divided into four groups, 

in each of which a fairly uniform topography prevails : 

(a) glaciated highlands and mountains, (b) glaciated 

low lands, (c) unglaciated highlands, and (d) unglacia ted lowlands. The. physiographic processes that prevail in each of these groups are discussed in the following four sections. The boundaries between the glaciated 

and unglaciated regions are not everywhere sharp, for 

in places where the older glacial advances were much 

more extensive than the younger glacial advances the 

glaciated topography produced by the older advances 

has been greatly modified by nonglacial erosional 

processes. 

The material in the following four sections is based 

in large part on the following books and articles : 

Black (1951, 1954); Bostock (1948); Coats (1950); 

Eakin ( 1916, p. 76-92) ; Eardley ( 1938b) ; Eckel 

(1958); Flint (1957); Hopkins (1949); Hopkins and 

Sigafoos (1951); Hopkins, Karlstrom, and others 

( 1955) ; Lachenbruch ( 1960a, 1960b, 1962) ; Leffingwell 

(1919, p. 179-214); Livingston (1954); Muller (1947); 

Pewe ( 1954, 1955a) ; Pewe and others ( 1953) ; Plafker 

and Miller (1958).; Porsild (1938); Sharp (1947, 

1958); Taber (1943); Tarr and Martin (1914); 

Trainer (1953); Twenhofel (1952); Wahrhaftig 

(1949, 1958a); Wahrhaftig and Cox (1959); Wallace (1948); Washburn (1956); and Williams (1958). 
0 0 

I 

I 

. 

~ST MA'ITHEW ISLAND 

C:>~"tGULF OF 

PRIBILOF ISLANDS 

F 

p c 

I ~174" 

ATT\J 

----GJ~--------,~------

ALASKA 

I c 0 c 

EXPLANATION 

--20--

Isothenn 

Lint! of equal minimum temperature. lntervalgenerCul! 4 • F; !" F and s• F in p14us 

FIGURE 2.-Mean dally m.inlmum temperature (deglees Fahrenheit) in Alaska in January (January mean daily maximums are generally 100 higher). From Watson (1959, p. 21). 
0 """"' 

68" 

c E: .-4 

EXPLANATION 

--120---

Isotherm 

Lim of equal maximum temperature. Inter- va!Qemrally ll" F; 4 • F in places 

I 

I 

./ '"d 

/ , 

~ 

~ 

ss'¥-,, r:JJ 

1-4 

~~ 0 

0 

~ 

r; ST LAWRENCE ISLAND ~-

1-4 

c 

t;:j 

~ 1-4 

r:JJ \ST MATTHEW ISLAND 1-4 

0 

~~ z '? r:JJ 

0 (l l'!llj 

~\~ 

~ '9v,; 

> Ul 

-~ 

4)1), 

ALASKA GULF OF '0 

PRJBILOF ISLANDS 

c F c 0 c 

p A E A N 

lJ 

o o o"::::! 

J7o• ~___L_J__L_-L-~~--~-L-~-~~-J_~~-L-L-_L ________________________________ ~-~_J _ _L_~_J-~ 

FIGUBE 3.-Mean dally maximum temperatures (degrees Fahrenheit) in July (July mean dally minimums are generally 100 lower in coastal areas and 20"-25° cooler in the interior). Modified from Watson (1959, p. 22). 
oo o 0 oc::J 

. 

~ ST MATTHEW ISLANO 

~~to 

I 

I 

I 

I 

GULF OF 

F c 0 c p A 

~ 178'·~ANI78' 

~ 0 ~--- .. ~ 

3Z <:)~ : 

pa• ~ 

F!GUBE 4.-Average annual precipitation, in incbes. From Watson (1959, p. 19). 

C E A 

EXPLANATION 

--16--

lsohyet 

Lim of ~ual average annual JWeeipitetion. 

1ntenxd variable, gtnnall11 -' i111:he• 

611' 

~ 

~ 

t:' 

rn 

0 

'%J 

tn 

llol' I 

re 

~ 0 

0 

~ 

~ ~ 

~ 

~ ...... 

0 

~ 

~ 

~ 

~ t'4 

;:s.. 

r:tJ 

1-3 

~ ~ 

~ ;:s.. 

ttl 

r:tJ 
68" 

oo o 0 oc::t 

I 

I 

/ 

~,' GAMBELL 

~~-~,. .. ~, 

~ST MATTHEW ISLAND 

C:>v,'tPRIBILOF ISLANDS 

,s..,. ... os 

~~C>'!. 

p A 

lJ 

EXPLANATION 

Existing glaciers 

Areas covered by Pleistocene glaciers 

Boundaries of permafrost regions 

GULF OF ALASKA 

A N 

c F c C E 0 

/] o-.:.o 0 

t7s• ~ 

FIGURE 5.-Extent of existing glaciers, Pleistocene glaciers, and permafrost regions in Alaska. A, continuous permafrost. B, dis90ntinuous permafrost. C, sporadic permafrost. D, no permafrost. (Moditled from 

Hopkins, Karlstrom, and others, 1955, fig. 11, and Williams, 1958, fig. 2.) 
DETAILS OF SCULPTURE-PHYSIOGRAPHIC EVOLUTION IN THE LAST MILLION YEARS 13 

GLACIATED mGHLANDS AND MOUNTAINS 

During the glacial expansions of the Pleistocene, 

snow accumulated on the mountains and avalanched 

into the heads of valleys, where it compacted into ice 

and flowed down the valleys as glaciers, just as it does 

on a smaller scale in the higher mountains of Alaska 

today. Eventually, most parts of the Pacific Mountain 

System and the Brooks Range were buried beneath a 

great network of glaciers and icefields; and smaller ice 

sheets existed on the Ahklun Mountains, on many 

mountains in the Intermontane Plateaus, and on the 

Seward Peninsula. 

The grinding and quarrying action of the glaciers 

enlarged the heads of the valleys into steep-walled 

flat-floored theaterlike basins or cirques and steepened 

or undermined the surrounding mountainsides (pl. 5, 

figs. 9 and 10; pl. 6, figs. 6 and 7). Freezing of water 

in joint cracks in the mountains that stood above the 

ice split out blocks that fell to the glaciers below to be 

carried away by the ice. As a result these mountains 

were left as jagged knife-edge ridges ( aretes) and 

mountain spires (horns) with steep craggy cliffs that 

are commonly accessible only to experienced mountaineers (pl. 6, figs. 1, 4, and 6). In the glaciated regions, the upper limit that was reached by the most recent ice sheet can be recognized as the lowest level at 

which these jagged cliffs occur. 

The cliffs and pinnacles are higher and steeper in 

areas of widely jointed rocks such as granitic intrusions 

and are less steep in closely jointed or slabby rocks 

such as schist and shale. Mountains formed of gently 

dipping sedimentary rocks have a cliff-and-bench topography (pl. 3, fig. 2); the cliffs are made of resistant widely jointed rocks such as limestone and quartzite and the benches are formed on soft marls and shales. 

'The ice generally flowed in the direction that its upper surface sloped whether or not this coincided with 

the slope of the buried htndscape. As it flowed, the 

ice-using as tools the rock fragments embedded in it 

-quarried, ground, and polished the buried land and 

carried away all weathered and broken material. Hilltops overridden by the ice were rounded and flattened. 

Layers of soft rock and cracks and planes of weakness 

SQch as joints and faults were etched out by the ice, 

n,nd the intervening masses were left as rounded knobs. 

Snch glaciated country, free of all soil ·and most loose 

materin,l, presents magnificent fresh outcrops for geologic stQd,y (pl. 6, figs, 7 and 11; pl. 5, fig. 11). 

Glacial erosion widened valleys so that they now 

have lJ.,shn,ped cross profiles with steep bounding walls 

t~nd. broad gentle floors; it straightened them by planil)g off projecting spurs; and it gave them irregular 

lOt1gitudi1101 profiles, eroding parts into deep rock 

baslnf:> (now filled by lakes) and in other parts forming 

773-~!}~ 0-66-3 

giant steps by quarrying action. In mountainous areas 

almost completely buried by ice, the movement of the 

glaciers tended to lower the passes between the former 

drainage systems; and such areas eventually came to 

consist of blocklike mountains separated by a network 

of valleys and low passes (pl. 5, fig. 4). 

In most of their erosion the ice sheets merely modified a pattern of valleys· that already existed; they did 

not entirely destroy old drainage systems, nor did they 

create new valleys. The material removed was carried 

to the lower margins-where melting and evaporation 

balanced the inflow of ice-and was deposited there as 

heaped-up lines of ridges or end moraines. Melt water 

flowing along the sides of the glaciers carved notches 

and valleys that are now one-sided (the former other 

side was ice) and deposited plains of sand and gravel 

that now stand as benches (pl. 2, fig. 10). Beyond these 

lines of marginal deposits the topography of the unglaciated parts of the mountains is usually markedly 

different (pl. 5, fig. 7) ; however, this distinct margin 

is visible only around the later great glacial advances. 

Where ancient glaciation was more extensive than later 

advances, its forms can be recognized in subdued sharpcrested mountains and open cirquelike valleys without 

steep headwalls or lakes (pl. 5, fig. 6), but in most 

places the older morainal deposits have largely been removed by erosion (pl. 3, fig. 7). 

GLACIATED LOWLANDS 

Glaciated lowlands are largely regions in which material was deposited by ice. The material deposited 

directly from ice (till) is generally a very poorly sorted 

mixture of boulders, sand, and clay. The few basins 

eroded by the glaciers in the low lands, generally where 

the glaciers flowed out of the bordering mountains, are 

now filled by lakes many miles across. 

As a glacier advances it may push up a ridge of 

debris at its front. This ridge, or moraine-generally 

an arc enclosing the mouth of the valley from which 

the glacier flowed-remains when the glacier melts. 

There may be many parallel ridges, each pushed up by 

a short advance that punctuated a general period of 

glacier retreat. Few of the arcuate ridges enclosing the 

mouths of glacial valleys are of such simple ice-push 

origin, however. The debris scraped up by the glacier 

tended to be concentrated near the glacier front. When 

the glacier melted away, this debris was left as a belt 

of hilly country somewhat higher than the ground it 

encloses (pl. 3, fig. 10; pl. 4, fig. 13). 

Some till was plastered directly on the ground from 

the lower part of the moving ice. If the resulting sheet 

of till is thin, it merely subdues the topography that 

existed before it was deposited. ·If it is thick, the preghtcial topography· may be obliterated, and a new to-
14 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

pography imposed, which generally has smooth streamlined hills (drumlins) and hollows elongated in the 

direction of ice flow. Such sheets of till, whether thick 

or thin, are known as ground moraine. 

As the glaciers melted away, the ice that was protected from sunlight by a covering of moraine did not 

melt as rapidly as the bare ice on either side of it. 

Rapid lowering of the bare ice surface left the morainecovered ice standing as steep-sided ridges. The moraine 

slid off these ridges onto the bare ice, and the formerly 

protected ice melted down in turn. The repeated inversion of topography that this process produced 

caused the debris to slide back and forth and resulted 

eventually in accumulation of the debris as great piles 

of open bouldery till (pl. 2, fig. 10). In the last stages 

of this process the glacier was too thin to flow, and the 

ice became stagnant. The last blocks of ice to melthalf buried by accumulations of till around them- . 

left hollows that are now commonly filled by irregular 

ponds and lakes. Large areas of the glaciated lowlands 

are marked by this chaotic stagnant ice topography 

(pl. 3, fig. 10; pl. 4, fig. 13). 

Melt water from the glaciers circulated through and 

between the blocks of stagnant ice, sorting and reworking much of the morainal material. Gravel deposited 

by water flowing in tubes within and beneath the ice 

stands as narrow sinuous ridges (eskers) now that the 

ice has melted away (pl. 2, fig. 13). Elsewhere, the 

water deposited the gravel to form plains bounded by 

walls of stagnant ice. The ice later melted, leaving 

these plains as flat-topped ridges and hills (kames). 

Some of these flat ridges coalesce downstream to form 

outwash plains-plains made of the sand and gravel 

washed out of the ice by glacial melt water (pl. 5, fig. 

3; pl. 6, fig. 5). 

Much glacial melt water and water trapped from 

surrounding uplands flowed along the margin of the 

ice sheet; in many places its channel 'YOuld have one 

wall of ice; some segments of its channel would be (mtirely in ice; and other segments would be cut across 

low spurs of the surrounding uplands. The remains of 

such channelways form benches and notches on the 

gently sloping valley walls or are narrow flat-floored 

steep-sided winding valleys that end abruptly downstream and upstream where the water formerly passed 

over ice. The streams, if any, that flow in these valleys 

today are too small to have cut them; at many places 

their direction of flow is the reverse of that of the melt 

water (pl. 5, fig. 2; pl. 6, fig. 9) .. 

Large parts of some lowlands, the Copper River 

Lowland, for example, were .flooded by lakes made 

when the rivers draining them were dammed by glaciers from the surrounding mountains. Finely ground 

rock debris that was washed into these lakes from the 

surrounding glaciers accumulated as layers of clay on 

the lake floors; toaay these floors are flat plains (pl. 

·6, fig. 3). 

The result of this variety of processes of deposition 

and erosion accompanying the advance and retreat of 

the glaciers is that the glaciated lowlands are much 

more irregular and· more diversified topographically 

than are the lowlands of unglaciated regions. 

UNGLACIATED UPLANDS 

The slopes of the unglaciated uplands of Alaska are 

modeled through the freezing and thawing of the thin 

surface layer above the permafrost. This thin layer 

of debris is formed by the freezing of water in- joints 

and cracks that shatters the bedrock into small fragments. During freezing the ground heaves outward· 

perpendicular to the slope. This heaving is caused 

partly by the expansion that water undergoes when it 

turns to ice and partly by the growth of ice crystals as 

water is drawn to them through capillary openings in 

the soil. When the ground thaws it tends to settle vertically downward under the influence of gravity. The 

small displacements that result shift the surface layer 

downslope, and over the years their cumulative effect 

is considerable. This slow, almost imperceptible motion 

is called creep. 

The layer of repeatedly frozen and thawed material. 

i~ kept close to saturation by ice melting in the frozen 

soil beneath it. In its saturated condition during the 

spring thaw it flows downslope as a thick sludge, a type 

of motion known as solifluction. Both creep .and solifluction can take place on very slight slopes. 

Freezing and thawing not only transport the surface layer, they also rearrange the soil and sort the 

soil constituents. The manner in which this rearrangement and sorting are accomplished is not yet completely understood and what is known is too complex 

to be told in this short review. However, the products 

are striking and are easily recognized. On nearly level 

surfaces the coarse fragments in the soil are sorted 

from the fine constituents and are arranged into polygonP1 networks of stones about centers of silt Or clay 

(pl. 2, fig. 12). The silt and clay centers of the polygons are commonly raised into low mounds. This is 

one type of patterned ground (pl. 2, fig. 11). On some 

sloping surfaces the polygons are elongated downslope 

through creep and solifluction and pass into stripes of 

stones and fine earth extending down . the slope (pl. 2, 

fig. 6). On other slopes the soil is arranged into small 

benches or terraces having steep banks of st9nes or turf. 

In some parts of Alaska, notably the Alaska Range, 

the stripes occur on south-fa.cing slopes and the terraces 

on north-facing slopes. 
DETAILS OF SCULPTURE-PHYSIOGRAPIDC EVOLUTION IN THE LAST MILLION YEARS 15 

The rate at which hills are eroded by creep and soli-· 

fluction and the forms of the hills that are produced 

depend to a very large extent upon the rate at which 

the material is moved down the slope by these processes. 

The rate of movement, in turn, depends upon many 

factors-among which are the steepness of the slope, 

the dP-pth of thaw, the amount of water in the soil, the 

size of the soil fragments, and the extent of vegetation. 

These factors vary not only from place to place but 

from year to year. In general, one may assume that! 

other things being equal, the rate of movement increases with steepness of slope and with increase in 

water content of the soil. Large blocks move more 

slowly than fine soil, and vegetation inhibits movement 

by decreasing the depth of penetration of the thaw and 

by holding the soil fast with its roots. 

If the rate of movement on the upper part of the 

slope is greater than that on the lower part, material 

will pile up at midslope. Lobelike masses (solifluction 

lobes)., particularly common near the upper limit of 

vegetation, show that this piling up of material is common (pl. 2, fig. 5). If the rate of transport is constant 

throughout the slope, erosion can take place only near 

the top of the slope, for the layer of material moving 

down the slope protects the lower parts from frost 

penetration and erosion. The tops of the hills will be 

flattened, whereas the lower parts of the slopes will retain their steepness and will be eroded only where the 

rate of transport increases at least in proportion to the 

distance from the top of the slope. Hence, where the 

rate of transport increases with the steepness of the 

slope, erosion of the lower part of the slope takes place 

only where the steepness increases downslope. The tendency of erosion by creep and solifluction, therefore, 

is to produce hills with broad gently rounded or flat 

summits and convex side slopes. Such hills are characteristic of the uplands throughout the unglaciated parts 

of Alaska (pl. 3, figs. 5, 6, and 9; · pl. 4, figs. 5, 10, 

and 11). 

If the downslope increase in the rate of transport is 

greater than the increase necessary to erode the slope 

evenly, the lower part of the slope is degraded more 

rapidly than the upper part. The part of the slope 

where degradation increases downslope must be growing steeper, because its base is being lowered more 

rapidly than its top. This part of the slope may grow 

into a craggy outcrop or a cliff (pl. 3, fig. 4). Common 

manifestations of this downslope increase in rate of 

degradation are tors, or bosses; these are resistant 

masses of unjointed bedrock a few tens of feet across 

and as high as a hundred feet, left standing on hill-. 

tops as the material around them moves downslope by 

creep and solifluction (pl. 2, fig. 3). 

An extreme example of downslope mass move~ent is 

a landslide. Where saturated with water, poorly consolidated or badly shattered rock may suddenly or 

slowly move downhill over surfaces of slipping. Contrary to popular impression, the water does not act as 

a lubricant; its effect is much more complicated. In 

part it breaks down the soil structures, such as clods, 

that hold the mineral and rock fragments together or 

dissolves salts or other chemicals binding or cementing 

the rock; thus the rock is weakened for sliding. Its 

greatest influence, however, is its buoyancy. The rock 

· is buoyed up by the weight of water filling its pores 

much as a stone is easier to lift when it is submerged in 

water, because the weight of the water it displaces acts 

against the weight of the stone. This buoyant weight 

counteracts the component of weight directed against 

the slope, which is the component that maintains the 

frictional resistance against sliding. At the same time 

the weight of the water is added to the component· 

directed along the slope-the component that causes the 

sliding. Permafrost provides abundant ground water 

that keeps the ground saturated during the summer; because the permafrost is impervious (its pores are 

clogged with ice) this water cannot drain away. Hence, 

permafrost areas have frequent landslides (pl. 2, fig. 7). 

A major ·factor in the landslide hazard is the steepness of the slope. Saturated silt and clay will slide or 

flow on slopes of 10° or less, but more massive material 

will stand on much steeper slopes, even in vertical 

cliffs, although it may contain much water. Anything 

that undercuts or steepens a slope is likely to cause 

landslides. The outer banks of meanders and the walls 

of canyons that are being deepened by streams are 

likely places for landslides. 

Landslides are characterized by hummocky topogra- · 

phy and irregular hillocks and depressions. At the 

upper end is a bowl-shaped hollow, bounded by steep 

scarps that mark the limits of the area of landslide 

subsidence. The lower end of some landslides is a bulging prominence, which may dam a stream to form a 

lake. The rocks of a landslide area are displaced, 

broken, and disturbed ; characteristically, blocks are 

rotated backward toward the mountain as they move 

downslope. 

Poorly consolidated rocks are generally protected 

from the erosional activity of rainwash by a blanket of 

vegetation. Areas laid bare by landslides lack this 

protection, and rainwash quickly carves exposures of 

sand and clay and of poorly consolidated sandstone 

and claystone into intricate patterns of steep-walled 

gullies. In Alaska the activity of rainwash alternates 

with freezing and thawing, and this alternation produces in the poorly consolidated rocks erosional forms 

of great beauty and regularity. The finest of these are 
16 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

the exposures of coal-bearing rocks in the Nenana coal 

field, in the Northern Foothills of the Alaska Range 

(pl. 2, fig. 8). On exposures of conglomerate, pebbles 

and cobbles are loosened by freezing and thawing and 

·bounce down the slopes, loosening other pebbles in their 

paths; the faint hollows formed by the first-falling 

pebbles channel other pebbles to fall their way so that 

an initially smooth cliff is gradually transformed into 

many closely spaced ravines which have rounded floors 

and are separated by knifelike ridges (pl. 2, fig. 9). 

The higher ridge crests and mountain tops in the unglaciated parts of Alaska are notched into giant steps 

or terraces several hundred to a thousand feet wide, 

whose banks of coarse rubble are 50-200 feet high (pl. 

2, fig. 1). The material on the upper surfaces of these 

terraces is progressively finer and more saturated with 

water toward the back of the terrace. The origin of 

these altiplanation terraces is not clearly understood, 

for they have not been studied in detail. They are 

probably an example of erosion produced by solifluction and creep acting with the frost-sorting process. 

The lower slopes of the upland hills are mantled 

with loess (wind-deposited silt) blown from the flood 

plains of the glacial streams. Part of this loess mantle 

is moved to the adjacent valley bottoms by torrents, 

mudflows, or· landslides; so, the lower slopes of the 

hills are marked by a fine tracery of shallow gullies 

(pl. 3, fig. 9). In its transport to the valley bottoms, 

the reworked loess carries down and buries great quantities of vegetable material and even animal remains. 

Subsequently the whole mass freezes. The placer 

gravels of interior Alaska are commonly covered with 

several tens to a few hundred feet of this frozen muck. 

