M

M

Geologic Investigations 

of Proposed Powersites 

at Sheep Creek, Carlson 

Creek, and Turner Lake, 

Alaska

GEOLOGICAL SURVEY BULLETIN 1031-F

Geologic Investigations 

of Proposed Powersites 

at Sheep Creek, Carlson 

Creek, and Turner Lake, 

Alaska

By GEORGE PLAFKER

GEOLOGY OF WATERPOWER SITES IN ALASKA

GEOLOGICAL SURVEY BULLETIN 1031-F

A description of the proposed 

reservoir, dam, and tunnel sites 

at each power site, with 

conclusions and recommendations

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D.C.
CONTENTS

Page

Abstract___.________________________________________________ 127

Introduction._____________________________________________________ 128

Present investigation_________________________________________ 128

Previous investigations.________________________________________ 128

Geography, _ _ ________________________________________________ 130

Regional geology.______.._-____________---______-_-_-____---------- 131

Bedrock______________________________________________________ 131

Unconsolidated deposits___________-__-____-________-__--_-__--- 133

Earthquakes._________________________________________________ 133

Sheep Creek._____________________________________________________ 134

Reservoir site-_______-_______.________-__-________-___--_____-- 134

Damsite- _ ____________________________________________________ 135

Powerhouse site _______________________________________________ 136

Diversion alinement_ _-_____-______-_____-_-___________--__---_ 136

Conclusions and recommendations-_-_-____-___-__---__---------- 136

Carlson Creek___________________________________________________ 138

Reservoir site_________________________________________________ 139

Damsite-__________________________._______________ 140

Powerhouse site_______________________________________________ 141

Tunnel route________________________________________________ 141

Conclusions and recommendations,____________-_________-----_-- 141

Turner Lake__-______________________________-_____-_--___----_-_- 143

Reservoir site___________________________________----_-_-----_ 144

Damsite ________ _ ___________________________________________ 145

Conclusions and recommendations__________________--____---___- 146

References cited-_-_---___-__-_-_______-_________________-_-_-_-- 148

ILLUSTKATIONS

[Plates in pocket]

PLATE 10. Geologic maps and sections of proposed powersite at Sheep Creek.

11. Geologic maps and sections of proposed powersite at Carlson Creek.

12. Geologic maps and section of proposed powersite at Turner Lake.

Page

FIGURE 24. Generalized geologic map of the Juneau, Taku Inlet area, 

Alaska, showing regional setting of the proposed powersites.__-_--______-_______._________________ 129

25. Aerial view of part of Carlson Creek valley-_______________ 139

26. Aerial view of lower end of Turner Lake______-___-__---- 144

in

GEOLOGY OF WATERPOWER SITES IN ALASKA

GEOLOGIC INVESTIGATIONS OF PROPOSED POWERSITES

AT SHEEP GREEK, GARLSON GREEK, AND TURNER

LAKE, ALASKA

BY GEORGE PLAFKER

ABSTRACT

Geologic conditions have been investigated at proposed sites for hydroelectric 

power development at Sheep Creek, Carlson Creek, and Turner Lake. The proposed sites are on the rugged mainland of southeastern Alaska along Gastineau 

Channel and Taku Inlet near Juneau. Bedrock in the area consists of a coastal 

strip of northwestward-trending foliated metamorphic rocks with steep northeasterly dips. This belt of rocks is adjacent to the Coast Range batholith on the 

northeast, and between the main batholith and the metamorphic rocks is a zone, 

2 to 3 miles wide, of injection gneiss. Unconsolidated glacial and postglacial 

deposits of Quaternary age mantle the bedrock over large parts of the area. 

The valleys of Sheep and Carlson Creeks have been modified by glaciers of Pleistocene age, and Turner Lake occupies a rock basin formed by glacial scour.

There is an excellent site in greenstone bedrock at Sheep Creek for either a 

concrete or a rock-fill dam. A conduit from the dam to a powerhouse along 

Gastineau Channel would be on bedrock for most of the distance. Slate bedrock 

suitable for a powerhouse site is exposed near the mouth of Sheep Creek. To 

the northwest along Gastineau Channel, bedrock is concealed by a mantle of 

glacial deposits of unknown thickness. The reservoir is in virtually impermeable 

bedrock; however, a main haulage adit of the Alaska-Juneau gold mine would 

probably have to be sealed off to prevent flooding of the mine workings or 

possible loss of water from the reservoir.

The dam, diversion tunnel, and powerhouse at Carlson Creek would all be 

fresh injection gneiss bedrock. This rock is well suited as the foundation of a 

concrete or rock-fill dam, but foundation treatment would be required to seal 

off closely spaced open joints trending perpendicular to the proposed dam axis. 

The diversion tunnel would stand unsupported except possibly where it would 

intersect two zones of closely spaced joints. The reservoir would be in virtually 

impermeable bedrock.

Both the main dam and auxiliary structure at Turner Lake would be on an 

excellent foundation of granitic rock (granodiorite). Loose landslide debris 

would have to be removed at the damsite to expose fresh, sound bedrock. There 

is a powerhouse site in bedrock along Turner Creek at a stream altitude of 

16 feet. Foundation conditions for a powerhouse at tidewater, near the mouth

127
128 GEOLOGY OF WATERPOWER SITES IN ALASKA

of Turner Creek were not studied. The conduit would be on sound granitic 

rock throughout its length, and the reservoir is entirely in relatively tight granitic 

bedrock.

INTRODUCTION

PRESENT INVESTIGATION

The present investigation was undertaken in furtherance of the 

Geological Survey's program for systematic study and evaluation of 

potential waterpower sites in Alaska. A reconnaissance study of the 

geology at the three powersites described in this report was made 

during the period from August 22 to September 5, 1954. Base maps 

used were prepared by the Conservation Division of the U.S. Geological Survey except for the map of the Turner Lake reservoir site, 

which is from the Taku River (B-6) quadrangle, Alaska. The 

topography in the vicinity of the tunnel alinement at Carlson Creek 

was modified from the Juneau (B-l) quadrangle, Alaska. The entire 

area is covered by vertical aerial photographs taken by the U.S. Navy 

at a scale of approximately 1: 40,000.

PREVIOUS INVESTIGATIONS

The geology of the area under consideration was the subject of 

intermittent study, both regional and local in nature, after discovery 

of gold in 1880 near the present site of Juneau. The entire Juneau 

gold belt, extending from Port Houghton on the south and northwestward to the boundary of British Columbia, was mapped at reconnaissance scale by Spencer and Wright (1906). Buddington and 

Chapin (1929) extended this regional study to include most of southeastern Alaska. Detailed surface mapping in the Juneau area has 

been largely restricted to the "Juneau and Vicinity 1: 24,000" special 

topographic map, which includes most of Sheep Creek basin and 

parts of the Sheep Fork and Salmon Fork of Carlson Creek (see fig. 

