Please do not destroy or throw away this publication. If you have no further use 

for it write to the Geological Survey at Washington and ask for a frank to return it

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 857 C

THE GURRY DISTRICT, ALASKA

BY

RALPH TUCK

Mineral resources of Alaska, 1932 

(Pages 99-140)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1934

For sale by the Superintendent of Documents, Washington, D. C. ------ Price 10 cents
CONTENTS

	Page 

Abstract _________________________________________________________ 99

Introduction _____-________-------____-_-__-____-_----_________-__ 100

Location and area.______ ______________________________________ 100

Previous investigations,___---_____--------____---__________-__ 100

Present investigation_______________'___________________________ 103

Geography. ________________________________ ______________________ 103

Drainage. ________________________-_-__-_____._-________'______ 103

Topography._________________________________________________ 106

Climate___---__-_-_-__----------------_------------------____ 107

Routes and trails______-___-_-___--_--__.;__-____----___________ 108

Vegetation ___-____________-_-_____-------_-___---_-_______--- 10&

Game____---_____---_--__-_-__------_---------_-_-------_-.__- 111

Settlements and industries_-_-______----_-______----_-________- 112'

---.--.----------------------------------------- 113

Principal features _____________________________________________ 113

Sedimentary rocks.___________________________________________ 114

Pre-Permian (?) chert, quartzite, and argillite_______________ 114

Permian (?) tuff and agglomerate_---_----___---__________-_ 117

Mesozoic rocks___________________________________________ 117

Eocene coal-bearing rocks.____-_--_---___-__-_-_--__.______ 123

Tertiary gravel.__________________________________________ 125

Quaternary deposits____--_____----_--_--_-_----.__-_______ 126

Glacial deposits___--_-_____--_--_______-_--___________ 126

Moraines--_-------------------_---------_--_-__-_ 126

Bench gravel-____________________________________ 127

Recent deposits._____-_--__-_-_-_--_-__-_-----_-__-__. 127

Igneous rocks.-______-___.--________----_-_-___.-__-__________ 127

Influence of rock type on topography__-__________---____________ 131

----.-...-----------.--------------------------- 132

.___._-.....-__-_.____________________________ 132

Present glaciers._____---_____-_----.--.-_-_-____---.______ 133

Economic geology._____-_._-__________-_-_-__-_________--_______-_ 135

Lode prospecting____________________________________________ 136

Boedeker claims._____________-_-__-_____-----____-___________ 138

Coal--_-_--_-__----.__-_-___---_-__-----_-.----_------_---. 139

Conclusions.________.__-_________---_--__--_-_-_-_-_-___-____ 140'

ILLUSTRATIONS

Page 

PLATE 1. Geologic reconnaissance map of the Curry district, Alaska_____ 112

2. A, Eocene coal-bearing rocks and vegetation-covered moraine 

of Ruth Glacier; B, Rugged granitic mountains on the east 

side of Mount McKinley---__-----_-----_--------_------ 112

3. Rugged topography along Eldridge Glacier__________________ 112

4. Buckskin Glacier with Mount McKinley in the background_ _ 112 

FIGUKE 4. Index map showing the location of the Curry district____-_-_ 101

5. Sketch map showing the distribution of timber in the Curry

district._________________---______-----_'______-_---- 111

ii
THE CURRY DISTRICT

By RALPH TUCK

ABSTRACT

The Curry district lies on the south flank of the Alaska Range, on the southeast side of Mount McKinley. Most of it is west of the Alaska Railroad. The 

eastern portion can be easily reached from several points along the railroad 

route, but the western portion is much more difficult of access, owing to the 

numerous glacial streams and the rugged topography. The relief of the 

area is great, the elevation ranging from 500 feet along the Chulitua River 

to 20,300 feet at Mount McKinley. The Chulitna River, a tributary of the 

Susitna River, drains the larger part of the area described. It flows wi a 

broad valley in the eastern part of the district, and here the maximum 

relief is about 3,000 feet. The western part of the district is very niggled, 

with numerous peaks over 6,000 feet in elevation which have sheer slopes 

and almost unscalable pinnacles. Winding down through this maze of rugged 

mountains are four major valley glaciers Eldridge, Buckskin, Ruth, and 

Tokichitna and many tributary and smaller glaciers. Practically the entire 

district, with the exception of the higher peaks and ridges, has been glaciated. 

Timber grows along the main streams and extends to an elevation of 2,000 

feet, but a large portion of the district lies above that elevation.

The oldest rocks consist of slate, graywacke, schist, argillite, and phyllite, 

with lesser amounts of chert, quartzite, limestone, conglomerate, tuff, and breccia. 

These rocks are divided into three groups, which range in age from Paleozoic 

to late Mesozoic. Tertiary sand, gravel, and clay, which contain some coal seams, 

are present. The Quaternary is represented by glacial and stream deposits. 

Intrusive into the Paleozoic and Mesozoic metamorphic rocks are granitic sills, 

dikes, stocks, and batholiths. These intrusives form a large part of the rock 

outcrops in the district and in some places extend almost unbroken from the 

Chulitna River to the south peak of Mount McKinley. The granite is believed 

to be of late Mesozoic or early Tertiary age. The regional strike of the metamorphic rocks is northeast and parallels the trend of the Alaska Range in this 

locality. Details of structure are in many places difficult to determine, owing 

to the high degree of folding in the older rocks.

The area has been but little prospected, and only one lode discovery has been 

made; it consists of several small gold-quartz veins on the north side of the 

Hidden River. These veins cut across the metamorphosed sediments, and, 

although they contain high-grade ore, the present exposures are too small to be 

of commercial value. In the vicinity are strong fissure veins that have not yet 

proved to contain valuable deposits, although their genetic relationship with 

the small veins is encouraging. Quartz veins are numerous in the sedimentary 

rocks at a distance of several thousand feet from the margin of the granite, 

but immediately adjacent to the contact the chief action of the intrusive has

99
100 MINERAL RESOURCES OF ALASKA, 1932

been to silicify the sediments. No evidence of mineralization has been found in 

the granite, which is usually fresh and massive. The most favorable prospecting ground appears to be in the metamorphic rocks in the vicinity of Eldridge 

Glacier and the Hidden River. In the same locality there is evidence of lead 

and copper mineralization.

Small amounts of placer gold have been recovered from the bars of the 

Chulitna River, but it is extremely doubtful if in this highly glaciated area 

there are placers that will yield any commercial production.

The coal that occurs at several localities along the Chulitna River and its 

tributaries is of lignitic rank and of value only locally as fuel.

INTRODUCTION

LOCATION AND AREA

The district here described receives its name from the settlement 

of Curry, a division point on the Alaska Railroad and the place at 

which practically all its through trains stop over night. The district 

lies southeast of Mount McKinley (fig. 4). The part of this area 

which has been examined in most detail is bounded by Eldridge 

Glacier on the north, the divide between the Susitna and Chulitna 

Rivers on the east, and Tokichitna Glacier and River on the south 

and southwest. The divide lying east of the Chulitna River was not 

examined with any thoroughness in the course of the work described 

in this report. The district lies between latitude 62°35' and 63° and 

longitude 149°40' and 150°50'. The area studied in most detail 

covers about a thousand square miles.

PREVIOUS INVESTIGATIONS

The major part of the district was heretofore unmapped, and 

little was known of the details of the topography and drainage or of 

the character of the formations. A few prospectors and trappers 

have visited the region; but owing to its difficulty of access, the 

failure to locate any deposits of economic importance, and the small 

number of fur-bearing animals that live there, it has been but little 

frequented.

A large part of the, surrounding country has been covered in a 

reconnaissance manner by members of the United States Geological 

Survey, and their reports have greatly facilitated the present work. 

The explorations and surveys in contiguous areas, which have a bearing on this report and the known prospecting in the area itself are 

outlined below.

In 1898 G. H. Eldridge 1 made a reconnaissance of the Susitna 

Basin, and a part of his traverse was along the eastern edge of the 

area that is included in this report. In 1902 a Geological Survey

1 Eldridge, G. H., A reconnaissance in the Sushltna Basin and adjacent territory, 

Alaska, in 1898 : U.S. Geol. Survey 20th Ann. Kept., pt. 7, pp. 1-29, 1900.
THE CURRY DISTRICT 101

party under the direction of Alfred H. Brooks 2 made a traverse 

from Cook Inlet northwestward across the Alaska Range and thence 

northeastward along the north side of Mount McKinley. Although

154

66

FIGURE 4. Index map showing the location of the Curry district.

his field work did not touch the Curry district, many similar formations were encountered; his report, also contains an account and sum2 Brooks, A. H., The Mount McKinley region: U.S. Geol. Survey Prof. Paper 70, 1911.
102 MINERAL RESOURCES OF ALASKA, 1932

mary of all the explorations and scientific work to that date, thereby 

including areas contiguous to the Curry district.

In 1906 a private expedition under the leadership of Dr. F. A. 

Cook 3 was organized for the purpose of climbing Mount McKinley. 

The attempt was made from the south side by way of Ruth Glacier. 

R. W. Porter, topographer of the expedition, mapped a large, area, 

the northern portion of which borders on the area examined by the 

writer and includes parts of the Tokichitna and Ruth Glaciers.

In 1910 Belmore Browne 4 and Herschel Parker explored the 

southeast side of Mount McKinley in an attempt to climb the mountain, and their account contains some information concerning the 

general nature of the country, particularly in the vicinity of Ruth 

Glacier.

In 1911 S. R. Capps 5 made -a study of the Yentna district and 

used parts of Porter's map as a base for some of his geologic 

mapping.

A prospector, Gene Bartholf, reports that in 1915 he made a 

prospecting trip into the southern part of the area and found some 

rich gold-quartz float on Whistler Creek. Later he made a number of other trips into the district.

In 1917 Capps 6 investigated the mineral resources and mapped 

in a reconnaissance way the upper Chulitna region, which lies adjacent to the Curry district on the northwest.

In 1929 Elmer and Roy Boedeker prospected in the vicinity of 

Eldridge Glacier and the Hidden River and located gold-bearing 

quartz veins on the north side of the river. During 1931 and 1932 

they were engaged in the further development of these veins.

In 1930 Capps 7 continued the geologic mapping on the West 

Fork of the Chulitna and extended it across the Alaska Range into 

previously mapped districts on the north side.

In 1931 a prospecting party organized by Gene Bartholf traversed part of the area lying west of the Chulitna River. This 

party cut a large amount of trail and obtained considerable general 

information which greatly facilitated the mapping and geologic 

work during the summer of 1932.

In 1931 C. P. Ross 8 mapped in detail and reported on the mineral 

resources of the West Fork of the Chulitna River, which lies immediately north of the district described in this report.

* Cook, F. A., To the top of the continent, New York, 1908.

* Browne, Belmore, The conquest of Mount McKinley, G. P. Puitnaitfs Sons, 1913. 

6 Capps, S. R.,.The Yentna district, Alaska: U.S. Geol. Survey Bull. 534, 1913.

6 Capps, S. R., Mineral resources of the upper Chulitna region: U.S. Geol. Survey Bull. 

692, pp. 207-232, 1919.

7 Capps, S. R., The eastern portion of Mount McKinley National Park: U.S. Geol. Survey Bull. 836, pp. 219-300, 1932.

*Ross, C. P., Mineral deposits near the West Fork of the Chulitna River: U.S. Geol. 

Survey Bull. 849-E, 1933.
THE CUREY DISTRICT 103 

PRESENT INVESTIGATION

The present investigation was conducted by the United States 

Geological Survey with funds provided by the Alaska Railroad 

through its special authorization to investigate the mineral resources 

adjacent to its route. The discovery of gold-bearing veins during 

the last few years in this unmapped and little-known area had 

aroused much interest, and there was a demand for further information regarding these discoveries and the area in general. The 

objects of the work were to ascertain of what importance they 

might be as a future source of revenue to the railroad, to map the 

area as an aid to prospecting, and, if possible, to delimit the more 

favorable portions so as to facilitate future exploration and development. To accomplish these objects a joint topographic and geologic party was formed, with C. P. McKinley as topographer and 

the writer as geologist. Other members of the party were E. J. 

FitzGerald, recorder, and C. C. Tousley, H. Sagers, and J. Waddell, camp hands. Ten horses were used for the packing pf equipment and supplies, and in addition arrangements were made to have 

an airplane land at Spink Lake during the middle of the summer 

with additional supplies, as the ruggedness of the country prevented heavy packing.

The party left the Alaska Railroad at mile 276.5 June 13, 1932, 

and the field work started immediately. The route from that point 

was westward to the cable crossing of the Chulitna Eiver near the 

mouth of Coal Creek, across the foot of Eldridge Glacier, and then 

in a general southwesterly direction across the drainage lines of 

the region to the foot of the Tokichitna Glacier. The Tokichitna 

River, which marked the western limit of the new surveys made in 

the course of the field work, was crossed September 5. From that 

point the party went up Ramsdyke Creek, thence to the Peters 

Creek trail and by that trail and the wagon road, reaching Talkeetna 

(mile 222 on the Alaska Railroad) September 10.

The topographic and geologic mapping was done in the field on a 

reconnaissance scale of 1:180,000, or about 3 miles to 1 inch.