Transitional in character between the forms of glaciated uplands and those of unglaciated uplands are 

rock glaciers; these are tonguelike or lobelike masses 

of coarse blocky rubble 50-250 feet high, resembling 

glaciers or lava flows, that move through the flow of 

their interstitial ice. They move outward at a rate of a 

few feet per year from the lower ends of talus cones, 

and hence are found only at the bases of steep cliffs 

in areas of frequent rockfalls. The interstitial ice is 

·necessary for the movement of rock glaciers, and the 

accumulation of boulders is necessary for the protection of the ice, which would otherwise melt. They are 

common in cirques and along the walls of glaciated 

valleys a few hundred to 2,000 feet below the firn line. 

The many cycles of glaciation in the glaciated parts 

of Alaska were matched by alterations of intense and 

mild frost action, creep, and solifluction in the unglaciated parts. In general, during the cold and wet glacial periods the level at which the more alpine forms 

of erosion were active was lowered, and the accumulation of loess was more rapid. During the warmer interglacial periods the silt tended to slide into the valleys to form muck, and the hillsides were moderately 

gullied. From a study of these deposits one can work 

out a succession of alternately severe and mild climates 

in interior Alaska that corresponds with at least the 

later stages of glacial advance and retreat in the adjoining glaciated areas. 

UNGLACIATED LOWLANDS 

The topography of the unglaciated lowlands of 

Alaska has been formed by the deposition of material 

brought in from adjacent highlands and glaciated areas 

by rivers and wind and by the action on this material 

of processes involving freezing and thawing that take 

place in permafrost areas. Most of the great rivers that 

flow through these low lands had their sources in ice 

sheets during the Pleistocene Epoch, and many of them 

still head in glaciers. They brought and are still bringing great quantities of sand and gravel and finely 

ground rock flour from the glaciers. Where the rivers 

enter the lowlands, this coarse material was deposited 

in the form of broad, low fan-shaped deposits (outwash fans) that are crossed by the bare flood plains of 

the braided rivers (pl. 3, fig. 8). The gravel deposits 

raise the beds of the rivers and cause them to overspill 

their banks and change their courses to flow through 

adjacent lower areas. Such a shift of the Nenana River 

in 1921 destroyed a segment of the newly built Alaska 

Railroad. This shifting of the streams builds the outwash fans. Most of the fans were built· during the 

Pleistocene ice advances, when the rivers were much 

more heavily laden than they are now. Because they 

have less material to carry from the glaciers, the rivers 

have removed some of the gravel they formerly deposited and now flow through the upper parts of their 

outwash fans in terraced valleys a few feet to a few 

hundred feet deep and * -4 miles wide. The outwash 

terraces can be traced for miles upstream into the surrounding mountains, where they generally end at the 

end moraines of the ice advances of the time they were 

deposited (pl. 4, fig. 13; pl. 6, fig. 2). 

Downstream from the fans the rivers carry silt and 

clay. Banks of these compact sticky materials are not 

as easily eroded as are the loose banks of gravel and 

sand. Consequently, the rivers. cannot spread freely 

over their flood plains in networks of small channels 

but instead concentrate in one or two large channels, 

which meander across the silt-covered plains (pl. 4, 

figs. 6 and 7). 

Many of the streams rise in unglaciated regions. 

Some of these are provided with abundant debris by 

frost action in highland source areas and behave much 

as glacial streams do. Others carry very little inorganic 

debris and meander sluggishly over flat marshy lake-
DETAILS OF SCULPTURE-PHYSIOGRAPIDC EVOLUTION IN THE LAST MILLION YEARS 17 

dotted plains. Peat accumulates in the lowland flats 

along these sluggish streams and extensive logjams 

occur in their courses. 

The glacial rivers are subjected to daily and annual . 

floods. The major annual flood occurs during the 

spring ice breakup, which progresses from the headwaters downstream. The ice floes form great jams and 

back up the rivers, which then flood the lowlands and 

deposit silt and clay in the vegetation of their flood 

plains. Freezing of this mixture of silt, clay, and 

slowly decaying vegetation keeps pace with accumulation. Generally the percentage of ice in this type of 

permafrost is as great as or greater than the combined 

percent of inorganic silt and organic matter. 

During periods of low water the wind blows great 

clouds of dried mud and sand from the beds of the glacial streams. The fine material settles out of the air to 

mantle the plains and lower slopes of the surrounding 

hills as loess, which has accumulated to great thickness. The great dust storms that blow across the Alaska 

and Richardson Highways from the beds of the Delta, 

Donjek, and White Rivers are examples of the loessforming process in action. Such storms must have been 

· much m.ore common and extensive during the glacial 

advances of the Pleistocene. 

The sand that was blown from the river flats accumulates as dunes. Some dunes form long low ridges 

parallel to the direction of the wind. Others are great 

wavelike ridges at right angles to the wind and have 

gentle windward slopes and steep lee slopes (pl. 4, fig. 

12). Most of these are now stable and overgrown with 

vegetation, but active dune deserts, barren as any in the 

Sahara, cover parts of the Koyukuk Flats and Kobuk 

Valley. 

Ice accumulates in the silt in the form of interstitial 

cement, thin horizontal sheets, and thick vertical 

wedges that form polygonal networks, another type of 

polygonal ground (pl. 2, fig. 2). The ice wedges start 

from tension cracks that open during winter periods 

of rapid and profound drop in temperature. Later, 

water trickles into these cracks and freezes, adding to 

the permafrost. The cracks open during cold spells of 

following winters, and the ice wedges gradually 

thicken. The ice wedges are marked at the surface by 

shallow troughs bordered by low ridges of material 

thrust aside when the ground warmed and expanded 

in spring and summer after the contraction crack had 

filled with ice. Generally, the vegetation growing in 

these troughs is different from that growing in the intertrough areas. When the climate warms or the vegetation cover is removed, the ice wedges melt and the 

ground above them settles. Fields cleared in such icewedge terrain have to be abandoned after a few years. 

The meandering rivers rapidly erode the frozen silty 

outer hanks of their meanders at the same time that 

silt and sand bars are built in the slack water at the 

insides of the meanders. The rate of migration of the 

channels by this process has been estimated td be as 

much as 75 feet per year. The pattern of delicate alternation of bars and swales (known as meander-scroll 

pattern) left behind as the rivers migrate laterally .is 

slowly buried by silt and vegetation, which is added to 

the body of permafrost (pl. 4, figs. 6 and 7). 

The permafrost beneath the great silt-covered flats, 

50 percent or more ice by volume, is in delicate equilibrium with the prevailing temperature and is generally 

protected from thawing by an insulating layer of moss, 

grass, and other low plants. If this vegetation layer 

is broken, the soil beneath it thaws and collapses, forming a pit which is filled with water. This water, in 

turn, thaws the banks of the pit, which is thus enlarged 

to a pond or lake . called a thaw or thermokarst lake ; 

the lake grows by collapse of the walls of the pit until 

the water has an opportunity to drain off. Silt and 

vegetation again cover the hollow and ice forms in the 

soil once more. The cycle may then repeat itself (pl. 4, 

fig. 3). 

Loess and muck on· hillsides, also frozen, can thaw 

and collapse by this process. Generally, much of the 

water drains out of the pits so formed, and an irregular topography of steep-walled flat-bottomed thaw 

sinks, which are a few feet to a few tens of feet deep 

and some of which contain lakes, forms on rolling 

silt-covered lowlands and terraces (pl. 4, fig. 7). Such 

topography is easily mistaken for morainal topog-. 

raphy. 

Pingos, rounded or conical ice-covered turf mounds 

a few feet to 100 feet high, are characteristic features 

of the lowlands of the northern parts of Alaska and in 

valleys in central Alaska (pl. 2, fig. 4). Pingos form 

when water trapped under great pressure in layers 

within the permafrost (between the permafrost and 

newly frozen ground) or beneath permafrost breaks 

through the confining frozen ground and forms a great 

blister of ice just beneath the turf-for water kept 

liquid at subfreezing temperatures only by high confining pressure freezes instantly when the pressure 

is released. 

The processes that affect the unglaciated lowlands 

are for the most part depositional processes that reduce or erase irregularities on the lowland surface. 

The permafrost prevents downward percolation of 

ground water, and summer melting of ice at the top of 

the permafrost keeps the vegetation on these relatively 

smooth plains saturated. Consequently, large parts of 

the unglaciated lowlands are marshy flats, impassable 
18 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

to overland travel except in winter (pl. 4, figs. 1, 3, 

and 7). 

DESCRIPTION OF THE PHYSIOGRAPHIC DIVISIONS 

Two of the major physiographic features of North 

America extend into Alaska-the Interior Plains and 

the North America Cordillera. The Arctic Coastal 

Plain is the only continuation of the Interior Plains in 

Alaska. The North American Cordillera, which includes most of Alaska, consists of three of the major 

divisions of Fenneman's (1946) classification-the 

Rocky Mountain System, the Intermontane Plateaus, 

and the Pacific Mountain System, which form three 

parallel belts from the conterminous United States 

through Canada to Alaska (pl. 1). In Bostock's ( 1948) 

terminology, the Rocky Mountain System is the Eastern System and the Pacific Mountain System, the 

Western System. The names used by Fenneman had 

been applied to Alaska by Brooks in 1906, and there 

seems to be no reason for abandoning them here in 

favor of Bostock's terms. 

The Rocky Mountain System in Alaska is represented 

by the Brooks Range-a mountainland 80 miles wide 

and 600 miles long that rises to altitudes of 4,000-9,000 

feet-and by the Arctic Foothills-a rolling upland 

about 80-100 miles wide on the north side of the Brooks 

Range. The Brooks Range faces the Arctic Foothills 

with an abrupt scarp, and similarly rises abruptly 

above low lands and low plateaus on the· south (pl. 1). 

The Intermontane Plateaus system in Alaska consists 

of a heterogeneous assemblage of low mountain ranges, 

rolling uplands, and alluvium-floored lowlands that decline in average altitude and relief westward from the 

Canadian border to the Bering and Chukchi Seas. Altitudes of uplands and mountains rarely exceed 6,000 

feet in the east and 4,000 feet in the west, and are 

generally below 3,000 feet. 

The Pacific Mountain System is an arcuate belt of 

high mountains that borders the Pacific Ocean. Generally, the system consists of two ranges of mountains 

·and a belt of intervening lowlands. The northern range 

is represented in Alaska by the Aleutian Range, the 

Alaska Range, and the Coast Mountains; and the 

southern range, by the Kodiak, Kenai-Chugach, 

Baranof, and Prince of Wales Mountains. Intervening 

lowlands include the Cook Inlet-Susitna Lowland, the 

Copper River Lowland, and the Kupreanof Lowland. 

The northern and southern ranges come together and 

culminate in the St. Elias Mountains. Relief in the 

Pacific Mountain System is extreme: the lowlands lie 

near or even below sea level and the mountains ·rise. to 

altitudes of 10,000-20,000 feet. 

The· Intermontane Plateaus are drained by the 

Yukon River,' the largest river in Alaska, and by other 

streams flowing to the Bering and Chukchi Seas. The 

divide between the Bering and Pacific drainages :follows in part the northern ridge of the Pacific Mountain 

System and is in part in the depressions south of that 

ridge. The divide between the Bering-Chukchi and 

Arctic Ocean drainage lies mostly in the Brooks Range, 

the main part of the Rocky Mountain System in 

Alaska. The major rivers and their drainage basins are 

shown in figure 6. 

INTERIOR PLAINS 

ARCTIC COASTAL PLAIN (1) 

General topography.-The Arctic Coastal Plain is a 

smooth plain rising imperceptibly from the Arctic 

Ocean to a maximum altitude of 600 feet at its southern 

margin. The coastline makes little break in the profile 

of the coastal plain and shelf, and the shore is generally 

only 1-10 feet above the ocean; the highest coastal 

cliffs are only 50 feet high. The Arctic Coastal Plain 

province is divided into the Teshekpuk ( 1a) and White 

Hills (1b) ·sections. Scattered groups of low hills rise 

above the plain in the .White Hills section; the 

Teshekpuk section is flat. Locally, an abrupt scarp 

50-200 feet high separates the coasta,l plain from the 

Arctic Foothills. Locally pingos are sufficiently abundant to give an undulatory skyline. The part of the 

coastal plain between the Kuk and Colville Rivers has 

scattered longitudinal sand dunes 10-20 feet high 

trending N. 55°-75° E. 

Drainage.-The Arctic Coastal Plain is very poorly 

drairied and consequently is very marshy in summer. 

It is crossed by rivers which head in highlands to the 

south. Rivers west of the Colville River meander sluggishly in valleys incised 50-300 feet; those east of the 

Colville cross the plain in braided channels and are 

building deltas into the Arctic Ocean. 

Lakes.-The Teshekpuk Lake section of the Arctic 

Coastal Plain ·province is covered by elongated thaw 

lakes oriented N. 15 o W.; these range from a few feet 

to 9 miles long, are from 2 to 20 feet deep, and are oval 

or rectangular in shape (pl. 4, fig. 3). The lakes expand 

about 1 meter per year in places, and several generations of drained lake basins may be seen. 

Glaciers and permafrost.-There are no glaciers. The 

entire land area is underlain by permafrost at least 

1,000 feet thick. The permafrost table (base of zone of 

summer thaw) is %-4 feet below the surface. A network of ice-wedge polygons covers the coastal plain 

(pl. 2, fig~ 2). These are oriented parallel and perpendicular to receding shorelines because of stress differences set up by horizontal temperature gradients. 

Random polygons form in areas of more uniform 

stress. 
56' 

~T MATTHEW ISLAND 

. PRIBILOF ISLANDS 

~ 

GULF OF ALASKA 

p A C F I C 

FIGURE 6.-D rainsge basins . . of major rivers of AI sska. 

E 0 c A 

EXPLANATION 

LoD wlands and alluvial plains 

Bou~~e basi;-~~ nes of ba8ins of tribu es Yukon are dashedtaries to the 
20 PHYSIOGRAPIDC DIVISIONS OF ALASKA 

Geology.-The Teshekpuk Lake section is underlain 

by 10-150 feet of unconsolidated Quaternary marine 

sediments resting on nearly flat Cretaceous sedimentary 

rocks containing coal. The White Hills section contains, in addition, lower Tertiary sedimentary deposits. 

References.-Black (1952, 1955); Black and Barksdale (1949) ; W. P. Brosge (oral commun., 1959); 

Chapman and Sable ( 1960) ; Coulter and others 

(1960); Lachenbruch (1960a, 1960b, 1962); · A. H. 

Lachenbruch (oral commun., 1962); Leffingwell (1919, 

p. 150-155, 211); W. W. Patton, Jr. (oral commun., 

195~); Porsild (1938); Smith and Mertie (1930) ;-I. L. 

Tailleur (oral commun., 1959). 

The Arctic Coastal Plain is covered by the following 

1:250,000 topographic maps: Barrow, Barter Island, 

Flaxman Island, Beechy Point, Harrison Bay, Teshekpuk, Meade River, Wainwright, Demarcation Point, 

Mount Michelson, Sagavanirktok, Umiat, Ikpikpuk 

River, Lookout 'Ridge, Utukok River, and Point Lay. 

ROCKY MOUNTAIN SYSTEM 

ARCTIC FOOTHILLS (2) 

General topography.-The Arctic Foothills consist 

of rolling plateaus and low linear mountains; they are 

divided into two sections. The northern section (2a) 

rises from an altitude of 600 feet on the north to 1,200 

feet on the south and has broad east-trending ridges, 

dominated locally by mesalike mountains. The southern 

section (2b) is 1,200-3,500 feet in altitude, has local 

relief of as much as 2,500 feet, and is characterized by 

irregular buttes, knobs, mesas, east-trending ridges 

and intervening gently undulating tundra plains (pl. 3, 

figs. 3 and 4). 

Drainage.-The Arctic Foothills are crossed by 

north-flowing rivers from sources in the Brooks Range. 

The Colville River, the largest stream, has an anomalous east-trending course for more than 220 miles along 

the boundary between the northern and southern sections. Most streams have swift, braided courses across 

broad gravel flats that are locally covered in winter 

with extensive sheets of aufeis, or anchor ice, that 

freezes to the riverbeds ; this filling of the channels 

causes the streams to flood their gravel flats. . 

Lakes.-A few thaw lakes are present in the river 

va.lleys and on some divides. The upper valleys of 

major rivers from the Brooks Range contain many 

morainal lakes. 

Glaciers and permafrost.-There are no glaciers. The 

entire province is underlain by permafrost. Ice wedges, 

stone stripes, polygonal ground, and other features 

of a frost climate are common. 

Geology.-The northern ·section is underlain by 

Cretaceous sedimentary rocks deformed into long 

linear folds of the Appalachian type. Unequal erosion 

of layers of rock that differ in_ hardness has produced 

the linear-ridge topography. The southern section is 

underlain by diverse sedimentary rocks of Devonian to 

Cretaceous age together with mafic intrusions, all 

tightly folded and overthrust to the north. A preglacial gravel-covered pediment surface is preserved on 

some divides between north-flowing rivers. Hummocky 

morainal ridges border most valleys issuing from the 

central Brooks Range. 

References.-Chapman and Sable (1960) ; J. T. 

Dutro (oral commun., 1959); Keller and others (1961); 

W. W. Patton, Jr. (written commun., 1959) ; Payne 

and others (1951); Schrader (1904, p. 45-46); Smith 

and Mertie (1930); I. L. Tailleur (written commun., 

1959). 

The Arctic Foothills are covered by the following 

1: 250,000 topographic maps: Meade River, Wainwright, Demarcation Point, Mount Michelson, Sagavanirktok, Umiat, Ikpikpuk River, Lookout Ridge, 

Utukok River, Point Lay, Philip Smith Mountains, 

Chandler Lake, Killik River, Howard Pass, Misheguk 

Mountain, De Long Mountains, Point Hope, and 

Noatak. 

ARCTIC MOUNTAINS PROVINCE 

The Arctic Mountains province consists of mountains and hills carved chiefly from folded and over~ 

thrust Paleozoic and Mesozoic sedimentary rocks. It is 

divided into the following sections: De Long Moun~ 

tains (3), Noatak Lowlands (4), Baird Mountains (5), 

central and eastern Brooks Range ( 6), and AmblerChandalar Ridge and Lowland section (7). 

DE LONG MOUNTAINS (3) 

General topography.-The central part of the De 

Long Mountains consists of rugged glaciated ridges 

that are 4,000-4,900 feet in altitude and have a local 

relief of 1,500-3,000 feet. Narrow even-crested ridges 

in the lower eastern and western parts rise to 3,000-

4,000 feet. Many passes about 3,500 feet in altitude 

cross the range. The north boundary with the Arctic 

Foothills is irregular and indistinct, but the south 

front is abrupt. 

Drainage.-Streams from the De Long Mountains 

flow south and west to the Noatak River and the 

Chukchi Sea and north to the Arctic Ocean. The 

drainage divide is at the north edge of the mountains. 

Asymmetry of passes, . barbed drainage, wind gaps, 

perched tributaries, and abandoned valley systems suggest that the divide has moved northward by stream 

capture. 

Lakes, glaciers, and permafrost.-There are no lakes 

or glaciers in the De Long Mountains. The entire section is under lain by permafrost. 
ARCTIC MOUNTAINS PROVINCE 21 

Geology.-The De Long Mountains consist of folded 

and faulted sedimentary rocks of Devonian to Cretaceous age, intruded by massive diabase sills that are the 

chief cliff-forming units; structural trends are westward in the eastern and northern mountains and 

change to southwestward in the southwestern part. The 

eastern and northern De Long Mountains are· a great 

sheet thrust north over the rocks of the Artie Foothills. 

ReferenAJes.-Mangus and others (1950); Smith and 

Mertie (1930); I. L. Tailleur (written commun., 1959). 

The De Long Mountains are covered by the following 1 : 250,000 topographic maps: Howard Pass, Misheguk Mountain, and De Long Mountains. 

NOATAK LOWLANDS (4) 

General topography.-Two broad lowlands surrounded by hills and separated by a rolling upland lie 

along the Noatak River. The Mission Lowland ( 4a) is 

a broad tundra flat, containing thaw lakes and pingos 

25-300 feet high and crossed by the forested flood plain 

of the Noatak River; it merges with the surrounding 

foothills by silt uplands intricately dissected by thaw 

sinks. The Aniuk Lowland ( 4b) is an irregular rolling 

plain that slopes gradually upward on the south to 

merge with a subsummit upland in the Baird Mountains. The intervening upland is the Cutler River 

Upland ( 4c). · 

Drainage.-The two lowlands and the Cutler River 

Upland are drained entirely by the Noatak River, 

which rises in the western part of the Schwatka Mountains. The Noatak crosses the Cutler River Upland 

and the Igichuk Hills south of the Mission Lowland 

by narrow cliffedgorges a few hundred feet deep. 

Lakes.-The Mission Lowland has numerous thaw 

lakes. There are scattered morainal and thaw lakes 

in the Aniuk Lowland. 

Glaciers and permafrost.-There are no glaciers. The 

entire section is underlain by permafrost, and pingos 

abound in the Mission Low land. 

Geology.-Bedrock geology beneath the lowlands is 

probably similar to that of surrounding uplands and 

mountains. The entire valley of the Noatak was probably glaciated in pre-Wisconsin time, but· glaciers of 

Wisconsin time occupied only part of the Aniuk Lowland and reached only the north edge of the Mission 

Lowland. The depth of alluvial fill in the lowlands is 

unknown. Rounded gravel is reported 850 feet above 

the Noatak in the Cutler River Upland, and the course 

of the Noatak across the upland may be superposed. 

References.-Smith (1913, p. 27-33, 92-93); Smith 

and ~fertie ( 1930) ; I. L. Tailleur (written commun., 

1949). 

The Noatak Low lands are covered by the following 

1 : 250,000 to'pographic maps: Howard Pass, Misheguk 

Mountain, De Long Mountains, Ambler River, Baird 

Mountains, and Noatak. 