24). Spencer and Eakin (Eakin, H. M., 1922, unpublished data) 

mapped this area at a scale of 1:24,000 and subdivided and named 

the formations described in this report. Subsequent detailed surface 

mapping in the area by Twenhofel (1952), Sainsbury (1953), and 

Barker (written communication, 1954), was directed primarily toward 

completion of unmapped portions of the "Juneau and Vicinity" special map, and refinement of Spencer and Eakin's earlier work. In 

connection with his study on the correlation of the Mesozoic stratigraphy of Alaska, Martin (1926) assigned tentative ages to the formations in the Juneau area, which are followed in this report. No 

previous detailed mapping is known in the vicinity of the Carlson 

Creek or Turner Lake powersites.
EXPLANATION

Base map modified from Juneau and Taku Rive 

topographic quadrangles, scale 1:250000

Geology compiled from all available sources by George Plafker, 1954

Contact, dashed 

where gradational

Fault, dashed where 

inferred

Damsite

OO

CONTOUR INTERVAL 1000 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 24. Generalized geologic map of the Juneau-Taku Inlet area, Alaska, showing regional setting of the proposed powersites. fcO

CD
130 GEOLOGY OF WATERPOWER SITES IN ALASKA

GEOGRAPHY

Physiography. The area discussed in this report is on the mainland in southeastern Alaska, at approximately lat 58°15'N". and 

long 134°00'W. in the Juneau and Taku River 1:250,000 quadrangles. 

The powersites are on streams that drain into Taku Inlet and 

Gastineau Channel. Within the mapped area shown on figure 24 

the mountains rise abruptly from sea level to a maximum altitude 

of about 5,000 feet, but average local relief is 3,500 to 4,000 feet. 

In the vicinity of the powersites small patches of permanent ice and 

snow occur only in sheltered basins above an altitude of 2,000 feet. 

Northeast of the area shown on figure 24 permanent ice and snow 

covers the higher peaks and ridges and from these ice caps several 

valley glaciers extend to low altitude along upper Taku Inlet and 

the Taku River. One of the most important factors in sculpturing 

of the present topography was the extensive piedmont ice sheet which, 

during the Pleistocene epoch, filled all the valleys in this area and 

spilled over the tops of some of the ridges that lay below a present 

altitude ranging from 3,200 to 4,000 feet. The ice flowed southwestward throughout most of the area and extended across southeastern 

Alaska to the Pacific Ocean (Buddington and Chapin, 1929, p. 24).

Below the upper surface of the ice sheet, ridges and mountains 

are smooth and rounded although on the higher slopes they are 

locally scarred by cirques. The higher peaks and.ridges that stood 

above the surface of the ice field are serrate and pinnacled, owing to 

continued exposure to frost action and headward erosion of cirques. 

The larger valleys in the area are broad, flatfloored, and U-shaped as 

a result of glaciation which widened, steepened, and straightened the 

preexisting river valleys. Gouging of the valley floors by these 

glaciers has produced the deep troughlike basins that now contain 

lakes or formerly contained lakes now filled with alluvium. Gastineau 

Channel and Taku Inlet are fiords that probably were former stream 

valleys deepened below sea level by glacial scouring and subsequently 

invaded by the sea upon melting of the ice. Following retreat of 

the glaciers and general uplift of the area relative to sea level, many 

of the streams cut deep, narrow gorges in the broad valley floors.

Climate. The climate of the area under study is characterized by 

rather mild temperatures for the latitude, high precipitation, and 

generally overcast skies. The temperature and precipitation record 

at a station near sea level in Juneau over periods of 54 and 56 years, 

respectively, are summarized below. The average annual snowfall at 

Juneau is 107.2 inches for a period of 37 years and 239.9 inches at 

Annex Creek along Taku Inlet (Federal Powrer Commission, 1947, 

p. 24). Temperatures drop about 1° F for each 300 feet in altitude,
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 131

and the precipitation rises correspondingly up to an estimated altitude of 4,000 feet. Above this altitude, precipitation tends to drop 

off rapidly (Federal Power Commission, 1947, p. 13 and 17). Southerly winds of light to moderate force are the rule in the area studied. 

At times during the winter months, however, a steep pressure gradient 

between the high ice caps in northwestern Canada and the relatively 

warm low eastern portion of the Gulf of Alaska may result in sustained wind velocities of 50 miles per hour, with a recorded extreme 

velocity of 70 miles per hour at Juneau in February 1923 (Federal 

Power Commission, 1947, p. 27).

Average monthly temperature and precipitation at Juneau, Alaska 

[Data from U.S. Weather Bureau, 1955, p. 184, 186]

Month

January _

FebruaryMarch _

April __ May __ _

June

July... __________

August. _

Temperature

29. 5

29. 9

34. 4

40. 4

47.8

54. 5

56. 0

55. 9

Precipitation

8.0

5.78

6. 43

5. 73

K 1 4.

4. 13

6.04

7. 37

Month

TfpppTYi V^PT*

Temperature

51.8

44. 0

36. 2

30.8

42. 65

Precipitation

10. 49

13. 03

10. 38

7.73

90. 25

Vegetation.. The combination of high precipitation and rather 

mild temperatures encourages a luxuriant growth of vegetation below 

an altitude of about 2,000 feet. Above this general altitude an alpine 

flora prevails. The forest is predominantly western hemlock and 

spruce with small amounts of cedar. A wide variety of berry bushes, 

devilsclub, and other shrubs is present as a dense undergrowth, and 

a carpet of moss 6 inches or more in thickness, generally covers much 

of the forest floor. Most talus slopes, alluvium, and landslides are 

covered by thickets of thorny brush; young alluvial soils support 

a tangled growth of alders with some cottonwood and willow trees. 

All this area is in the Tongass National Forest.