GEOGRAPHY

DRAINAGE

The Susitna River receives all the drainage of the Curry district. 

The drainage pattern is decidedly asymmetric, however, owing to 

the location of the district on the south flank of the Alaska Range. 

The Susitna flows across the southeastern part of the district; the 

Chulitna River, about 10 miles west of the Susitna, has a parallel 

course and joins the Susitna at the town of Talkeetna, which lies a 

few miles south of the district. Almost all the surface waters from
104 MINERAL RESOURCES O.F ALASKA, 1932

the west discharge directly into the Chulitna River. The major 

western tributaries of the Chulitna that drain the area are, from 

north to south, Ohio Creek, the Fountain River, the Hidden River, 

the Coffee River, and the Tokichitna River with its tributaries 

Alder Creek and the Ruth River. All these streams have a general 

south and southeast course. The eastern tributaries of the Chulitna 

in this area are Pass Creek, Troublesome Creek, and several other 

small streams that head in the ridge between the Susitna and Chulitna Rivers. The Susitna and Chulitna have a south-southwesterly 

course, which has been determined in part by the structure of the 

underlying rocks.

The Chulitna River is a swift stream whose course alternates 

between canyon-like stretches in which it flows in a single channel 

between rock walls and more open stretches where the river emerges 

as a braided stream onto flood plains a mile or more in width. 

Small power boats can navigate on the Chulitna except during very 

low stages. As many of the tributary streams rise in glaciers, the 

Chulitna River carries a large amount of silt, particularly during 

times of high water, and is constantly shifting its course, cutting 

into its banks or forming bars and flood plains. On both sides of 

the flood plain of the Chulitna are gravel and rock walls several 

hundred feet high that form benches representing the floor of a 

broader older valley. This old valley is larger and more mature than 

the old valley of the Susitna and suggests that the Chulitna at one 

time may have been the master stream, although at present the 

Susitna has a greater volume of water. An explanation of this 

anomaly is suggested by Moffit, 9 who states that probably as a result 

of glacial damming the Nenana River was able to capture the headwaters of the Chulitna. At the present time the Chulitna River rises 

in Broad Pass, and it is probable that in preglacial time its source 

was at least 50 to 60 miles farther east, in Monahan Flats. The 

geomorphic development of the Susitna and Copper River Basins 

has been profoundly affected by their repeated invasion by glacial 

ice during Pleistocene time, and many great changes in drainage 

have resulted. It is possible that at some time in the past large areas 

of what is now the Copper River Basin drained to the Susitna River 

by way of the Chulitna.

The Fountain River flows 8 miles from Eldridge Glacier before 

joining the Chulitna River. A part of the water emerges from the 

base of the glacier as a fountain 3 to 10 feet in height, throwing ice 

and boulders as large as 6 inches in diameter. The fountain is the 

outlet of almost all of the Eldridge Glacier drainage, and it is 

constantly changing its position, sometimes breaking out on one

9 Moffit, F. H., The Broad Pass region, Alaska: U.S. Geol. Survey Bull. 608, pp. 72-73, 

1915.
THE CTJRKY DISTRICT 105

side of the glacier and then on the other. Below the glacier the 

Fountain River flows on a treeless flood plain about 2 miles in width. 

On this flood plain the river is constantly changing its channel, 

often breaking up into a number of small streams. Partin Creek 

is the largest tributary of the Fountain River. It originates in 

several small glaciers north of Eldridge Glacier and flows through 

a narrow glacial valley for about 10 miles before cutting into the 

ice and moraine of Eldridge Glacier. Two miles before it reaches 

the glacier it flows into a narrow gorge with vertical walls several 

hundred feet in height. After reaching the glacier it flows along 

the north edge of the ice and finally emerges on the flood plain of 

the Fountain River.

The source of the Hidden River is a small lake that lies on the 

moraine-covered lower end of Buckskin Glacier. From the lake 

it cascades over the terminal moraine and follows a narrow glacial 

valley within which it has a shifting course upon a flood plain only 

a few hundred yards in width. Ten miles from the foot of the glacier 

the river enters a low-walled granite gorge through which it flows 

for several miles to join the Chulitna River a short distance below 

the mouth of the Fountain River. At high water lightdraft boats 

can be taken up the river for a few miles, to a point where the stream 

emerges from the granite gorge.

The Coffee River is about 20 miles in length and has its source in 

a number of hanging glaciers. It is similar in general features to 

the Hidden River except that it has a smaller volume of water.

Alder Creek, whose basin lies between that of the Coffee River 

and Ruth Glacier, receives part of its water from several small hanging glaciers and is about 18 miles long, joining the Tokichitna 

River 2 miles above its mouth. In the upper part of its course it 

is confined to a narrow U-shaped valley. It reaches Ruth Glacier 

about 12 miles from its source and flows along the north side of 

that glacier for about 4 miles to its terminus, at which it debouches 

onto the outwash plain of the glacier.

The Ruth River emerges from the moraine on the south side and 

near the foot of Ruth Glacier and flows turbulently for about 4 miles, 

to its junction with the Tokichitna.

The Tokichitna River originates at the terminus of the Tokichitna. 

Glacier and flows 25 miles before it joins the Chulitna. In its upper 

course it is a swift braided stream, but 4 or 5 miles below its source 

the gradient becomes gentle, and the stream is sluggish and meandering and is confined to one channel. It is probable that at one time 

the Tokichitna flowed directly southeastward to the Chulitna, but, 

possibly owing to glacial damming, its course was changed, and it 

now enters the Chulitna by a circuitous route. The Tokichitna

59017 34 2
106 MINERAL RESOURCES OF ALASKA, 1932

River is navigable by small power boats from its mouth up to Home 

Lake, a distance of about 15 miles.

Each of the major streams of the district has glaciers as its source, 

and all are typical glacial streams in that during periods of high 

water they carry enormous quantities of silt and are constantly 

changing their channels. Periods of high water occur in the spring 

and summer, when with warm weather the snow and ice are rapidly 

melted. Heavy warm rains are also effective, and during the summer 

of 1932 a few hot days followed by several weeks of rain turned even 

the small streams into torrents and swelled the Chulitna River into a 

wide stream reaching from bank to bank where ordinarily there are 

long stretches of bars and gravel. In the fall, with the oncoming of 

freezing weather, the melting of the ice ceases and the. volume of 

all the streams is lowered, a condition which lasts all winter. As a 

result of the extreme changes in water level, all the stream valleys 

are similar in that they exhibit broad flood plains on which the 

streams build up or cut down according to local conditions.

TOPOGRAPHY

The topographic map of this area shows a greater amount of 

relief than any other Alaska map of a comparable area. The 

Chulitna River, in the southeastern part of the area, has an elevation 

of 500 feet, and Mount McKinley (the highest peak in North 

America), in the northwest corner, has an elevation of 20,300 feet. 

(See pi. 1.) Within a distance of 35 miles there is thus a relief of 

nearly 20,000 feet.

Viewed from a distance the western part of the district is a chaotic 

mass of peaks and is awe-inspiring in its grandeur. Not only is 

the regional relief great, but even within short distances great 

differences in elevation are encountered. Sculptured by erosion, 

glaciation, and extreme changes in temperature, sheer granite walls 

rise from 2,000 to 4,000 feet and are surmounted by innumerable 

unscalable pinnacles. Unnamed peaks 5,000 to 11,000 feet high, 

rising 4,000 to 8,000 feet above their bases, are common; and 

within this maze of imposing mountains, glaciers wind downward 

from the culminating and dominating point, Mount McKinley 

(pi. 2, B}. The topography of a large part of the area has been 

glacially modified, and cirques, aretes, U-shaped valleys with 

oversteepened slopes, and truncated spurs are common.

The eastern half of the area, including the Chulitna River, the 

lower parts of its tributaries, and the divide between the Susitna 

and Chulitna, is of a different aspect, as it was entirely overridden 

by the Pleistocene glaciers. The slopes are smooth and rolling 

and do not culminate in pinnacles, and the valleys are wide with
THE CURRY DISTRICT 107

broad flood plains. The elevation of this portion of the area ranges 

from 500 to 3,500 feet.

CLIMATE

The Pacific coast region of south-central Alaska is characterized 

by cool, moist summers and moderate winters. The annual precipitation is heavy, and the range in temperature during the entire 

year is small. In contrast with this climate the interior of Alaska 

has cold winters and dry summers, its annual rainfall is small and its 

yearly range in temperature great. Lying 200 miles inland from 

the Pacific Ocean and yet on the south side of the Alaska Range, 

the Curry district has a climate that is intermediate in character 

between these two extreme types. The rainfall is heavy but not as 

heavy as in the typical Pacific coast region, and in winter the Pacific 

Ocean has a tempering effect and the extreme low temperatures of the 

Yukon Valley are not encountered.

No climatic records have been made in the Curry district. The 

nearest point at which records have been kept is the town of 

Talkeetna, which is about 20 miles south of the area, at the confluence 

of the Susitna and Chulitna Rivers, and has an elevation of only 

about 400 feet. Records over several years show that Talkeetna has 

an average rainfall of 30.31 inches. September has the greatest 

monthly precipitation with an average of 5.1 inches. The mean 

annual temperature is 33.6° F.; July is the warmest month, with an 

average temperature of 57.8°, and January is the coldest, with an 

average of 9°. The climate of the Curry district is probably similar 

to that of Talkeetna except that the precipitation is greater.

During the summer of 1932, from June 19 to September 11. a total 

of 85 days, there were 46 days which were partly or entirely rainy, 

19 days were clear, and 20 were cloudy. As 1932 was an extremely 

wet season throughout central Alaska, this record cannot be considered a fair average. Capps 10 reports that in the region to the 

south, which climatically is similar, during the summer of 1906 it 

rained 50 out of 110 days.

The winters are about 7 months long, extending from October to 

April, and the active prospecting season is limited to a season of 

about 4 months, from June to September. The rivers and streams 

are usually free of ice by the middle of May. Snow remains at the 

lower elevations until May, but in the higher regions there are large 

areas of perpetual snow. On sheltered slopes the snow line in summer is around 5,000 feet, whereas on exposed southern slopes it lies 

much higher. Snowstorms were encountered at elevations of 5,000 

and 6,000 feet in July and August, and around Mount McKinley 

blizzards and snow flurries are common throughout the year. A

10 Capps, S. K., The Yentna district, Alaska : U.S. Geol. Survey Bull. 534. p. 17, 1913.
108 MINERAL RESOURCES OF ALASKA, 1932

member of the Lindley-Strom Mount McKinley expedition in 1932 

states that from the time they climbed the mountain in May until 

they returned in July, it had snowed and drifted about 10 feet on 

Muldrow Glacier at an elevation of about 10,000 feet.

Most of the clear days during the open season occur in May and 

June. July, August, and September are usually rainy, with poor 

visibility and only occasional clear days. The weather is particularly unfavorable in the vicinity of the glaciers, and it is probable 

that locally these ice masses influence the climate, because often when 

the weather is bad in the vicinity of the glaciers it is good a few 

miles away.

BOTJTES AND TRAILS

The Alaska Eailroad follows the east bank of the Susitna River, 

and the part of the district that lies between the railroad and the 

Chulitna River is easily accessible. Old trapper trails can occasionally be found on the long ridge lying between the Susitna and 

Chulitna Rivers, but the only developed trail is a short one between 

Curry (mile 248.5 on the Alaska Railroad 11 ) and the top of the 

ridgo between the two rivers, a distance of 4 miles. The trail ends 

at a shelter or observation house called Curry Lookout. Both the 

shelter and the trail were built and have been maintained by the 

Alaska Railroad as a scenic attraction, for on clear days the lookout 

affords an excellent view of Mount McKinley and the Alaska Range.

The western part of the area, west of the Chulitna River, is much 

more difficult of access and can be reached only from the north and 

south. The southern point of entry is Talkeetna (mile 226.7), and 

the northern point is Chulitna station (mile 273.8). The route from 

Talkeetna is by boat across the Susitna River, where it is necessary 

to swim horses. From the west bank of the Susitna a road built 

and maintained by the Alaska Road Commission leads to the mining 

districts of Cache and Peters Creeks. From the Peters Creek district two routes are practicable either up Willow Creek and down 

Ramadyke Creek to the Tokichitna River or up Poorman Creek and 

down the south slope of the Tokichitna Valley. Old trails exist on 

both routes. Both the Tokichitna and Ruth Rivers must be crossed 

in order to reach the heart of the Hidden River country, but both 

of these glacial streams can be forded with horses near the glaciers, 

except during periods of exceptionally high water. Farther downstream difficulty with soft ground may be encountered.

An alternative and more direct route than by the Peters Creek 

trail would be to proceed up the west bank of the Chulitna River 

after crossing the Susitna River at Talkeetna. No trail has been

11 Mileage is measured from Seward, the southern terminus of the Alaska Railroad.
THE CURRY DISTRICT 109

opened over that route, however, and it is likely that heavy brush, 

soft ground, and deep streams would offer considerable difficulty 

to its use.