BAIRD MOUNTAINS (6) 

General topography.-Moderately rugged mountains 

having rounded to sharp summits 2,500-3,000 feet in 

altitude rise abruptly from lowlands on the south and 

. west to a subsummit upland along the crest of the 

Baird Mountains. This s11bsummit upland slopes gently 

northward and merges with the Aniuk Lowland and 

Cutler River Upland. Scattered groups of higher 

mountains ( 3,500-4,500 feet in altitude) rise above 

the subsummit upland; they were centers of glaciation 

in Pleistocene time. The indistinct boundary with the 

Schwatka Mountains on the east is drawn where the 

relief increases abruptly eastward. 

Drainage.~ The Baird Mountains are drained by 

streams that flow north to the Noatak River and south 

to the l{obuk River. The south-flowing streams head 

in narrow ravines having steep head walls, several 

hundred feet high, incised in broad flat passes that are 

the beheaded parts of north-draining valleys. This relationship indicates that the divide is migrating to the 

north by headward erosion. 

Lakes and glaciers.-There are no lakes or glaciers in 

the Baird Mountains. 

Geology.-Schist, quartzite, and limestone of Paleozoic age make up most of the Baird Mountains. Structural trends are eastward and the internal structure is 

probably anticlinoria!. Differential erosion involving 

limestone and volcanic rocks of a northeast-trending 

anticline along the northwest border of the mountains 

has produced prominent northeast-trending ridges. 

References.-Smith and Mertie (1930) ; I. L. Tailleur (written commun., 1959). 

The Baird Mountains are covered by the following 

1: 250,000 topographic maps: Ambler River, Baird 

Mountains, and. Noatak. 

CENTRAL AND EASTERN BROOKS RANGE (6) 

General topography.-The central and eastern 

Brooks Range is a wilderness of rugged glaciated easttrending ridges that rise to generally accordant summits 7,000-8,000 feet in altitude in the northern part 

and 4,000-6,000 feet in altitude in the southern part. 

The easterly grain of the topography is due to belts of 

hard and soft sedimentary and volcanic rocks. The 

mountains have cliff-and-bench slopes characteristic of 

glacially eroded bedded rocks. Abrupt mountain fronts 

face foothills and low lands on the north (pl. 3, figs. 1, 

2, and 3, pl. 4, fig. 4). 

Drainage.-The drainage divide between the Bering 

Sea and Arctic Ocean drainages is near the north edge 

of the range west of long. 149° W. and in the center 

of the range east of long. 149° W. The major rivers 
22 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

flow north to the Arctic Ocean and south to the Yukon, 

Koyukuk, and Kobuk Rivers in flat-floored glaciated 

valleys *-2 miles wide; they have a broad dendritic 

pattern. Minor tributaries flow east and west parallel 

to the structure, superposing a trellised pattern on the 

dendritic pattern of the major drainage. 

Lakes.-Large rock-basin lakes lie at the mouths of 

several large glaciated valleys on the north and south 

sides of the range. The Brooks Range in general is 

characterized by a _paucity of lakes for a glaciated area. 

Glaciers.-Small cirque glaciers are common in the 

higher parts of the range, in the Schwatka Mountains 

( 6a), and in mountains around Mount Doonerak. The 

firn line is at an altitude of about 6,000 feet in northfacing cirques and about 8,000 feet in south-facing 

cirques. Valley glaciers 6 miles long are fed from 

cirques and small icecaps in the Romanzof Mountains 

(6b). 

Geology.-The central and eastern Brooks Range is 

com posed chiefly of Paleozoic limestone, shale, quartzite, slfl,te, and schist. Northeast of the Sagavanirktok 

River the Paleozoic rocks are in faulted folds overturned to the north. Elsewhere, they are in giant plates 

or nappes thrust to the north. The deformation is of 

Laramide age. The north front of the range is made 

of light-colored cliff-forming Mississippian limestone 

(see pl. 3, figs. 2 and 3). Rocks south of lat. 68° N. 

are metamorphosed and generally equivalent in age to 

those farther north. Granitic intrusions underlie the . 

higher parts of the Schwatka Mountains ( 6a) and 

Romanzof Mountains ( 6b), both of which rise to 

8,500-9,000 feet in altitude. 

References.-Brosge ( 1960; oral commun., 1959) ; 

Brosge and others (1952} ;. Chapman and Eberlein 

(1951); R. L. Detterman (oral commun., 1959}; 

Detterman and others ( 1958) ; Keller and Detterman 

(1951); Keller and Morris (1952}; Keller and others 

(1961); Mangus (1953) ; Mangus and others (1950); 

W. W. Patton, Jr. (oral commun., 1959); Patton and 

others (1951); Payne and others (1951}; Schrader 

( 1904) ; Smith ( 1913, p. 32-35) ; Smith and Mertie 

(1930); I. L. Tailleur (oral commun., 1959}. 

The central and eastern Brooks Range is covered by 

the following 1 : 250,000 topographic maps: Demarcation Point, Mount Michelson, Sagavanirktok, Table 

Mountain, Arctic, Philip Smith Mountains, Chandler 

Lake, Killik River, Howard Pass, Christian, Chandalar, Wiseman, Survey Pass, and Ambler River. 

AMBLER-CHANDALAR RIDGE AND LOWLAND SECTION (7) 

General topography.-This section consists of one 

or two east-trending lines of lowlands and low passes 

3-10 ·miles wide and 200-2,000 feet above sea level, 

bordered on the north by the abrupt front of the 

Brooks Range. Along the south side is a discontinuous 

line of rolling to rugged ridges, 25-75 miles long and 

5-10 miles wide, rising to 3,000-4,500 feet in altitude. 

Some of these ridges were intensely glaciated. Within 

the lowlands are east-trending ridges 5-10 miles long. 

Drainage.-The western part of the section is 

drained by tributaries of the Kobuk River; the central 

part, by the l{oyukuk River and its tributaries; and the 

eastern part, by the Chandalar River. Most streams 

flow south out of the Brooks Range across both the lowlands and the ridges to lowlands farther south. The 

drainage was probably superposed but may have been 

disoriented later by glaciers. The Chandalar River 

flows east along the eastern part of the trough. 

Lakes.-Severallarge lakes fill ice-carved rock basins 

in deep narrow canyons across the southern ridge. 

Areas of ground and end moraines contain many 

ponds. The flood plains of the major streams have thaw 

lakes and oxbow lakes. 

Glaciers and permafrost.-The section contains no 

_ glaciers but ,is underlain by continuous permafrost. 

Geology.-The ridges are composed in part of resistant massive greenstone (metamorphosed basalt) 

of Mesozoic ( ~) age. The lowlands are underlain 

largely by Cretaceous sedimentary rocks, folded into 

sync1ines. P1eistocene glaciers from the Brooks Range 

extended across the lowland and through passes in the 

line of ridges. 

References.-Brosge (1960; oral commun., 1959}; 

W. vV. Patton, Jr., (oral commun., 1959); I. L. Tailleur, (oral commun., 1959) ; Smith and Mertie, ( 1930). 

The Ambler-Chandalar Ridge and Lowland section 

is covered by the following 1 : 250,000 topographic 

maps: Chandalar, Wiseman, Survey Pass, Ambler 

River, Bettles, Hughes, and Shungnak. 

INTERMONTANE PLATEAUS 

NORTHERN PLATEAUS PROVINCE 

The Northern Plateaus province consists of uplands 

and lowlands carved chiefly in Paleozoic and Precambrian ( ~) rocks. It is divided into the following sections: Porcupine Plateau (8), Old Crow Plain (9), 

(not described}_, Ogilvie Mountains (10}, Tintina 

Valley (Eagle Trough) (11}, Yukon-Tanana Upland 

(12}, Northway-Tanacross Lowland (13}, Yukon Flats 

section (14}, Rampart Trough (15), and KokrineHodzana Highlands ( 16). 

PORCUPINE PLATEAU (8) 

General topography.-Low ridges ·having gentle 

slopes and rounded to flat summits 1,500-2,500 feet in 

altitud~ dominate the topography_ of the Porcupine 

Plateau; a few domes and mountains rise to, 3,500 feet. 

Valley floors are broad; .~nd valley patterns, irregular, 

having many" imperceptible divides. Thazzik Mountain 
NORTHERN PLATEAUS PROVINCE 23 

(Sa) in the extreme west, a rugged glaciated mountain 

group, rises to 5,800 feet. 

Drainage.-The entire plateau, except the extreme 

northeastern part, is drained by tributaries of the 

Yukon River. The Chandalar, Sheenjek, and Coleen 

Rivers rise in the Brooks Range and flow south across 

the plateau in broad valleys floored with moraines and 

outwash terraces. The Porcupine River ·crosses the 

plateau in a narrow cliff-lined canyon 50-500 feet deep. 

The Black and Little Black Rivers, which drain the 

southeastern part of the area, meander through broad 

irregular flats. 

Lakes.-A few moraine-dammed lakes lie in glaciated passes and valleys along the north margin of the 

plateau. The largest of these is Old John Lake, 5 miles 

long and 2 miles wide. Scattered thaw lakes occur in 

lowlands and low passes. 

Glaciers and permafrost.-There are no glaciers. 

The entire section is underlain by continuous permafrost. 

Geology.-The northern part is underlain by crystalline schist, granite, quartzite, slate, and mafic rocks, 

probably mostly Paleozoic in age; the southeastern part 

is underlain by moderately deformed Paleozoic and 

Mesozoic sedimentary rocks. Basinlike areas of Tertiary rocks and flat-lying Cenozoic flows occur along 

the Porcupine River. 

References.-Bostock {1948); W. P. Brosge (oral 

commun., 1959); FitzGerald {1944); Kindle {1908); 

Mertie ( 1930·a). 

The Porcupine Plateau is covered by the following 

1 : 250,000 topographic maps: Table Mountain, Arctic, 

Coleen, Christian, Chandalar, Black River, and Charley River. 

OGILVIE MOUNTAINS (10) 

General Topography.-The Ogilvie Mountains have 

sharp crestlines, precipitous slopes, and deep narrow 

valleys; they rise to 5,000 feet in altitude, and local 

relief is as much as 4,000 feet. The ridges are interconnected and passes are few. The narrow valleys are 

interrupted by gorges where rivers cross cliff-forming 

layers of rock. 

. Drainage.-The Ogilvie ~fountains are drained by 

the J(andik, Nation, and Tatonduk Rivers, all tributaries of the Yukon River. 

Lakes.-Small thaw lakes and oxbow lakes are along 

t.he Yukon River in the southern part of the mountains. 

Glaciers and perrnaf'rost.-There are no glaciers. 

Most of the section is underlain by permafrost, and 

pingos are common. 

Geology.-Moderately folded and faulted sedimentu.ry n.nd volcanic rocks ranging in age from late Precnmbrian to Cretaceous make up the mountains. Some 

formations of limestone~ dolomite, quartzite, and greenstone are in massive cliff-forming beds. Continental 

sandstone and conglomerate of Late Cretaceous and 

early Tertiary ( ~) age underlie a lowland on the upper 

.Nation River. 

References.-Bostock {1948, p. 59); Brabb {1962, 

oral commun., 1962); Mertie {1932). 

The Ogilvie Mountains are covered by the following 

1: 250,000 topographic maps: Charley River and Eagle. 

TINTINA VALLEY (11) 

General topography.-The Tintina Valley is a narrow belt of low country consisting of low rounded 

ridges and open valleys, which pass northwest into 

· loess-covered terraces and a lake-dotted plain that 

connects ·with the Yukon Flats section. Relief in the 

southeastern part (southeast of Woodchopper Creek) 

is 1,000-1,500 feet, and ridges rise to 2,000-2,500 feet 

in altitude. Discontinuous low hills on the north separate this part from the Yukon River, and the mountains of the Yukon-Tanana Upland rise gradually 

above it on the southwest. 

The northwestern part, around Circle Hot Springs 

and Birch Creek, is a lake-dotted plain that slopes 

gradually upward to the base of surrounding hills, and 

that is separated from the Yukon River by a flattopped gravel ridge about 400 feet high and 3-4 miles 

wide. 

Drainage. -The southeastern part in Alaska is 

drained chiefly by small north-flowing streams that 

rise in the upland to the south and have superposed 

courses to the Yukon River in narrow valleys acro~s 

hills of resistant rocks on the north. The northwestern 

part is drained largely by Birch Creek, which flows 

parallel to the Yukon into the Yukon Flats. 

Lakes.-There are no large lakes in the southeastern 

part. The plain of the northwestern part has several 

thaw lakes; the largest, l\fedicine Lake, is nearly 2 

miles across. 

Glaciers and permafrost.-The section contains no. 

glaciers but is generally underlain by permafrost. 

Geology.-The Tintina Valley is underlain by a synclinal belt of highly deformed, easily eroded continental sedimentary rocks of Cretaceous and Tertiary 

age that are probably in sedimentary contact with the 

metamorphic and granitic rocks of the Yukon-Tanana 

Upland on the south and with the well-consolidated 

Paleozoic and Mesozoic sedimentary rocks of the Ogilvie Mountains on the north. Northwest of W oodchopper Creek, loess mantles flat-topped ridges and hides 

most bedrock outcrops. The geology beneath the plain 

near Circle Hot Springs is unknown. 

References.-Brabb {1962; oral commun., 1962); 

Mertie ( 1930b, 1937, and 1942). 
24 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

The Tintina Valley is covered by the following 

1:250,000 topographic maps: Charley River, Eagle, 

and Circle. 

YUKON-TANANA UPLAND ·(12) 

General topography.-The Yukon-Tanana Upland 

is the Alaskan equivalent of the Klondike Plateau in 

Yukon Territory. Rounded even-topped ridges with 

gentle side slopes characterize this section of broad undulating divides and flat-topped spurs (pl. 3, figs. 6 

and 9). In the western part ( 12a) these rounded ridges 

trend northeast to east; they have ridge-crest altitudes 

of 1,500-3,000 feet and rise 500-1,500 feet above adjacent valley floors. The ridges are surmounted by compact rugged mountains 4,000-5,000 feet in altitude. 

Ridges in the eastern part (12b) have no preferred direction, are 3,000-5,000 feet in altitude but have some 

domes as high as . 6,800 feet, and rise 1,500-3,000 feet 

above adjacent valleys (pl. 3, fig. 6). In the extreme 

northeast the ridges rival the Ogilvie Mountains in 

ruggedness. Valleys in the western part are generally 

flat, alluvium floored, and * -¥2 mile wide to within a 

few miles of headwaters. Streams in the eastern part 

that drain to the Yukon flow in narrow V-shaped terraced canyons, but the headwaters of the Fortymile 

and Ladue Rivers are broad alluvium-floore~ basins. 

Drainage.-The entire section is in the Yukon drainage basin. Streams flow south to the Tanana River and 

north to the Yukon River. Most streams in the western 

part follow courses parallel to the structural trends of 

bedrock, and several streams have sharp bends involving reversal of direction around the ends of ridges of 

hard rock. Drainage divides are very irregular. Small 

streams tend to migrate laterally southward (pl. 4, 

fig. 5). 

Lakes.-The few lakes in this section are mainly 

thaw lakes in valley floors and low passes. 

Glaciers and permafrost.-There are no glaciers. 

The entire section is underlain by discontinuous permafrost. Periglacial mass-wasting is active at high altitudes, and ice wedges lace the frozen muck of valley 

. bottoms. 

Geology.-A belt of highly deformed Paleozoic 

sedimentary and volcanic rocks containing conspicuous 

limestone units, overthrust and overturned to the 

north, extends along the north side of the upland. The 

rest of the upland is chiefly Precambrian ( ~) schist and 

gneiss but. has scattered small elliptical granitic intrusions in the northwestern part; large irregular 

batholiths make up much of the southeastern part. In 

the western part a thick mantle of windborne silt lies 

on the lower slopes of hills, and -thick accumulations 

of muck overlie deep stream gravels in the valleys. 

Alluvial deposits of gold and other metals abound 

throughout the upland. Pingos are common in valleys 

and on lower hill slopes (pl. 2, fig. 4). 

References.-Bostock (1948, p. 59-73); Holmes and 

others (1965); D. M. Hopkins (oral commun., 1959); 

Mertie (1937) ; Pewe (1955a, 1955b, 1958) ; Prindle 

( 1905, p. 17) ; Williams ( 1959) ; Williams and others 

(1959). 

The Yukon-Tanana Upland is covered by the following 1: 250,000 topographic maps: Charley "River, 

Circle, Livengood, Tanana, Eagle, Big Delta, Fairbanks, Kantishna River, Tanacross, and Mount Hayes. 

NORTHWAY-TANACROSS LOWLAND (13) 

General topography.-The Northway-Tanacross 

Lowland consists of three small basins, separated by 

screens of low rolling hills. The two basins along the 

north side of the lowland are nearly level plains, 

broadly oval in plan. Scattered longitudinal dunes 

mark the floor of the eastern one of these two basins. 

The third basin, on the southeast, is a gently rolling 

moraine-covered plain. 

Drainage.-The entire lowland is drained by the 

Tanana River, which may have captured the lowland 

in early Pleistocene time, for the drainage divide with 

the Yukon River is only 2-5 miles north of the Tanana 

and the north tributaries of the Tanana are steep 

barbed streams. The headwaters of the Yukon drainage north of the divide are underfit streams in broad 

valleys that head in wind gaps. 

The main tributaries of the Tanana rise in glaciers 

in mountains to the south, and their deposits of outwash have pushed the Tanana against the north side 

. of the lowland. The upper courses of these streams 

are swift and braided; their lower courses and the 

course of the Tanana are sluggish and meandering. 

Lakes.-Large lakes in reentrants in the surrounding hills may be caused by alluviation of the lowland. 

Thaw lakes abound in areas of fine alluvium, which are 

as much as 70 percent lake surface. Oxbow lakes and 

morainal ponds are also present. 

Glaciers and permafrost.-The lowland has no glaciers; it is in the area of discontinuous permafrost . 

Geology.-The basins are mantled with outwash 

gravel, silt, and morainal deposits.· The two northern 

basins were probably occupied by a lake dammed by 

a glacier at Cathedral Rapids. Tertiary rocks hu,ve 

been reported on the north side and may e;xtend be, 

neath the Quaternary deposits. Bedrock hills are Precambrian ( ~) schist and l\fesozoic granitic intrusions. 

The Taylor Highway immediately north of Tetlin 

Junction passes through a field of stabilized sand dunes. 

References.-D. F. Barnes (oral commun., 1956); 

Black (1951, p. 98-100); Mertie (1937, pl. l); Moffit 

( 1954a, pl. 6) ; Wallace ( 1946) , 
NORTHERN PLATEAUS PROVINCE 25 

The Northway-Tanacross Lowland is covered by the 

following 1:250,000 topographic maps: Tanacross, 

Mount Hayes, and N abesna. 

YUKON FLATS SECTION (14) 

General topography.-The central part of the Yukon 

Flats section consists of marshy lake-dotted flats rising 

from 300 feet in altitude on the west to 600-900 feet 

on the north and east. The northern part of the flats .is 

made up of gently sloping outwash fans of the Chandalar, Christian, and Sheenjek Rivers; the southeastern 

part of the flats is the broad gentle outwash fan of the 

Yukon River. Other areas are nearly flat flood plains. 

Rolling silt- and gravel-covered marginal terraces having sharp escarpments 150-600 feet high rise above the 

fln,ts and slope gradually upward to altitudes of about 

1,500 feet at the base of surrounding uplands and 

mountains. Their boundaries with surrounding uplands and mountains are gradational. 

Drainage.-The Yukon Flats section is drained by 

the Yukon River, which has a braided course southeast of the bend at Fort Yukon and a meandering 

course, containing many sloughs, southwest of the bend 

at Fort Yukon. Most tributaries rise in surrounding 

uplands and mountains and have meandering courses 

through the flats. 

Lakes.-Thaw lakes are abundant throughout th~ 

flats. Thaw lakes and thaw sinks are common on the 

marginal terraces. 

Glaciers and per"mafrost.-There are no glaciers. 

Permafrost probably underlies most of the section except rivers, recently abandoned meander belts, and 

large thaw lakes. 

Geology.-Escarpments bounding the Yukon Flats 

expose well-consolidated or crystalline rocks of Paleozoi~ and possibly ~{esozoic age. The marginal terraces 

are capped with gravel on which rests a layer of windborne silt. A well drilled at Fort Yukon in 1954 disclosed 48 feet of aeolian sand of late Pleistocene or 

Recent age, underlain by 100 feet of sandy gravel of 

Pleistocene age, underlain in turn by at least 292 feet 

of fine lnke sediments of late Pliocene or e~rly Pleistocene age. On the basis of this well it is thought that 

the Yukon Flats are the site of a late Tertiary lake 

that occupied a downwarped basin. 

Beferenoes.-Williams (1955, p. 124-125; 1960; 

wdtten communs., 1955-1959). 

The Yukon Flats section is covered by the following 

l; 2507000 topographic maps: Coleen, Christian, Black 

River, Fort Yukon, Beaver, Charley River, Circle, and 

Liven~ood! 

RAMPART TROUGH (16) 

General topog·raphy.-The Rampart Trough is a 

structnrq,lly controlled depression having gently rolling topography 500-1,500 feet in altitude; it is incised 

500-2,500 feet below highlands on either side. Terraces on tributaries of the Yukon River near Rampart 

are 20 feet, 100 feet, 150 feet, 250 feet, and 500 feet 

above stream level. 

Drainage.-The Yukon River enters the east end of 

the trough through a narrow rocky gorge and swings 

in broad bends from one side of the trough to the other 

within a narrow flood plain. Near the southwest end, 

a ridge of hard rock separates the Yukon River from 

the trough. Short tributaries rise in hills to the south, 

and flow across the trough and through the bedrock 

ridge on its north side to the Yukon. The Yukon and 

its tributaries appear to be superposed from a surface 

at least 1,500 feet in altitude. 

Lakes.-Scattered thaw lakes lie on the Yukon flood 

plain and elsewhere in the trough. . 

Glaciers and permafrost.-The Rampart Trough 

contains no glaciers. Permafrost underlies all the lowland except the Yukon flood plain. 

