UNITED STATES DEPARTMENT OF THE INTERIOR 

J. A. Krug, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

Water-Supply Paper 866

GEOLOGY OF DAM SITES ON THE

UPPER TRIBUTARIES OF THE COLUMBIA RIVER

IN IDAHO AND MONTANA

By

C. E. ERDMANN

»t, coPy is PUBLIC PROPERTY * *

to rMaoyad from the official file*. PRIVATE ^

POSSESSION IS UNLAWFUL (R- s- S*** Vol « Z* W* 

f»c. 749)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON: 1947

CONTENTS

[The letters in parentheses preceding the titles are those nsed to designate the papers for separate

publication]

Page

(A) Part 1, Katka, Tunnel No. 8, and Kootenai Falls dam sites, Kootenai

River, Idaho and Montana. __________________________________ 1

(B) Part 2, Hungry Horse dam and reservoir site, South Fork Flathead

River, Flathead County, Mont________________________________ 37

(C) Part 3, Miscellaneous dam sites on the Flathead River upstream from

Columbia Falls, Flathead County, Mont_____________________ 117

ILLUSTRATIONS

PLATE 1. Index map of northwestern Montana and northeastern Idaho

showing location of dam sites on Kootenai River__________ 2

2. Geologic map of Katka dam site, N% sec. 31, T. 62 N., R. 3 E.,

Boundary County, Idaho__-___---_______-----__--_--_-- 18

3. A, View upstream through Katka dam site, Idaho; B, Kootenai

River trench upstream from Katka dam site, Idaho_______ 26

4. A, View downstream through Tunnel No. 8 dam site, Montana; 

B, Kootenai River trench upstream from Tunnel No. 8 dam 

site, Montana_________________________________________ 27

5. Geologic map and cross sections of Kootenai Falls dam site,

sees. 13 and 14, T. 31 N., R. 33 W., Lincoln County, Montana. 34

6. A, Kootenai River valley above Kootenai Falls, Mont.; B,

Right abutment of lower dam site at Kootenai Falls, Mont- 34

7. A, Suggested new location of left abutment at lower Kootenai 

Falls dam site, Montana; B, View southeast along axis of 

upper Kootenai Falls dam site, Montana.____________---- 35

8. Geologic map of Hungry Horse dam site, Flathead County,

Mont___________________________________________ In pocket

9. Geologic cross sections, Hungry Horse dam site________ In pocket

10. Map of Lion Hill-Abbott Ridge district-________________ In pocket

11. Cross sections of Abbott gorge and Lion Hill gorge, Hungry

Horse project____________________________________ In pocket

12. Index map showing location of dam sites and principal reservoirs on Flathead River and tributaries above Columbia 

Falls, Flathead County, Mont., and British Columbia, 

Canada---_-__-______________-____________-__-_-_- In pocket

13. Geologic map of Columbia Falls dam site, sec. 17, T. 30 N., R.

20 W., Flathead County__________________________ In pocket

14. Geologic map of Bad Rock Canyon dam site, sec. 1, T. 30 N.,

R. 20 W., Flathead County___________________ In pocket

15. Geologic cross sections at Bad Rock Canyon dam site, sec. 1,

T. 30 N., R. 20 W., Flathead County____________ In pocket
IV CONTENTS

PLATE 16. Geologic map of Coram Canyon dam site, south of center sec.