REGIONAL GEOLOGY 

BEDROCK

Bedrock in the area consists principally of a coastal band of northwestward-trending metamorphic rocks dipping steeply to the northeast. This band is adjacent to an extensive complex of granitic rocks 

to the northeast, and between the granitic and metamorphic rocks 

is a zone, 2 to 3 miles wide, of injection gneiss (fig. 24). The belt of 

metamorphic rock is part of the Wrangell-Revillagigedo belt (Bud624573 0 62 2i
132 GEOLOGY OF WATERPOWER SITES IN ALASKA

dington and Chapin, 1929, p. 49) that occurs along the southwest flank 

of the Coast Range batholith throughout southeastern Alaska. The 

metamorphic rocks in the area were subdivided by Spencer and Eakin 

(Eakin, H. M. 1922, unpublished data) into (a) Clark Peak schist 

unfossiliferous varieties ofv foliated quartz-andesine-biotite-hornblende 

schist and a few thin calcareous beds, (b) Perseverance slate unfossiliferous black graphitic slate, possibly 3,000 feet thick, and (c) 

the Gastineau volcanic group andesitic greenstone and greenstone tuff 

and minor amounts of limestone and fossiliferous calcareous slate. In 

this report the Coast Range batholith is subdivided into a border f acies 

of injection gneiss consisting largely of quartz diorite that shows 

prominent foliation and many relatively thin "screens" and remnants 

of schist; and a massive quartz diorite and granodiorite with relatively 

few schist remnants. The contact of the injection gneiss with the 

Clark Peak schist to the southwest and with the massive more homogeneous granitic rocks to the northeast is gradational over a broad zone. 

Away from the shores of Taku Inlet the contacts are only very approximately located.

Structure. The prevalent dip of bedding, slaty cleavage, and foliation in the crystalline rocks is 60 0-80° NE. All the metamorphic rocks 

are apparently conformable, but there is some uncertainty as to the 

structure of this section and whether it is right side up or overturned. 

As these considerations are not relevant to the present engineering 

geology study they will not be discussed in this report.

Stratigraphy. Martin (1926, p. 94) states that "there is no conclusive evidence on the age of any of the rocks at Juneau, except for the 

slate in the Gastineau volcanic group, which has yielded characteristic 

Upper Triassic fossils. The other beds have yielded no fossils, and 

there is only indirect and inconclusive evidence on their age." However, 

on the basis of the scanty fossil evidence from slate within the 

Gastineau volcanic group, long range correlations with rocks in adjacent areas to the southeast and northwest, and on the assumption 

that the section is overturned, Martin considers the Perseverance slate 

to be Triassic or older and the Clark Peak schist to be Paleozoic with 

possibly some infolded Triassic rocks (1926, p. 93). Martin's tentative 

age assignments for these formations are followed in this report, but it 

should be borne in mind that the age of only part of the Gastineau 

volcanic group is satisfactorily determined. In considering the age of 

the granitic rocks of southeastern Alaska and the bordering zone of 

injection gneiss, Buddington (Buddington and Chapin, 1929, p. 253) 

concludes "that all the Mesozoic intrusive rocks may be of Lower 

Cretaceous age, but the data given for adjacent territory suggest that 

they may be in part of Upper Jurassic and in part of Lower Cretaceous 

age."
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 133

Faults. The major faults in the vicinity of Juneau are shown 

on figure 24. The best known of these, the Silver Bow fault, has 

been mapped on the surface and underground in this area. The Silver 

Bow fault has a general easterly trend and dips steeply to the north. 

The north side is displaced about 1,400 feet downward and 2,000 feet 

westward in the vicinity of Juneau (Eakin, H. M., 1922 unpublished 

data); further east near Carlson Creek, there is 3,500 feet of horizontal displacement (Sainsbury, 1953, p. 18). The faults postdate 

the Upper Jurassic or Lower Cretaceous granitic rocks and the mineralization in this area. Although no displacement of glaciated surfaces has been reported or can be detected on the aerial photographs, 

it is possible that there may have been relatively recent movement. 

The sheared zones along the faults are readily susceptible to frost 

plucking. Thus, surface traces of the faults are commonly steepsided cuts, in part filled with talus; the fault traces generally stand 

out prominently on vertical aerial photographs.

UNCONSOLIDATED DEPOSITS

Glacial scouring during the Pleistocene epoch removed any weathered and unconsolidated material that may have been present in the 

area. All of the unconsolidated deposits that now mantle the crystalline bedrock are glacial or postglacial in age. They can be classified 

in five main groups as follows: (a) a relatively thin veneer of ground 

moraine deposited on the lower slopes in the area by glaciers of 

Pleistocene age; (b) ground moraine, end and lateral moraine, and 

outwash, deposited by post-Pleistocene glaciers; (c) alluvial deposits 

along the streams and in the Form of deltas built out into lakes and 

fiords; (d) deposits of marine mud in the tidal zones; and (e) unstfatified coarse talus and landslide debris found at the base of the 

steeper slopes.

EARTHQUAKES

Earthquakes of moderate intensity are felt frequently in the JuneauTaku Inlet area. The strongest earthquake recorded at Juneau was 

on February 11,1934, with a magnitude of 5 on the Gutenberg-Bichter 

scale. This earthquake caused "some cracked plaster and other slight 

damage to buildings1 ' (U.S. Coast and Geodetic Survey, 1947, p. 80). 

The epicenters of earthquakes felt at Juneau are grouped in three 

distinct zones: (a) along the west side of Chichagof Island, (b) in 

the Glacier National Monument area, and (c) in a strip from Skagway to Kluane in Canada. Earthquakes of the intensity that have 

previously been recorded in the area would probably cause relatively 

little damage to structures of the type that are discussed in this report.
134 GEOLOGY OF WATERPOWER SITES IN ALASKA

SHEEP CREEK

Sheep Creek empties into Gastineau Channel 0.4 mile southeast of 

Thane, 4.1 miles by road from Juneau at lat 58°15.5/ N., and long 

134°19.4/ W. Sheep Creek heads in a steep-walled amphitheater 

southwest of Hawthorne Peak, and in its middle course flows at a low 

gradient in a U-shaped basin, which trends in a broad arc from northwest to west to southwest. From the site of the proposed dam to sea 

level, a distance of 1 mile, the creek falls 600 feet through a steepsided, narrow postglacial canyon. The drainage area of Sheep Creek 

is 6.0 square miles with 4.6 square miles draining to the damsite 

(Juneau and Vicinity special map scale 1:24,000, 1950 edition). 

Small cirque glaciers and snow fields drain into Sheep Creek at the 

head of the valley, but provide only a small percentage of the total 

runoff.

According to Johnson and Colbert (written communication, 1959) 

power development on Sheep Creek would be accomplished by the 

construction of a dam at about mile 1.0, conveyance of water from 

the resulting reservoir by a tunnel or pipeline to a powerhouse located 

on tidewater at or near Thane. A reservoir with a maximum surface 

altitude of about 800 feet would be required to attain adequate regulation of the streamflow. The field investigation of the reservoir site 

and damsite were, therefore, based on the assumption that the maximum reservoir surface altitude would be limited to 800 feet.