Geology.-The Rampart Trough was eroded along 

a tightly folded belt of soft continental coal-bearing 

rocks of Tertiary age. Hard rock hills and the surrounding uplands are partly metamorphosed sedimentary and volcanic rocks of Mississippian age that strike 

about N. 60° E. and are cut by granitic intrusions. 

Referenoes.-D. M. Hopkins (oral comm~n., 1959); 

Mertie (1937, p. 174-185); R. A. Paige (written commun., 1958). 

The Rampart Trough is covered by the following 

1:250,000 topographic maps: Livengood and Tanana. 

KOKRINE-HODZAN A HIGHLANDS (18) 

Gener·al topography.-The 1\:okrine-Hodzana Highlands consist of even-topped rounded ridges rising to 

2,000-4,000 feet in altitude surmounted by isolated 

areas of more rugged mountains. A rugged compact 

highland in the northeastern part has many peaks between 4,500 and 5,700 feet in altitude. The Ray Mountains (16a), rising to 5,500 feet, have cirques and glaciated valleys and craggy cliffed tors that rise abruptly 

from broad granite ridgetops. Valleys have alluviated 

floors to within a few miles of their heads. 

Drainage.-The irregular drainage divide between 

the Yukon River and its large tributary, the Koyukuk 

River, passes through these highlands. Drainage to 

the Yukon is by way of the Hodzana, Tozitna, Melozitna and Dall Rivers and many shorter streams. 

Drainage to the Koyukuk is by the Kanuti River and 

the South Fork of the I\:oyukuk. 

Lakes. There are a few thaw lakes in the lowland 

areas and a few lakes in north-facing cirques in the 

J{:okrine Hills (16b) and the Ray Mountains. 
26 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

Glaciers and permafrost.-There are no glaciers. 

The entire section is probably underlain by permafrost. 

This section contains classic examples of altiplanation 

terraces, stone polygons, and other periglacial phenomena. 

Geology.-The highlands are underlain chiefly by 

Paleozoic and Precambrian ( ~) schist and gneiss having a northeast-trending structural grain, cut by several granitic intrusions, the largest of which is the 

granite batholith that upholds the Ray Mountains. 

Small placers of tin and gold occur in the southern 

part of the highlands. 

References.-Eakin (1916) ; Maddren (1913) ; J. 

R. 'Yilliams (written commun., 1959). 

The Kokrine-Hodzana Highlands are covered by the 

following 1: 250,000 topographic maps: Chandalar, 

Wiseman, Beaver, Bettles, Livengood, Tanana, Melozitna and Ruby. 

WESTERN ALASKA PROVINCE 

The Western Alaska province consists of uplands and 

lowlands underlain chiefly by folded and faulted Cretaceous rocks. It is divided into the following sections: 

Kanuti Flats (17), Tozitna-Melozitna Lowland (18), 

Indian River Upland (19), Pah River section (20), 

Koyukuk Flats (21), Kobuk-Selawik Lowland (22), 

Selawik Hills (23), Buckland River Lowland (24), 

Nulato Hills (25), Tanana-Kuskokwim Lowland (26), 

Nowitna Lowland (27), Kuskokwim Mountains (28), 

Innoko Lowlands (29), Nushagak-Big River Hills 

(30), Holitna Lowland (31), and Nushagak-Bristol 

Bay Lowland (32). 

XANUTI FLATS (17) 

Gene'ral topography.-The Kanuti Flats form an irregular shaped lake-dotted plain 400-1,000 feet in altitude that merges with low surrounding hills. Scattered 

low irregular hills rise in the central part of the plain, 

which is crossed by the forest-covered meander belts 

of the Koyukuk and Kanuti Rivers. 

Drainage.-The Kanuti Flats are drained by the 

Koyukuk River and its tributaries. The Kanuti River, 

which drains the southern part of the plain, flows 

through a narrow canyon in the Indian River Upland 

before joining the Koyukuk River. 

Lakes.-There are numerous thaw lakes, some as 

large as 2 miles across. Some parts of the flats are more 

than 50 percent lake surface. 

Glaciers and permafrost.-The flats contain no glaciers. The section is underlain by permafrost except 

beneath large lakes, rivers, and recently formed flood 

plains. · 

Geology.-The geology of the Kanuti Flats is unknown. 

References.-N one. 

The Kanuti Flats are shown on Bettles 1: 250,000 

topographic rna p. 

TOZITNA·MELOZITNA LOWLAND (18) 

General topography.- The Tozitna-Melozitna Lowland is a long, narrow rolling plain, 5-10 miles wide, 

at the heads of the Tozitna and Melozitna Rivers. The 

pass between these streams is less than 1,000 feet in altitude. 

Drainage.-The lowland is drained by the Tozitna 

and Melozitna Rivers, which flow south from the lowland in narrow gorges across the Kokrine-Hodzana 

Highlands to the Yukon River. 

Lakes.-The lowland contains numerous thaw lakes. 

Oxbow lakes are common along the Melozitna River. 

Glaciers and permafrost.-The section has no glaciers; it is in the area of discontinuous permafrost. 

Geology.-Nothing is known of the geology of this 

lowland. 

References.-None. 

The Tozitna-Melozitna Lowland is covered by the 

following 1:250,000 topographic maps: Tanana and 

Melozitna. 

INDIAN RIVER UPLAND (19) 

General topography.-Groups of low gentle ridges 

having rounded accordant summits at 1,500-2,000 feet 

altitude are interspersed with irregular lowlands and 

broad flat divides. The ridges in the southeastern part 

are generally parallel and trend northeastward; ridges 

in the north western part have irregular trends. A few 

mountains rise to 4,000 feet in altitude. The Koyukuk 

and Kanuti Rivers cross the upland in narrow canyons 

a few hundred feet deep. 

Drainage.-Most of the Indian River Upland is 

drained by the Koyukuk River and its tributaries. The 

northwest corner drains to the Kobuk River and the 

southeastern part drains by the Melozitna River to 

the Yukon. Many of the streams have extremely irregular courses. 

Lakes.-Numerous thaw lakes, the largest 2¥2 miles 

across, are in the low lands, valleys, and broad passes. 

Glaciers and permafrost.-There are no glaciers. 

The entire land area, except recent flood plains, is 

underlain by permafrost, and periglacial processes predominate. Altiplanation terraces are common at high 

altitudes. · 

Geology.-The Indian River Upland is underlain 

chiefly by folded sedimentary and volcanic rocks of 

Mesozoic age, in which sandstone, shale, and conglomerate predominate. These rocks are intruded by small 

granitic stocks, and are overlain by remnants of flatlying lavas of Tertiary or Quaternary age. Structural 

trends are northeastward in the southeastern part but 

are poorly 'defined in the northern part. 
WESTERN ALASKA PROVINCE 27 

References.-Cass (1959e); W. W. Patton, Jr. (oral 

commun., 1959). 

The Indian River Upland is covered by the following 1: 250,000 topographic maps: Bettles, Hughes, 

Tanana, Melozitna, Kateel River, Ruby, and Nulato. 

PAR RIVER SECTION (20) 

General topography.-The Pah River section is an 

area of diversified topography. Compact groups of 

hills and low mountains 20-40 miles long and rising 

to 4,000 feet in altitude are surrounded by rolling 

plateaus 500-1,500 feet in altitude and broad lowland 

flats 5-10 miles across. The lower parts of the mountain groups consist of gently rounded ridges; their 

higher glaciated parts contain broad, shallow cirques 

having flaring walls (pl. 3, fig. 7). 

Drainage.-The northern and western parts of the 

Pah River section drain to the Selawik and Kobuk 

Rivers. The southern and eastern parts drain via the 

Huslia and Hogatza Rivers to the Koyukuk River. 

The major streams meander sluggishly through the 

broad lowlands. The Pah River, which drains the 

P.ah River flats (20b), flows north to the Kobuk 

through a narrow canyon across the Lockwood Hills 

(20a). 

Lakes.-Numerous thaw lakes lie in the lowland flats. 

The central part of the Pah River flats is probably 50 

percent lake surface. (See pl. 3, fig. 7.) A few small 

cirque lakes occur in the higher glaciated parts of the 

Lockwood Hills and the Zane Hills ( 20c) . 

Glaciers and permafrost.-There are no glaciers. The 

entire section is underlain by permafrost, and periglacial erosional processes predominate. Alti planation 

terraces are common below the level of glaciation in the 

Zane Hills and the Purcell Mountains (20d). 

Geology.-The Pah River section is underlain by 

Mesozoic volcanic and sedimentary rocks that are 

intensely deformed and locally contact metamorphosed, 

without strong persistent structural grain, and by 

Mesozoic granitic stocks and batholiths. 

References.-W. ,V. Patton, Jr. (oral commun., 

1959) ; I. L. Tailleur (oral commun., 1959). 

The Pah River section is covered . by the following 

1: 250,000 topographic maps: Hughes and Shungnak. 

KOYUKUK FLATS (21) 

General topography.-The Koyukuk Flats form an 

extensive lowland of irregular outline at the junction 

of the Yukon and l{oyukuk Rivers. The central parts 

of the l{oyukuk Flats are flat plains 5-20 miles wide, 

along the major rivers. The parts immediately adjacent to the rivers are meander belts 5-10 miles wide; 

the parts farther a way are dotted by thaw lakes. Broad 

rolling silt plains, in part mantled by dunes and in part 

pocked by thaw sinks, stand 100-200 feet above these 

central plains and merge imperceptibly with the surrounding uplands. Several low bedrock hills rise from 

the center of the lowland (pl. 4, fig. 7). 

Drainage.-The Koyukuk Flats are drained by the 

Yukon River and its tributaries.· Streams meander 

wildly across the lowland and have numerous meandering side sloughs. Lateral migration of meanders is as 

much as 75 feet per year, and elaborate patterns of 

bars and swales (meander-scroll pattern) are left behind (pl. 4, figs. 6 and 7). 

Lakes.-The meander belt has innumerable narrow 

meander-scroll lakes and some oxbow lakes; these are 

generally silted by floods, and the newly formed ground 

freezes perennially. Subsequently, thaw lakes form in 

. the frozen ground and pass through a complicated 

cycle of enlargement, coalescence, and destruction by 

infilling or drainage. These thaw lakes are abundant 

away from the rivers (pl. 4, fig. 7). 

Glaciers and permafrost.-No glaciers exist in the 

flats. All the land area except recently formed flood 

plains is underlain by permafrost. 

Geology.-The bedrock hills and surrounding uplands are chiefly Cretaceous sedimentary rocks, older 

Mesozoic volcanic rocks, and some intrusions. Low 

basalt hills rise from the central part of the lowland; 

The plains are underlain by water-laid and windborne 

silt. Sand dunes are common; a large barren area of 

active sand dunes lies in the northwestern part. Northeast-trending scarplets and low rises that cross the lowland presumably mark active faults. 

References.-Cass (1957, 1959e, 1959f); Eardley 

(1938a, 1938b); Elias and Vosburgh (1946); W. W. 

Patton, Jr. (oral commun., 1959); Pewe (1948). 

The Koyukuk Flats are covered by the following 

1: 250,000 topographic maps: Hughes, Shungnak, Melozitna, Kateel River, Ruby, and Nulato. 

KOBUK-SELAWIK LOWLAND (22) 

. General topography.-The Kobuk-Selawik Lowland 

consists chiefly of broad river flood plains and lakedotted lowlands that pass at their seaward margins 

into deltas. The Baldwin Peninsula, which separates 

Hotham Inlet from Kotzebue Sound, is a rolling lakedotted lowland containing hills as high as 350 feet in 

altitude, bordered by bluffs. The Waring Mountains 

(22a) are an east-trending group of low rounded hills 

less than 2,000 feet in altitude. The upper valley of 

the Kobuk River is bordered by gravel and sand 

terraces 100-200 feet above river level that are dotted 

with thaw lakes and thaw sinks and, on the south side 

of the river, have large areas of both stabilized and 

active sand dunes. 

Drainage.-The lowland is drained mainly by the 

Kobuk and Selawik Rivers. Most streams are sluggish, 
28 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

meandering, of low gradient, and have numerous side 

sloughs. 

Lakes.-The area around the Selawik River, in particular, has numerous large thaw lakes. Hotham Inlet 

and Selawik Lake are large bodies of water at sea level 

that are kept nearly fresh by the great outflow of the 

Selawik, Kobuk, and Noatak Rivers. 

Glaciers and permafrost.-Glaciers are absent. Most 

land area is underlain by permafrost. Pingos are abundant in the lowland around the Selawik River. 

Geology.-Most of the lowland areas are underlain 

by morainal deposits and by stream and lake deposits 

of unknown thickness. Baldwin Peninsula is probably 

the end moraine of a pre-Wisconsin glacial advance. 

In Wisconsin time glaciers from the Brooks Range 

sent tongues into the upper valley of the Kobuk but did 

not advance farther. The Waring Hills are underlain 

by Cretaceous sedimentary rocks. 

References.-A. L. Fernald (written commun., 

1958) ; D. M. Hopkins (oral commun., 1959) ; W. W. 

Patton, Jr. (oral commun., 1959); Smith (1913); 

Smith and Mertie (1930); I. L. Tailleur (oral 

commun., 1959). 

The Kobuk-Selawik Lowland is covered by the following 1: 250,000 topographic· maps: Ambler River, 

Baird Mountains, Noatak, Shungnak, Sela w.ik, and 

Kotzebue. 

SELAWIK HRLS (23) 

General topography.-The Selawik Hills are gentle 

hills having rounded to flat summits as much as 3,300 

feet in altitude. The hills rise fairly abruptly, with a 

relatively straight scarp, from the Kobuk-Selawik 

Lowland on the north and decline gently to the Buckland River Lowland on the south. Altiplanation terraces are common on the higher summits (pl. 2, fig. 1). 

Drainage.-The hills are drained by short streams 

that flow south and west to the Buckland River or 

north to the Kauk River, Selawik River, and Selawik 

Lake. 

Lakes, glaciers, and permafrost.-There are no lakes 

or glaciers. The entire section is underlain by permafrost. 

Geology.-The Selawik Hills are underlain chiefly 

by Paleozoic and Mesozoic metamorphosed volcanic 

rocks and granitic intrusive rocks. Quaternary volcanic 

rocks lie on the flanks. 

References.-W. W. Patton (oral commun., 1959). 

The Selawik Hills are covered by the following 

1: 250,000 topographic maps: Selawik and· Candle. 

BUCKLAND RIVER LOWLAND (24) 

General topography.-The Buckland River Lowland 

is a rolling lowland having slopes of a few feet to a 

few hundred feet per mile and consisting largely of the 

original surfaces of lava flows. 

Drainage.-The low land is. drained mostly by the 

Buckland River. The Tagagawik River drains the extreme eastern part, and the Koyuk River the southern 

prong. 

Lakes.~Small thaw and oxbow lakes are common 

along the Buckland River and in other flat valleys. 

A few thaw lakes lie on some flat interfluves. 

Glaciers and permafrost.-There are no glaciers. The 

entire section is probably underlain by permafrost. 

Geology.-The lowland is underlain chiefly by flatlying lava flows of Quaternary age, mantled by a thick 

layer of windborne silt. 

References.-D. M. Hopkins (oral commun., 1959); 

W. W. Patton, Jr. (oral commun., 1959). 

The Buckland River Lowland is shown on the 

1: 250,000 topographic map of Candle quadrangle. 

NULATO HnLS (26) 

General topography.-The Nulato Hills consist, in 

general, of northeast-trending even-crested ridges, 

1,000-2,000 feet in altitude, having rounded summits 

and gentle slopes. Valleys are narrow and have flat 

floors that are generally trenched in their upstream 

parts to depths of about 30 feet. Local relief is 500-

. 1,500 feet. The topography is relatively fine textured; 

gullies are spaced 500-1,500 feet apart and secondorder tributaries are ¥2-1 mile apart (pl. 4, fig. 10). 

Three highland areas of steeper ridges rise to about 

4,000 feet in altitude. 

Drainag~.-Streams on the east side of the section 

flow to the Yukon River and those on the west side to 

Norton Sound. Major streams are markedly parallel, 

flowing either northeast or southwest, and their courses 

.are eroded along northeast-trending fault zones. Valley 

heads are generally connected by low passes along the 

faults. 

Lakes.-There are a few thaw lakes in the valleys. 

Glaciers and permafrost.-There are no glaciers. The 

entire section is probably underlain by permafrost. 

Geology.-Almost all the hills are com posed of 

tightly fol~ed sandstone, conglomerate, and shale of 

Cretaceous age. The folds trend about N. 45° E. but 

bend around to north ward in the northern part. The 

rocks are cut by northeast- and north-trending faults. 

A few mountains are underlain by post-Cretaceous intrusive and volcanic rocks. Older rocks, chiefly of 

volcanic origin, make up the hills in the extreme 

northern part and extreme southern part. 

References.-R. S. Bickel (oral commun., 1958); 

Cass (1957, 1959a, 1959b, 1959c, 1959f); Harrington 

( 1918) ; Hoare and Coonrad ( 1959b) ; Patton and 

Bickel ( 1956a, 1956b) ; Smith and Eakin ( 1911). 
~ESTERN ALASKA PROVTINCE 29 

The Nulato Hills are covered by the following 

1: 250,000 topographic maps: Shungnak, J{ateel River, 

Candle, Nulato, Norton Bay, Unalakleet, St. Michael, 

Holy Cross, K wiguk, Russian Mission, and Marshall. 

TANANA-KUSKOKWIM LOWLAND (28) 

General topography.-The Tanana-l{uskokwim 

Low land is a broad depression bordering the Alaska 

Range on the north; its surfaces are of diversified 

origin. Coalescing outwash fans from the Alaska 

Range slope 20-50 feet per mile northward to flood 

plains along the axial streams of the lowland. Rivers 

from the range flow for a few miles at the heads of the 

fans in broad terraced valleys 50-200 feet deep. Semicircular belts of morainal topography lie on the upper 

ends of some fans. (See pl. 3, fig. 10 and pl. 4, fig. 13.) 

The flood plains of the Kuskokwim and Kantishna 

Rivers and of the Tanana River west of Tolovana are 

incised 50-200 feet below the level of the low land. 

Several nearly level projections of the low land extend 

into uplands on the north. Large fields of stabilized 

dunes cover the northern part of the lowland and lower 

slopes of adjacent hills between Nenana and McGrath 

(pl. 4, fig. 12). 

Drainage.-The central and eastern parts of the lowland are drained by the Tanana River, and the southwestern part is drained by the Kuskokwim River. 

Braided glacial streams rising in the Alaska Range 

(pl. 3, fig. 8) flow north across the lowland at intervals 

of 5-20 miles. Outwash has pushed the axial streams-. 

the Tanana, l{uskokwim, and Kantishna Riversagainst the base of hills on the north side. Tightly 

meandering tributaries of low gradient flow into the 

section from the north. 

Lakes.-Thaw lakes abound in areas of fine alluvium. 

Thaw sinks are abundant in areas of thick loess cover. 

Glaciers and permafrost.-The lowland contains no 

glaciers. The entire section is an area of permafrost. 

Porous gravel at the heads of the outwash fans, however, has a deep water table and dry ·permafrost 

(ground perennially at temperatures below freezing 

but having no ice). . 

Geology.-The outwash fans grade from coarse 

gravel near the Alaska Range to sand and silt along the 

axial streams. Areas north of the axial streams are 

underlain by thick deposits of "muck," a mixture of 

frozen organic matter and silt. Parts of the southwestern part of the lowland have thick loess cover, but 

the central and eastern parts are free of loess south of 

the Tanana River. Scattered low hills of granite, ultramafic rocks, and Precambrian ( ~) schist rise above the 

outwash. Tertiary conglomerate in the foothills of the 

Alaska Range plunges beneath the low land in a monocline, and the heads of the outwash fans may rest on a 

pediment cut across this conglomerate. The base of the 

alluvial fill near Fairbanks is at or below sea level. 

References.-D. F. Barnes (oral commun., 1956) ; 

Barnes and McCarthy (unpub. data, 1954); Drury 

( 1956) ; Fernald ( 1955, 1960) ; Holmes and Benninghoff (1957); Kachadoorian (1956); Pewe (1954, 1955b, 

1958) ; Pewe and others ( 1953) ; Reed ( 1961) ; W ahrhaftig ( 1958a) ; Williams and others ( 1959) ; Andreasen and others (1964). 

The Tanana-Kuskokwim Lowland is covered by the 

following 1:250,000 topographic maps: Livengood, Big 

Delta, Fairbanks, Kantishna River, Mourit McKinley, 

Medfra, Talkeetna, and McGrath. 

NOWITNA LOWLAND (21) 

General topography.-The Nowitna Lowland is a 

rolling silt-covered tableland ranging from 250 to 900 

feet in altitude and having a local relief of 50-250 feet 

and slopes of 100-150 feet per mile into which the flat 

flood plains of the rna j or rivers (valleys 1¥2-10 miles 

wide) have been incised 150-300 feet. A line of gentle 

bedrock hills in the center rises to 1,500 feet. The tablehind is pocked with thaw sinks. The part of the tableland south of the line of hills is covered with longitudinal and sigmoid dunes and has been dissected by 

steep-walled gullied canyons (pl. 4, fig. 8). 

Drainage.-The entire lowland is drained by the 

Yukon River, which follows the north boundary. The 

confluence of the Yukon with the Tanana River is in 

the eastern part of the low land. The southern part of 

the lowland is drained by the Nowitna River, a tribu· 

tary of the Yukon, and its tributaries. Parallel drainage of small tributaries of the Chitinana River and · 

other streams in silt uplands of the eastern part may be 

consequent upon the flanks of a recent upwarp (pl. 4, 

fig. 9). 

Lakes.-Oxbow lakes are common in the central 

parts of the meander belts. Thaw lakes abound in the 

marginal areas and throughout the silt- and dune- . 

covered uplands. 

Glaciers and permafrost.-The lowland contains no 

glaciers; it is underlai:J?. by permafrost, except in recently abandoned flood plains. 