The route from the north, which was followed by the Geological 

Survey party of 1932 and over which horses were taken without 

great difficulty, was to leave the railroad at male 276.5 and follow 

the trail westward to the Chulitna River near the mouth of Pass 

Creek. The trail thence leads down the east bank of the river to a 

point near the mouth of Coal Creek, where there is a cable crossing. 

Here it is necessary to swim horses across the river, although it is 

reported that at some seasons of the year the stream is easily forded. 

From the western terminal of the cable considerable cutting has been 

done on a trail that leads west to the front of Eldridge Glacier. 

Here the Fountain Eiver is easily forded, or it may be avoided by 

persons on foot, who can cross on thte moraine of the glacier. 

Thence the trail strikes over the low ridge between the Fountain and 

Hidden Rivers and up the north side of the Hidden River to Swift 

Creek, where the Boedeker brothers have a short trail leading to 

their prospect. A tram at this point crosses the river, which is 

easily forded with horses. From the Hidden River a route to the 

southwest that runs transverse to the drainage is the only one that 

can be taken with horses. It follows a narrow belt of metamorphosed sediments that affords several low passes over divides that 

elsewhere are sharp granitic ridges. The Coffee River and Alder 

Creek are easily forded, and the route crosses the lower end of Ruth 

Glacier and thence leads to Talkeetna by way of the Peters Creek 

trail.

An alternative route from the north is to leave the Alaska Railroad at Honolulu (mile 288.7). Two miles to the south there is a 

bridge that crosses the Chulitna River. It is reported that from that 

point a trail leads to the southwest along the high bench ground 

on the west side of the river.

Spink Lake, 1% miles in length, a few miles north of the Coffee 

River, is an ideal landing point for airplanes; from it a large part 

of the area can easily be reached.

Light power boats can ascend the Chulitna River, and a large 

part of the district can be reached in that manner. The Tokichitna 

River is also navigable for about 15 miles. It is probable that 

prospectors or trappers can reach the district more easily and 

cheaply by boat from Talkeetna than by any other means.

VEGETATION

As soon as the snow melts in the spring vegetation grows with 

remarkable rapidity at the lower elevations. Although the growing
.110 MINERAL RESOURCES OF ALASKA, 1932

season is usually not more than 100 days in length, its shortness is 

compensated by the amount of daylight, as in June the days are over 

20 hours long. Before the snow has entirely melted, the trees are 

budding and soon after it has left the ground the grass has attained 

a growth of several inches. Late in the summer the vegetation is 

so profuse along the river valleys that it is almost tropical in aspect, 

and considerable- trail cutting is necessary in order to travel with a 

pack train. In places, as in the vicinity of the front of Ruth Glacier, 

the growth is so junglelike that four men can cut only a mile or two 

of trail a day.

White spruce, birch, and cottonwood grow in the well-drained 

areas along all the major streams and on the hillsides up to elevations of 1,800 feet. Diameters of 3 feet are attained by many of 

these trees. Stunted black spruce are the only trees in the poorly 

drained areas below timber line, and sphagnum mosses cover the 

muskegs and swamps. Timber does not end abruptly but merges 

almost imperceptibly into a zone of thickly growing alders, or, in 

the poorly drained parts, into willow thickets. This alder and 

willow zone extends up to an elevation of about 2,500 feet and is 

often almost impenetrable even to one on foot, so that cross-country 

traveling is very difficult. Because much of the area lies above timber line (see fig. 5) green alders are often the only available fuel. 

The so-called sweet and sour willows are not limited to areas above 

timber line but grow in many places along the streams. Above the 

upper limit of the alder and willow, only buckbrush, mosses, and 

heatherlike plants are found. In many places the mosses grow in 

dome-shaped clumps, or " niggerheads ", a foot in diameter and 8 

to 10 inches high.

Feed for stock is abundant throughout the summer. The commonest variety of grass is one called red top ( Calamagrostig} . It 

grows luxuriantly in open parks along the valley bottoms and hillsides up to elevations of 2,500 feet, and it often attains a height of 

5 or 6 feet. Late in the summer, when it attains maturity and is 

beaten by the winds, it becomes matted, so that progress through it 

is slow and fatiguing. It is excellent forage from the timei it 

appears in the spring until after the first heavy frost in the fall, 

although gradually decreasing in nutriment as the season progresses. 

Ordinarily it has acquired a sufficient growth to be of value to stock 

by June 10 and will sustain pack animals until the early part of 

September in favorable localities in the valley bottoms and on low 

hillsides.

In the valleys as well as up to an elevation of several thousand 

feet, bunch grass is abundant and of great value as horse feed. A 

jointed rush (Eqwsetum} and a wild vetch, locally known as " pea
THE CURRY DISTRICT 111

vine ", both of which grow chiefly on gravel bars along the rivers, 

also furnish excellent forage for stock.

In the northern part of the area edible berries are few, but in 

the southern part currants, blueberries, and cranberries are common.

Area in which 

timber occurs

FIGUHB 5. Sketch map showing the distribution of timber in the Curry district.

GAME

There are few large game animals in the part of this area that 

lies west of the Chulitna River. In the northern part of the district caribou are occasionally seen, but they seldom reach the southern part. A few moose live along the Susitna and Chulitna Rivers, 

but they rarely travel up the western tributaries of the Chulitna. 

Even the brown and grizzly bears that are common in other parts 

of the Alaska Range are scarce here. During the summer of 1932 

only four were seen by the Geological Survey party, though their 

tracks are common near the headwaters of the Toldchitna River,
112 MINERAL RESOURCES OF ALASKA, 1932

where there is a considerable run of salmon during the spawning 

season. No mountain sheep or goats were seen, although sheep are 

very abundant a few miles to the north, in Mount McKinley National Park.

Of the smaller game, beaver are especially abundant along the 

Chulitna River and its tributaries, the Tokichitna River, Alder 

Creek, the Coffee River, and the Hidden River, and many ponds 

show fre,sh beaver cutting. In fact, the beaver dams have turned 

almost all of the valley bottoms adjacent to these streams into 

countless swamps, making parts of the country almost inaccessible 

in the summer. Other fur-bearing animals, such as otter, mink, 

marten, muskrat, wolverine, and fox are present in scanty numbers 

in the territory adjacent to the major streams.

Game birds such as ptarmigan and grouse were found only infrequently.

In most of the clear-water streams grayling and rainbow trout 

occur in small numbers. At Spink Lake, which is accessible by 

airplane, rainbow trout are very abundant, and many of them 

measure over 20 inches in length. Fish also occur in Pass, Coal, 

Partin, and Alder Creeks and in Lucy Lake.

Naturally, the animal life is restricted mainly to the area that 

supports some vegetation. The extreme western part of the district 

is so high that it is either covered with perpetual snow and. ice, 

or only steep, barren rock slopes are visible.

SETTLEMENTS AND INDUSTRIES

With the exception of the stations along the railroad there are 

no permanent settlements in the district. The stations from which 

the railroad maintenance is carried on are, from south to north, 

Curry, Sherman, Gold Creek, and Canyon. At each of these places 

from two to eight men are employed, depending on the season, as 

in the winter no improvements can be made and only work which is 

directly concerned with keeping the line open is carried on. At 

Curry a roundhouse and hotel are maintained, as the trains from 

Seward to Fairbanks use that station as an overnight stop. The 

census of 1930 gives Curry a population of 91. In addition to the 

railroad employees, there are several fur farmers and a few prospectors who winter along the railroad, and these together constitute 

what might be called the permanent population. In the western 

part of the district a few men trap along the rivers in winter, but 

in summer there have never been more than a few prospectors at 

work, so that there is practically no permanent population in the 

portion of the district that lies west of the Chulitna River.

The nearest permanent settlement other than those maintained 

by the railroad is Talkeetna, which lies outside the southern limit
U. S. GEOLOGICAL SURVEY BULLETIN 857 PLATE 1

EXPLANATION 

SEDIMENTARY ROCKS

Stream gravel, sand, and silt

with some glacial deposits

BroWnexToWer ,

Glacial moraines, outwash,

Coal-bearinsr formation with

overlying Tertiary gravel

(slightly indurated sand, clay* and

gravel -with lignitic coal seams)

Slate, argillite, graywacke, phyl

lite, and various kinds of schist

(with intercalated thin beds of limestone, conglomerate, and quartzite)

Chert, argillite, and quartzite

Granite and granodiorite with

associated acidic and basic

Base by U. S. G. S. Alaskan Branch 

Topography by C. P. McKinley and 

others

GEOLOGIC RECONNAISSANCE MAP OF CUREY AND VICINITY, ALASKA

BY RALPH TUCK 

SURVEYED IN COOPERATION WITH THE ALASKA RAILROAD

Scale 2so ooo

3___________________O____________________5__________ tO 15 Miles

2O Kilometers

Contour interval 200 feet

Datum is mean sea level

1934

DECLINATION 1912
U.S. GEOLOGICAL SURVEY BULLETIN 857 PLATE 2

A. EOCENE COAL-BKAFtING HOCKS (ON LEFT) AND VEGKTATIO.N-COVERKD MORAINE 

OF RUTH GLACIKR (ON RIGHT).

B. HUGGED GRANITIC MOUNTAINS ON THE EAST S1DK OF MOUNT McKINLEY.
U.S. GEOLOGICAL SURVEY 

HUGGED TOl'OGHAl'HY ALONG ELDR

Typical granite slopes in left foreground; smooth slopes of slate, gray wack
U.S. GEOLOGICAL SURVEY 

BUCKSKIN GLACIER, WITH MOUNT McKINLEY 
THE CURRY DISTRICT 113

of the district. The census of 1930 gives Talkeetna a population of 

89. It has several stores and is the railroad point of entry to the 

placer-mining districts of Cache and Peters Creeks.

Practically no freight is furnished to the Alaska Railroad by this 

district. The trapping of wild fur supports only a few men and 

will never be a potent factor in the settlement of the region. Several 

fur farms could be supported, but they also would offer only a small 

amount of business to the railroad, and there are many other places 

that are more advantageously located for such enterprises. Agriculture will probably never be important, as the tillable ground is 

confined to the stream bottoms and is therefore of small extent and 

of value only locally for gardens.

On the other hand, the district offers unusual scenic possibilities, 

for from a number of easily accessible places along the railroad 

superb views of Mount McKinley and the Alaska Range can be 

obtained. Opportunities also might be made for longer trips by 

pack train into this rugged glacier-filled country, but the scarcity 

of big game makes it unattractive to the hunter.

GEOLOGY

PRINCIPAL FEATURES

The areal distribution of the surface rocks and their division into 

lithologic units is shown on plate 1. The field work upon which 

this report is based was of a reconnaissance nature only, and although 

it is believed that the mapping of the formations is accurate within 

the limits of the scale used (1 inch equals 4 miles), nevertheless detailed work will no doubt make possible the more accurate mapping 

of the contacts of the various formations and a separation of the 

members of the metamorphosed sediments that have here been classified as one series into a number of separate formations.

The oldest rocks consist of thin-bedded chert, quartzite, and argillite that are exposed in only a small part of the area. Lying unconformably on these rocks is a volcanic formation composed of tuff 

and agglomerate, exposed only in the northern part of the area. 

Later another series of sediments, now exposed as chiefly slate, graywacke, and schist, was deposited, and all the rocks were folded, 

faulted, and changed to their present highly metamorphosed condition. Subsequent to the regional metamorphism, or as its last phase, 

the district was invaded by a granitic batholith that now occupies 

its greater part. This igneous intrustion further altered the metamorphic rocks and along its margin sent acidic dikes and sills ramifying into the surrounding sediments. The last phase of igneous 

activity was the intrusion of a few basic dikes that cut the granite

50017 34 3
114

as well as the metamorphosed sediments. The formation of the ore 

deposits in the district was probably associated with the granitic 

intrusion, in that the vein minerals were brought in by the granite 

magma and were liberated during its crystallization.

The intrusion of the granite batholith was followed by a long 

period of erosion, in which a topography with a general similarity to 

that of today was carved into the metamorphosed sediments and 

granite. At the end of this period much of the region, particularly 

what are now the valleys, was a low-lying region close to sea level, 

with many swamps. In this low region vegetation grew rank for 

long periods of time. Then followed periods of rapid deposition 

which resulted in the covering of the vegetation by clay, sand, and 

gravel. This cycle recurred several times, as is indicated by the 

different coal seams, separated by deposits of clay, sand, or gravel. 

After the deposition of the coal-bearing rocks was completed a sheet 

of gravel many hundreds of feet thick completely covered the coal 

series. At the end of this period of active sedimentation an uplift 

of the land mass slightly tilted the coal-bearing rocks and rejuvenated the streams, which once more began to erode actively. After a 

long period of erosion climatic changes resulted in the accumulation 

of large amounts of ice at several centers in the higher parts of the 

Alaska Kange. From these centers the ice moved down the valleys 

and modified the earlier stream-carved topography. Still later, with 

a return to milder climatic conditions, the glaciers retreated, leaving 

behind morainal material liberated by the melting ice. Most of the 

morainal material has since been removed by erosion, but a great 

thickness of glacial outwash gravel remains in the valleys in the 

form 'of well-defined terraces. Still more recently the present 

streams have been engaged in transporting and depositing silt, sand, 

and gravel. Many of these recent deposits, as well as the glacial 

deposits, are too small to be shown on the accompanying map.