Much of the Sheep Creek basin is patented mineral land, mill sites, 

and valid mining claims, none of which were being worked in 1956. 

There is an existing power development on this creek which consists 

of a low log crib diversion dam immediately above the proposed damsite (pi. 10). A 2,486-foot long timber flume and a 2,687-foot penstock conduct the water to a powerhouse located 400 feet from the 

creek mouth at tidewater. In 1956 no power was being generated at 

this site because of breaks in the flume. Approximately 7,100 feet 

of the Annex Creek to Juneau transmission line is within the reservoir 

area and would have to be rerouted if Sheep Creek is developed. The 

relative values of mineral resources and power must be assessed before 

development of Sheep Creek is undertaken.

A good trail leads from the road at Thane to the damsite, and from 

the damsite along the Annex Creek to Juneau transmission line into 

the upper Sheep Creek valley. The location, topography, and geology 

of the Sheep Creek powersite is shown on plate 10.

RESERVOIR SITE

As pointed out in the previous section the maxim-urn reservoir surface altitude is assumed to be 800 feet. At this altitude the reservoir
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 135

would extend upstream from the dam for a distance of about 1% 

miles. The reservoir would occupy a broad, U-shaped basin whose 

profile is due to widening and steepening by a valley glacier during 

the Pleistocene epoch. The reservoir area is underlain by the Gastineau volcanic group, a bedded sequence of slightly metamorphosed 

massive fine-grained greenstone, thin-bedded fine-grained greenstone 

tuff, and black graphitic slate. Upstream from the reservoir area 

the Sheep Creek valley is underlain by the Perseverance slate, which 

is apparently conformable with the Gastineau volcanic group. The 

beds strike northwest and dip 60°-75° NE. The bedrock areas generally support a scattered growth of hemlock and spruce.

A thin discontinuous veneer of talus mantles the lower slopes of 

areas shown as bedrock on plate 10. The talus consists of poorly 

sorted coarse angular debris derived from the steep valley walls. 

These deposits were not delineated on the map of the reservoir area. 

Alluvium with subordinate amounts of talus forms the valley floor 

within the reservoir area. Along Sheep Creek the alluvium is moderately well sorted clean subangular to rounded sand, granules, pebbles, cobbles, and boulders. There is a gradual decrease in average 

grain size from the upstream end of the valley toward the damsite. 

Along the base of the steep valley walls small talus cones and sheets 

consisting of poorly sorted coarse angular material grade into, and 

are mapped with, the alluvial deposits. The thickness of unconsolidated deposits is not known. A sparse growth of cotton wood, willow, 

and hemlock trees is found on the alluvium, and the talus is in general 

covered by a dense growth of devilsclub, alders, and berry bushes.

DAMSITE

Bedrock. The Sheep Creek damsite is a narrow steep-walled notch 

at the outlet of the broad Sheep Creek basin (pi. 10). Bedrock at 

the damsite is predominantly thin- to thick-bedded slabby greenstone 

tuff but includes minor amounts of fissile black graphitic slate. All 

gradations between the tuff and slate are found. The greenstone tuff 

is a moderately hard, tough rock that breaks into thick, irregular 

slabs and small blocks. The slate cleaves readily into flat slabs generally less than 2 inches thick, and the fresh surfaces have a silky sheen.

In thin section the greenstone is seen to consist primarily of green 

chlorite flakes as much as 0.2 mm long, and idioblastic prisms of yellow 

epidote as much as 0.08 mm long in a colorless groundmass, probably 

largely albite. Minor constituents are sharply crystallized octahedra 

of magnetite 0.1 to 0.4 mm in diameter, granular clusters of sphene, and 

irregular patches of idioblastic calcite. Phenocrysts and amygdules in 

the original rock are drawn out into elongated streaks owing to shear-
136 GEOLOGY OF WATERPOWER SITES IN ALASKA

ing. The slaty rocks are composed of grains generally less than 0.04 

mm in diameter, which consist of finely divided white mica flakes, 

xenoblastic quartz and albite, dusty opaque graphite, and prisms of 

pale-yellow epidote and accessory magnetite octahedra and sphene.

Bedding and foliation of the rock at the damsite strikes N. 40°-75 Q 

W. and dips 600-75° NE. There is a strong set of joints spaced from 

4 inches to 5 feet apart, which trends N. 55°-75° E. and dips 60°-85° 

SE. Poorly developed joints include a nearly horizontal set, and one 

having the same strike as the major set, with a near-vertical dip.

Unconsolidated deposits. At the damsite the lower slopes are 

mantled with loose talus debris probably less than 25 feet thick. This 

material consists of poorly sorted loose angular slabs and blocks of 

greenstone tuff and slate, generally less than 4 feet across. The talus is 

overgrown with a tangled growth of alders, devilsclub, and salmonberry bushes.

Alluvial deposits consisting of moderately well sorted subrounded to 

rounded sand, granules, pebbles, and cobbles have filled in the area behind the existing diversion dam above the proposed damsite. The alluvium supports a sparse growth of hemlock, cottonwood, and willow 

trees.

POWERHOUSE SITE

The powerhouse site would be at tidewater between Thane and the 

mouth of Sheep Creek. Black graphitic slate bedrock is exposed at 

the creek mouth and along the road for a distance of about 650 feet 

to the west of the creek mouth. West of the area of slate outcrop bedrock is concealed by a veneer of mixed unconsolidated glacial deposits 

and rockslide debris of unknown thickness. The glacial deposits are 

not exposed in place in this area. East of the mouth of Sheep Creek 

probably similar material is well exposed in a roadcut, and consists of 

poorly sorted angular to subrounded sand, granules, pebbles, cobbles, 

and scattered boulders in a clayey silt matrix. The area is heavily 

timbered, mainly with hemlock.

DIVERSION ALINEMENT

The diversion alinement would depend upon the location of the 

powerhouse. Any alinement in this area, however, would be on the 

same type of bedrock and structure as that described at the damsite. Locally, bedrock may be mantled by a thin discontinuous cover 

of talus or glacial material.

CONCLUSIONS AND RECOMMENDATIONS

Reservoir site. Several small mine workings and one large drift 

lie within the proposed reservoir site. None of the smaller workings
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 137

would be sources of leakage from the reservoir. The Sheep Creek adit, 

however, has its portal at an altitude of about 720 feet at the Portal 

Camp (pi. 10), and extends northward about 10,000 feet to the workings of the "Perseverance ore body" in the Alaska-Juneau gold mine. 