5, T. 30 N., R. 19 W., Flathead County. _.________ In pocket

17. Geologic cross sections at Coram Canyon dam site, south of

center sec. 5, T. 30 N., R. 19 W., Flathead County____ In pocket

18. Geologic map of Lower Canyon Creek dam site, sec. 35, T. 32

N., R. 20 W., Flathead County..___---__________ In pocket

19. Geologic map of Upper Canyon Creek dam site, sec. 27, T. 32

N., R. 20 W., Flathead County...____________ In pocket

20. Geologic cross sections at Upper Canyon Creek dam site, sec.

27, T. 32 N., R. 20 W., Flathead County________ In pocket

21. Preliminary geologic map of Fool Hen dam site, N}_ sec. 23,

T. 32, N., R. 20 W., Flathead County___________ In pocket

22. Preliminary cross sections Fool Hen dam site, Flathead River,

NH sec. 23, T. 32 N., R. 20 W., Flathead County... In pocket

23. Index map of Glacier View project showing relation of buried 

gorges to reservoir area and present drainage, Flathead 

County and Glacier National Park_________________ In pocket

24. Preliminary geologic map of Glacier View dam site, sees. 14,

15, 22, and 23, T. 33 N., R. 20 W., Flathead County In pocket

25. Geologic cross sections Glacier View dam site, Flathead River 

in vicinity southwest corner sec. 14, T. 33 N., R. 20 W., 

Flathead County._______________________________ In pocket

26. Geologic cross sections illustrating leakage possibilities from 

Glacier View reservoir, Flathead County and Glacier National 

Park________________________________-____________ In pocket

FIGURE 1. Geologic map and cross section of Tunnel No. 8 dam site,

center NJ_ sec. 28, T. 33 N., R. 34 W., Lincoln County, Mont- 27

2. Index map showing Hungry Horse dam and reservoir site in 

their relation to the drainage area of South Fork of Flathead 

River_________________________________ 38

3. Mechanical analyses of glacial boulder clays___ _____-______ 71

4. Diagrammatic section showing regional geologic setting of

Hungry Horse dam site._____________-__---_--__-_-_--- 89

5. Diagram showing relation of strike of beds and joints to

direction of river flow.________________-__---____---_-__ 92

6. Graphic comparison of dam sections, Hungry Horse site____ 99

7. Typical analyses of river and spring waters, Hungry Horse

project-______________________________________________ 103

8. Index map showing relation of buried glacial groges to South

Fork of Flathead River and Hungry Horse reservoir. ______ 106

9. Map showing probable major drainage changes of the Upper

Flathead River, Flathead County...._____________ 126

10. Geologic cross section at Columbia Falls dam site along streamgaging cable, sec. 17, T. 30 N., R. 20 W., Flathead County.. 145

11. Geologic cross sections at Lower Canyon Creek dam site, sec.

35, T. 32 N., R. 20 W., Flathead County................. 177
UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Water-Supply Paper 866-A

GEOLOGY OF DAM SITES ON THE

UPPER TRIBUTARIES OF THE COLUMBIA RIVER

IN IDAHO AND MONTANA

PART 1. KATKA, TUNNEL NO. 8, AND KOOTENAI FALLS

DAM SITES, KOOTENAI RIVER

IDAHO AND MONTANA

By 

C. E. ERDMANN

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1941

For sale toy t&e Superintendent of Documents, Washington, D. C. - - - - Price 25 cents

CONTENTS

Page

Abstract. _________________________________________________________ 1

ntroduction_ _____________________________________________________ 1

Location of the dam site6-___---_-_______-___-___-____-_________ 2

Purpose of proposed dams______________________________________ 2

Literature and mapS-___-_--_--___-_-_-_-_______-_-____________ 3

Cultural development-_________________________________________ 4

Climate ______-______-___--__--___-____-__-____---_____-______ 5

Topography and drainage-__-----_--_______--___---__---__-____ 6

Kootenai River---____-_-___-_-_________-_____-__-__-______ 7

Discharge and drainage area._______________________________ 7

Valley profile____-----------_----_-____--___---_--___-___- 8

Gradient _________________________________________________ 9

Geology __________________________________________________________ 10

Stratigraphy _ _________________________________________________ 10

Pre-Cambrian rocks (Belt series)_________-___---__--________ 10

Tertiary and Quaternary deposits.___________________________ 11

Igneous rocks _________________________________________________ 11

Moyie sills________________________________________________ 11

Geologic structure.________-----__-_____-___-_____-___-________ 12"