In this report formation names have not been given to the various 

rock groups,- as the data as to their age, subdivision, and correlation 

are incomplete; instead they are here separated into divisions based 

on rock types and stratigraphic relations.

SEDIMENTARY ROCKS 

PRE-PERMIAN (?) QUARTZITB, CHERT, AND ARGILLJTE

Distribution and character. The oldest rocks that have been recognized in the Curry district occur in its northeastern part in the 

vicinity of the front of Eldridge'Glacier, from which they extend 

northeastward for several miles. They are al^o present on the west 

side of the lower end of the glacier, and they form the walls of the 

steep gorge that Partin Creek cuts before reaching Eldridge Glacier,
THE CUREY DISTRICT. 115

as well as the prominent ridge that separates Partin Creek from the 

headwaters of Coal Creek. South of the front of Eldridge Glacier 

these rocks are not exposed, and if they are present there they underlie the silt, sand, and gravel in the valleys of the Fountain and Chulitna Rivers.

Most of these rocks are dark gray to black on fresh surfaces. 

Weathered surfaces are sometimes light gray, but more commonly a 

rusty red-brown, owing to the alteration of the disseminated pyrite 

that they contain. In many places the beds range in thickness from 

1 to 12 inches and so give the outcrops a banded appearance. Finegrained quartzite, chert, and cherty argillite constitute the major 

parts of the series. In a few places tuff and small bodies of massive 

serpentinized rock are interbedded, the serpentinized rocks possibly 

having been derived from the metamorphism of impure sediments 

or br,sic igneous rocks. All the rocks are highly metamorphosed, 

and parts of them show a great deal of silicification. In addition to 

containing disseminated pyrite, they are cut by numerous small 

veinlets carrying quartz, sericite, and pyrite, sericite in small oriented flakes being a common accessory constituent of the quartzite. 

Most of the cherts also contain sericite and considerable kaolin. The 

argillite usually includes large amounts of carbonaceous material. 

Basic dikes that occur in places are difficult to distinguish in the 

field from the metamorphosed sediments and are usually composed 

predominantly of andesine, which is highly altered, and chlorite, 

which has probably been derived from a pyroxene mineral.

Structure and thickness. Locally the strike of these rocks ranges 

from north to east, but the average or regional trend is about N. 

25°-30° E. Their dip also varies greatly, ranging from 45° either 

northwest or southeast to vertical. Repeated close folds are the most 

common type of structure, and their intricate character, the absence 

of recognizable horizons, and the lack of time prevented the working 

out in detail of any of them. Many of the rocks have well-developed 

cleavage that parallels the bedding. Only minor faults were observed ; but as the beds are intensely folded, it is probable that faults 

with large displacements are present.

The thickness of this group of rocks is not definitely known, as 

neither the base nor the top of the series was recognized. Outcrops 

along Eldridge Glacier indicate a thickness of 5,000 feet, but inasmuch as close folding and faulting have resulted in a repetition of 

beds this figure may be excessive.

Age and correlation. Early Tertiary (Eocene) deposits that 

occur nearby are almost flat-lying and are but slightly consolidated, 

and the interbedded coal is only of lignitic rank; so that it is apparent that these highly metamorphosed sediments .at the base of
116 MINERAL RESOURCES OF ALASKA, 1932

Eldridge Glacier are much older than the Tertiary. No exposure 

of the actual contact of this formation with the slate, graywacke, 

and schist immediately to the west was found, and although the 

presence of a definite unconformity between them can only be surmised, nevertheless it is believed to be present, for the chert-quartzite series is lithologically dissimilar to the slate, graywacke, and 

schist group and has suffered a greater degree of folding and 

metamorphism.

During the present investigation a few fossils were collected from 

a calcareous shale on a small eastern tributary of Partin Creek that 

heads against Little Shotgun Creek. J. B. Reeside, Jr., identified 

the material as follows:

Pecten sp.

Cardinia sp.

Arniotites, several species.

Fragmentary ammonites, undetermined.

He states that " This fauna has never been adequately studied, and 

few names can be given to the species. There is no doubt, however, 

that it is of early Jurassic age (lower Liassic)." The fossiliferous 

shale at this locality is conformably overlain by shaly slate and 

underlain by agglomerate and red tuff. In turn the agglomerate 

and tuff are underlain by the chert, quartzite, and argillite, so that 

apparently the latter are of pre-Jurassic age.

Immediately north of the area where these rocks occur, Boss 12 

found on Ohio Creek a formation that from his description is in 

general similar to that here under discussion, except that it has 

considerable calcareous material with the cherty rocks. It is not 

definitely established that these formations are continuous; in the 

Curry district this formation has been traced from Eldridge Glacier 

several miles up Partin Creek, and the formation described by Ross 

was traced southward to a point near the mouth of Shotgun Creek, 

thus leaving a gap of about 8 miles. The probability that the rocks 

continue through this unmapped area is apparent, as they occur 

on the same strike. On the West Fork of the Chulitna River the 

overlying Permian beds rest with angular unconformity on these 

calcareous and cherty rocks; hence Ross considers them pre-Permian and, owing to their lithologic similarity to fossiliferous Devonian limestones in the Broad Pass district, probably Devonian. 

Capps 13 in an earlier report calls the same rocks pre-Triassic, as 

overlying rocks contain Triassic fossils.

The evidence in the Curry district itself indicates a pre-Jurrassic 

age for these metamorphosed sediments, and tentative correlation

u Ross, C. P., Mineral deposits near the West Fork of the Chulitna River: U.S. Geol. 

Survey Bull. 849-E, 1938.

13 Capps, S. R., Mineral resources of the upper Chulitna region: U.S. Geol. Survey Bull. 

692, p. 218, 1919.
THE CURRY DISTRICT 117

with formations exposed north of the district suggests that they 

are pre-Permian.

PERMIAN(?) TUFF AND AGGLOMERATE

Distribution and character. A few exposures of volcanic rocks 

occur in a narrow band on a small northeastern tributary of Partin 

Creek that heads against Little Shotgun Creek. No other exposures 

of this formation were recognized in the district, and although it 

is probable that they may occur farther up Partin Creek, the field 

work was not carried beyond the locality mentioned. These volcanic 

rocks consist of varicolored breccias or agglomerates made up chiefly 

of angular fragments of fine-grained igneous rock with a tuffaceous 

matrix. Interbedded with and locally grading into the agglomerates 

are beds that are composed entirely of red tuff. The exposures at 

this locality suggest a distinct formation, largely of volcanic origin, 

although the presence of a few shaly members indicates that a part 

of it may have been waterlaid.

/Structure and thickness. The few exposures show but little structure, as both the- agglomerates and the tuffs are massive. At one 

locality the bedding strikes northeast and dips steeply to the northwest an altitude that conforms in general with that of the overlying 

formation, which is predominantly shale. The thickness of the volcanic formation at this locality is about 300 feet.

Age and correlation. The volcanic rocks overlie the quartzite, 

chert, and argillite series that has tentatively been referred to as 

pre-Permian. Overlying the agglomerate and tuff are calcareous 

shales that contain Lower Jurassic fossils, so that it is evident the 

volcanic rocks are older than Lower Jurassic. Similar formations 

a few miles to the north have been mapped by Capps,14 who has 

referred to them as Triassic or pre-Triassic. Later and more detailed 

work by Eoss 15 proves that at least a part of the volcanic rocks 

are of Permian age, so that it appears probable that the agglomerates 

and tuffs on Partin Creek are Permian.

MESOZOIC ROCKS

Distribution and character. A thick group of sedimentary rocks, 

predominantly slate and graywacke but with intermediate and more 

highly metamorphosed phases, has a wide distribution within this 

district. (See pi. 1.) It is quite possible that this group is composed of several formations, but data for subdivision are lacking. 

They extend from the north and the northeast side of the area to

11 Capps, S. R., Mineral resources of the upper Chulitna region : U.S. Geol. Survey Bull. 

692, pp. 215-217, 1919.

15 Boss, C. P., Mineral deposits near the West Fork of the Chulitua River: U.S. Geol. 

Survey Bull. 849-E, 1933.
118 MINERAL RESOURCES OF ALASKA, 1932

the southern margin and also underlie a large part of the Chulitna 

Valley. Farther west they occur in a northeastward-striking belt 

that is almost entirely surrounded by granite. This belt is nearly 

continuous from the Yentna district, where it was previously mapped, to the upper Chulitna region, where it has also been recognized. 

The major part of the moraine of Eldridge Glacier is composed of 

these rocks, suggesting that the greater part of the Eldridge Glacier 

basin is underlain by them. The moraine of Buckskin Glacier consists mainly of granitic debris, but one long moraine ridge of slate 

and graywacke fragments extends for 15 miles up the glacier, indicating that an isolated mass of metamorphosed sedimentary rocks 

occurs in the granite near the base of Mount McKinley. Although 

this series of rocks forms a large part of the Alaska Range and of 

south-central Alaska, its stratigraphic limits are only imperfectly 

known. Its character is so uniform and beds that can be traced 

continuously over considerable distances are so rare that it is exceedingly difficult to work out the structural details. Moreover, fossils 

are almost lacking, so that the age limits of the group are still 

obscure.

The rocks of this sedimentary series include a wide range of metamorphic materials that originally were shale and impure sandstone. 

Regional metamorphism, as well as contact metamorphism due to 

the intrusion of granite has changed them to slate, argillite, phyllite, 

schistose graywacke and arkose, and a wide variety of schists. Definite evidence, either lithologic or paleontologic, that would justify 

the subdivision of the series is lacking, and on plate 1 all the metamorphosed sediments are mapped as a unit. However, on the basis 

of their distribution and their megascopic and microscopic differences, it is simpler here to discuss them as two subdivisions. One 

extends from Ruth Glacier northeastward to Eldridge Glacier and 

forms the western portion of the metamorphosed sedimentary group. 

This^part consists predominantly of schist, phyllite, argillite, slate, 

and graywacke. Thin beds of limestone, conglomerate, serpentine, 

and quartzite are interbedded in places, particularly in the vicinity 

of Eldridge Glacier. Most of the rocks are fine to medium grained 

and dark gray to black. They weather into smooth slopes composed 

of small shaly fragments, although beds of graywacke, which are 

subordinate in amount to the other types, are more resistant. This 

series is easily distinguishable, even at a distance, from the intrusive 

granite, which is cream-colored and on weathering forms a rough, 

precipitous topography. (See pi. 3.) In some places the series is 

thin-bedded, and in others it is massive. Cleavage and schistosity 

may or may not be well developed and where present are usually 

parallel to the bedding.
THE CURRY DISTRICT 119'

As determined by microscopic study, andalusite, cordierite, biotite, sericite, and hornblende schists are abundant, particularly near 

the granite contacts. Quartz, feldspar, and kaolin are also abundant, with lesser amounts of chlorite, epidote and magnetite. In 

places along the western margin of this band of sediments, where 

they are very argillaceous, and immediately adjacent to the granite 

contact, there is a well-defined belt of andalusite schist. This schist 

contains disseminated pheriocrysts of andalusite and chiastolite as 

much as an inch in length and a quarter of an inch in diameter. 

Carbonaceous material is present in many of the rocks, and some 

of the slates and graywackes are slightly calcareous. Under the 

microscope almost all the rocks have a well-defined schistosity, 

with a parallel orientation of the component minerals, although in 

the hand specimens this schistose character is not always evident, 

owing to the fineness of the grain.

A typical section of the metamorphosed sediments in the northern 

part of the area is shown by good exposures on the north side of 

Buckskin Glacier.

Section of rocks on north side of Buckskin Glacier 1 mile west of terminus

Feet 

Fine-grained dark-gray slate ________ 500

Graywacke, sheared conglomerate, and quartzite_______ SO 

Thin-bedded shaly sericite schist with small lenses of serpentine__________________________________ 350 

Fine-grained black phyllite_-_______ _. 200 

Fine-grained black andalusite schist____ __-_______ 150

All these beds are conformable, with a dip of 50°-70°SE. The 

andalusite schist is in direct contact with the intrusive granite, and 

the two grade into each other.

At the contact with the granite the sediments are as a rule highly 

metamorphosed into a dense silicified rock that contains a finegrained mass of quartz, biotite, muscovite, andalusite, cordierite, 

and garnet. Medium-grained biotite and hornblende schists border 

the granite, and in places there is a thickness of several inches of 

biotite flakes at the margin of the granite.

Quartz veins occurring both as tiny veinlets and also as large 

fissure veins are found throughout the series. Many of the veins 

contain small amounts of pyrite, chalcopyrite, and free gold. As 

a rule the veins are larger and better defined 1,000 feet or so away 

from the granite than at the contact, as immediately adjacent to 

the intrusive the chief action of the granite has been to silicify the 

sediments.

The other subdivision of the metamorphosed sediments occurs 

just south of the front of Euth Glacier and is a continuation of at
120 MINERAL RESOURCES OF ALASKA, 1932

least a part of the slate and graywacke of the Yentna district. 