This adit would have to be sealed off in order to prevent flooding of 

the mine workings, and possible loss of water from the reservoir. The 

remainder of the reservoir is in bedrock or bedrock mantled with unconsolidated deposits which would be virtually impermeable.

Damsite. Bedrock in the damsite is well suited as a foundation 

for either a concrete or rock-fill dam. The narrow valley at this site 

would be ideal for a concrete arch structure. However, the loose talus, 

probably less than 20 feet thick, would have to be removed from the 

abutments to expose fresh, sound bedrock. Bedrock is exposed at creek 

level on either side of the creek, and it is unlikely that stripping in the 

creek bed would involve more than removal of a few feet of loose material. The joints and bedding planes are relatively tight so that seepage and foundation treatment would be at a minimum. The abutments 

are well suited for driving tunnels for either diversion or outlet structures. Tunnels through these abutments would intersect the steeply 

dipping beds approximately at right angles, which is the most favorable alinement for tunneling. Lining or support would not be necessary except possibly at the portals.

Construction material's. It may be possible to obtain suitable 

natural concrete aggregate from the alluvial deposits along Sheep 

Creek. The alluvium should be sampled by dug pits or auger holes 

to determine the quality and volume of potential aggregate available. 

Crushed aggregate and dimension stone could be obtained from the 

massive fine-grained greenstone that crops out on both sides of Sheep 

Creek valley upstream from the damsite. Although some clay for 

the impervious core of a rock-fill dam may be obtained from the glacial deposits along Gastineau Channel it is unlikely that large sources 

of suitable material could be found in these deposits.

Powerhouse and conduit sites. The shortest alinement for conducting water from the dam to a powerhouse at tidewater in the vicinity of Thane would be along section A-A' (pi. 10). Along line 

A-A' the conduit and penstock would be on sound bedrock most of 

the way with a local cover of talus or glacial deposits that has an 

estimated average thickness of 10 feet. A powerhouse site in the vicinity of Thane would be underlain by glacial deposits of unknown 

thickness. Before a powerhouse is located in this area the thickness 

of the unconsolidated material should be ascertained by either drilling 

or geophysical exploration to determine if the structure could be 

founded on bedrock.
138 GEOLOGY OF WATERPOWER SITES IN ALASKA

Slate bedrock exposed at the mouth of Sheep Creek and along the 

road for a distance of 650 feet west of the creek mouth would be an 

excellent foundation material for a powerhouse. Location of a powerhouse in this area would require an increase of about 200 feet in the 

length of the penstock. This may be offset by a somewhat lower slope 

along the penstock alinement which would minimize the possibility of 

disruption by landslides and snowslides. The conduit and penstock 

would cross virtually the same type of material as that along line 

A-A'.

CARLSON CREEK

Carlson Creek discharges into Sunny Cove on the west shore of 

Taku Inlet at lat 58° 18.4' N., and long 134°08.5' W., a distance of 

20 miles by sea from Juneau (fig. 24). Carlson Creek is formed at 

the confluence of its tributaries, Salmon Fork and Gold Fork, on the 

west flank of Olds Mountain. From this point the creek flows with 

a steep gradient to its junction with Sheep Fork wThich heads between 

Sheep Mountain and Hawthorne Peak. Carlson Creek then flows 

eastward at a low gradient across a flat-floored basin for slightly over 

1 mile before plunging through a narrow, northeastward-trending 

canyon half a mile long. After emerging from the canyon the creek 

turns sharply southeastward, and flows on a slightly meandering 

course for 1% miles to its mouth at Sunny Cove. The drainage area 

of Carlson Creek is 26.7 square miles, of which 23.3 square miles drains 

to the proposed dam site. The creek is clear with only a small proportion of melt water derived from isolated ice and snow patches in the 

drainage basin. See figure 25 for aerial view- of part of Carlson 

Creek valley.

A good trail leads from Sunny Cove to the Alaska-Juneau Gold 

Mining Co. cabin, a distance of about l1/^ miles. Above the cabin 

the trail continues up Carlson Creek and Sheep Fork along the transmission line from Annex Creek to Juneau, but in this area it is largely 

grown over with brush. A little more than 2 miles of the transmission 

line would have to be relocated if the Carlson Creek project is 

developed.

The development of power on Carlson Creek according to Johnson 

and Colbert (written communication, 1959) wrould be accomplished 

by the construction of a dam at either mile 1.8 or mile 2.3, conveying 

the water from the resulting reservoir by tunnel and penstock to a 

powerhouse at or near tidewater near the mouth of Carlson Creek. 

In this report only the damsite at mile 1.8 is considered. It was 

assumed that the maximum reservoir altitude would be about 500 

feet requiring a dam 250 feet high with crest length of 900 feet.

The location, topography, and geology at the Carlson Creek powersite is shown on plate 11.
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 139

FIGURE 25. Aerial view of part of Carlson Creek basin looking upstream (west) from 

a point over the mouth of Carlson Creek. Damsite is in gorge cut through ridge in 

foreground. Trend of creek at the damsite and parallel gullies on the ridge in foreground define prominent northeastward-trending Joint set. Creek in lower right corner of picture defines trend of the foliation. .Flat-floored basin above the damsite is 

an alluvium-filled lake.

BESEBVOIB SITE

Development of waterpower from Carlson Creek would require a 

storage reservoir with a maximum estimated altitude of about 500 

feet. The reservoir would cover a portion of the Carlson Creek and 

Sheep Fork valleys (pi. 11).

As shown on plate 11 the reservoir site is underlain predominantly 

by injection gneiss consisting largely of foliated quartz diorite and 

minor amounts of schist. Along the Sheep Fork the ratio of schist 

to gneiss increases to approximately equal amounts of each. In this 

area thin beds of marble interbedded with quartz-andesine-biotite 

schist and quartz-andesine-biotite-hornblende schist are found. Both 

the schist and gneiss are cut by light-colored dikes of aplite and pegmatite. Bedrock areas are characterized by growth of hemlock, 

spruce, and cedar.

Overlying the bedrock are unconsolidated deposits of talus consisting of unsorted to poorly sorted angular boulders and cobbles and 

interstitial sand and gravel. The largest deposits are delineated on 

plate 11 although most of the areas shown as bedrock on the map are
140 GEOLOGY OF WATERPOWER SITES IN ALASKA

also concealed by a thin discontinuous veneer of talus. The talus slopes 

are generally covered with a dense growth of brush. The flat-floored 

basin upstream from the damsite (fig. 25) is interpreted to be a former 

glacial lake that was filled with alluvium. The alluvium supports a 

tangled growth of alders.