Leonia fault._____________________________________________ 13

Tunnel No. 8 fault_____----_---__--_______-____--______ 14

Savage Lake fault_________________________________________ 14

Mountain folds__________---_--___-____-___-___-_-___-____ 15

Earthquake probability.___________________________________ 17

atka dam site _____-__---__--_-_-_-_---___-___-___--_____________ 18

Location _____________________________________________________ 18

Stream gradient.______________________________________________ 18

Catchment area_______________________________________________ 18

Purpose of dam.___---_____-_-_-----__--_________-__-_________ 18

Valley profile._.____________________________________ ____ 18

Apparent possible height of dam_______________________________ 18

Character and depth of valley fill________________________________ 18

Country rock_________________________________________________ 18

Dips_________________________________________________________ 1$

Joints._______________________________________________________ 1&

Faults______________________________________________________ 20

Ground-water conditions.__--_-____--__--___---__-_-____-______ 20

Permeability, _________________________________________________ 20

Dam section __________________________________________________ 21

Abutments and foundation_____________________________________ 21

Height and length of possible dam_______________________________ 21

Appurtenant works__---_---_-_-_-__---_______-________________ 22

Reservoir area_ _______________________________________________ 22

Conclusions and recommendations_______________________________ 22

in
IV CONTENTS

Page 

Tunnel No. 8 dam site-_____-___-___-_-_-_____________----__-______

Location _____________________________________________________

Stream gradient.______________________________________________

Catchment area______________________________________________

Purpose of dam_______________________________________________

Valley profile_________________________________________________

Apparent possible height of dam_______________________________

Character and depth of valley fill________________________________

Country rock _________________________________________________

Dips.________________________________________________________

Joints. _______________________________________________________

Faults______________________________________________________

Ground-water conditions_______________________________________

Permeability __________________________________________________

Dam section._________________________________________________

Abutments _____________________--_-_-___--___--___-___--____-

Foundation-__________________________________________________

Appurtenant works____________________________________________

Heservoir area________________-__---_---_-___-___--_-__-______

 Construction materials.________________________________________

Conclusions and recommendations_______________________________

Kootenai Falls dam sites.__________________________________________

Location._________________-____----_-_--__-----_-_-___-______

Stream gradient._______________-_---_----_--_-__----_-_--_____

Catchment area_______________________________________________

Purpose of dam________-__-_-_-----_--__----_--__-_---_----__-

Valley profile_______________-__-_-----__----_--------__-______

Apparent possible height of dam__________-_-_________-__________

Character and depth of valley fill _____________________________

Country rock.________________________________________________

Dips_ _--______-________-__----_----_-----------------------__

Joints._________________-__-_-_----------------_-----_-------_

Faults and folds-________-_--_-_-----------_---_-----_---------

Ground-water conditions.________---__-----___-_-_--____-______

Permeability- ________________-__---__--_---_--_--_-------__--_

Original section at lower dam site______________________________

Relocated section at lower dam site________-_____________________

Section at upper dam site_____________________________________

Comparison of sections.________________________________________

Choice of section_____________________-_--____-___--__-_--____-

Appurtenant works.___________________________________________

Reservoir area_________________-_--__-----_--__-----_-----____

ILLUSTRATIONS

PLATE 1. Index map of northwestern Montana and northeastern Idaho 

showing location of dam sites on Kootenai River._________

2. Geologic map of Katka dam site, N>_ sec. 31, T. 62 N., R. 3 E., 

Boundary County, Idaho_______________-_-_-____________

3. _4, View upstream through Katka dam site, Idaho; B, Kootenai 

River trench upstream from Katka dam site, Idaho.________
CONTENTS V

Page

PLATE 4. A, View downstream through Tunnel No. 8 dam site, Montana; 