These rocks are also exposed along the Chulitna River in the vicinity of Pass Creek and Chulitna Butte, and they border the granite 

mass that lies between the Susitna and Chulitna Rivers. They are 

dark gray and fine to medium grained. Sheared graywacke and 

arkose with lesser amounts of slate form the predominant rock 

types. Microscopically they are composed of subangular grains 

of quartz and feldspar and small fragments of quartzite, argillite, 

and fine-grained igneous rocks. The groundmass usually contains 

kaolin and sericite, with but little carbonaceous material. The rocks 

south of the front o,f Ruth Glacier have in many places disseminated 

pyrite crystals half an inch across, and on weathered surfaces only 

the cavity and iron stain are left by the oxidation of the pyrite. 

The bedding is difficult to determine, as in the vicinity of Pass 

Creek the rocks are massive, and farther south they are highly 

sheared.

The metamorphosed sediments, in addition to being intruded by 

the granite, are cut by both acidic and basic dikes. As a result of 

the small scale of the map no attempt has been made to map the 

dikes separately, and they have been included with the sediments.

Structure and thickness. All the metamorphosed sediments are 

highly folded. The strike of the beds ranges from east to north but 

is usually about N". 45° E., paralleling the trend of the Alaska 

Range. The dip ranges from vertical to 20°, either to the northwest 

or to the southeast. At the headwaters o.f Alder and Whistler 

Creeks the rocks dip northwest. In the vicinity of Buckskin Glacier the prevailing dip is to the southeast. On the north side of 

Eldridge Glacier and on the Chulitna River north of Pass Creek 

it is to the northwest. At many other localities there is close folding, with the beds vertical. In the district here described there is 

probably not a regional dip; instead there are a number of folds. 

Structure and lithologic similarity suggest that the axis of one 

such anticline probably strikes across Ruth and Buckskin Glaciers. 

This fold was intruded by granite, which cut across the axis at an 

acute angle, and a remnant of the west limb is preserved at the heads 

of Alder and Whistler Creeks and a part of the east limb at the 

foot of Buckskin Glacier. South of this district Capps 16 found 

a great variance in the direction of dip, due to the small folds, but 

in general it is to the southeast. To the north Ross 17 found a general northwest dip.

Only faults of small displacement were recognized, but it is probable that with the high degree of folding large faults are present.

18 Capps, S. R., The Yentna district, Alaska: U.S. Geol. Survey Bull. 534, pp. 26-27, 

1913.

17 Ross, C. P., Mineral deposits near the West Fork of the Chulitna River: U.S. Geol. 

Survey Bull. 849-B, 1933.
THE CURRY DISTRICT . 121.

The uniform character of the sediments makes it difficult to detect 

faults as well as to decipher the major folding. Cleavage and 

schistosity are developed to some degree in almost all the rocks, and 

microscopically they are very apparent in the alinement and orienta-^ 

tion of the rock-forming minerals.

The thickness of the series is great. At the fronts of both Whis-_ 

tier Glacier and Buckskin Glacier 4,000 feet of sediments are exposed without any apparent repetition. The exposures of gray-, 

wacke and slate in the Chulitna Valley are not as good, but it is, 

probable that these rocks are there at least several thousand feet 

thick, and as a conservative estimate it appears probable that in this, 

district there are over 6,000 feet of metamorphosed sediments. 

Capps 18 believes that an estimated thickness of 3,000 feet is war-., 

ranted for a similar series in the Yentna district.

Age and correlation. The scarcity of fossils in this series is a, 

serious handicap to any determination as to its age. Stratigraphic 

evidence is also inadequate. Lignitic coals of Eocene age lie uncon-. 

formably on these older sediments, so that direct evidence from 

this district can do but little more than point to a pre-Tertiary age.. 

During this investigation a few Lower Jurassic fossils were collected 

on a small tributary of Partin Creek that heads against Little Shotgun Creek. These fossils were found in a shaly slate which may 

be a part of the series that occurs on the Hidden River. Field workin adjacent areas affords a basis for correlation and an approximate, 

age determination of these sediments. Similar formations have a. 

wide distribution in south-central Alaska and have long furnished 

a difficult geologic problem.

In the eastern part of this district Eldridge 19 noted a series ofslates along the Susitna River, but he made no statement as to their 

age. In the Yentna district, which lies immediately south of the. 

Tokichitna River, Capps 20 mapped a series of highly folded slates 

and graywackes that continue into the Curry district. Lacking - 

conclusive evidence, he provisionally assigned the series to the Paleozoic or Mesozoic. Capps further correlated the rocks in the Yentna, 

district with a series that occurs in the Kichatna Valley, described by - 

Brooks 21 as a series of slates, and on structural and stratigraphic 

grounds tentatively placed in the Paleozoic, although with the reser-. 

vation that it was by no means impossible that they might be Mesozoic. 

More definite information as to the age of the slate and gray wacke,

18 Capps, S. R., The Yentna district, Alaska: U.S. Geol. Survey Bull. 534, p. 27, 1913.

18 Eldridge, G. H., A reconnaissance in the Sushitna Basin and adjacent territory in 

1898 : U.S. Geol. Survey 20th Ann. Rept., pt. 7, pp. 15-16, 1900.

80 Capps, S. R., The Yentna district, Alaska: U.S. Geol. Survey Bull. 534, pp. 24-28, 

1913.

21 Brooks, A. H., The Mount McKinley region, Alaska: U.S. Geol. Survey Prof. Paper 70, 

pp. 67-68, 1911.
122 MINERAL BESOURCES OF ALASKA, 1932

of the Yentna district was obtained by Mertie,22 who discovered 

fossils of probable Upper Cretaceous age on Long Creek, a tributary 

of the Tokichitna Kiver.

Directly north of this district, Capps 23 noted a group of rocks 

that are predominantly black argillite with minor amounts of graywacke and some fine conglomerate. His conclusion as to their age 

was that they are younger than a part of the Triassic and older 

than Eocene. During a later investigation in the same district 

Capps 24 collected fossils of late Jurassic or early Cretaceous age 

from the same rocks. Still later Ross 25 mapped the argillite as 

Triassic but stated that part of it might be of a later Mesozoic age. 

Farther north, in the Broad Pass district, a group of rocks consisting predominantly of slate, with lesser amounts of graywacke, conglomerate, and limestone, has tentatively been placed in the Jurassic 

by Moffit 26 and correlated with similar rocks in the Susitna Valley, 

Yentna and Kichatna districts, and other localities in the Alaska 

Hange.

From the foregoing summary it is apparent that there is a large 

group of rocks in adjoining and nearby districts that are lithologically and structurally similar and can be traced along the strike 

almost without a break for at least 200 miles, from the Yentna River 

to the Broad Pass district, and that form one of the dominant lithologic units of the south slope of the Alaska Range. For the most 

part recent estimates as to the age have assigned the series to various 

parts of the Mesozoic (Triassic to Cretaceous). In view of the 

wide areal extent and varied nature of the sediments and the conflicting fossil evidence, it is doubtful if a definite period can be 

assigned to the entire group. Instead, it is probable that throughout 

the Mesozoic era the area was subjected to fluctuating conditions of 

sedimentation, which varied from place to place, so that there was 

.an overlapping of formations, with the result that a large part of 

Mesozoic time is represented.

No direct information as to age was gained in this district other 

than that the series was pre-Tertiary. Mertie's discovery of Cretaceous fossils on Long Creek indicates that the slate and graywacke near the front of Ruth Glacier and along the Chulitna River 

are probably Cretaceous. Whether the rocks on the Hidden River 

are the same, or younger, or older, is not proved, so that provisions'3 Mertie, J. B., Jr., Platinum-bearing gold placers of the Kahiltna Valley: U.S. Geol. 

Survey Bull. 692, pp. 236-237, 1919.

23 Capps, S. R., Mineral resources of the upper Chulitna region: U.S. Geol. Survey Bull. 

 692, pp. 217-218, 1919.

24 Capps, S. R., The eastern portion of Mount McKinley National Park: U.S. Geol. Survey Bull. 836, pp. 260-263, 1932.

25 Ross, C. P., Mineral deposits near the West Fork of the Chulitna River: U.S. Geol. 

Survey Bull. 849-E, 1933. : .

26 Moffit, F. H., The Broad Pass region, Alaska: U.S. Geol. Survey Bull. 608, pp. 32-38, 

1915.
THE CUKRY DISTRICT 123

ally they are assigned to the Mesozoic and are believed to belong possibly to the Jurassic or Cretaceous. 

Mesozoic sediments of similar character are not confined to the

-areas mentioned on the south slope of the Alaska Range but are 

widespread throughout south-central Alaska* on Kenai Peninsula,27 

in the Turnagain-Knik River 28 and the Knik River-Matanuska 

.River 29 districts, and in parts of the Talkeetna Mountains.80 

Moffit 81 has also suggested their correlation with a great thickness 

of Mesozoic beds of similar character in the Nutzotin Mountains, 

which form the eastern part of the Alaska Range.

EOCENE COALrBEARING ROCKS

Distribution and character. Deformation and a long period of

 erosion followed the deposition of the slate and graywacke series, as 

is shown by a pronounced unconformity between the highly folded 

metamorphic rocks and the overlying slightly indurated and almost 

flat coal-bearing rocks. At the time of the deposition of the coalbearing series the topography had already acquired the major features that it now exhibits. The principal features of the Alaska 

Range had already been formed, and the drainage was essentially 

along the same lines as at present. In the Susitna and Chulitna 

Yalleys vegetation flourished and accumulated for long periods of 

time, after which it was covered with sand, gravel, and clay from 

streams that headed back in the mountains. This cycle was repeated 

several times, as is indicated by the alternation of beds of coal with 

beds of clay, sand, and gravel.

The wide-spread deposition of the coal-bearing rocks is indicated 

by the outcrops and float from that formation throughout the Susitna 

and Chulitna Valleys. Exposures of this coal series were found 

in several localities in the Curry district. The largest and best 

exposure is south of the front of Ruth Glacier, where it forms a 

part of the ridge between the Ruth and Tokichitna Rivers. A few 

exposures occur on Alder Creek near the point where it flows along 

the moraine of Ruth Glacier. Farther north exposures are found 

along the Chulitna River in the vicinity of Little Coal Creek. It is 

also reported that coal occurs on Troublesome Creek, the large eastern 

tributary of the Chulitna opposite the front of Ruth Glacier. 

Float occurs at several localities along the Chulitna River and the.

27 Martin, G. C., Johnson, B. L., and Grant, U. S., Geology and mineral resources of 

Kenai Peninsula, Alaska: U.S. Geol. Survey Bull. 587, p. 33, 1915.

28 Capps, S. R., The Turnagain-Knik region: U.S. Geol. Survey Bull. 642, pp. 155-161, 

1916. .,

28 Landesl K. K., Geology'of the Knik-Matanuska district: U.S. Geol. Survey Bull. 792, 

pp. 5'6-57,'.1927.

30 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U.S. Geol. Survey Bull. 327, pp. 11-12, 1907.

^Mofflt, F. H., op. cit. (Bull. 608), p. 38.
124 MINERAL RESOURCES OF ALASKA, 1932

lower parts of many of its tributaries. As the float is lignitic coal,, 

which breaks down rapidly when exposed to the weather, it is 

evident that the coal outcrops occur not far from the places where. 

the float is found, and the formation is probably widespread beneath the younger gravel. A short distance beyond the eastern 

limit of the district several exposures occur along the Susitna River 

above its junction with the Chulitna. Concerning these outcrops 

Eldridge 82 says:

The third coal field along the main river [Susitna], 4 to 10 miles above the 

Chulitna, appears to outcrop for a distance of 6 or 7 miles and is, perhaps, theexposed portion of an extensive area. The strata form bluffs 100 to 300 feet 

high and consist of clays and sandstones, the former predominating, with coal 

seams from 6 inches to 6 feet thick. There are perhaps 10 or 15 coal beds 

exposed in the entire length of the outcrop. Their general dip is 5° to 15° 

SSE. with undulations. The thickness of the series is perhaps 50 feet.

Where the writer observed these exposures they were essentially the 

same as those on the south side of Ruth Glacier.

No doubt at some time during the Eocene the Chulitna and Susitna 

Valle}7 s and the lower parts of their tributary valleys were covered 

with the coal-bearing series. Subsequent erosion by these streams 

has resulted in the removal of a larger part of the series, so that only 

remnants are left in the lowlands or in protected localities.

Good exposures of the coal-bearing series are rare, for the rocks 

are but slightly consolidated and quickly erode to gentle slopes covered with vegetation; where clay predominates in the series, the beds 

stand up as bluffs. Along the south side of Ruth Glacier a good section is exposed at a place where a small creek that flows at the contact, 

of the coal-bearing series and the moraine has cut into the coal-bearing formation. (See pi. 2, A.) This section shows a series of 

interbedded, slightly indurated layers of clay, sand, and gravel,, 

with lenticular lignitic coal seams from a .few inches to 6 feet thick. 

The sands are usually buff and friable, and the clays are yellow or 

gray and very plastic. Where the clay directly underlies the coal 

it is commonly rusty-colored, suggesting that it may represent the 

top-soil zone upon which vegetation grew, but there was no" other 

evidence of the residual origin of the coal; instead, .the lenticular 

nature of the lignite seams and the associated material suggests that 

the vegetable material may have been transported. Much of the 

gravel shows cross-bedding and is composed of slate, graywacke^ 

and granite pebbles and boulders as much as 10 inches in diameter. 