Geology.-Bedrock in the hills is similar to that of 

surrounding highlands~schist and gneiss on the west 

and Cretaceous sedimentary rocks on the east, all cut 

by granitic intrusions. Tilted and faulted Tertiary and 

possibly Quaternary sedimentary deposits are exposed 

on the south bank of the Yukon. Most of the low land 

is covered by windborne silt and sand of unknown 

thickness. Depth of alluvium is at least 180 feet. 

References.-Cass (1959d, 1959e); Eakin (1914, 

1918) ; Eardley ( 1938, 1938b). 
30 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

The Nowitna Lowland is covered by the following 

1:250,000 topographic maps: Tanana, Melozitna, Kantishna River, and Ruby. 

KUSKOKWIM MOUNTAINS (28) 

GeneTal topogTaphy;-The Kuskokwim Mountains 

are a monotonous succession of nqrtheast-trending 

ridges having rounded to flat summits 1,500-2,000 feet 

in altitude and broad gentle slopes (pl. 4, fig. 11) . 

Ridge crests north of the Kuskokwim River are accordant at about 2,000 feet and are surmounted at 

intervals of 10-30 miles by isoiated circular groups of 

rugged glaciated mountains 3,000-4,400 feet in altitude. 

Valleys have flat floors 1-5 miles wide. 

DTainage.-The Kuskokwim Mountains are drained 

by tributaries of the Yukon and Kuskokwim Rivers. 

Major streams generally flow northeast to southwest 

along valleys that are probably controlled by faults; 

streams are fast and meandering and generally lie near 

the northwest walls of their valleys. The Kuskokwim 

River crosses the mountains in a gorge 100-400 feet 

deep incised in an older valley about 1,000 feet deep 

and 2-8 miles wide. 

Lakes.-Lakes are few. There are oxbow and thaw 

lakes in the valleys and a few cirque lakes in the 

glaciated mountains. 

Glacier's and permafTost.-There are no glaciers. 

Permafrost underlies most of the section, and periglacial erosional processes predominate. 

Geology.-Most of the Kuskokwim Mountains are 

made of tightly folded Cretaceous rocks that strike 

northeast. Graywacke upholds the ridges, and argillite 

underlies the valleys. The northeastern and northwestern parts are under lain by Paleozoic sedimentary 

rocks and Precambrian ( ? ) schist. The isolated circular groups of high mountains are underlain by 

monzonitic intrusions and their surrounding hornfels 

aureoles. Flat-lying basalt caps the remnants of a midTertiary erosion surface. Pleistocene and Recent block 

faulting has occurred south of the Kuskokwim River. 

RefeTences.-Brown (1926a, 1926b); Cady and 

others (1955); Eakin (1918); Hoare and Coonrad 

(1959a, and 1959b); Mertie and Harrington (1924). 

The Kuskokwim Mountains are covered by the following 1:250,000 topographic maps: Kantishna River, 

Ruby, Nulato, Mount McKinley, Medfra, Ophir, Unalakleet, McGrath, Iditarod, Holy Cross, Sleetmute, 

Russian Mission, Taylor Mountains, and Bethel. 

INNOKO LOWLANDS (29) 

GeneTal topogTaphy.-The Innoko Lowlands are a 

group of flat river flood plains, dendritic in pattern, 

whose bounding slopes are generally steep banks cut 

into the surrounding hills; in places, however, gentle 

silt-covered slopes merge with the surrounding hills. 

DTainage.-The Yukon River and a large tributary, 

the Innoko River, cross the lowlands. The main part 

of the lowlands has a complex intersecting network of 

meandering sloughs of these two streams. . 

Lakes.-Oxbow and meander-scroll lakes are abundant in recently abandoned flood plains and partly 

silted sloughs. Thaw lakes abound in old fiood plains 

and on gentle silt-covered slopes. The lower parts of 

many tributaries from surrounding hills are dammed 

by alluvium from the Yukon and form narrow dendritic 

lakes. 

Glacier's and permafTost.-N o glaciers exist in the 

lowlands. Much of the section is underlain by permafrost. 

Geology.-Bedrock geology is probably the same as 

that of the surrounding hills. The plains are .mantled 

by river-flood-plain deposits and by windborne silt, 

which also extends up the slopes of the surrounding 

hills. 

Re feTences.-None. 

The Innoko Low lands are covered by the following 

1:250,000 topographic maps: Ophir, Unalakleet, Iditarod, Holy Cross, and Russian Mission. 

NUSBAGAK-BIG RIVER BILLS (SO) 

General topogTaphy.-The Nushagak-Big River 

Hills are .largely rounded, flat-topped ridges rising to · 

an altitude of 1,500 feet on the west and 2,500 feet on 

the east; the hills have broad gentle slopes and broad 

flat or gently sloping valleys. Local relief is 1,000-

2,500 feet. Mountains in the northeastern part rise to 

an altitude of 4,200 feet. Ridges trend northeastward 

in the eastern part but have no preferred trend in the 

southwestern part. 

DTainage.-The northern part of the hills drains to 

the Kuskokwim River via the Big, Stony, Swift, and 

Holitna Rivers; the southern part is drained by the 

Mulchatna and Nushagak Rivers. The rivers that rise 

from glaciers in the Alaska Range and flow across the 

hills, like the Stony and Swift, are braided muddy 

streams. Others, like the Holitna, are clear and meandering. 

Lakes.-A few thaw lakes are in some valleys. Ponds 

are abundant in the moraine-mantled eastern part of 

the hills. 

Glacier's and permafTost.-There are no glaciers. 

Most of the section is underlain by permafrost, and 

periglacial erosional processes predominate. 

Geology.-Most of the hills consist of tightly folded 

Mesozoic graywacke, argillite, conglomerate, and 

greenstone flows. There is a central northeast-trending 

belt of Paleozoic rocks, including. steep isolated ridges 

of limestone. Early Tertiary intrusions and their meta-
SEWARD PENINSULA 31 

morphic aureoles uphold two small circular groups of 

high mountains in the southwestern part. 

References.-Capps (1935); J. M. Hoare (written 

commun., 1958) ; C. L. Sainsbury (oral commun., 

1959); Smith (1917)~ 

The Nushagak-Big River Hills are covered by the 

following 1: 250,000 topographic maps: ~cGrath, Iditarod, Lime Hills, Sleetmute, Lake Clark, Taylor 

Mountains, Iliamna, and Dillingham. 

HOLITNA LOWLAND (Sl) 

General topography.-The Holitna Lowland is 

largely a moraine-covered plain 300-800 feet in altitude 

and is cross~d by ·several low arcuate hummocky 

ridges marking the end moraines of glacial advances 

and by broad outwash and meander plains along rivers. 

The Lime Hills, conspicuous isolated steep-sided ridges 

in the southern part of the lowland, rise to an altitude of 1,000-2,300 feet. 

Drainage.-The Holitna Lowland is drained by the 

l(uskokwim River and three of its tributaries, the 

Stony and Swift Rivers, which are glacial streams 

from the Alaska Range that have braided gravelly 

courses, and the ·Holitna River, a clear meandering 

stream that rises in uplands to the south. 

Lakes.-There are numerous morainal and thaw 

lakes throughout the lowland. 

Glacier·s and permafrost.-There are no glaciers. 

This section is probably one of discontinuous permafrost. 

Geology.-The bedrock hills are of Mesozoic graywacke, argillite, and conglomerate and early Paleozoic 

limestone. Most of the lowland is underlain by moraine 

and outwash together with thick accumulations of 

windborne silt. 

Re/erences.-J. M. Hoare (oral commun., 1959) ; 

J. N. Platt (written commun., 1956); Smith (1917). 

The Holitna Lowland is covered by the following 

1:250,000 topographic maps: McGrath, Iditarod, Lime 

Hills, Sleetmute, and Taylor Mountains. 

NUSHAGAK-BRISTOL BAY LOWLAND (32) 

General topog·raphy.-The Nushagak-Bristol Bay 

Lowland is a moraine- and outwash-mantled lowland 

having local relief of 50-250 feet and rising from sea 

level to an altitude of 300-500 feet at its inner margins. High steep-sided outliers of the Ahklun Mountains rise from the western part. Arcuate belts of 

morainal topography, 100-300 feet high and 1-5 miles 

wide, enclose large deep glacial lakes on the southeast 

margin and cross parts of the low land west of the 

N ushagak River. 

D'rain'age.-The lowland is drained by the Nushagak 

and other large rivers that flow into Bristol Bay. Most 

streams rise in large lakes in ice-carved basins bordering the surrounding · mountains and flow into tidal 

estuaries that appear to be drowned river mouths. 

Lakes.-The .lowland is dotted with morainal and 

thaw lakes. Large lakes occupy ice-scoured basins 

along the margins of the lowland. The largest of these, 

Lake Iliamna, is 80 miles long and 20 miles wide. 

Glaciers and permafrost.-There are no glaciers in 

this section, and permafrost is sporadic or absent. 

Geology.-The lowland is underlai:n by several hundred feet of outwash and ·morainal deposits that are 

mantled in part by silt and peat. Outwash deposits 

are coarse near the mountains and grade to fine sand 

along the coast. Quarternary deposits thin to a featheredge along the base of surrounding mountains. A 

small area of low stabilized and active dunes lies east 

of the Nushagak River. 

References.-Muller (1952, 1953, 1955, 1956). 

The Nushagak-Bristol Bay Lowland is covered by 

the following 1: 250,000 topographic maps: Taylor 

Mo~ntains, Iliamna, Dillingham, Naknek, N ushagak 

Bay, Ugashik, Bristol Bay, Chignik, Port Moller, Fort 

Randall, False Pass, and Un.imak. 

SEWARD PENINSULA (33) 

General topography.-The Seward Peninsula contains: extensive uplands of broad convex hills and flat 

divides that are 500-2,000 feet in altitude and are indented by sharp V-shaped valleys (pl. 3, fig. 5); isolated groups of rugged glaciated mountains, 20-60 

miles long and 10 miles wide, having peaks 2,500-4,700 

feet in altitude (pl. 4, fig. 2) ; and coastal lowland and 

interior basins. 

Drainage.-Many small rivers, whose lower courses 

are sluggish and meandering, drain the peninsula. 

Some of these build deltas into the heads of protected 

lagoons and bays. The interior basins are drained 

through narrow canyons across intervening uplands. 

Lakes.-The lowlands have numerous thaw lakes. 

There are several rock-basin and morainal lakes in the 

glaciated Bendele ben ( 33a) and Kigluaik ( 33b) 

Mountains. Lakes fill several large shallow volcanic 

craters in the northern part of the peninsula and several depressions between lava flows in the central upland; some of the depressions were accentuated by 

faulting and warping. 

Glaciers and permafrost.-The Seward Peninsula 

has no glaciers. The entire peninsula is underlain by 

permafrost; periglacial erosional processes predominate (pl. 2, fig. 5) and ice-wedge polygons are common. 

Geology.-The bedrock of the peninsula is chiefly 

Paleozoic schist, gneiss, marble, and metamorphosed 

volcanic rocks, all of which are cut by granitic intrusive 

masses. Structural trends in the metamorphic rocks 

are chiefly northward. The York Mountains ( 33c) are 
32 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

carved in a mass of resistant marble (pl. 4, fig. 2). 

The Kigluaik, Bendeleben, and Darby Mountains have 

recent scarplets along their bases and may be Cenozoic 

uplifts. A Quaternary lava plateau lies in the northcentral part. The southern and western mountains are 

extensively glaciated. In exposures of ;beach placer deposits along the south coast, layers of till are interbedded with beach and shore deposits that are both 

above and below sea level; it is therefore poss.ible to 

correlate glacial advances in the Seward Peninsula 

. with the history of rise and fall of sea level in late 

Cenozoic time. 

References.-Collier (1902); Collier and others 

(1908); Hopkins (1949, 1955, 1959a, 1959b, 1963; written communs., 1956, 1959) ; Hopkins and Hopkins 

( 1958) ; Hopkins and others ( 1960) ; Moffit ( 1913, pl. 

1); Smith (1910); A. R. Tagg (oral commun., 1962). 

Seward Peninsula is covered by the following 1 : 250,-

000 topographic maps: Selawik, Kotzebue, Shishmaref, 

Candle, Bendeleben, Teller, Norton Bay, Solomon, and 

Nome. 

BERING SHELF 

The Bering Shelf is the largely submerged, nearly 

level plain close to sea level that joins Alaska with 

the Chukotsk Peninsula of Siberia. It contains two 

sections, the Yukon-Kuskokwim Coastal Lowla~d, a 

largely emerged area, and the Bering Platform, a 

largely submerged area. 

YUXON-XUSXOXWDI COASTAL LOWLAND (34) 

General topography.-The Yukon-Kuskokwim 

Coastal Lowland is a triangular lake-dotted marshy 

plain rising from sea level on its west margin to 

100-300 feet at its east end. Many low hills of 

basalt surmounted by cinder cones and broad shallow 

volcanic craters and a few craggy mountains of older 

rocks 2,300-2,450 feet high, rise from the western part 

of the plain. Low beach ridges, marked by lines of 

thaw lakes, lie along part of the west coast. 

The Norton Bay Lowland (34a) is· a lake-dotted 

coastal plain on the east side of Norton Bay, similar to 

the northern end of the Yukon-Kuskokwim Coastal 

Lowland. At its western extremity is an isolated range 

of hills, the Denbigh Hills. 

Drainage.-The lowland is crossed by meandering 

streams of extremely low gradiant, many of them distributaries or former channels of the Yukon River; 

these flow to the Bering Sea. The Yukon River flows 

along the base of hills on the north side of the lowland 

and is building a delta into the Bering Sea. The Kuskokwim River on the southeast side ends in a marine 

estuary that appears to be a drowned river mouth. 

Lakes.-The lowland is dotted with innumerable 

thaw lakes, many of them 10 or more miles long. Some 

have scalloped shorelines and probably formed through 

the coalescence of several smaller lakes. Probably 30-

50 percent of the lowland is lake surface. 

Glaciers and permafrost.-The area contains no glaciers; it is underlain by discontinuous permafrost. 

Geology.-Thelowland is underlain by Quarternary 

sand and silt to unknown depth. Basalt flows and 

cinder cones are of Tertiary and Quarternary age. 

Other bedrock hills consist of Cretaceous sedimentary 

rocks, cut by early Tertiary intrusions, and of crystalline rocks of unknown age. 

References.-Coonrad (1957). 

The Yukon-Kuskokwim Coastal Lowland is covered 

by the following 1:250,000 topographic maps: Unalakleet, Saint 1\fichael, Holy Cross, K wiguk, Black, Russian Misson, Marshall, Hooper Bay, Bethel, Baird Inlet, Nunivak Island, Goodnews, and Kuskokwim Bay. 

BERING PLATFORM (35) 

General topography.-The Bering Platform is a 

montonously smooth submarine plain 100-500 feet 

deep bordered on the southwest by a submarine scarp 

several thousand feet deep. A coastal lowland at the 

head of Norton Sound is included in the platform. 

Several islands rise abruptly from the plain. Most of 

the islands are rolling uplands a few hundred to 1,000 

feet high bordered by wave-cut cliffs. St. Lawrence 

Island ( 35a), the largest, is about 100 miles long and 

20 miles wide. It is chiefly a lake-dotted bedrock plain 

less than 100 feet in altitude above which isolated mountain groups bordered by old sea cliffs rise to altitudes 

of 1,000-1,500 feet (pl. 4, fig. 1). A large shield volcano with many vents is on the north coast of St. Lawrence Island. St. Paul and Nunivak Islands consist 

largely of undissected volcanic topography. 

Drainage.-Many small rivers drain St. Lawrence 

Island and N uni vak Island ; most small islands have 

no permanent streams. 

Lakes.-Thaw lakes abound on the lowlands of St. 

Lawrence Island and the lower parts of Nunivak 

Island; there are small crater lakes on N univak and 

the Pribilof Islands. 

. Glaciers and permafrost.-There are no glaciers. 

Part of St. Lawrence Island and possibly Nunivak 

Island may be underlain by permafrost. 

Geology.-The Pribilof Islands ( 35b), St. Matthew 

Island ( 35c) , N uni vak Island ( 35d) , and north-central 

St. Lawrence Island ar~ made of Cenozoic basalt flows 

and pyroclastic debris interbedded with some sediments. Cinder cones are present on ·the Pribilofs and 

Nunivak Island. St. Lawrence, Diomede, and King 

Islands are underlain largely by intensely deformed 

Paleozoic and Mesozoic sedimentary and volcanic 

rocks and granitic intrusions. 
ALASKA-ALEUTIAN PROV~CE 33 

References.-Barth (1956); Dutro and Payne 

(1957); Flint (1958); Hopkins (1959a). 

Land areas of the Bering Platform are covered by 

the following 1: 250,000 topographic maps: Norton 

Bay, St. Lawrence, St Matthew, Nunivak Island, Cape 

Mendenhall, and Pribilof. 

AHKLUN MOUNTAINS (86) 

General topography.-Groups of rugged steepwalled mountains, having sharp summits 2,000-5,000 

feet in altitude, separated by broad flat valleys and 

lowlands, rise abruptly above the lowlands and low 

hills on the north and east. Mountains in the southwestern part have rounded summits 1,500-2,500 feet 

in altitude. 

Drainage.-The Ahklun Mountains are drained by 

shallow, clear streams that flo:w directly to the Bering 

Sea on the south and west, to the Nushagak River via 

the N uyakuk River on the northeast, and to the Kuskokwim River on the northwest. Most rivers are incised 

in bedrock gorges 20-50 feet deep in the downstream 

parts of their valleys. Drainage is roughly radial, and 

several streams in the northwestern part flow through 

canyons that cut directly across structurally controlled 

ridges. 

Lakes.-This province is outstanding for the number and beauty of its glacial lakes, which are long 

narrow bodies of water in U-shaped canyons. The largest, Lake N erka, is 29 miles long, and at least 40 lakes 

are more than 2 miles long. Lake depths as great as 

900 feet have been reported. 

Glaciers and permafrost.-A few small cirque glaciers are found in the highest parts of the mountains 

from Mount Waskey northward. Permafrost occurs 

sporadically. 

Geology.-The mountains are made of strongly deformed sedimentary and volcanic rocks of late Paleozoic and Mesozoic age together with some bodies of 

older schist. These rocks are cut by great northeasttrending faults along which many of the valleys have 

been eroded. Structural trends control many ridges. 

Small granitic masses surrounded by more resistant 

hornfels have formed many ringlike mountain groups. 

Late Cenozoic basalts lie on the floor of Togiak valley. 

The entire province was intensely glaciated. 

References.-Harrington (1921); J. M. Hoare (written commun., 1958); ·Hoare and Coonrad (1959a, 1959b, 

1961a, 1961b); Mertie (1938, 1940). 

The Ahklun Mountains are covered by the following 

1:250,000 topographic maps: Taylor . Mountains, 

Bethel, Dillingham, Goodnews, N ushagak Bay, and 

Hagemeister Island. 

PACIFIC MOUNTAIN SYSTEM 

ALA.SKA·.A.LEUTIAN PROVINCE 

The Alaska-Aleutian province consists of an arcuate 

belt of mountain ranges along the north side of the 

Pacific Mountain System in Alaska. It is divided into 

the following sections: Aleutian Islands (37), Aleutian Range ( 38) , Alaska Range (southern part) ( 39) , 

Alaska Range (central · and eastern parts) ( 40) , and 

Northern Foothills of the Alaska Range ( 41). 

ALEUTIAN ISLANDS (37) 

General topography.-The Aleutian Islands are a 

chain of islands surmounting the crest of a submarine 

ridge 1,400 miles long, 20-60 miles wide, and 12,000 

feet high above the sea floor on either side. An arcuate 

line of 57 volcanoes of Quaternary age, 27 ·reported 

active, rise 2,000-9,000 feet above sea level along the 

north side of the Aleutian Islands. Other topography 

in the .Aleutian Islands is of two types: (a) wave-cut 

platforms less than 600 feet above sea level, bordered by 

low sea cliffs, and (b) intensely glaciated mountainous 

islands 600-3,000 feet above sea level, indented with 

fiords and bordered by cliffs as high as 2,000 feet (pl. 

5, fig. 12). Broad level intertidal platforms border 

some islands; they were probably produced by frost 

weathering. 

Drainage.-Streams in . the Aleutian Islands are 

short and swift. Many plunge into the sea over waterfalls. Volcanoes of porous rock have widely spaced 

stream courses that are filled with water only during 

exceptionally heavy rains. 

Lakes.-Many small lakes occupy irregular icecarved basins in rolling topography on the glaciated 

islands. Numerous ponds were enlarged when ice, expanding by freezing, shoved the banks aside to form 

ramparts of soil and turf. Lakes fill a few volcanic 

craters and calderas. 

Glaciers and permafrost.-The firn line is at an altitude of about 3,000 feet east of Unimak Pass and about 

4,500 feet west of it. Most high volcanoes bear icecaps 

or small glaciers, and there are a few cirque glaciers on 

the mountainous islands. There is probably no permafrost in the Aleutian Islands, but periglacial erosional 

processes are active.because of the cold, wet climate. 

Geology.-The linear chain of volcanoes on the north 

side of the islands is of constructional origin and late 

Cenozoic age; it includes many calderas. The remaining islands appear to be emerged parts of tilted fault 

blocks consisting chiefly of faulted and folded Cenozoic volcanic rocks, locally mildly metamorphosed; 

granitic intrusions of Cenozoic age are present on 

Sedanka, Unalaska, Jlak, and other islands. Submarine 

topography of the Aleutian ridge shows it to be complexly blockfaulted along its crest. 
34 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

References.-Bradley (1948); Byers (1959); Coats 

( 1950, 1953, 1956a, 1956b, 1956c, 1959a, 1959b) ; Coats 

and others (1961); Drewes and others (1961); Fraser 

and Barnett ( 1959) ; Fraser and Snyder ( 1959) ; Gates 

and Gibson (1956); J. P. Schafer (unpub. data, 1956); 

Q-ibson and Nichols ( 1953) ; Kennedy and Waldron 

( 1955) ; Murray ( 1945) ; Nelson ( 1959) ; Powers and 

others (1960); P. C. Scruton (unpub. data, 1953); 

Sharp ( 1946) ; Simons and Mathewson ( 1955) ; Snyder 

(1957, 1959). 