DAMSITE

Bedrock. The damsite area is underlain by fairly massive quartz 

diorite injection gneiss. This rock is medium-grained mottled black 

and white foliated quartz diorite with widely spaced partings and 

inclusions of gray to black schist. The schist "screens" are generally 

less than 6 inches in thickness and are planes of weakness along which 

the rock cleaves readily. In thin section the more massive rock is 

seen to range from 0.5 to 3 mm in grain size and to average about 

30 percent shreds of brown biotite and ragged laths of hornblende, 

45 to 50 percent subhedral andesine, 15 to 20 percent anhedral quartz, 

and minor amounts of accessory apatite, sphene, zircon, and calcite. 

The biotite is locally altered to chlorite, plagioclase is partly sericitized, and slender rods of epidote are found intergrown with the 

hornblende. Protoclastic texture in some sections is indicated by 

bent biotite, granulated and drawn out plagioclase, and bent plagioclase twin lamellae. The schist remnants in the injection gneiss average 1 mm or less in grain size, and are composed of virtually the 

same minerals as described above, with a higher percentage of welloriented biotite and correspondingly less hornblende. A band of 

thinly bedded schist crosses the lower end of the damsite and probably extends southeastward along Carlson Creek to Sunny Cove as 

shown on plate 11. The schist in this band is dark colored, fine 

to medium grained, and consists mostly of quartz-andesine-biotite 

and quartz-andesine-biotite-hornblende. Some of these schists contain 

considerable amounts of muscovite, and in others diopside is abundant. 

Minor accessory minerals are magnetite, pyrite or pyrrhotite, apatite, 

and sphene. Both the schist and injection gneiss are cut by dikes of 

light-colored potassium-rich granite-pegmatite and aplite. Hemlock 

interspersed with sparse amounts of cedar grow in areas where bedrock 

is near the surface.

Foliation of the rock in the damsite area trends uniformly N. 25°- 

50° W. and dips 65°-80° NE. The rocks are cut by a major set of 

joints spaced 6 inches to 4 feet apart which trend N. 60°-85° E. and 

dip 65°-85° SE. The course of Carlson Creek at the damsite follows 

the strike of this prominently jointed zone (fig. 25). The combination of northwestward-trending foliation, northeastward-trending 

major joints, and a relatively minor set of flat-lying joints, all tend
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 141

to cut these rocks into rectangular rocks which are elongated parallel 

to the foliation.

Vnconsolidated deposits. The. lower slopes at the damsite area are 

mantled with loose talus derived from injection gneiss. This material 

consists of poorly sorted or unsorted angular cobbles and boulders, 

some of which are as much as 25 feet across. The talus debris is 

mantled with a tangled growth of devilsclub and berry bushes.

POWERHOUSE SITE

A powerhouse could be located in bedrock on the south bank of 

Carlson Creek about 3,200 feet upstream from the mouth, at a stream 

altitude of 20 feet. Below this point a very small increase in head 

could be obtained at the expense of markedly increasing the overall 

tunnel or conduit length. The powerhouse site would be in injection 

gneiss bedrock similar to that described for the dam foundation. At 

this site a steep gully is cut along a zone of closely spaced northeastward-trending joints similar to those which control the course of 

Carlson Creek at the damsite.

TUNNEL ROUTE

An approximate tunnel alinement for diverting water from the 

reservoir to the powerhouse is shown on plate 11. The exact type 

and alinement for this diversion would depend upon the minimum 

surface altitude of the reservoir. Assuming this to be 450 feet, the 

tunnel would be about 4,250 feet long with a penstock above or 

below ground about 200 feet long. The tunnel would be in fresh, 

massive injection gneiss similar to the foundation rock at the damsite and powerhouse site. The rock is foliated almost parallel to the 

tunnel alinement, and is cut by the same major set of northeastwardtrending joints with high angle southeasterly dips as found at the 

damsite (fig. 25). Two zones of closely spaced joints indicated by 

distinct linear depressions would be crossed by a tunnel with an alinement as shown on plate 11 (section A-A').

CONCLUSIONS AND RECOMMENDATIONS

Reservoir site. The floor and walls of the reservoir would be composed of bedrock or bedrock mantled with unconsolidated deposits, 

which is sufficiently tight to insure minimum water loss through 

leakage.

Damsite. Bedrock in the damsite area is suitable as a foundation 

for either a concrete or rock-fill dam as much as 350 feet high. Section 

B-B' (pi. 11) is in the vicinity of one of the more favorable aline-
142 GEOLOGY OF WATERPOWER SITES IN ALASKA

ments. At this site the loose talus debris, probably less than 15 feet 

in maximum thickness, would have to be removed to expose fresh, 

sound injection gneiss bedrock. Only a thin mat of vegetation and 

organic soil would have to be stripped from the bedrock. The foundation rock has sufficiently high compressive and shear strength to 

support the contemplated load.

The foundation rock itself is virtually impermeable and insoluble. 

However, the major joints, which trend parallel to the creek and are 

perpendicular to the dam axis, wT ould be natural seepage channels under the proposed dam. These joints are closely spaced, and are open 

near the surface owing to water seepage and frost action along them. 

They would have to be sealed with a grout curtain along the proposed 

dam alinement. The depth to which grouting would be required 

could be determined by pressure tests from drill holes along the axis 

of the dam.

Construction materials. Satisfactory crushed aggregate or dimension stone could be produced from the injection gneiss in the damsite 

area. Natural aggregate may be available from the alluvium along 

Carlson Creek upstream from the damsite. This alluvium along the 

creek consists of subrounded to rounded sand, granules, pebbles, and 

cobbles, and minor amounts of interstitial silt. Away from the creek 

channel the flood plain is mantled by a surficial layer of micaceous 

silt of unkno\vn thickness. The average grain size of the alluvium 

increases gradually upstream and it may be possible to produce a 

well-graded aggregate by blending of material from pits at selected 

points along the creek. Washing would probably be required to remove the silt. Test pits should be dug on a grid within the alluvial 

deposits to determine whether suitable aggregate is available in the 

required quantity. The only fine-grained material available for an 

impervious core would be the glacial rock flour deposited in the tidal 

zone at Sunny Cove. The physical characteristics of this material 

should be determined if a rock-fill dam is contemplated for this site.

Powerhouse site. The fresh injection gneiss would be an excellent 

foundation material for the proposed powerhouse at the site shown on 

plate 11, or along the south side of Carlson Creek and Sunny Cove 

to the east of this site.