The lignite contains carbonized fragments of bark, twigs, anoT limbsand breaks down quickly on exposure to weather. In the northern 

part of the district, along the Chulitna River, the series is represented 

chiefly by coaly shale beds.

«= Eldridge, G. H., op. cit., p. 22.
THE CURRY DISTRICT 125

Structure and thickness. In detail the section shows lenticular 

beds and much cross-bedding, suggesting a rapid deposition of at 

least a part of the formation and fluctuating conditions of sedimentation. In places there is a suggestion that the material was 

deposited as the delta of a stream. Except for the cross-bedding 

the formation is almost horizontal or has a slight southeast dip. 

The greatest inclination observed was 12° SW. As a rule the series 

has been but little disturbed.

Near the southern edge of the moraine of Ruth Glacier about 500 

feet of unconsolidated sediments are exposed. The coal-bearing portion occurs in the lower part of the section. Several hundred feet 

of gravel lies conformably upon the coal-bearing portion, and the 

conformable relations suggest that the gravel may be a part of the 

coal formation. Exclusive of the gravel there is a thickness of more 

than 300 feet of the coal-bearing series exposed in this section. At 

other localities throughout the Cook Inlet and Susitna region, the 

thickness of similar coal-bearing rocks ranges from 100 to 10,000 

feet.

Age and correlation. Geomorphic evidence in the Curry district 

shows that this formation has suffered considerable erosion and has 

been glaciated and is thus of pre-Pleistocene age. Fossil plant 

remains in similar rocks south of the Toldchitna River and also 

throughout the Chulitna and Susitna Valleys and Cook Inlet region 33 

indicate an Eocene age for the coal-bearing formation; and there 

is every likelihood that the series in this district also is of that age.

TERTIARY GRAVEL

On the ridge between Ruth Glacier and the Toldchitna River the 

coal-bearing formation is overlain by coarse stream-washed gravel, 

which is probably a continuation of gravel deposits in the area south 

of the Tokichitna River, described by Capps.34 No other exposures 

of this gravel were found in the district, but possibly it may continue 

to the north beneath a cover of younger gravel and vegetation.

The gravel consists of well-rounded pebbles and boulders as much 

as 10 inches in diameter. Slate, graywacke, conglomerate, and various types of igneous rocks are represented in it. The boulders are 

partly cemented in a plastic clay and are usually oxidized and 

partly decomposed. The few exposures examined show that the

88 Capps, S. R., The Yentna district, Alaska: U.S. Geol. Survey Bull. 534, pp. 28-33, 

1913; The Skwentna region, Alaska: U.S. Geol. Survey Bull. 797, pp. 86-88, 1929. 

Elclridge, G. EL, op. clt., pp. 16-17. Brooks, A. H., The Mount McKinley region, Alaska: 

U.S. Geol. Survey Prof. Paper 70, pp. 94-103, 1911. Capps, S. R., Mineral resources of 

the upper Chulitna region: U.S. Geol. Survey Bull. 692, pp. 219-220, 1919. Martin, G. C., 

and others, Geology and mineral resources of Keiiai Peninsula, Alaska: U.S. Geol. Survey 

Bull. 587, pp. 67-89, 19151 .

84 Capps, S. R., op. cit. (Bull. 534), pp. 33-36.
126

gravel has a thickness of at least 300 feet. A greater thickness is 

probable, as the boulders are found covering the ridges at much 

higher elevations.

So far as could be ascertained the gravel lies conformably on the 

coal-bearing rocks, with no time break indicated. The gravel is 

believed to represent an uninterrupted continuation of the sedimentation that produced the coal-bearing series. In the Bonnifield district, on the north side of the Alaska Range, Prindle 35 and Capps 3G 

found similar deposits of gravel overlying coal-bearing rocks of 

similar age.

Large granite glacial boulders, some of them 20 feet across, lie on 

the gravel and indicate that the gravel has been glaciated and is 

older than Pleistocene. Correlation with similar gravel in the Yentna 

district also indicates that it is Tertiary and possibly of Eocene age.

QUATERNARY DEPOSITS

GLACIAL DEPOSITS

Moraines. True glacial deposits are not abundant in the Curry 

district. Terminal moraines are entirely lacking except those at 

the present termini of the living glaciers, and these are being 

removed by the glacially .fed streams as rapidly as the glaciers 

retreat. A few lateral moraines are still preserved, a conspicuous 

one lying on the north side of the lower portion of Elclridge Glacier, 

where long parallel ridges, composed mainly of large angular 

boulders, rise several hundred feet above the present surface of the ice. 

These ridges are partly covered with vegetation and are separated 

from the living glacier by another more recent lateral moraine that 

is still bare. The hummocky character of the ridge between the 

Fountain and Chulitna Rivers suggests that it may be composed, 

at least in part, of morainal material, perhaps from a medial moraine formed by the coalescing of Eldridge Glacier with the glacier 

that formerly occupied the valley of the Chulitna. Similar topographic conditions exist on the lower ends of the ridges between 

the Fountain and Hidden Rivers, Hidden and Coffee Rivers, Coffee 

and Tokichitna Rivers, and Ruth and Tokichitna Rivers. It is 

highly probable that these areas also are paved with morainal material, but the heavy mantle of vegetation made it difficult to ascertain 

this fact definitely. Ground moraine is probably present in all 

the valleys but is overlain by later gravel and vegetation. On the 

Hidden and Coffee Rivers it covers the valley floor for several 

miles below the present fronts of the glaciers. Glacial till, con35 Prindle, L. M., The Bonnifield and Kantishna regions: U.S. Geol. Survey Bull 314 

pp. 221-222, 1907.

3(1 Capps, S. R., The Bonnifield region, Alaska : U.S. Geol. Survey Bull. 501, pp 30-34 

1912.
THE CUBBY DISTBICT 127

misting of boulders and clay, is present in a few localities; but for 

the most part, as the glaciation was of the valley type and as the 

district lies in an area where ice accumulation was taking place, 

the glacial work was erosive, and upon the retreat of the glaciers 

the valleys were swept clean by water from the melting ice or 

covered with stream-washed material.

Bench gravel. In almost all the valleys, particularly those of 

the Susitna and Chulitna Rivers, large deposits of gravel are common. With the gradual retreat, by melting, of the glaciers that 

occupied all the valleys, a large amount of water was liberated, 

which reworked much of the glacial debris and deposited it as sand, 

gravel, and silt. This glacial outwash material, which was formed 

beyond the terminus of the ice, occurs as benches or terraces above 

the present stream levels. In some localities, as on the Chulitna 

River, these benches lie several hundred feet above the present river 

and generally slope gently toward the center of the valley and 

downstream.

RECENT DEPOSITS

As all the major streams have their sources in glaciers, they carry 

large amounts of -gravel, sand, and silt and gradually deposit it 

downstream. This outwash material is coarsest near the glaciers, 

and becomes progressively finer downstream, as a result of the 

decrease in gradient and therefore in velocity. The Chulitna, 

Tokichitna, Hidden, Coffee, and Ruth Rivers all have wide flood 

plains, which are composed of these recent deposits of sand, gravel, 

and silt. Another type of recent deposits is the slide rock or talus 

formed from the disintegration of the rocks on steep slopes and its 

downward movement by gravity. These deposits are unimportant 

in the low country but are common and in places of considerable 

extent in the higher country.

IGNEOUS ROCKS

Distribution and character. The distribution of the igneous rocks 

is shown on plate 1. They constitute most of the rock outcrops in 

the district, forming a part of the ridge east of the Chulitna River, 

as well as a large part of the west wall of the Chulitna Valley, and 

extending almost continuously to the top of Mount McKinley. The 

south face of the mountain is composed of granite, and the contact 

of this rock with the sedimentary series probably strikes between 

the north and south peaks, as from a distance of a few miles it is 

plainly evident that the north peak is composed of sedimentary 

rocks. In addition to these major masses of igneous rock, small 

isolated masses or stocks occur as intrusives into the metamorphosed 

sedimentary series. A few such smaller masses are found on Crys-
128 MINERAL EESOUECES OF ALASKA, 1932

tal and Cloud Creeks, on the north side of Buckskin Glacier, and on 

the Chulitna River at the cable crossing near the mouth of Coal 

Creek.

In detail the margin of the intrusive igneous rock is not always as 

smooth as it is depicted on the geologic map; instead it is in places 

very irregular, with dikes and sills ramifying into the surrounding 

sediments, but these smaller features cannot be shown on a map of 

this scale. On plate 1 the contact has been drawn at the margin of 

the major mass of the igneous rock. The west margin of the intrusive that forms the mass immediately west of the Chulitna River is 

irregular in detail yet in general follows the strike of the adjoining 

sedimentary rocks. Farther west the eastern margin of the main 

batholith that extends to Mount McKinley is comparatively straight 

and vertical, with but few branching dikes, and it also follows in 

general the strike of the intruded rock. It is highly probable that 

locally the intrusion has been controlled by the regional structure 

of the metamorphosed sedimentary rocks. The igneous mass that 

forms the ridge between the Chulitna and Susitna Rivers also suggests the local structural control of the intrusion, for it follows the 

regional strike of the metamorphosed sediments. At other localities 

the intrusive rock cuts directly across the sediments.

Granite and granodiorite form the greater part of the intrusive 

igneous masses. Generally they are medium to coarse grained, and 

the individual minerals can easily be seen with the naked eye. Here 

and there porphyritic varieties contain feldspar crystals several 

inches in length. The predominance of feldspar and quartz gives 

the rock a light-gray to cream color. Upon weathering, which in 

this district is largely mechanical, owing to extreme changes in 

temperature, the granitic rocks break down into coarse granular 

sand of feldspar and quartz, with bronze-colored flakes of bleached 

biotite. The weathering of the granite also results in a characteristic rugged topography of sheer cliffs and pinnacles.

Microscopically the granodiorite is composed of quartz, feldspar, 

and biotite. In places it contains such accessory minerals as hornblende, zircon, and tourmaline. The commonest feldspar is albite, 

but orthoclase may also be present. Microcline is developed in places 

along the margin of the intrusive. Zonal growth of feldspar is 

common.

Although the intrusive is largely acidic that is, it contains a high 

percentage of silica, as is shown by the quartz, albite, and orthoclase there are more basic phases. On the ridge between the 

Coffee River and Slide Creek a basic differentiate, a diorite porphyry, 

is composed largely of andesine with some pyroxene that has altered 

to chlorite, epidote, and biotite. Small basaltic dikes cut the granite
THE CURRY DISTRICT 129

as well as the sedimentary rocks. These dikes are fine-grained and 

are composed of labradorite, pyroxene, and magnetite. Such secondary minerals as epidote, calcite, and chlorite are present. The 

acidic dike rocks and sills, offshoots of the batholith, are very abundant in the sedimentary rocks but have not been mapped separately. 

They are essentially of the same composition as the parent rock but 

are usually finer-grained.

The coarse texture of the intrusive rocks suggests that they crystallized at a considerable depth below the surface. Later erosion 

has stripped off much of the overlying rock, exposing the granite. 

The similarity in chemical composition indicates that the isolated 

masses of granite are connected with one another beneath the surface, and that the bands of sediments are roof pendants of the 

batholith and if removed would show granite underneath. There is 

little evidence of extensive hydrothermal alteration in the intrusive 

rock, though some of the feldspars are partly altered to sericite, 

paragonite, and kaolin by weathering.

Structwre. The intrusive igneous rocks are generally massive. 

In places sets of widely spaced joints have been developed, but shearing and gneissic structure are absent. The presence of vertical jointing in the granite has contributed to the development of sheer cliffs 

by erosion. In some localities, such as the ridge between the Coffee 

River and Slide Creek, a combination of vertical joints and sheeting 

that dips 20° S. has produced several northward-facing escarpments. 

Faults have not been observed, and if present they would be difficult 

to detect in a rock so uniform in character as the intrusive.

Age and correlation. The precise determination of the age of the 

intrusives in the Curry district as well as in adjacent districts is of 

great economic importance, for some of these igneous rocks have 

been the means by which the valuable minerals have been brought 

into the region. Geologic work in the future may show that only 

intrusives of a certain age or ages have been the cause of the introduction of valuable mineral deposits, so that intrusives of a later age 

would be barren of valuable minerals. These facts would greatly 

facilitate prospecting and development work, for areas underlain by 

postmineral intrusives could be eliminated from consideration in the 

search for ore deposits.

During the present investigation definite evidence as to the age 

of the igneous intrusions was not found. They are intrusive into 

the slate, graywacke, and schist series and are thus younger, but the 

age of the metamorphosed sediments is not definitely known, although they may be Cretaceous in part. As the intrusives have suffered little or no deformation and even the dikes that extend from 

the main igneous mass are undeformed, it is apparent that the
130 MINERAL EESOUECES OF ALASKA, 1932

granite was intruded after the folding of the sediments had been 

completed, or as the very last phase of the regional metamorphism. 