The Aleutian Islands are covered · by the following 

1: 250,000 topographic maps: Port Moller, Fort Randall, False Pass, U nimak, Unalaska, U mnak, Samalga 

Island, Amukta, Seguam, Atka, Adak, Gareloi Island, 

.Rat Islands, Kiska, and. Attu. 

ALEUTIAN RANGE (38) 

General topogT.aphy.-The Aleutian Range consists 

of rounded east-trending ridges 1,000-4,000 feet in 

altitude, surmounted at intervals of 5-85 miles by volcanoes 4,500-8,500 feet in altitude (pl. 6, fig. 8). It 

merges northward· with the Bristol Bay-Nushagak 

Lowland and has an abrupt and rugged south coast. 

The range is extensively glaciated. as shown by the Ushaped valleys, cirques, and other features of glacial 

erosion. Most of the volcanoes reached their final 

growth after the extensive glaciation of the range. 

Drainage.-The drainage divide between the Bering 

Sea and the Pacific Ocean is generally along the highest ridges, within 10 miles of the south coast. Streams 

to the Pacific are short and steep; those flowing to 

Bering Sea are longer and have braided channels. 

Lakes.-Along the north side of the range are many 

large lakes, partly held in by end moraines. Most of 

them extend well below sea level. The largest is Lake 

Iliamna. 

Glaciers and permafrost.-The firn line is at an 

altitude of about 3,000-3,500 feet along the axis of the 

range and rises northward across the range to 4,000-

5,000 feet in the northwestern part. Most volcanoes 

have glaciers on all sides and some have summit icefields. There is probably no permafrost, but periglacial 

erosional processes are active in the cold, wet climate. 

Geology.-Most of the range is composed of mildly 

deformed folded and faulted Mesozoic and Cenozoic 

sedimentary rocks, locally intruded by granitic stocks 

and surmounted at intervals by volcanic piles of late 

Tertiary to Recent age. Many volcanoes are calderas 

(pl. 5, fig. 5). A major fault extends along the north 

side of the eastern part of the range, separating the 

sedimentary rocks from a large Mesozoic granitic 

batholith on the north. 

References.-Atwood (1911); Coats (1950); Curtis 

and others ( 1954) ; Griggs ( 1922) ; Keller and Reiser 

(1959); Knappen (1929); Mather (1925); Muller and 

others (1954); Smith (1925a); Smith and Baker-

(1924); Wilcox (1959). 

The Aleutian Range is covered by the following 

1: 250,000 topographic maps: Iliamna, Afognak, 

Mount Katmai, Naknek, I{arluk, Ugashik, Bristol 

Bay, Sutwik Island, Chignik, Stepovak Bay, Port 

Moller, and Semeonof Island. 

ALASKA RANGE (SOUTHERN PART) (39) 

General topography.-Between Rainy Pass and Lake 

Chakachamna the Alaska Range consists of many 

parallel rugged glaciated north-trending ridges 7,000-

12,000 feet in altitude ; south of Lake Chakachamna 

the ridges trend northeast and are 4,000-6,000 feet 

in altitude. Between the ridges lie broad glaciated valleys which have floors less than 3,000 feet in altitude. 

Local relief is between 4,000 and 9,000 feet. Many 

spirelike mountains rise in the central part of the 

range. 

Drainage.-Large braided glacial streams follow 

the north- and northeast-trending valleys; they flow 

north or south to the Kuskokwim River,- southwest 

to the N ushagak or K vichak Rivers, and east to the 

Susitna River and Cook Inlet. 

Lakes.-Many large lakes occupy glaciated valleys 

within· and on the margins of the range; the largest of 

these is Lake Clark, 49 miles long and 1-4 miles wide. 

Glaciers and permafrost.-Extensive systems of valley glaciers radiate from the higher mountains. The 

firn. line is lower and the glaciers are larg~r on the 

southeast side of the range than on the northwest and 

west side of the range. The extent of permafrost is 

unknown. 

Geology.-Most of the range is underlain by large 

.granitic batholiths, intrusive into moderately metamorphosed and highly deformed Paleozoic and Mesozoic volcanic and sedimentary rocks, which form scattered areas of lower mountains. Structural trends are 

generally northerly, but change abruptly to northeasterly and easterly northward across Rainy Pass. Mount 

Spurr, Mount Iliamna, and Mount Redoubt are large 

active volcanoes. well-bedded Jurassic sedimentary 

rocks form prominent hogbacks and c:uestas dipping 

southward off the south flank of the range toward 

Cook Inlet (pl. 2, fig.10). 

References.-Capps (1935, 1940); Juhle (1955); 

Juhle and Coulter (1955); Moffit (1927); Spurr 

(1900). 

The southern part of the Alaska Range is covered 

by the following 1 :250,000 topographic maps: Talkeetna, McGrath, Tyonek, Lime Hills, Kenai, Lake 

Clark, Seldovia, and Iliamna. 
ALASKA-ALEUT~ PROV~CE 35 

ALASKA RANGE (CENTRAL AND EASTERN PART) (40) 

General topography.-The central and eastern part 

of the Alaska Range consists of two or three parallel 

rugged glaciated ridges, 6,000-9,000 feet in altitude, 

surmounted by groups of extremely rugged snowcapped mountains more than 9,500 feet in altitude (pl. 

6, fig. 1). The Mentasta-Nutzotin Mountain ·segment 

( 40a) at the east end of the Alaska Range has a single 

axial ridge. The ridges are broken at intervals of 

10-50 miles by cross-drainage or low passes; most of 

the drainage appears superposed (pl. 5, fig. 1 and pl. 6, 

fig. 2). The range rises abruptly from lower country 

on either side, and its longitudinal profile, seen from a 

distance, is irregular. Mount McKinley, 20,269 feet 

high and the highest mountain in North America, is in 

this part of the Alaska Range. (pl. 6, fig. 2). 

Drainage.-The central and eastern part of the 

Alaska Range is crossed at places 25-100 miles apart 

by north-flowing tributaries of the Tanana and Yukon 

Rivers. Most of the range drains to the Tanana. The 

western part drains to the Kuskokwim River and parts 

of the south flank drain to the Susitna and Copper 

Rivers. Streams are swift and braided, and most rivers 

head in glaciers. 

Lakes . ....:....There are a few rock-basin lakes and many 

small pon4s in areas of ground moraine. Lakes are 

rare for a glaciated area. 

Glaciers and permafrost.-The firn line on the south 

side of the range is 5,000-7,000 feet in altitude and on 

the north side is 6,000-8,000 feet in altitude; this 

change reflects the northward decrease in cloudiness 

and precipitation as one passes from the Gulf of Alaska 

coast to the interior. The high mountains are sheathed 

in ice, and valley glaciers as much as 40 miles long and 

5 miles wide radiate from them. For some glaciers (for 

example, Black Rapids Glacier and Muldrow Glacier) 

short periods of rapid advance have alternated with 

long periods of stagnation. Short valley glaciers lie in 

north-facing valleys in the lower parts of the range. 

Rock glaciers are common. Permafrost is extensive and 

solifluction features are well developed. 

Geology.-The internal structure of. the Alaska 

Range is a complex synclinorium having Cretaceous 

rocks in the center and Paleozoic and Precambrian ( ~) 

rocks on the flanks. This synclinorium is cut by great 

longitudinal faults that trend approximately parallel 

to the length of the range and are marked by lines of 

valleys and low passes. The synclinorium was probably 

formed near the close of the Mesozoic Era. Many 

roughly oval granitic stocks and batholiths. support 

groups of high mountains that have cliffs as high as 

5,000 feet (pl. 6, fig. 1). 

Synclinal areas of Tertiary rocks "Q.nderlie lowlands 

that trend parallel to the length of the range. Much of 

the major topography of the range was probably ·produced from mid-Tertiary structures by removal of 

easily eroded Tertiary rocks to form low lands. Recently formed scarplets as high as 30 feet can be seen 

on several longitudinal faults. At least four periods of 

glaciation have been recognized; the earliest is indicated only by scattered giant granite erratics on uplands in the foothills to the north. 

References.-Brooks (1911); Capps (1912, 1913, 

1916a, 1932, 1940); Maddren (1917); Moffit (1912, 

1914, 1954a) ; W ahrhaftig ( 1958a, 1958b) ; W ahrhaftig 

and Cox (1959). 

The central and eastern Alaska Range is covered by 

the following 1 : 250,000 topographic maps; Tanacross, 

Mount Hayes, Healy, Mount McKinley, N abesna, 

Gulkana, Talkeetna Mountains, Talkeetna, McGrath, 

and Tyonek. 

NORTHERN FOOTHILLS OF THE ALASKA RANGE (41) 

General topography.-The Northern Foothills of the 

Alaska Range are flat-topped east-trending ridges 

2,000-4,500 feet in altitude, 3-7 miles wide, and 5-20 

miles long that are separated by rolling low lands 700-

1,500 feet in altitude and 2--10 miles wide. The foothills are largely unglaciated, but some valleys were 

widened during the Pleistocene Epoch by glaciers from 

the Alaska Range. Colorful badlands abound in areas 

of rapid erosion in soft Tertiary rocks (pl. 2, figs. 8 

and 9). 

Drainage.-The major streams of the foothills are 

superimposed across the topography. Most streams ·are 

nearly parallel, rise for the most part in the Alaska 

Range, and flow north toN. 20° W. across the ridges 

in rugged impassable V -shaped canyons and across the 

lowlands in broad terraced valleys. The entire section 

drains to the Tanana River. 

Lakes.-A few small lakes of thaw origin lie ·in the 

lowland passes, and morainal areas have shallow irregular ponds. 

Glaciers and permafrost.-The entire section is below 

the firn line, and there are no local glaciers, although a 

few glaciers from the Alaska Range terminate in the 

foothills. Permafrost is extensive, and polygonal 

ground and solifluction features are well developed 

(pl. 2, figs. 6 and 11). 

Geology.-Crystalline schist and granitic intrusive 

rocks make up most of the ridges, which are anticlinal. 

Poorly consolidated ·Tertiary rocks underlie the lowlands; thick coarse conglomerate near the top of the 

Tertiary section forms cuestas and ridges where it dips 

20°-60°, and broad dissected plateaus where it is flat 

lying. The topography reflects closely the structure of 
36 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

monoclines and short, broad flat-topped anticlines having steep north flanks. Flights of tilted terraces on 

north-flowing streams indicate Quaternary tilting and 

uplift of the Alaska Range. The Ter.tiary rocks contain thick beds of subbituminous coal. 

References.-Capps (1912, 1919, 1940); Holmes and 

Benninghoff (1957); Maddren (1917); Wahrhaftig 

( 1951, 1958a, 1958b) ; W ahrhaftig and Hickcox 

(1955); Wahrhaftig and others (1951). 

The Northern Foothills of the Alaska Range are 

covered by the following 1: 250,000 topographic maps: 

Big Delta, Fairbanks, Kantishna River, Mount Hayes, 

Healy, and Mount McKinley. 

COASTAL TROUGH PROVINCE . 

The Coastal Trough province is a belt of lowlands 

extending the length of the Pacific Mountain System, 

interrupted at intervals by oval mountain groups. It is 

divided into the following sections: Cook Inlet-Susitna 

Lowland ( 42), Broad Pass Depression ( 43), Talkeetna 

Mountains ( 44), Upper Matanuska Valley ( 45), Clearwater Mountains ( 46), Gulkana Upland ( 47), Copper 

River Lowland ( 48), Wrangell Mountains ( 49), Duke 

Depression (50) (not described), Chatham Trough 

(51), and Kupreanof Lowland (52). 

COOK INLET-SUSITNA LOWLAND (42) 

General topography.-The Cook Inlet-Susitna Lowland is a glaciated low land containing areas of ground 

moraine and stagnant ice topography, drumlin fields, 

eskers, and outwash plains (pl. 6, figs. 5 and 9) . Most 

of the lowland is less than 500 feet above sea level and 

has a local relief of 50-250 feet. Rolling upland areas 

near the bordering mountain ranges rise to about 

3,000 feet in altitude, and isolated mountains as high 

as 4,800 feet rise from the central part of the low land. 

The Cook Inlet-Susitna Lowland is the major population center of Alaska and contains most of the developed agricultural land. 

Drainage.-The lowland is drained by the Susitna 

River and other streams that flow into Cook Inlet. 

Most of these streams head in glaciers in the surrounding mountains. The shores of Cook Inlet are for the 

most part gently curving steep bluffs 50-250 feet high. 

Lakes.-Three large lakes-Tustumena, Skilak, and 

Beluga-fill ice-carved basins at the margins of surrounding mountains. Lake Tustumena, the largest, is 

23 miles long and. 7 miles wide. Hundreds of small 

irregular lakes and ponds occur in areas of stagnant 

ice topography and on ground moraines. Strangemoore ponds are common in marshes. 

Glaciers and permafrost.-The section js almost icefree, although one glacier reaches the lowla11d from 

the Alaska Range on the west, and sporadic permafrost 

is present in the northern part. 

Geology.-Bedrock beneath the lowland consists 

mainly of poorly consolidated coal-bearing rocks of 

Tertiary age, generally mildly deformed or flat lying; 

this rock is mantled by glacial moraine and outwash and 

marine and lake deposits. Sequences of moraines record 

successive glacial advances. The boundaries of the low,. 

lands are of two kinds: (a) abrupt straight mountain 

fronts that are probably faultline scarps, and (b) uplands of hard pre-Tertiary rocks that slope gently 

toward the lowland. The uplands are probably uplifted parts of the surface on which the Tertiary rocks 

were deposited; the edge of the lowland generally 

marks the edge of the Tertiary cover, which dips 

gently away from the mountains. The isolated mountains in the center of the low land generally consist of 

metamorphic and granitic rocks of Mesozoic age. 

References.-Barnes and Cobb (1959); Barnes and 

Payne ( 1956) ; Barnes and Sokol ( 1959) ; Brooks 

(1911); Capps (1940); T. N. V. Karlstrom (written 

commun., 1957) ; Karlstrom ( 1955, 1960) ; Martin and 

others ( 1915) ; Miller and Dobrovolny ( 1959) ; Trainer 

(1953, 1960). 

The Cook Inlet-Susitna Lowland is covered by the 

following 1 : 250,000 topographic maps: Talkeetna 

Mountains, Talkeetna, Anchorage, Tyonek, Kenai, and 

Seldovia. 

BROAD PASS DEPRESSION (4S) 

General topography.-The Broad Pass Depression, 

1,000-2,500 feet in altitude and 5 miles wide, is a trough 

· having a glaciated floor ; it opens on the east to a broad 

glaciated lowland with rolling morainal topography 

and central outwash flats. The bounding mountain 

walls of the trough are several thousand feet high. 

Long, narrow drumlinlike hills on the floor of the 

trough trend parallel to its axis, and the main streams 

in the trough are incised in rock-walled gorges a few 

hundred feet deep. The trough opens on its south end 

to the Cook Inlet-Susitna Lowland. 

Drainage.-The divide between the Bering Sea and 

Pacific Ocean drainages crosses this depression in two 

places and is marked by nearly imperceptible passes. 

The southwestern part drains by the Chulitna River 

to ·the Susitna River; the central part, by the Nenana 

River north to the Yukon River; and the eastern part, 

by the headwaters of the Susitna. Most streams head 

in glaciers in the surrounding mountains and are swift, 

turbid, and braided. 

Lakes.-Many long, narrow lakes lie in morainal depressions in the central part of the trough. Morainal 

and thaw lakes are corp.mon in the eastern part. 

Glaciers and permafrost.-Ther~ are no gl11cier~, 

Most of the depressipn 1s underlain by perm.afro!'t· 

Geology.~Patche!' of poorly consolldated T~rtiary 

coal-bearing rocks, in fault contact with older rocks 
COASTAL TROUGH PROVLNCE 37 

of the surrounding mountains, show that this depression marks a graben of Tertiary age. Most of the 

bedrock consists of highly deformed slightly metamorphosed Paleozoic and Mesozoic rocks that are also exposed in the surrounding mountains. Ground moraine 

mantles the lowland. 

References.-Capps (.1940); Hopkins (1951); Wahrhaftig ( 1944, 1958a) . 

The Broad Pass Depression is covered by the following 1:250,000 topographic maps: Healy, Talkeetna 

Mountains, and Talkeetna. 

TALKEETNA MOUNTAINS (44) 

Generril topography.-The ·Talkeetna Mountains 

are an oval highland of diversified topography that 

interrupts the belt of lowlands of the Coastal Trough 

province. The central Talkeetna Mountains ( 44c) are 

a compact group of extremely rugged radial ridges 

6,000-8,800 feet in altitude, having only few low 

passes, that isolate steep-walled U-shaped valleys. 

Accordant flat ridge crests in the western and eastern 

parts of the central Talkeetna Mountains suggest a 

warped peneplain that plunges beneath Tertiary rocks 

in the adjacent lowlands (pl. 6, fig. 5). The glaciated 

Chulitna Mountains ( 44a), a compact group of mountain blocks separated by low passes, are isolated from 

the central Talkeetna Mountains by the Fog Lakes 

Upland ( 44b), a northeast-trending area of broad rolling summits, 3,000-4,500 feet in altitude, which has a 

glacially sculptured mammillated surfaqe in its southwestern part but is unglaciated in the northeastern 

part. A similar upland (the Clarence Lake Upland, 

44d) borders the mountains on the east. 

Drainage.-The central Talkeetna Mountains have a 

radial drainage of large braided glacial streams that 

are tributary to the Susitna, Matanuska, and Copper 

Rivers. The extreme northern part drains to the Yukon 

River via the Nenana River. The Susitna River flows 

west across the Talkeetna Mountains in a narrow steepwalled gorge that in places is more than 1,000 feet deep. 

West-flowing streams in the southwestern Talkeetna 

Mountains have many long southern tributaries and 

few or no northern tributaries; low slanting solar rays 

from the south, favoring the growth of glaciers in 

shaded north-facing yalley heads and inhibiting their 

growth on sunny south-facing slopes, probably caused 

this asymmetry. 

Lakes.-There are few lakes in the southern part of 

the Talkeetna Mountains. Many lakes, some 5 miles 

long, occupy ice-carved and moraine-dammed basins 

in the nor~hern part. 

Glaciers and permafrost.-The firn line is between 

altitudes of 6,500 and 7,000 feet. Glaciers 5-15 miles 

long lie at the heads of most valleys in the central 

Talkeetna Mountains. A few cirque-glaciers occupy 

north-facing valley heads in the northeastern Talkeetna 

Mountains and Chulitna Mountains. Rock glaciers are 

common in the southeastern Talkeetna Mountains and 

in the Chulitna Mountains. Permafrost probably 

underlies most of the section; altiplanation terraces 

are present in unglaciated parts of the northeastern 

Talkeetna Mountains. · 

Geology.-A large mid-Jurassic batholith in the 

central and western Talkeetna Mountains Intrudes 

Jurassic volcanic rocks and older rocks and is eroded 

into cliffs and spires. The southeastern Talkeetna 

foothills ( 44e) are composed of soft sandstone and 

shale of Jurassic and Cretaceous age, capped by flatlying cliff-forming Tertiary basalt flows aggregating 

several thousand feet in thickness. The northern part 

of the Talkeetna Mountains consists of Paleozoic and 

Mesozoic greenstone, graywacke, and argillite in northeast-trending belts. The greenstone forms rugged 

mountains. 

References._:_Barnes (1962) ; Capps (1927, 1940) ; 

Chapin (1918); Grantz (1953, 1960a, 1960b, 1961a, 

1961b, oral commun., 1957); Moffit (1915); Paige and 

Knopf (1907); J. R. Williams, oral commun. 1957). 

The Talkeetna Mountains are covered by the following 1:250,000 topographic maps: Healy, Talkeetna 

Mountains, Talkeetna, and Anchorage. 

UPPER MATANUSKA VALLEY (46) 

General topography.-The Upper Matanuska Valley 

is a glaciated trough 2--5 miles wide containing longitudinal bedrock hills 500-1,000 feet high and having 

steep bounding walls several thousand feet high. Altitude of its floor ranges from 800 feet on the west to 

2,000 feet on the east. 

Drainage.-The Upper Matanuska Valley is drained 

entirely by the Matanuska River, which. flows westward 

along the trough. 

Lakes.-Many small narrow lakes occupy ice-carved 

bedrock basins, and ponds are common in morainal 

areas. 

Glaciers and .permafrost.-The terminus of the 

Matanuska Glacier reaches the east end of the trough. 

Permafrost is present in the eastern part of the trough, 

but its extent is unknown. 

Geology.-The Upper Matanuska Valley is a structurally controlled trough bounded on the north by a 

major fault, the Castle Mountain fault, and on the 

south by a steep unconformity and faults. It is underlain by easily eroded rocks of Cretaceous and Tertiary 

age, which are highly deformed and were intruded by 

gabbro sills and stocks. It contains several coal fields. 

The bordering mountains are of older and more resistant rocks. 
38 PHYSIOGRAPIDC DIVISIONS OF ALASKA 

References.-Barnes (1962); Barnes and Payne 

(1956); Capps (1927) ; Grantz (1953, 1960b, 1961a; 

oral commun., 1959); Grantz and Jones (1960); 

Martin and K·atz (1912). 

The Upper Matanuska Valley is shown on the 

1:250,000 topographic map of Anchorage quadrangle. 

CLEARWATER :MOUNT.ADlS (48) 

General topography.-The Clearwater Mountains 

consist of two or three steep, rugged east-trending 

ridges rising to altitudes of 5,500-6,500 feet, separated 

by U-shaped valleys 3,000-3,500 feet in altitude. They 

are intensely glaciated. The ridges are asymmetrical; 

long spurs on their north sides separate large compound cirques; their south sides are relatively smooth 

mountain walls grooved by short· steep canyons. 