JB, Kootenai River trench upstream from Tunnel No. 8 dam 

site, Montana_________________________________________ 27

5. Geologic map and cross sections of Kootenai Falls dam site, sees.

13 and 14, T. 31 N., R. 33 W., Lincoln County, Mont___._ 34

6. A, Kootenai River valley above Kootenai Falls, Mont.; B, Right

abutment of lower dam site at Kootenai Falls, Mont________ 34

7. A, Suggested new location of left abutment at lower Kootenai 

Falls dam site, Montana; B, View southeast along axis of upper 

Kootenai Falls dam site, Montana._______________________ 35

FIGURE 1. Geologic map and cross section of Tunnel No. 8 dam site, center

NM sec. 28, T. 33 N., R. 34 W., Lincoln County, Mont___ 27

GEOLOGY OF DAM SITES ON THE UPPER TRIBUTARIES OF 

THE COLUMBIA RIVER IN IDAHO AND MONTANA

PART 1. KATKA, TUNNEL NO. 8, AND KOOTENAI FALLS DAM 

SITES, KOOTENAI RIVER, IDAHO AND MONTANA

By C. E. ERDMANN

ABSTRACT

Geologic conditions and cultural development in three dam-site areas on the 

Kootenai River between Katka, Idaho, and Kootenai Falls, Mont., are discussed.

The main line of the Great Northern Railway parallels the left bank of the 

Kootenai River between Katka and Kootenai Falls, and for long stretches the 

track level is not far above the water surface. An important control on river 

ievelopment is exerted by the railroad, as it is the principal cultural feature in 

the valley. The dam sites are considered primarily, as though the railroad did 

lot exist, and the effect of cultural control on the sites is developed secondarily, 

[f cultural control had been given primary consideration, it would have precluded 

geologic examination of two of the sites.

The Katka site, in the N}£ sec. 31, T. 62 N., R. 3 E., Boundary County, Idaho, 

ippears to be the best natural location for a high dam to control the Kootenai 

River in the United.States. The favorable features of the site are, however, 

lullified by the presence of the railroad at low elevations in the dam and reservoir 

site.

Tunnel No. 8 site, in the E^NW^ sec. 28, T. 33 N., R. 34 W., Lincoln County, 

Mont., has geologic and cultural conditions that make it unsuitable as a dam site.

The Kootenai Falls sites, in sees. 13 and 14, T. 31 N., R. 33 W., Lincoln County, 

Mont., have favorable geologic conditions and can be developed without endangerng the railroad.

Topographic and geologic investigation of the sites was made during the field 

season of 1934 by engineers and geologists of the conservation branch of the 

jreological Survey, United States Department of the Interior, through funds 

lupplied by the Public Works Administration.

INTRODUCTION

Under a comprehensive program of surveys of western rivers for 

Dower-classification purposes, expedited greatly during 1933-37 by 

'unds of the Public Works Administration, the survey of the Kootenai 

Eliver was extended upstream from a point 1 mile below the mouth of 

he Moyie River l to a point 3 miles below Troy,2 and from a point 3

1 Plan of Kootenai River, Idaho, international boundary to a point 1 mile below Moyie River, scale; 

:12,000, contour interval, 2 feet, 9 sheets, U. S. Geol. Survey, Washington, 1928.

2 Plan and profile of Kootenai River, Mont., from a point 3 miles below Troy to a point 3 miles above 

Jibby, scale 1:48,000, contour intervals. 20 feet and 5 feet, U. S. Geol. Survey, Washington, 1932. This map 

las been enlarged to 1:31,680 and published as sheet B of the 1937 edition of Kootenai River maps.

1
2 BAM SITES ON TRIBUTARIES OF COLUMBIA RIVER

miles above Libby to the international boundary at Gateway, Mont. 

Three dam-site areas were selected by W. C. G. Senkpiel, associate 

hydraulic engineer, Geological Survey, United States Department of 

the Interior, and mapped under his supervision by Norman B. Benson, 

Gilbert Griswold, and D. H. Griswold, junior topographic engineers,. 