The igneous rocks were not found to intrude the Eocene coal-bearing 

series. It therefore appears that they were intruded after the deposition and folding of the metamorphosed sediments and before the. 

deposition of the coal-bearing series and thus may be of. late Mesozoic 

or early Eocene age.

Correlation with similar intrusives in adjacent districts throws, 

some light on the age of the intrusives in this district. Rocks of 

granitic character form a large part of the Alaska Range, extending 

from Iliamna Lake to and beyond Broad Pass and making up the 

major part of the Talkeetna Mountains. In all of this area the intrusive rocks are similar to those in this district that is, they are 

predominantly acidic,, with granite and granodiorite prevailing. 

Whether or not they all represent parts of the same intrusion has not 

been determined, bat they are evidently from a common underlying 

source.

In the past determinations of the age of the granites of the Alaska 

Range and of south-central Alaska have usually been based on correlation with similar intrusives in the eastern part of the Talkeetna 

Mountains and in the Iliamna district. In the Talkeetna Mountains 37 quartz diorite intrudes lower Middle Jurassic formations,, 

and granitic material is abundant in Upper Jurassic conglomerates; 

hence it is inferred that the intrusions are of Middle to Upper Jurassic age. In the Iliamna district 38 granitic rocks cut Lower 

Jurassic rocks but are not known to intrude Middle Jurassic formations. Furthermore, the Upper Jurassic conglomerates contain 

granitic material, and the conclusion is that at least some of the 

granitic rocks are Lower or Middle Jurassic. As a result of these 

determinations it has generally been assumed that a large part of 

the intrusions of the Alaska Range and south-central Alaska are 

Jurassic. Later work, however, indicates that at least a part of the 

intrusions are younger.

South of the Tokichitna River Capps 39 found granitic rocks 

that can be traced into this district. The evidence in that area 

indicates that the granites are later than the period of metamorphism 

of the sediments they intrude and are older than the coal-bearing 

Tertiary beds. With this evidence, and on the basis of correlation 

with similar intrusives in the Iliamna and Talkeetna regions, Capps 

provisionally assigned the granites to the Lower or Middle Jurassic.

37 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and. 

Falkeetna Basins, Alaska: U.S. Geol. Survey Bull. 327, pp. 19-20, 1907.

88 Martin, G. C., and Katz, p. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U.S. Geol. Survey Bull. 485, pp. 74-77, 1912.

80 Capps, S. R,, The Yentna district, Alaska : U.S. Geol. Survey Bull. 534, pp. 45-47, 

3913.
THE CURRY DISTRICT 131

At a later date, in the Skwentna region, which lies directly south of 

the Yentna district, Capps 40 found a continuation of the granites. 

There they intrude formations that contain plant remains of late 

Upper Cretaceous or early Eocene age, and inasmuch as they do 

not intrude the coal-bearing series he concluded that they are probably late Cretaceous or early Eocene.

Brooks 41 mapped similar granites on the north slopes of Mounts 

McKinley, Foraker, and Russell. He states that the granites of the 

Alaska Range are in part Middle Jurassic but suggests the possibility of an Upper Cretaceous age. The granites forming parts of 

Mounts McKinley, Foraker, and Russell are probably a part of the 

same granitic batholith that occurs in the Curry, Yentna, and 

Skwentna regions, as the granite strikes uninterruptedly across the 

range.

On the east side of Broad Pass Moffit and Pogue 42 mapped many 

of the granites as Tertiary, inasmuch as they intrude Eocene sediments. They also recognized the possibility of a succession of 

intrusions ranging from Jurassic on into the Tertiary. In the area 

drained by the West Fork of the Chulitna both Capps 43 and 

Ross 44 recognized the possibility of a Tertiary age for some of 

the granite intrusions. Capps 45 believes that many of the granitic 

rocks in the eastern part of Mount McKinley National Park are 

Eocene, inasmuch as they cut the Cantwell formation, which is 

believed to be early Eocene.

The more recent work on the slate and graywacke series has indicated that parts of it are probably Cretaceous. It is apparent that, 

if this determination is correct, much of the granite of the Alaska 

Range is late Cretaceous or early Eocene. The granite that forms 

the ridge between the Susitna and Chulitna Rivers may be of the 

same period, and the lithologic similarity of the batholith of the 

Talkeetna Mountains further suggests that it also may be late Mesozoic or early Tertiary.

INFLUENCE OF ROCK TYPE ON TOPOGRAPHY

Although the topography has been modified by active glaciation, 

the underlying rock has had a profound influence on the detail of the

40 Capps, S. R., The Skwentna region, Alaska: U.S. Geol. Survey Bull. 797, pp. 88-90, 

1929.

"Brooks, A. H., The Mount McKinley region, Alaska: U.S. Geol. Survey Prof. Paper 70, 

p. 52, 1911.

^Mofflt, F. H., and Pogue, J. E., The Broad Pass region, Alaska: U.S. Geol. Survey 

Bull. 608, p. 59, 1915.

43 Capps, S. R., Mineral resources of the upper Chulitna region: U.S. Geol. Survey Bull. 

692, pp. 220-221, 1919.

44 Ross, C. P., Mineral deposits near the West Pork of the Chulitna River: U.S. Geol. 

Survey Bull. 849-E, 1933.

45 Capps, S. R., The eastern portion of Mount McKinley National Park: U.S. Geol. Survey Bull. 836, pp. 284-286, 1932.
132 MINERAL RESOURCES OP ALASKA, 1932

surface features. The rocks that crop out in the district can be 

divided into two broad classes granite and metamorphosed sediments. Almost invariably the granitic areas show pointed peaks, 

sheer slopes, sharp divides, and pinnacles on the slopes and summits. 

In contrast the areas underlain by the metamorphosed sediments exhibit smoother and less precipitous slopes and summits and broad, 

low divides. This is largely a result of the relative difference in 

resistance that the granite and sediments offer to weathering and 

erosion. (See pi. 3.)

This topographic expression of the rock type greatly .facilitates 

the geologic mapping and prospecting, as from a high point the contact between the granite and the sediments can be followed with the 

eye for miles. In addition to the difference in topography, the 

granite is cream-colored and the sediments are gray to black; and 

as the area is largely above timber line and therefore has little 

vegetation, this color difference greatly aids any reconnaissance 

mapping.

At lower elevations the surface expression of the type of rock has 

been modified to a greater extent by glaciation. The parts of the 

granitic slopes that have been overridden by the glaciers have been 

smoothed off and, where overgrown with vegetation, resemble the 

slopes underlain by the metamorphosed sediments. The ridge lying 

between the Susitna and Chulitna Kivers is partly granite, yet it 

exhibits smooth features, for, lying between elevations of 2,000 and 

3,000 feet, it was completely covered by ice and therefore severely 

glaciated.

GLACIATION 

HISTORY

Climatic changes during Pleistocene time that included an increased annual snowfall causecl the gradual accumulation of ice in 

the Alaska Range. As this ice increased in thickness to thousands 

of feet, it took the paths of least resistance the then existing valleys and slowly moved down them. As the ice flowed, it picked 

up rock fragments, and with these as tools it ground and eroded the 

country over which it moved. Thus many ice tongues, moving 

down separate tributary valleys, coalesced in the main valleys and 

so formed great, many-branching ice streams. The glacier that 

moved down the Chulitna Valley was joined by ice masses from Eldridge, Hidden River, Coffee River, Ruth, and Tokichitna Glaciers. 

Ultimately the Chulitna ice stream joined a similar one in the 

Susitna Valley at the present site of Talkeetna and formed a single 

mighty ice tongue that moved down into Cook Inlet. At places the 

ice attained a thickness of 3,000 feet, so that the ridges and hills 

were covered partly or completely.
THE CUBBY DISTBICT 133

At the end of Pleistocene time another change in climate occurred, 

possibly brought about by a lowering of the elevation by a sinking 

of the land mass, a decrease in precipitation, or other causes, with the 

result that the ice ceased to form in excess of melting, and gradually 

the ice tongues retreated by melting at their fronts. As the ice had 

been carrying a large amount of rock debris, the melting released it 

as morainal material. Much of it was transported by water from 

the melting ice and redeposited as glacial outwash or bench gravel in 

the valleys. As the ice retreated the land so bared showed a topography that had been, modified from the one that existed prior to 

glaciation. The preglacial valleys had been V-shaped in cross section, with interlocking spurs and many sharp ridges. As a result 

of glaciation the valleys had been straightened by the truncation 

of spurs and the overdeepening of the valley bottom and given a 

U-shaped cross section. Many of the tributary valleys were left 

hanging. The general effect in the lower regions was to smooth off 

the topography, and ridges that had been overridden now showed 

smooth, rolling tops. A large part of the ridge lying east of the 

Chulitna River had been so glaciated. Glaciation not only smoothed 

and polished the tops of many of the ridges but left numerous large 

erratics or boulders that are foreign to the country rock. In the 

areas of great relief, such as that lying west of the Chulitna, many 

of the ridges and peaks, although they were the gathering grounds 

for the ice that formed the glaciers, were never covered by moving 

ice and do not exhibit smooth, round, glaciated surfaces. Nevertheless, the ice in many places undercut and plucked these slopes, 

leaving sharp ridges and rounded amphitheaterlike basins (cirques).

The upper limit of glaciation depended on the thickness of ice and 

the height and relief of the surface and is therefore extremely variable in the Curry district. In the Susitna and Chulitna Valleys 

it attained elevations of 3,500 to 4,000 feet or more. West of the 

Chulitna River, toward the summit of the Alaska Range, it reached 

a much greater elevation, and on Mount McKinley it was over 

19,000 feet.

PRESENT GLACIERS

All the larger glaciers in the district originate in the snow fields 

on or near the slopes of Mount McKinley and extend radially outward. There are four large glaciers Eldridge, Buckskin, Ruth, 

and Tokichitna and almost innumerable small tributary and 

hanging glaciers.

Eldridge Glacier has a length of about 35 miles and is about 2^ 

miles wide at its terminus. Ten miles above its lower end it forks, 

the main part heading to the west, near the foot of Mount McKinley, 

and two branches heading to the north, against the Alaska Range
134 MINERAL RESOURCES OF ALASKA, 1932

northeast of Mount McKinley. The lower 10 miles of the glacier is 

covered with moraine, and the ice is exposed only on the margins 

where it is cut by streams or in fissures extending through the 

moraine. The moraine of Eldridge Glacier differs from that of 

the other major glaciers in that it does not support any vegetation. 

This lack of vegetation suggests that in recent times glacial movement has been active, although the glacier front may not have 

advanced, melting a,t the front having kept pace with or exceeded 

the forward movement. No terminal moraine exists beyond the 

front of the glacier, and apparently the volume of water from the 

melting ice has been sufficient to remove the morainal material as 

fast as it accumulated. Old lateral moraines are found several 

hundred feet above the present glacier on its north side along 

Partin Creek, and some of them are completely covered with vegetation. They are relics of the time when Eldridge Glacier was 

much larger than it is at present.

Buckskin Glacier has a sinuous course of about 15 miles from a 

source close to the east side of Mount McKinley. (See pi. 4.) It is 

about a mile wide at its lower end. About 10 miles from its 

terminus a branch joins it at a right angle from the north and northeast, and at its head, a short distance farther west, only a low saddle 

separates it from the upper part of Ruth Glacier. Its lower 3 or 

4 miles is covered with a moraine of cream-colored granite, from 

the color of which the glacier derives its name. A terminal moraine 

at its front is covered with vegetation, which suggests a stable condition of equilibrium at the present time. For a distance of 3 or 4 

miles below the terminus the valley bottom is covered with ground 

moraine which the Hidden River has not yet been able to remove. 

It is probable that before it reached the present stable condition 

the glacier retreated very rapidly and so left this accumulation of 

ground moraine unremoved by the draining stream.

Ruth Glacier is the largest one on the southeast side of Mount 

McKinley. Originating near the base of the mountain, it winds 

its way to the southeast for a distance of about 30 miles and is 4 

miles wide at its front. The lower 6 miles is covered with moraine, 

and of this moraine the lower 2 miles carries a thick growth of 

vegetation with spruce and birch 2 feet in diameter not unusual. 

It is thus apparent that the glacier beneath this moraine has been 

stagnant long enough for soil to form and trees to grow to such a 

size.

Tokichitna Glacier, which has already been described by Capps,48 

is formed by the union of two glaciers, the larger of which appears 

to head on the east side of Mount Hunter and probably also on the

46 Capps, S. R., The Yentna district, Alaska: U.S. Geol. Surrey Bull. 534, p. 42, 1913.
THE CURRY DISTRICT 135

south slope of Mount McKinley. The lower 6 miles of the glacier 

is covered with moraine. Large spruce trees directly below the terminus indicate that its front is now as far advanced as it has been 

for many years.

The glaciers of this district have many common characteristics, 

but in spite of these similarities there are differences that must be 

due to different conditions in their respective feeding basins.