Drainage.-The entire section is tributary to the 

Susitna River. 

Lakes.-There are a few rock-basin lakes in cirques 

and passes. The largest lake is less than 1 mile long. 

Glaciers.-The north slopes of the highest peaks 

have a few cirque-glaciers. 

Geology.-The Clearwater Mountains are underlain 

chiefly by Triassic greenstone and Mesozoic argillite 

and graywacke. The rocks are highly deformed, strike 

generally east, and dip steeply. 

References. Kachadoorian and others (1954); Moffit 

(1912); Ross (1933). · 

The Clearwater Mountains are covered by the following 1: 250,000 topographic maps: Mount Hayes and 

Healy. 

G11LKANA 11PLAND (47) 

General topography.-The Gulkana Upland consists 

of rounded east-trending ridges separated by lowlands 

2-10 miles wide. The ridge crests, 3,500-5,500 feet in 

altitude, are 4-15 miles apart and are cut at intervals of 

5-15 miles by notches and gaps that were eroded by 

glaciers or glacial melt water (pl. 5, fig. 2). The lowlands are floored by glacial deposits showing morainal 

and stagnant-ice topography and contain large esker 

systems (pl. 5, fig. 3) . 

Drainage.-The southeastern and eastern part drains 

south to the Copper ·River; the western part drains 

southwest to the Susitna River; and the north-central 

part drains north via the Delta River to the Tanana 

and Yukon. The drainage divide between the Pacific 

Ocean and Bering Sea has an irregular course through 

this section and is in part along eskers (pl. 5, fig. 3). 

Lakes.-Many long, narrow lakes occupy rock-cut 

basins in notches through the ridges. Irregular lakes 

abound in some areas of morainal topography. 

Glaciers and permafrost.-A few cirque glaciers lie 

on the north sides of the highest ridges. The lower 

ends of a few glaciers from the Alaska Range are in 

this section. The upland is underlain by permafrost 

and contains ice-wedges, pingos, and altiplanation 

terraces. 

Geology.-Bedrock is chiefly greenstone and of late 

Paleozoic ·and Mesozoic age; structure trends eastward. 

Areas of relatively low relief in the northern part are 

underlain by poorly consolidated Tertiary sedimentary 

rocks. 

References.-Kachadoorian and others (1954) ; 

Kachadoorian and Pewe (1955); Moffit (1912, 1954a). 

The Gulkana Upland is covered by the following 

1: 250,000 topographic maps: Mount Hayes, ·Healy, 

Gulkana, and Talkeetna Mountains. 

COPPER RIVER LOWLAND (48) 

General topography.-The eastern part of the Copper River Lowland ( 48a) is a relatively smooth plain, 

1,000-2,000 feet in altitude trenched by the valleys of 

the Copper River and its tributaries, which have steep 

walls 100-500 feet high (pl. 6, fig. 3). The Copper and 

Chitina valleys, eastward prongs of this lowland, contain longitudinal morainal and ice-scoured bedrock 

ridges that rise above axial outwash plains. The 

western part of the Copper River Lowland, the Lake 

Louise Plateau ( 48b), is a rolling upland, 2,200-3,500 

feet in altitude, and has morainal and stagnant-ice 

topography; the broad valley of the N elchina and 

Tazlina Rivers separates this upland from the Chugach 

Mountains. 

Drainage.-The eastern and southern parts of the 

Copper River Lowland are drained by the Copper 

River and its tributaries. The northwestern part is 

drained by the Susitna River. Low passes lead to the 

heads of the Delta, Tok, and Matanuska Rivers. Most 

rivers head in glaciers in surrounding mountains and 

have braided upper courses. Salty ground water has 

formed salt springs and mud volcanoes. 

Lakes.-Large lakes occupy deep basins in the mountain fronts. Thaw lakes are abundant in the eastern 

plain. Lakes occupy ·abandoned melt-water channels; 

those in morainal depressions in the western upland are 

as much as 6 miles across. Beaches and wave-cut cliffs 

border lakes more than 2 miles wide whereas irregular 

muskeg marshes encroach on smaller lakes. 

Glaciers and permafrost.-There are no glaciers. The 

entire lowland is underlain by permafrost. The permafrost table is within 5 feet of the surface and permafrost is at least 100 feet thick. 

Geology.-Bedrock beneath the southern part of the 

low land is chiefly easily eroded sandstone and shale of 

Mesozoic age; bedrock beneath the northern part is 

chiefly resistant late Paleozoic and Mesozoic metamorphosed volcanic rocks. Tertiary gravels cap some hills. 

Ground and end moraine and stagnant ice deposits 
PACIFIC BORDER RANGES PROVINCE 39 

mantle much of the lowland. The eastern plain. is 

underlain by glaciolacustrine and glaciofluvial deposits 

at least 500 feet thick. 

References.-Andreasen and others (1958) ; Grantz 

(1961b; oral commun., 1959); Grantz and others 

(1962); Mendenhall (1905); Moffit. (1938, 1954a); 

D. R. Nichols (written commun., 1960); J. R. Williams 

(written commun., 1957). 

The Copper River Lowland is covered by the following 1:250,000 topographic maps: Nabesna, Gulkana, 

Talkeetna Mountains, McCarthy, Valdez, and Anchorage. 

WRANGELL MOUNTAINS (49) 

General topography.-The Wrangell Mountains are 

an oval group of great shield ·and composite volcanoes 

(Mount Wrangell, 14,005 feet in altitude, is still active) that rises above a low plain on the north and west 

and above heavily glaciated cliffed and castellated 

ridges on the south -and east (pl. 6, fig. 3). Six volcanoes at altitudes higher than 12,000 feet-the highest 

is Mount Blackburn, 16,523 feet-make up the greater 

part of the mountains. 

Drainage.-Seventy-five percent of the section drains 

to the Copper River, which encircles the· mountains on 

the west. The remainder drains to the Tanana River 

via the Nabesna and Chisana Rivers and to the Yukon 

River via the White River. 

Lakes.-There are a few rock-basin lakes in the extreme northern part. Several ice-marginal lakes lie in 

Skolai Pass at the east end of the mountains. 

Glaciers and permafrost.-The firn line is at an altitude of ·about 7,000 feet. A large icecap covers most of 

the high mountains and feeds large valley glaciers. 

Rock glaciers are common in the. southeastern Wrangell 

Mountains. Permafrost is probably present in the 

glacier-free areas, but its extent is unknown. 

Geology.-The Wrangell Mountains are a great pile 

of Cenozoic volcanic rocks that rests on deformed 

Paleozoic and Mesozoic sedimentary and volcanic 

rocks, among which are cliff-for:ming units of limestone 

and greenstone. Some granitic masses intrude the 

Mesozoic rocks. An important belt of copper deposits, 

including the Kennicott Mine, lies on the south side of 

the Wrangell Mountains. 

References.-Capps (1915, 1916a); Mendenhall 

(1905); Moffit (1938, 1954a). 

The Wrangell Mountains are covered by the following 1:250,000 topographic maps: Nabesna, Gulkana, 

McCarthy, and Valdez. 

OIIATIIAM TBOUGII (01) 

General topography.-The Chatham Trough is a 

deep, straight trench, 4-15 miles wide, which is entirely 

below the sea except for its north end. .Average depth 

of water in the trough is more .than 1,900 feet, and its 

maximum depth is 2,900 feet. Mountains on either side 

rise to 2,500-5,000 feet above sea level. 

Geology.-The Chatham Trough probably marks a 

major fault line .. Rocks on opposite sides of the trough 

do not match across the trough, either in .their structure 

or in their age. It probably owes its greater depth to 

glacial erosion of relatively soft rocks. 

References.-Lathram and others (1959). 

The Chatham Trough is covered by the following 

1: 250,000 topographic maps: Skagway, Juneau, Sitka, 

and Port Alexander. 

KUPRBANOF LOWLAND (09) 

General topography.-The Kupreanof Lowland consists of islands and channels. Islands of rolling heavily 

glaciated terrain having a local relief of 300-500 feet 

and a maximum relief of 1,000-1,500 feet are separated 

by -an intricate network of waterways. (See northeast 

part of fig. 11, pl. 5.) Scattered blocklike mountains 

having rounded hummocky summits 2,000-3,000 feet in 

altitude rise above the general level of the lowland. 

Parts of same islands are plains which are a few feet 

above sea level and are cut across rocks of varying 

hardness. 

Drainage.-The islands of the lowland are drained 

by many short clear streams that generally follow 

linear depressions etched by the Pleistocene ice sheets 

along joints, faults, bedding, and schistosity. 

Lakes.-There are abundant lakes in glacially 

scoured basins. Parts of some islands are almost 50 

percent lake surface. 

Glaciers and permafrost.-There are no glaciers or 

permafrost. 

Geology.-The lowland is underlain mainly by wellconsolidated faulted and folded Paleozoic and Mesozoic 

sedimentary rocks, locally metamorphosed. Small elliptical granitic and ultramafic masses underlie most of 

the high mountains. The northern part of the lowland 

has an extensive Cenozoic basalt field. Small patches 

of Tertiary sedimentary rocks have been found. 

Re.ferences.-Buddington and Chapin (1929); G. D. 

Eberlein (oral commun., 1957); Sainsbury (1961); 

S-ainsbury and Twenhofel ( 1954). 

The Kupreanof Low land is covered by the following 

1: 250,000 topographic maps: Sumdum, Sitka, Petersburg, Port Alexander, Ketchikan, Craig, and Prince 

Rupert. 

PACIFIC BORDER RANGES PROVINCE 

The Pacific Border Ranges province consists of 

several mountain ranges bordering the Pacific Coast 

and a coast-al shelf that is present in places between 

them and the ocean. It is divided into the following 

sections: Kodiak Mountains (53), Kenai-Chugach · 
40 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

Mountains (54), St. Elias Mountains (55), Fairweather Range ( 55a) , Gul-f of Alaska coastal section 

(56), Chilkat-Baranof Mountains (57), and Prince of 

Wales Mountains (58). 

KODIAK MOUNTAINS (63) 

Ge'MTal topogTaphy.-The Kodiak Mountains include a group of mountainous islands that are the 

structural continuation of the Kenai-Chugach Mountains (54) but whose tqpography is more finely textured and on a smaller scale than that of the KenaiChugach Mountains. The Kodiak Mountains section is 

mostly glaciated, but the glaciation of western Kodiak 

Island was very early. Summit altitudes are between 

2,000 and 4,000 feet. Kodiak Island has a rugged northeast-trending divide having horns and aretes from 

which broad smooth ridges extend northwestward. The 

topography southeast of the divide has a strong northeasterly grain normal to the drainage (pl. 5, fig. 7). 

The coastline is extremely irregular, having many 

fiords and islands. The northern. part of Afognak 

Island is a hilly lowland, and the western part of 

Kodiak Island has many broad valleys. 

DTainage.-The islands of the Kodiak Mountains are 

drained mostly by swift, clear streams that are less 

than 10 miles long. Two rivers, each about 25 miles 

long, drain much of southwestern Kodiak Island. 

Lakes.-There are several lakes more than a mile 

long in the south western part of Kodiak Island and 

on Afognak Island. Small ponds are scattered over the 

glacially sculptured topography. The glaciated valleys 

heading in the main divide have chains of paternoster 

lakes. 

Glacier's and permafTost.-The firn line is between 

altitudes of 3,000 and 3,500 feet along the main divide 

of Kodiak Island, which has 40 cirque glaciers, all less 

than 2 miles long; the firn line rises to much more than 

4,000 feet in the northwestern part of Kodiak Island. 

Permafrost is probably absent. 

Geology.-The Kodiak Mountains are underlain 

mostly by Mesozoic argillite and graywacke. Older 

rocks, chiefly greenstone and schist, lie along the northwest coast. The main divide of Kodiak Island is underlain by a granitic batholith. Northeast-trending belts 

of downfaulted and easily eroded Tertiary rocks lie 

on the southeast side of Kodiak Island and also make 

up the Trinity Islands. Lateral mqraines, ice-marginal 

drainage channels through the ends of ridges, and old 

greatly modified cirques half buried in alluvium (pl. 

5, fig. 6) indicate that western Kodiak Island was not 

covered by ice of the last glaciation and that ice from 

the Aleutian Range banked against its western shore. 

RefeTences.-Capps (1937); Maddren (1919). 

The Kodiak Mountains are covered by the following 

1:250,000 topographic maps: Afognak, Kodiak, Karluk, Kaguyak, and Trinity Islands. 

KENAI-CHUGACH MOUNTAINS (64) 

GeneTal topogTaphy.-The Kenai-Chugach Mountains form a rugged barrier along the north coast of 

the Gulf of Alaska. High segments of the mountains 

are dominated by extremely rugged east-trending 

ridges 7,000-13,000 feet in altitude. Low s~gments consist of discrete massive mountains 5-.10 miles across and 

3,000-6,000 feet in altitude, separated by a reticulate 

system of through valleys and passes Y2-1 mile wide 

that are eroded along joints and cleavage (pl. 5, fig. 4). 

The entire range has been heavily glaciated, and the 

topography is characterized by horns, aretes, cirques, 

U-shaped valleys and passes, rock-basin lakes, and 

grooved and mammillated topography. The south coast 

is deeply indented by fiords and sounds, and ridges extend southward as chains of islands (pl. 5, fig. 8). rhe 

north front is an abrupt mountain wall. 

DTainage.-The drainage divide, generally an ice 

divide, is along the highest ridges, and is commonly 

only a few miles from the Pacific Ocean. Streams are 

short and swift ; most head in glaciers. The Copper 

River crosses the eastern part of the Chugach Mountains in a canyon 6,000-7,000 feet deep. 

Lakes.-Large lakes fill many ice-carved basins along 

the north margin of the Chugach Mountains and 

throughout the northern Kenai Mountains. Lake 

George is an ice-margin lake dammed by the Knik 

Glacier; it empties in an annual flood. 

Glacier's and peTmafTost.-:-The firn line rises from an 

altitude of 2,500-3,500 feet on the south side of the 

mountains to 7,000-8,000 feet on the north side of the 

central Chugach Mountains. All higher parts of the 

range are buried in great icefields, from which valley 

and piedmont glaciers radiate. Many of the glaciers 

on the south side of the mountains end in tidewater. 

The extent of permafrost is unknown. 

Geology.-The Kenai-Chugach Mountains are composed chiefly of dark-gray argillite and graywacke of 

Mesozoic age that are mildly metamorphosed and have 

a pronounced vertical cleavage that strikes parallel to 

the trend of the range. In the Prince William Sound 

area large bodies of greenstone are associated with the 

argillite and graywacke. A belt of Paleozoic and Mesozoic schist, greenstone, chert, and limestone lies along 

the north edge of the Kenai and Chugach ::Mountains. 

All these rocks are cut by granitic intrusions. 

RefeTences.-Barnes (1943); Capps (1916b, 1940); 

Capps and Johnson (1915); Grant and Higgins (1910, 

1913); Grantz (1961a, 1961b; oral commun., 1957); 

Landes (1927); Martin and others (1915); Miller 
PACIFIC BORDER RANGES PROVINCE 41 

(1958; oral commun., 1959); Moffit (1914, 1935, 1954b); 

Park (1933); Plafker (1955); Tarr and Martin (1914, 

p. 232--450); Tuck (1933); J. R. Williams (oral com· 

mun., 1957). 

The Kenai·Chugach Mountains are covered by the 

following 1 : 250,000 topographic. maps: McCarthy, 

Valdez, Anchorage, Bering Glacier, Cordova, Seward, 

Kenai, Blying Sound, and Seldovia. 

ST. ELIAS IIOlJNTAINS (611) 

General topography~-The St. Elias Mountains are 

probably the most spectacular mountains of North 

America. Massive isolated blocklike mountains.14,000-

19,000 feet in altitude rise at intervals of 5-30 miles 

from a myriad of narrow ridges and sharp peaks 8,000-

10,000 feet in altitude that, seen from a distance, gives 

the impression of a broad ice dome. The average altitude of icefields in the interconnected valley system is 

3,000-7,000 feet. Local relief is extreme and jagged 

cliffs abound (pl. 6, fig. 4) . 

Drainage.-Drainage is almost entirely by glaciers. 

The ice divides between drainages of the Yukon, Copper, and Alsek Rivers and the Pacific Ocean meet in 

this range. The Alsek River flows west to the Pacific 

across this range from lowlands on the northeast side 

and separates the Fairweather Range subsection from 

the rest of the mountains. 

Lakes.-There are no lakes. 

Glaciers and permafrost.-All parts of the range. 

gentle enough to hold snow are sheathed in glacial ice. 

A continuous network of icefields and glaciers 4-15 

miles wide and as much as 80 miles long penetrates the 

range and feeds piedmont glaciers to the south. The 

extent of permafrost is unknown. 

Geology.-The high mountains are probably under· 

lain by crystalline schist and granitic intrusive masses. 

A belt of Permian and Triassic volcanic and sediment· 

ary rocks extend along the north side of the range. 

Lower Cretaceous sedimentary rocks lie in down· 

faulted basins in the center of the range and probably 

underlie ice-filled valleys. The entire sequence is thrust 

southward against Cretaceous and Cenozoic rocks; 

thrusting may be active today. Cenozoic volcanoes are 

present in the northern part of the range; some of these 

may still be active. 

References.-Blackwelder (1907a, 1907b); Bostock 

(1948, p. 92-101, 1952, p. 6-8); Capps (1961a); Filippi 

(1900); Kindle (1953); l\1iller (1958); Moffit (1938); 

Muller (1954); Odell (1950); Plafker and Miller 

(1957, 1958); Russell (1893); Sharp (1943, 1947); 

Sharp and Rigsby ( 1956) ; Tarr and Butler ( 1909) ; 

Tarr and Martin (1912, 1914, p. 23-231); Washburn 

(1.936). 

The St. Elias Mountains are covered by the following 1:250,000 topographic maps: McCarthy, Bering 

Glacier, Mount St. Elias, and Yakutat. 

FAIRWEATHER RANGE (55a) 

(Subsection of the St. Elias Mountains) 

General topography.-The Fairweather Range is an 

exceedingly steep and high unbroken barrier between 

the Pacific Ocean and Glacier Bay; mountains rise to 

12,000-15,000 feet in altitude only 15 miles from tidewater (pl. 6, fig. 6). Peaks are high ice-clad pyramids 

having steep-cliffed walls, sharp ridges, and spirelike 

summits. There are a few subsummit ice plateaus but 

no passes across the range. 

Drainage.-The Fairweather Range is drained en-· 

tirely by glaciers ; most of these discharge into the 

Pacific Ocean or Glacier Bay. 

Lakes.-There are no lakes. 

Glaciers and permafrost.-Most of the range is above 

firn line ( 4,000 ft) and supports vigorous glaciers that 

descend to tidewater. Glaciers on the west side have 

not advanced or retreated in recent years; those on the 

east side have retreated in the last 60 years and expose 

fiords having walls nearly 6,000 feet high. Permafrost 

is probably absent. 

Geology.-The Fairweather Range is underlain 

mainly by crystalline schist that has northwesterly 

structural trends parallel to the length of the range. 

Many large granitic stocks and three large elliptical 

layered mafic bodies have intruded the schist. The 

range is bounded on its southwest side by a major 

fault, the Fairweather fault, on which a lateral displacement of 21 feet took place in July 1958; 

References.-Mertie (1931); Miller (1953b, 1960); 

Rossman ( 1963a, 1963b) ; Tocher and Miller ( 1959). 

The Fairweather Range is covered by the following 

1: 250,000 topographic maps: Skagway and Mount 

Fairweather. 

GULF OF ALASKA COASTAL SECTION (118) 

General topography.-The Gulf of Alaska coastal 

section has a diversified topography carved in Tertiary rocks. A coastal plain marked by longitudinal 

beach and dune ridges, crossed in places by outwash 

plains and by belts of morainal topography, is backed 

by marine terraces as high as 800 feet in altitude and 

by rugged intricately gullied mountain ridges as high 

as 12,000 feet. The straight exposed coastline is broken 

at intervals of 50-100 miles by large fiords (pl. 6, 

fig. 10). 

Drainage.-Short melt-water streams of large volume cross the low land. Bars built by coastal currents 

cause the river mouths to go through cycles of west-
42 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

ward migration followed by breakthrough at their 

original sites during periods of high runoff. 

Lakes.-There are many ephemeral lakes along the 

margins of the piedmont glaciers. A few large lakes 

occupy ice-carved basins. 

Glaciers and permaf'rost.-The firn line is at an altitude of 2,000-4,000 feet. Icefields on higher mountains 

and valley glaciers in most of the valleys coming from 

the St. Elias and Chugach Mountains feed enormous 

piedmont glaciers, of which the Malaspina Glacier (pl. 

6, fig. 4) is the largest. Glacial advances within the last 

thousand years are greater than any advance recorded 

in the Pleistocene. Permafrost is absent. 

Geology.-The Cenozoic rocks are intensely deformed yet easily eroded claystone, sandstone, and conglomeratic sandy mudstone, all tightly folded and 

thrust to the south. Large thrust faults separate this 

section from mountains to the north and northeast. 

Marine terraces show that the area has been uplifted 

rapidly. The conglomeratic sandy mudstone interbedded in the Cenozoic section is interpreted to be 

marine tillite; it indicates recurrent tidewater glaciation on this coast as far back as Pliocene time or earlier. 

An earthquake-induced landslide on July 9, 1958, 

created a flood wave on Lituya Bay that splashed to 

a height of 1,700 feet on the side of a mountain, sweeping the forest in its path into the bay. 

References.-Mertie (1931); Miller (1953a, 1953b, 

1957, 1958, 1960; written commun., 1957) ; Plafker and 

Miller (1957, 1958) ; Twenhofel (1952). 

The Gulf of Alaska coastal section is covered by the 

following 1: 250,000 topographic maps: Mount St. 