Public Works Administration. The writer, assisted by John S. 

James, of Helena, Mont., made a geologic field examination of the 

sites in the faU of 1934.

LOCATION OF THE DAM SITES

The location of each of the dam-site areas is shown on plate 1. 

The names of the four sites and a description of their respective 

locations by legal subdivisions follows:

Katka site NJ4 sec. 31, T. 62 N., R. 3 E., Boundary County, Idaho. 

Tunnel No. 8 site E^NW^ sec. 28, T. 33 N., R. 34 W., Lincoln

County, Mont. 

Kootenai Falls sites sees. 13 and 14, T. 31 N., R. 33 W., Lincoln

County, Mont.

The Katka site is about a mile upstream from the Katka station 

of the Great Northern Railway which is on the left bank of the river, 

10 miles above Bonners Ferry; the right bank of the site is 26 miles 

from Bonners Ferry by way of the road to Glass ranch. This road 

is shown on the topographic map of the Priest Lake quadrangle.

Tunnel No. 8 site is about \% miles east of the Idaho-Montana 

boundary and 2 miles upstream from Leonia, Idaho.

The Kootenai Falls sites comprise an upper site and a lower site. 

The upper site is 500 feet downstream from the Kootenai Falls station 

of the Great Northern Railway, 11 miles by road from Libby, and 

8 miles from Troy; the lower site is 4,500 feet downstream from the 

station.

PURPOSE OF PROPOSED DAMS

Development of hydroelectric power is the principal reason for 

considering the construction of dams hi the Kootenai River.

The highest dam that could be constructed at the Katka site would 

provide adequate storage capacity for irrigation or flood control, 

but cultural development in the area that would be affected makes 

such a dam impracticable. None of the other three sites would 

provide adequate storage capacity for such purposes.

Stream regulation throughout the Kootenai Valley would be beneficial, as it would afford protection not only to the railroad and Bonners 

Ferry but also to the agricultural development on the delta plain 

at the head of Kootenai Lake,3 in British Columbia. The lake 

itself is, however, the only reservoir available that would be suit-

»Spelled Kootenay in Canada.
GEOLOGICAL SURVEY WATEE-STTPPLY PAPEK 

USPLATE 1

DAM SITES 

Katka 

Tunnel No.8 

Kootenai Falls

INDEX MAP OF NORTHWESTERN MONTANA AND NORTHEASTERN IDAHO, SHOWING LOCATION OF DAM SITES ON KOOTENAI RIVER.

INTBODUfcTlON 6

able for stream regulation, and the benefits that could be derived 

therefrom would naturally obtain below the lake both in the Kootenai 

and the Columbia Rivers. A dam with facilities capable of storing 

water in Kootenai Lake was built several years ago in the Kootenai 

River below the lake, but authorization for regulation of the dam in 

a manner that would raise river levels in Idaho was not obtained 

until 1939.

The Kootenai River in Canada has been discussed briefly by the 

Army engineers 4 in their report on the Columbia River. With 

regard to power sites on the part of the river within the United States, 

the Army engineers 5 state:

761. There are but two important power sites on that portion of the Kootenai 

within the United States, the upper one at Kootenai Falls between Libby and 

Troy, Mont., and the lower one near Leonia, Idaho, at the Montana-Idaho 

line. E. W. Krarner estimated the power available at these sites to be 20,000 

horsepower at Kootenai Falls and 11,000 horsepower at Leonia. The Kootenai 

Power Construction Co., under date of June 4, 1921, applied to the Federal Power 

Commission for a preliminary permit for power development at the Kootenai 

Falls site, but the application was rejected by the Commission on March 2, 

1923. Mr. Krarner reported heads of 89 and 50 feet at these two sites, respectively. 

The mean monthly flow for the past 17 years at Libby, Mont., upstream from 

these sites, was 11,700 second-feet, and the Q50 flow was approximately 5,500 

second-feet, the Q90 flow was approximately 3,000 second-feet, and the Q100 

flow was 2,170 second-feet. To be conservative no allowance is here made for 

inflow below the gaging station. From these data the power duration with 

natural flow at 80 percent efficiency in kilowatts at these 2 sites is estimated to 

be as shown herewith:

Site

Kootenai Falls ___________ _______ _ __ .