The accumulation of large amounts of moraine on the lower portions of all the major glaciers is due to two factors (a) the falling 

of debris upon the ice and its transportation downward by slow 

movement at a period when the glacier is active or advancing; (Z>) 

in conjunction with this a melting at the front of the glacier, so 

that although the ice itself is advancing the front of the glacier may 

be retreating, stationary, or advancing more slowly than the movement of the ice. As a result of the interrelations of these two factors 

the amount of moraine on the different glaciers varies. Eldridge 

Glacier has the greatest amount, its lower 10 miles being morainecovered, thus indicating that there has been a heavy supply of 

detrital material in the upper basin of the glacier.

On three of the glaciers considerable amounts of vegetation cover 

the moraine which overlies the ice, indicating that recently the ice 

front has remained nearly stationery. Eldridge Glacier has no vegetation on its moraine and so appears to have been recently more 

active than any of the other glaciers.

Only one glacier, Buckskin, has marked deposits of moraine below 

the present ice front. In view of the fact that the size of the stream 

as compared with the size of the valley is practically the same for 

all the glaciers, it is probable that Buckskin Glacier, before its recent 

state of stability was reached, had retreated rather rapidly for 2 

or 3 miles and that the Hidden River has been unable to keep pace 

with it in removing the debris.

ECONOMIC GEOLOGY °

None of the mineral resources of the Curry district have been 

developed or even thoroughly examined. The inaccessibility of 

parts of the district has no doubt contributed largely to this lack 

of development, although there are large areas that appear unfavorable for future prospecting. Undoubtedly large parts of the 

more accessible sections of this country were scrutinized for mineral 

deposits, particularly for gold placers, in that period of successive 

gold discoveries from 1898 to 1910, but no record of this work is 

known, and it is probable that the region was quickly passed by for 

more favorable prospecting ground.

Since 1915 eight or ten parties have prospected in the region, most 

of these during the last 5 years. The known mineral discoveries are
136 MINEBAL EESOUECES OF ALASKA, 1932

few. In 1915 Gene Bartholf found some rich quartz float on the 

upper part of Whistler Creek. Since then several efforts to find the 

bedrock source from which the float came have failed. In 1929 Roy 

and Elmer Boedeker found gold quartz veins on the north side of the 

Hidden River, and since that date they have attempted to develop 

these veins. Other small quartz veins have been located, but superficial examination of them has failed to "disclose any value worthy 

of note.

Owing to the small amount of actual development work that has 

been done, this discussion of the mineral resources will be chiefly 

confined to suggestions as to what appear to be the more favorable 

areas for lode prospecting, although in a reconnaissance examination of this type there is' danger that such observations may lead to 

conclusions that in the light of more detailed work will require 

modification. It must therefore be kept in mind that many of 

the following statements are to be regarded as suggestive and not 

conclusive.

In addition to the lode prospecting, some placer prospecting has 

been done. There has been no notable placer production, however, 

and it is extremely doubtful if economically important placer concentrations occur in the district. Prospecting in the past has shown 

that gold exists in some of the gravel, but this gravel is very meager 

in extent and low in value. It is reported that some gold has been 

taken periodically from the bars of the Chulitna River, but that it 

was surficial and did not go down into the underlying sand and 

gravel, so that it afforded opportunity for only small operations.

LODE PROSPECTING

In a general way there are two major formations in the district 

(a) a series of highly folded and faulted metamorphosed sediments, 

(5) phases of a granitic batholith that is intrusive into these 

sediments.

The granite, which underlies the greater part of the area and 

extends from the Chulitna River in an almost unbroken belt to 

Mount McKinley and also forms a part of the ridge between the 

Susitna and Chulitna Rivers (see pi. 1), is not known to be mineralized. Where exposed the granite, with the exception of a few joints, 

is invariably massive. Even minor faults are uncommon, and 

neither gneissic nor schistose phases were observed, all of which 

indicates that, in the area examined, the granite has suffered but 

little deformation and that structural features suitable for ore deposition are few. Moreover, little evidence of hydrothermal alteration was seen. As granites are susceptible to alteration, evidences 

of hydrothermal alteration would suggest the likelihood of the presence at one time of ore-bearing solutions. Pannings from the small
THE CURRY DISTRICT 137

streams draining ^ nly granitic areas ordinarily do not yield any 

colors of gold, whereas pannings from streams that drain areas underlain by the metamorphosed sediments usually yield a few fine 

colors.

All the evidence above set forth suggests that the granite in the 

western part of the area is in general unfavorable for prospecting. 

However, in view of the fact that mineral deposits occur in granite 

in the Talkeetna Mountains and other localities and that granitic 

intrusives are believed to have been the cause of mineralization in 

a great number of districts, the evidence so far discovered in the 

Curry district cannot be considered conclusive. The gold quartz 

veins in the Willow Creek district are in granite which is a part 

of the Talkeetna Mountain batholith, and although this granite 

shows greater deformation than that in the Curry district, there is 

as yet no conclusive evidence that it is of different age. The difference in the degree of deformation could be explained as a result 

of local conditions, for even the Tertiary coal beds adjacent to the 

Willow Creek district show considerable deformation, whereas the 

coal-bearing formations in the vicinity of Ruth Glacier, which are 

probably of the same age, are comparatively undisturbed.

The contact of the intrusive rock, which is in many districts a 

favorable prospecting ground, did not indicate strong mineralization in the area examined, the chief effect of the intrusive being to 

silicify the invaded rock. Most of the veins appeared to be several 

thousand feet from the granite contact.

The area underlain by the metamorphosed sediments appears to 

be more favorable prospecting ground than the granite. The discoveries so far made have been in this formation, which has been 

highly deformed and so offers the possibility of providing structural features suitable for the deposition of minerals in commercial 

quantity. Usually the sand and gravel of streams draining the area 

underlain by the metamorphosed sediments yield at least a few 

colors of gold and so indicate that there has been some mineralization in the sediments themselves.

As the south-central and western portions of the district are predominantly granite, with only a few small belts of slate and graywacke, it is probable that most of the more favorable prospecting 

ground occurs in the area that lies north of the Hidden River, 

where the granitic outcrops are subordinate in amount to the metamorphosed sediments. However, one discovery of rich gold quartz 

float has already been noted in the southern part of the district, on 

Whistler Creek, and quartz veins are numerous in the metamorphosed sediments between the Coffee and Hidden Rivers.

North of the Curry district, in the basin of the West Fork of the 

Chulitna, there is a series of mineralized tuff, lava, chert, and ar-
138 MINERAL RESOURCES OF ALASKA, 1932

gillite that has been described by Capps 47 and Koss.48 Several 

prospects of merit are located in this belt of base-ore mineralization, 

which also contains, in some places, high values in gold. As the 

district here described is on the continuation of the strike of these-: 

same rocks, it was thought that a continuation of this belt of mineralization might be found. The field work has proved that it does 

not continue any farther south than Eldridge Glacier, in the vicinity 

of which it apparently lenses out.

The area in the vicinity of Eldridge Glacier and the Hidden 

River seems to offer the most encouragement for prospecting, for 

the metamorphosed sediments are much more abundant there than 

farther south. Several small but rich veins carrying free gold have 

been found, and strong fissure veins, which so far have not 'beetn 

found to contain metals in commercial amounts, are known to 

exist close by. In the vicinity of Eldridge Glacier many small 

veinlets carrying pyrite, pyrrhotite, chalcopyrite, and sphalerite 

were found. It has1 also been reported that galena float occurs on 

the moraine of the glacier, about 10 miles north of its front.

BOEDEKER CLAIMS

The only known prospects on which any development of gold 

lodes has so far been done are the Boedeker claims nos. 1 and 2, 

located and held jointly by Roy and Elmer Boedeker. The claims 

are on the north side of the Hidden River a short distance east of 

Swift Creek, at an elevation of 4,000 feet, or about 2,800 feet above 

the floor of the Hidden River Valley. The discovery was made in 

the fall of 1929, and the development work was done in 1931 and 1932. 

The developments consist of several open cuts, a 30-foot tunnel 

which was driven a few feet below several small flat-lying veins, 

and several open cuts on a large vein that lies about 100 feet down 

the hill from the small veins.

As the slope of the hill at this point is about 35°, there is a large 

amount of surface creep. Snow and rock slides have caused the 

caving of many of the pits soon after they were opened up and have 

also given false inclinations to the veins and country rock, so that 

in many places it is difficult to ascertain the true geologic conditions. 

The country rock consists of foliated slate and fine-grained schist, 

graywacke, and argillite that locally have variable attitudes but in 

general strike N. 30° E. and are vertical. Numerous veins cross the 

structure of the country rock. One group consists of several small 

irregular veins that strike N. 20° W. and lie flat or locally dip

47 Capps, S. R., Mineral resources of the upper Chulitna region : U.S. Geol. Survey Bull. 

692, pp. 216-217, 1919 ; The eastern portion of Mount McKinley National Park: U.S. 

Geol. Survey Bull. 836, pp. 257-260, 1932.

^Ross. C. P., op. cit. (Bull. 849-E).
THE CURRY DISTRICT 139

10°-20° W. They range in width from 2 to 10 inches, and none of 

them are persistent for more than 100 feet. The vein material consists of quartz that is tightly " frozen " to the graywacke walls. In 

addition to the quartz there is a very small amount of fine disseminated pyrite, a few flakes of sericite and galena, and considerable 

free gold. The gold in the veins is erratically distributed, barren 

places alternating with exceedingly rich spots.

About 60 feet vertically below the small veins, there is a large 

vein which has a strike similar to that of the small veins (N. 20° 

W.) but which dips about 70° E. This vein can be traced along 

its strike for over 800 feet and has a width of 3 to 12 feet. In the 

pit below the tunnel the vein walls are well defined and the quartz is 

separated from the country rock by seams of gouge. The vein is 

predominantly quartz, but it includes some gouge and several small 

sLate horses, which suggest a postvein. movement. The quartz at the 

surface is stained with limonite and appears to be identical with 

that in the small rich veins above, but the large vein does not carry 

any ore. Small amounts of finely disseminated pyrite and arsenopyrite can occasionally be seen in the vein material. Six samples 

taken at the most favorable places along the large vein assayed only 

traces of gold and silver.

To the northwest the large vein disappears under a cover of 

slide rock, but before that point is reached the vein material is but 

little iron-stained and the quartz loses its similarity to that in the 

small veins and appears barren. To the southeast the large vein 

apparently pinches out, as it cannot be located on a small ridge 

that offers good exposures. At several points along the large vein 

there are small offshoot veins extending up the hill in a manner 

similar to that of the small rich vein already described and seeming 

to have similar relationships. However, little indication of valuable 

minerals in these small offshoot veins has been found.

It is probable that there is a relationship between the small gold 

quartz veins and the large fissure vein directly adjacent to them, for 

their proximity and the similarity in strike and in the nature of 

the vein material are strongly suggestive of a close genetic association. If they are genetically the same, it is possible that further 

development on the large vein might disclose ore shoots of value.

The veins so far found that carry free gold are too small in extent 

and number to wrarrant successful mining, although if they were 

more accessible, it is highly probable that some gold could be profitably extracted from them.

COAL

Lignitic coal of poor to medium grade occurs in the district. Outcrops and coal float have been found at several localities, notably 

on Little Coal Creek, Alder Creek, and Bluff Creek (on the south side
140 MINERAL RESOURCES OF ALASKA, 1932

of Kuth Glacier). The lignite is dark brown to black, light in 

weight, and very woody and disintegrates quickly on exposure to 

the weather. It is probably of little value except for local use. 

As there have been no attempts at opening up any of it, all the material seen was badly weathered. The best outcrops occur on Bluff 

Creek, where about a dozen beds, ranging in thickness from a few 

inches to 6 feet, were seen in a 200-foot section. The section showed 

that the beds were lenticular. An analysis of an air-dried sample 

of the woody lignite, by M. L. Sharp, Bureau of Mines, Anchorage, 

Alaska, is as follows:

Moisture_________________________________ 14.10

Volatile matter_________________________ 45. 76

Fixed carbon_:____________________________ 33. 54

Ash ___________________________________ 6. 60

Sulphur________________________________ . 05

100. 05 

British thermal units_______________________ 9, 210

CONCLUSIONS

The immediate future of the Curry district seems to rest entirely 

on the possible development of its gold lode deposits. Under present 

economic conditions, largely because of the prevailing low prices 

of metals and the difficulties of transportation from the district to 

the railroad, it is doubtful whether even if base-metal deposits should 

be found in the district, unless they were of unusual richness and 

size, they could be profitably worked. However, some galena float 

has been found in the northern part of the district, and it might be 

worth while to ascertain the site and extent of the deposit from which

it came.

The gold prospects so far discovered are 20 miles from the railroad, yet gold deposits if of sufficient size and richness can be worked 

in almost any locality, and inasmuch as gold is known to be present, 

it would appear that further prospecting is justified, particularly 

in the northern part of the district and around the margin of the 

granite intrusive.

The present trail and tram across the Chulitna Eiver, though sufficient for prospecting, would be inadequate for any larger developments, and the cost of building a serviceable road and bridges 

across the Chulitna and Fountain Rivers is not justified at present. 

Heavy freight foi^.. prospecting and developing mining properties 

can be moved into the district more cheaply by sled in winter than 

by any means in summer; a.nd until more promising properties are 

discovered that would appear to be the logical way of bringing in 

supplies.

O