Elias, Bering Glacier, Cordova, Yakutat, Icy Bay, 

Middleton Island, and Mount Fairweather. 

CHII.KAT-BARANOF MOUNTAINS (117) 

General topography.-The Chilkat-Baranof Mountains are a highland of diversified topography, which 

is divided into four subsections : the Alsek Ranges 

(57a), a subsection of rugged glaciated mountains 

4,000-7,500 feet altitude, containing horns and aretes 

(pl. 6, fig. 6); the Glacier Bay subsection (57b), a lowland, largely drowned, that contains isolated rounded 

mountains; the Chichagof Highland (57 c), consisting 

mainly of northwest-trending ridges whose summits 

are accordant, rounded, and 3,000-3,500 feet in altitude 

and of long fiords and through valleys; and the Baranof Mountains (57 d), a rugged asymmetric chain 

3,000-5,300 feet in altitude, having a steep eastern slope 

(pl. 5, fig. 10) and a more gentle southwest slope 

deeply indented by fiords. The southern two-thirds 

of the Chilkat-Baranof Mountains consists of islands. 

A narrow strandflat lies on the west coast of Chichagof 

and Baranof Islands. · 

Drainage.-The Chilkat-Baranof Mountains are 

drained by short, swift streams that flow directly to 

the ocean. Chains of cascades are common on the east 

si4e of Baranof Island (pl. 5, fig. 10). 

Lakes.-Lakes abound in ice-carved basins in Baranof and southwestern Chichagof Islands (pl. 5, fig. 10). 

Elsewhere hl.kes are few. 

Glaciers and permafrost.-The Alsek Ranges have 

large icefields containing tidal glaciers; Glacier Bay 

was filled with ice at least 2,000 feet thick as late as 

1750, and glaciers have retreated more than 50 miles 

since then to expose the bay. Mountains on Baranof 

Island higher than 4,500 feet support cirque glaciers 

and small icefields (pl. 5, fig. 10). Permafrost is probably absent. 

Geology.-Northwest-trending belts of Paleozoic 

and Mesozoic sedimentary and volcanic rocks underlie 

the Alsek Ranges and Glacier Bay subsections; northwest-trending belts of crystalline schist and gneiss and 

large areas of migmatitic and granitic rocks underlie 

the Chichagof Highland and the northeastern part of 

the Baranof Mountains and are bordered on the west 

by a belt of Mesozoic graywacke and greenstone. The 

rocks arc cut by many northwest-trending faults. Quaternary volcanoes make up southern Kruzof Island. 

References.-Buddington and Chapin (1929) ; Guild 

and Balsley ( 1942) ; Knopf ( 1912) ; Lathram and 

others (1959) ; Reed and Coats (1942); Rossma11 

(1963h; oral commun., 1956); Sainsbury and Twenhofel (1954); Seitz (1959). 

The Chilkat-Baran of Mountains are covered by the 

following 1:250,000 topographic maps: Skagway, 

Juneau, Mount Fairweather, Sitka, and Port Alexander. 

PRINCE OF WALES MOUNTAINS (liB) 

General topography.-The Prince of Wales Mountains are moderately rugged glaciated mountains having rounded hu~ocky summits 2,000-3,500 feet in 

altitude and some spirelike aretes as much as 3,800 

feet in altitude. They are dissected by steep-walled Ushaped valleys and by fiords 600-1,000 feet deep. (See 

pl. 5, fig. 11.) Several passes less than 500 feet in 

altitude cross the range. The northeast front is 

abrupt, and the northwest boundary is indistinct. Karst 

topography is found in areas of marble on Dall and 

Long Islands in the southwest Prince of Wales Mountains. 

Drainage.-Short, swift streams, having many lakes 

and waterfalls, drain .the mountains and generally 

follow trenches eroded by Pleistocene glaciers along 

joints, faults, and bedding. 

Lakes.-There are many rock-basin and cirque lakes, 

a few as much as 2,000 feet above sea level. The largest lake is 7 miles long and 1 mile wide. 
REFERENCES CITED 43 

Glaciers and permafrost.-One or two very small 

glaciers lie on the protected north sides of the highest 

peaks. There is no permafrost. 

Geology.-The Prince of Wales Mountains are underlain in part by well-consolidated sljghtly metamorphosed Paleozoic :sedimentary and volcanic rocks and 

in part by crystalline schist and marble. Several small 

granitic stocks cut these rocks. The mountains were 

entirely covered by the Pleistocene cordilleran ice sheet, 

which was fed partly from local centers but mainly 

from the Coast Mountains to the ~st. 

References.-Buddington and Chapin (1929); Condon (1961); G. D. Eberlein (oral commun., 1959). 

The Prince of ~r ales Mountains are covered by the 

following 1 : 250,000 topographic maps: Ketchikan, 

Craig, Prince Rupert, and Dixon Entrance. 

COAST MOUNTAINS 

The Coast Mountains form a massive mountain 

barrier underlain by the Coast R-ange batholith. The 

province can be divided into the Boundary Ranges 

(59) and the Coastal Foothills ( 60). 

BOUNDARY RANGES (69) 

General topography.-The Boundary Ranges are a 

glacier-covered upland 5,000-7,000 feet in altitude 

dissected by a dendritic pattern of deep steep-walled 

U-shaped valleys. The ridges have rounded accordant 

summits and are surmounted by aretes and horns rising to 8,000-10,000 feet. Many of the valleys are 

drowned and form fiords. Passes are scarce, and valley 

heads are isolated. ·The mountains give an impression 

of great bulk and are bordered largely by cliffs that 

plunge several thousand feet to tidewater. (See pl. 5, 

fig. 9; pl. 6,.fig. 7.) 

Drainage.-The summit of the Coast Mount-ains coincides approximately with the international boundary; 

most of the range in Alaska is drained by glacial 

streams less than 20 miles long. Large braided rivers 

flow southwestward across the range ·at intervals of 

30-120 miles from low-lying areas in northwestern 

British Columbia. 

Lakes.-A few small lakes lie in rock basins on valley 

floors and in mountainside hollows in the western, 

glacier-free part of the range. 

Glaciers and permafrost.-The firn line is about 

4,500-5,000 feet in alti.tude. Extensive mountain icecaps, the largest 90 miles long, feed many valley 

glaciers, some of which descend to tidewater. Extent 

of per:ffiaf.rost is unknown. 

Geology.-The Boundary Ranges are underlain 

mostly by the massive granitic rocks of the Coast Range 

batholith; a belt of schist and phy\lite along its western 

margin and migmatized roof pendants within the 

batholith .give a strong northwesterly grain to the 

topography. 

References.-Buddington (1929); Buddington and 

Chapin (1929); Lathram and others (1959); Sainsbury 

and Twenhofel (1954); Twenhofel (1952). 

The Boundary Ranges are covered by the following 

1: 250,000 topographic maps: Atlin, Skagway, Taku 

River, Juneau, Sumdum, Bradfield Canal, Petersburg, 

Ketchikan, -and Prince Rupert. 

COASTAL FOOTHU.LS (80) 

General topography.-The Coastal Foothills consist 

of blocks of high mountains 3-30 miles across separated 

by flat-floored valleys and straits %-10 miles wide; 

they include closely spaced mountainous islands and 

peninsulas 1,000-4,500 feet in altitude. . Mountains 

less than 3,500 feet in altitude were glacially overridden and have rounded hummocky summits (pl. 6, 

fig. 11). Higher mountains are generally sharp crested. 

The boundaries with bordering sections are indistinct. 

Drainage.-Few streams are more than 10 miles long. 

The lower parts of most valleys are drowned, forming 

inlets and harbors. 

Lakes.-There are many rock-basin lakes, the largest 

8 miles long and 1 mile wide. 

Glaciers and permafrost.-The Coastal Foothills ~re 

almost entirely ice free. A few small glaciers lie on the 

north sides of the high peaks on Admiralty Island. 

There is no permafrost. · 

Geology .-Northwest-trending belts of metamorphic 

rocks, cut by many faults parallel to the northwesterly 

trend of the rocks, give the topography a pronounced 

northwest grain. Small granitic and ultramafic bodies 

and westerly projections of the Coast Range batholith 

cut the metamorphic rocks. Southwest Admiralty 

· Island is a high Tertiary basalt plateau. 

References.-Buddington and Chapin (1929) ; Lathram and others ( 1959) ; Sainsbury and Twenhofel 

(1954). 

The Coastal Foothills section is covered by the following 1:250,000 topographic maps: Taku River, 

Juneau, Sum dum, Sitka, Bradfield Canal, Petersburg, 

Ketchikan, Craig, and Prince Rupert. 

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44_ PHYSIOGRAPHIC DIVISIONS OF ALASKA 

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____ 1913, The Yentna district, Alaska: U.S. Geol. Survey 

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____ 1927, Geology of the upper Matanuska Valley, with a 

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____ 1959c, Reconnaissance geologic map of the Unalakleet 

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1959d, Reconnaissance geologic map of the Ruby 

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REFERENCES CITED 45 

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Chapman, R. M., and Sable, E. G., 1960, Geology of the UtukokCorwin region, northwestern Alaska: U.S. Geol. Survey 

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1953, Geology of Buldir Island, Aleutian Islands, 

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1956a, Geology of northern Adak Island, Alaska : 

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---- 1956b, Geology of northern Kanaga Island, [Alaska]: 

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1956c, Reconnaissance geology of some western 

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E, p. 83-100. 

1959a, Geologic reconnaissance of Gareloi Island, 

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J, p. 249-256 .. 

1959b, Geologic reconnaissance of Semisopochnoi 

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Coats, R. R., Nelson, W. H., Lewis, R. Q., and Powers, H. A., 

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Collier, A. J., 1902, A reconnaissance of the northwestern por- . 

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1908, The gold placers of parts of Seward Peninsula, 

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____ 1918, The Cosna-Nowitna region, Alaska: U.S. Geol. 

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46 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

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___ 1960b, Geologic map of Talkeetna Mountains (A-2) 

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---- 1919, The beach placers of the west coast of Kodiak 

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--- 1957, Geology of the southeastern part of the Robinson 

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48 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

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I 49 

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50 PHYSIOGRAPHIC DIVISIONS OF ALASKA 

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'· 

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. ' 

A Page 

Acknowledgments............................ 8 

Ahklun Mountains........................... ~ 

Alaska-Aleutian province--------------------- 88 

Alaska Range •••••• ---------------------- 5,36, 7,18 

Aleutian Islands ••••••••••• _--------------____ 88 

Aleutian Range·----------------------------- 18,34 

Alsek Ranges •• ·------------------------------ . 42 

Altlplanatlon terraces ••••• ____ •• _ 16, 26, 27, 28, 37, 88 

Ambler-Cbandalar Ridge and Lowland section ••• ··------------------------- II 

Anchor lee.................................... 20 

Anluk Lowland ••• ·-------------------------- 21 

Arctic Coastal Plain.......................... 18 

Arctic Foothllls •••••• ·-----------. ------------ to 

Arctic Mountains province___________________ to 

Arates. _________________________________ 13, 40, 42,43 

Aurets. __ ••• ___ • _____ • _________ • __ -------. __ __ 20 

B 

Badlands ••••••••••••••••• _. ___ • __ ••••• __ •• ___ 35 

Baird Mountains·--·------------------------- 11 Baranor Mountains ___________________________ 18,41 

Bars ••••• " ••• __ •• _ ••• ___ •••• __ •• __ •• _ ••• ___ ._. 17 

Bathollth •••••••••••• _____________ ------------ 5, 7 

Bering Platform______________________________ 81 

Bering Shelf. •••••••••••••• -----------------__ 31 

Blrch Creek Schtst........................... 5 

Bosses. ___________________ -------------------- 15 

Boundary Ranges •• ·------------------------- 43 

Broad Pass Depression_______________________ SB 

Brooks Range·--------------------------- 5,18,11, 7 Buckland River Low!and____________________ 18 

c 

Calderas ••• _ •••• ___ ------ ___ -------------- ___ 33, 34 

Canadian Cordillera •••••• -------------------- 3 

Cenozoic history______________________________ 7 

Chatham Trough·-·-------------------------- 89 Chichagof Highland__________________________ 42 

ChUkat-Baranof Mountains___________________ 41 

·Chugach Mountains__________________________ 7, 40 

Chulttna Mountains·------------------------- 37 

Cinder cones ••• ----------- ___ ---------------- 82 Cirque •••••• ______________________________ 13, 88,40 

Clarence Lake Upland_______________________ 37 

OlassUlcatlon, physiographic, basis........... 3 

Clearwater Mountains·----------------------- 38 

Cllft-and-bench topographY---·-------------- 13 Cllmate, Alaska __________________________ 8, 9,10,11 

Quaternary patterns______________________ 8 

Coastal Foothtlls •••• ------------------------- 4S 

Coastal Trough province_____________________ SB 

Coast Mountains _____________________________ 18,4$ 

Cook Inlet-Susltna Lowland ••••••.••••••.•••• 18,36 Copper River Lowland _______________________ 18,38 

Cordillera, North American _________________ 2, 7,18 

Craters, volcanic ••• ------------- __ -------____ 31 

CreeP---·--------------------------------- 14,15,16 Cretaceous history____________________________ 7 

Cutler River Upland·------------------------ 21 

INDEX 

D Page 

De Long Mountains ••• ·---------------------- to 

Devonlan history_____________________________ 5 

Drainage anomalles___________________________ 8 

Drumlins •••••••••..•••• ---------------------- 14, 36 

Dunes •• ·---------------------------- 17, ~ 27, 29,41 

E 

Earthquakes ••••• ----------·--------------- 7, 41,42 

End moraines ••••••••• ----------------------- 13,16 

Eskers·------------------------------------ 14, 36,88 

Exploration •••• -------------- _____ •• _______ •• 2 

F 

Fairweather Range___________________________ 41 

Fog Lakes Upland.·------------------------- 37 Fiord ___________________________________ 40, 41, 42,43 

Ftrn llne •• -·------------------ 33, 35, 37, 39, 40, 42,43 Frost cltmate ••• __ • _ ••• __ ••••• _ ••• _ •• ______ • _. 8 

G 

Geologic history, summary___________________ 6 

Geologic time scale___________________________ 6 

Glacial lakes ••• ------------------------------ 14,34 deposits •• ----- ____ • _____________ • ____ • __ • 39 

Glaciated areas, physiographic evolution...... 13 Glaciation _______________________________ 8,13, 35,42 

·Blacter Bay_.-·------------------------------ 42 

Glaciers •••••• ________ 22, 33, 34, 35, 37, 39, 40, 41, 42,43 Ground moraine ______________________________ 14,36 

Gulf of Alaska Coastal section________________ 41 

Gulkana Upland .•••••••••••.•••••••••••••••• 

H 

Holltna Lowland·------------------------~--- S1 

Horns.·----------------------------------- 13, 40,43 

Ice wedges ________________________ ------ 17, 20, 24,88 

polygonal ground •• ·---------------------- 18,31 Indian River Upland________________________ 26 

Innoko Lowlands.---------------------------- 30 

Interior Plains.·------------------------------ 18 

Intermontane Plateaus_______________________ 7 

1 

1urassic history_______________________________ 5 

K 

Kames ••• ------------------------------------ 14 

Kanuti Flats.---------------------------_____ 18 

Karst topographY--------------"------------- 42 

Kenai-Chugach Mountains ____________________ 18,-40 

Kobuk River valleY-------------------------- 17,27 

Kobuk-Selawik Lowland_____________________ 11 

Kodiak Mountains _________________________ 7,-40,18 

Kokrlne-Hodzana Highlands_________________ 16 

Koyukuk Flats·--------------------------·--- 17,11 

Kupreanof Lowland·------------------------- 18,39 

Kuskokwim Mountains •• ·---·---------------- SO 

L Page 

Lake Louise Plateau ••••••• ------------------- 88 

Lakes, glacial •••••••••••• 14, 22, 31, 33, 34,.36, 38, 39,42 

lee-marginal.-------------------------- 39, 40, 41 

thaw or thermokarst ••••••• --------------- 17 Landslldes _________________________________ 15, 16,42 

Lockwood Htlls______________________________ 27 

Loess ____________________________ . __________ 16,17, 29 

M 

Malaspina Glacier_____________________________ 42 

Mapping ______ ---- _____ •• ____ ••• -----••••••• __ 2 

Matanuska ValleY---------------------------- 37 

Meanders.------------------------------ 15,16,17, 27 

Meander-scroll pattern •••• -------------------- 17,27 

Mentasta-Nutzottn Mountain segment (of the 

Alaska Range)____________________ 35 

Mesozoic rocks ••••••• -----------------------.. 5 

Metamorphism_______________________________ 5 

Mission Lowland •••• ------------------------- 21 

Mississippian history ••••• -------------------- 5 Moraines ___________________________________ 13,14, 31 

Mountain buDding____________________________ 2, 5 

Mt. McKinley________________________________ 35 

Muck·------------------------------------- 18, 24,29 Mud1lows •••••••• ____ • ________ ••• __ • ___ ••••• _. 16 

Mud volcanoes •••••.• ------------------------- 38 

N 

Nikolai Greenstone ••••••• -------------------- 5 

Noatak Lowlands·--------------------------- 11 North American Cordillera __________________ 2,7,18 

Northern Plateaus province __________________ 7,!1 

Northway-Tanacross Lowland________________ 14 

Nowltna Lowland·--------------------------- 19 

Nulato Hllls ••• ~------------------------------ 18 

Nunlvak Island______________________________ 32 

Nushagak-Blg River Hllls____________________ 30 

Nushagak-Brlstol Bay Lowland______________ 31 

0 

Ogilvie Mountains·--------------------------- !3 

Ordovician history. __ ------~----------------- 5 

Orogenlc activity----------------------------- 5 Outwash, fans ________________________________ 16,29 

plains •• _------------------------------ 14, 31, 86 

p 

Pacific Border Ranges province.______________ S9 

Pacific Mountain System ___________________ 7,18, 33 

Pah River Flats·----------------------------- 27 

Pah River section____________________________ 11 

Paleozoic rocks________________________________ 5 

Patterned ground·---------------------------- 14,17 

Peat _______________ --------------------------- 17 

Peneplain •• ---- ____ ------ _____ --------------- 37 Permafrost ___________________________ 8,14,15,17,18 

dry ____________________________ ----------- 29 

Permafrost table·----------------------------- 18 

Permian historY------------------------------ 5 

51 
52 

Page 

Physiography, evolution ot___________________ 7, 8 

Pingos _________________________ 17, 18, 21, 23, 24, 28,38 

Pleistocene history___________________________ 6 

Polygonal ground ______________________ 14, 17, 20,35 

Polygons, stone_______________________________ 14 

Porcupine Plateau____________________________ SS 

Precambrian history-----_____________________ 5 

Pribilof Islands _____________________ ---------- 32 

Prince of Wales Mountains ____________________ 18,42 

Purcell Mountains ... _________________________ 27 

Q 

Quaternary history___________________________ 8 

R 

Rainwash____________________________________ 15 

Rampart Trough·---------------------~------ 26 

Ray Mountains_______________________________ 25 

Rock glaciers ___________________ -------- 16, 35, 37,39 

Rocky Mountain System ___________________ 7, 18,20 

Romanzof Mountains_________________________ 22 

s 

St. Elias Mountains.------------------------- 18,41 

St. Lawrence Island__________________________ 32 

St. Matthew Island ___________________________ . 32 

Schwatka Mountains ________________________ _ 

Selawik Hills ________________________________ _ 22 

28 

INDEX 

Page 

Seward Peninsula____________________________ 91 

SilUrian history-------________________________ 5 

Solifluction •. _-" ________________________ 14, 15, 16, 35 

Solifiuction lobes._--------------------------- 15 

Stagnant ice topography ____ • ______________ 14, 36, 38 

Stone stripe __________________________________ 14,20 

Strandfiat ___________ -------- ____ _______ __ ____ 42 

Stream capture _______________________________ 20,24 

Superposed drainage _________________ 21, 22, 23, 25,35 

Swales _________________ -----------____________ 17 

T 

Talkeetna Mountains ••• ______________________ 5, 97 

Tanana-Kuskokwim Lowland________________ 29 

Terminology_------------~----~-------------- 3 Terraces ••. ___________________________________ 16, 29 

outwash _________________ ----------------- 16 

Tertiary history------------ ______ ----------__ 7, 8 

Teshekpuk Lake section______________________ 18 

Thaw lake ____________ 17, 18, 20, 23, 24, 25, 26, 27, 30,32 

Thaw sink.----------"----------------------- 17,25 

Thazzik Mountain____________________________ 22 

Thermokarst. _. ___ _ _ ___ _ __ _____ _ _ _ __ _ _ _ _ _ _ _ _ _ 17 

Till·-·---------------------------------------- 13,14 

Tintina ValleY------------------------------- 29 

Torrents _____________________________ • _______ _ 

Tors •••• ______________________________ .-.----. 

16 

15 

Page 

Tozitna-Melozitna Lowland__________________ .26 

Triassic history _________________ ------________ 5 

u 

U-shaped valleys ___ ••• __ ------------ 13, 33, 40, 42,43 

Unglaciated areas, physiographic evolution ___ 14,16 

Upper Matanuska Valley_____________________ 97 

v 

Vegetation __________________________________ 8, 15,17 

Volcanic rocks, Quaternary _____________ 32, 33, 34,39 

Volcanism ••. _________________________________ 5 

Volcanoes, active.---------------------- 33, 34, 39, 41 

w 

Western Alaska province .••• ----------------- 7, 26 

White Hills section___________________________ 18 

Wrangell Mountains.------------------------- 99 

y 

Yukon Flats section__________________________ 26 

Yukon-Kuskokwim Coastal Lowland________ SB 

Yukon River _________________________________ 18,19 

Yukon-Tanana Upland ______________________ 5,24 

z 

Zane Hills .• _______________________ • _________ • 

U.S. GOVERNMENT PRINTING OFFICE : 1966 0-773·592