Tunnel route. Except for the two joint zones which cross the 

tunnel alinement (pi. 11), bedrock is fresh, sound, and tight. Gullies 

have been eroded along these zones of closely spaced joints, and they 

could be the source of considerable ground-water seepage during tunneling. Observations on a similar jointed zone exposed at the lower 

end of the damsite area, indicates that the joints are probably 6 

inches to 4 feet apart. Away from the portals the rock can be expected
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 143

to stand unsupported for an indefinite period, although some support 

may be required in the closely jointed zones.

A diamond-drill program should be undertaken prior to selection 

of the final tunnel alinement in order to determine the nature of the 

jointed zones at depth and inflo\v of ground water to be expected 

during tunneling.

TURNER LAKE

The outlet of Turner Lake is at lat 58°18.3' N. and long 133°56.1' 

W. The lake has an approximate area of 2,900 acres (Federal Power 

Commission, 1947, p. 69), and on August 14, 1952 it had a surface 

altitude of 73.2 feet. Turner Lake discharges into Turner Creek, 

which flows half a mile northwestward to its mouth on the west shore 

of Taku Inlet, 22 miles by sea from Juneau (fig. 24). The creek 

drops through a series of rapids to an elevation of 16.1 feet within 

500 feet of the lake outlet, and from there it flows on a gentle gradient 

to sea level. The \vidth of the lake ranges from a quarter of a mile 

just above the outlet to a maximum of three quarters of a mile near 

the center portion, and is 8y2 miles in length. The general trend is 

easterly with a 2-mile long southward-trending arm at the east end 

of the lake, and a small southwy ard-t rending embayment near the 

middle part of the lake.

Glacier-fed streams drain into the lake at the head of the southwardtrending arms, and one large stream drains into the east end of the 

lake. Several smaller clear wrater and glacial streams empty into the 

lake at various points along its length. The total drainage area is 

approximately 52 square miles.

A wTell-maintained forest service trail slightly over half a mile long 

leads from tidewater at the mouth of Turner Creek to Turner Lake. 

There is a forest service cabin and boathouse on the point south of 

the lake outlet, and a shelter cabin is located near the mouth of the 

creek that drains into the east end of the lake. See figure 26 for 

aerial view of lower end of Turner Lake.

According to Johnson and Colbert (written communication, 1959) 

the development of powy er at .Turner Lake would be accomplished by 

the construction of a lo\v dam and auxiliary structure to raise the 

surface altitude of the lake to approximately 116 feet or 43 feet 

above normal lake level, a powerhouse located on Turner Creek 450 

feet downstream from the lake outlet or near the mouth of Turner 

Creek at tidewater, and a penstock or combination conduit and penstock to conduct water from the reservoir to the powerhouse.
144 GEOLOGY OF WATERPOWER SITES IN ALASKA

FIGURE 26. Aerial view of Turner Creek and lower end of Turner Lake looking east from 

wver Taku Inlet. Note steep-sided glaciated valley occupied by Turner Lake. Large 

scar on steep slope to left of the lake outlet (light area); is probable source of rocksllde 

debris at the damsite. Light-colored area at creek mouth is tidal mud flat.

RESERVOIR SITE

The reservoir site is a glaciated valley with a steep-sided U-shaped 

profile up to about 1,500 feet altitude, a broad V-shaped profile from 

about 1,500 feet to 4,000 feet altitude, and steep-sided ragged ridges 

and peaks above an altitude of 4,000 feet (fig. 26; pi. 12). The 

basin occupied by Turner Lake was scoured out of bedrock by a 

westward-flowing valley glacier. The lake bottom falls off sharply 

from shore, and has been sounded to a depth of 682 feet by the field 

party that made the survey of the damsite at the lake outlet. Because 

of the extremely steep slopes surrounding Turner Lake, the lake area 

would be increased only slightly by the maximum practicable raising 

of the lake surface.

The entire lake basin consists of hard fresh massive granitic rock 

(hornblende-biotite granodiorite). The bedrock is concealed in places 

by small alluvial fans which are being built out into Turner Lake at 

the bend 2 miles from its head, and at the heads of the two southwardtrending arms. The gentler slopes are in part mantled with talus and 

small landslides. Morainal deposits, probably of Recent age, occupy 

small cirques on the higher slopes in the area.

The granite rocks are cut into large blocks generally more than 

5 feet across by several well-defined sets of joints. The traces and
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 145

attitudes of the major joints are shown on plate 12. All of the joints 

examined in the field were tight with no detectable weathering along 

them. Six high-angle northeastward-trending faults or probable 

faults occur within the reservoir area as shown on plate 12. These 

structural features show up clearly on the vertical aerial photographs 

as distinct linear depressions generally filled with talus. The fault 

planes could not be seen in the field because of their tendency to be concealed by talus owing to accelerated frost action along the shattered 

zones. None of the faults can be traced for more than a few miles in 

either direction from the lake, and it is probable that they actually represent relatively minor fractures between the major westward- and 

north west ward-trending faults of southeastern Alaska. One of these 

major faults intersects Taku Inlet a few miles north of Turner Lake 

near Davidson Creek (fig. 24). The faults are probably inactive as 

indicated from lack of displacement of smooth glaciated surfaces and 

absence of seismicity in the area.

DAMSITE

Bedrock. The damsite area is underlain by hornblende-biotite 

granodiorite. Bedrock is exposed in the point just south of the lake 

outlet, along both shores of the lake upstream from the outlet, and 

as small riblike outcrops at the outlet and along Turner Creek (pi. 12). 

The rock is generally medium grained, light colored, and mottled 

with black ferromagnesian minerals. Locally, there is a tendency 

toward a faint foliated or gneissic structure, with thin dark-colored 

clots of fine-grained material and prisms of hornblende or plates of 

biotite defining the plane of foliation. In thin section the rock is 

seen to be hypidiomorphic granular in texture with an average grain 

size of 2 to 4 mm. It consists of about 50 percent subhedral zoned 

andesine (An 30-35 ), 20 percent anhedral quartz, 18 to 20 percent subhedral brown biotite and green hornblende, and 6 to 10 percent anhedral orthoclase. Sphene in crystals as much as 2 mm long, anhedral 

magnetite, and euhedral apatite and zircon constitute the remaining 

2 to 4 percent of the rock. The minerals are in general fresh with 

only minor sericitization of the plagioclase cores, chloritization of 

biotite and hornblende, and replacement of hornblende by rods and 

granules of epidote.

Rockslide deposits. Near the lake outlet and along Turner Creek 

a jumbled mass of loose angular unsorted blocks, some of which are 

40 feet or more across, overlie the granodiorite bedrock. This mass 

of loose rock is interpreted to be a landslide that came down the slope 

north of the lake outlet from a cliff at an altitude of about 1,000 

feet (fig. 26), and filled most of the valley now occupied by Turner
146 GEOLOGY OF WATERPOWER SITES IN ALASKA

Creek. The landslide debris is extremely permeable and Turner 

Creek probably was able to maintain its course by flowing through 

the many openings within the mass. A part of the landslide debris 

has been cleared from the channel by the creek, but much of the creek 

course is still choked with large blocks and some water flows through 

openings in the debris on the south side of the lake outlet.

Landslide debris supports a dense growth of devilsclub and berry 

bushes and a few small hemlock and pine trees.

Talus deposits. A veneer of talus mantles the base of the steep 

slope southwest of the damsite. This talus consists of poorly sorted 

angular to subangular granules, pebbles, and cobbles, and scattered 

boulders in a silty sand matrix. Most of the talus fragments are of 

granodiorite, but a small percentage is schist and chert. These fragments of metamorphic rock may be derived from metamorphic inclusions within the granodiorite or could be ground or glacial moraine 

deposited on the slope. The thickness of the talus is not known.

The growth of large, straight hemlock trees on the talus deposit 

indicates that it has been fairly stable for a long period of time. 

There is a moderately dense undergrowth of devilsclub and berry 

bushes.

CONCLUSIONS AND RECOMMENDATIONS

Reservoir site. All the reservoir area is in bedrock overlain by a 

relatively thin mantle of overburden, which is sufficiently tight to 

insure minimum water loss through leakage.

Damsite. The foundation at the lake outlet consists of granodiorite 

bedrock largely concealed by blocks of landslide debris. The small 

outcrops of granodiorite at the outlet, as shown on plate 12, were 

distinguished from large, loose blocks of the same material by comparing the foliation and joint planes to those in nearby exposures of 

undoubted bedrock. Another distinguishing feature of the bedrock 

is that it is the only lithologic unit on which cedar trees grow in this 

area. All of the landslide debris and surficial organic matter would 

have to be removed to expose fresh rock at the damsite. The foundation rock here is excellently suited for a concrete or rock-fill dam. 

From surface indication the joints are sufficiently tight to insure a 

minimum of seepage through the foundation. It may be necessary 

to erect a diversion wall on the steep north abutment of the damsite 

to prevent slide rock from falling on the dam.

Auxiliary dam. There is a saddle about 200 feet southwest of the 

lake outlet, the low point of which is just under 100 feet in altitude. 

On the assumption that the maximum reservoir altitude would be 116 

feet it would be necessary to build an auxiliary dam across this saddle.
SHEEP CREEK, CARLSON CREEK, AND TURNER LAKE 147

Such a dam would be about 20 feet high and about 250 feet long. 

This saddle is in granodiorite bedrock and foundation treatment would 

probably require only stripping of the surficial organic matter and 

soil, which is less than 3 feet thick.

Spillway site. The low divide at 136 feet altitude west of the 

auxiliary damsite (pi. 12) may be suitable as a natural spillway. The 

saddle is filled with talus that probably is less than 15 feet thick. 

An open cut in the saddle down to the estimated reservoir level of 

116 feet would have to be only 25 feet deep at the maximum. A test 

hole should be put down in the saddle to ascertain the depth to bedrock 

and permit an estimate of the relative amounts of common and rock 

excavation that would be required.

Construction materials. Granodiorite in the damsite area would 

be excellently suited for crushed aggregate to be used in a concrete 

dam or as dimension stone for a rock-fill dam. There is no suitable 

natural aggregate in the vicinity of the damsite. The only finegrained material in the area that may be used for an impervious core 

for a rock-fill dam would be the marine glacial rock flour from the 

mud flats near the mouth of Carlson Creek. Physical tests of this 

material should be made to determine its suitability for this purpose.

Powerhouse site. One of the possible sites for a powerhouse would 

be near the base of the rapids along Turner Creek 500 feet downstream 

from the lake outlet. At this location granodiorite bedrock is exposed, which would be an excellent foundation for a powerhouse. 

The other site would be at tidewater near the mouth of Turner Creek. 

No examination of this area was made during the present investigation, 

but aerial photograph interpretation indicates that there is a possible 

powerhouse site on bedrock immediately north of the creek mouth.
148 GEOLOGY OF WATERPOWER SITES IN ALASKA

REFERENCES CITED

Buddington, A. F., and Chapin, Theodore, 1929, Geology and mineral deposits of

southeastern Alaska: U.S. Geol. Survey Bull. 800, 398 p. 

Federal Power Commission and U.S. Forest Service, 1947, Water powers of

southeastern Alaska: 168 p. 

Martin, G. C., 1926, The Mesozoic stratigraphy of Alaska: U.S. Geol. Survey

Bull. 776, 493 p. 

Sainsbury, C. L., 1953, Geology of the Olds Mountain-Clark Peak area, Juneau

vicinity, Alaska: U.S. Geol. Survey open-file rept. 43 p. 

Spencer, A. C., and Wright, C. W., 1906, The Juneau Gold Belt, Alaska: U.S.

Geol. Survey Bull. 287, 161 p. 

Twenhofel, W. S., 1952, Geology of the Alaska-Juneau lode system, Alaska:

U.S. Geol. Survey open-file rept. 170 p.

U.S. Coast and Geodetic Survey, 1947, Earthquake history of the United States. 

 1947-1952, United States earthquakes. 

U.S. Weather Bureau, 1955, Climatological data, Alaska, 1954: v. 40, no. 13,

p. 180-190.
Geology of 

Waterpower Sites 

in Alaska

GEOLOGICAL SURVEY BULLETIN 1031

This bulletin was printed as 

separate chapters A-F

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director
CONTENTS

[The letters in parentheses preceding the titles designate separately published chapters]

Page

(A) Geologic investigations of proposed powersites at Cooper, Grant,

Ptarmigan, and Crescent Lakes, Alaska, by George Plafker_ ______ 1

(B) Geologic investigations of proposed powersites at Baranof and Carbon

Lakes, Barnof Island, Alaska, by Kenneth S. Soward.___________ 25

(C) Geology of waterpower sites on the Bradley River, Kenai Peninsula,

Alaska, by Kenneth S. Soward_---____--_-__--___-____-_____-_ 47

(D) Geology of waterpower sites on Crater Lake, Long Lake, and Speel

River near Juneau, Alaska, by John Charles Miller._____________ 71

(E) Geology of waterpower sites on Scenery, Cascade, and Delta Creeks

near Petersburg, Alaska, by John Charles Miller._______________ 103

(F) Geologic investigations of proposed powersites at Sheep Creek, Carlson

Creek, and Turner Lake, Alaska, by George Plafker____.,-____.__ 127

III

o