Leonia ___ . ______________ ___ . __ __ _

50

Kilowatts 

33, 300

18,700

Percent of time

90

Kilowatts 

18,200

10,200

100

Kilowatts 

13,100

7,400

LITERATURE AND MAPS

The power possibilities of the Kootenai River have been made the 

subject of a reconnaissance report to the United States Forest Service 

by Kramer. 6 This report mentions briefly the Leonia and Kootenai 

Falls dam sites. Kramer 7 has also made a special report on the 

Kootenai Falls project. These reports have been summarized by the

4 Columbia River and minor tributaries, reports of the district engineers at Seattle, Wash., and Portland, 

Oreg., 73d Cong., 1st sess., H. Doc. 103, vol. 2, p. 801,1934.

1 Idem, p. 800.

' Kramer, E. W., Water power in Montana, ¥. 8. Forest Service, unpublished report, Jan. 28,1931.

i Kramer, E. W., District engineers' report on application of Kootenai Power Construction Co. for a 

final water power permit on the Kootenai River near Libby, Mont., Kootenai National Forest, Missoula, 

Mont., Feb. 15, 1913 (manuscript report on file in the offices of the Forest Service in Washington, D. C,. 

and Missoula and Libby, Mont.). 

250683 41 2
4 DiAM SITES ON TR'IBITiTAKIES OF COLUMBIA EIVEE.

Army engineers 8 and included in their voluminous report on the 

Columbia River.

The topographic map of the Kootenai National Forest (scale, 2 

miles to the inch; contour interval, 200 feet) is an excellent base map 

of the entire region. More detail of a part of this area, which includes 

the Kootenai Falls dam site, is furnished by the topographic map of 

the Libby quadrangle (scale, 1:125,000, contour interval, 100 feet). 

The 1913 edition of the map of the Priest Lake quadrangle (scale, 

1:250,000, contour interval, 200 feet) includes the Katka and Tunnel 

No. 8 dam sites. Late in 1937 the Geological Survey printed in nine 

sheets the plan and profile of the Kootenai River from a point 1 mile 

below Moyie River, Idaho, to the international boundary, Mont. 

The dam-site areas are shown on sheets A and B (scale, 1:31,680, 

contour interval, on land 20 feet, and on water 5 feet), and the detailed surveys of the dam sites (scale, 1:4,800, contour intervals, 

10 and 20 feet) are shown on sheets F and G.

With the exception of the early work of Daly 9 along the international boundary and the recent survey of the Libby quadrangle, 

little systematic geologic work has been done in that part of the 

Kootenai River Valley that lies within the United States. The pioneer 

investigation was made by Gibbs 10 in the course of his exploration 

of the northwest boundary of the United States in 1857-1860. In 

1905 Calkins, 11 in a reconnaissance of western Idaho and northwestern 

Montana, crossed the valley near Troy and Libby, Mont., and tfavversed it from Leonia to Port Hill, Idaho. Davis 12 passed through the 

valley in 1913 and 1914 and has given a vivid description of its glacial 

features, particularly of those in the part between Bonners Ferry, 

Idaho, and Kootenai Lake, in British Columbia.

Throughout the period 1920-34 Gibson 13 and his associates carried 

on a thorough study of the geology of the Libby quadrangle. Their 

comprehensive report affords an excellent basis for further study of 

the region. Numerous references are made to the report in the 

following pages.

CULTURAL DEVELOPMENT

The principal towns in the Kootenai River Valley are Bonners 

Ferry, Idaho, which has a population of 1,418 and whose chief indus-

« 73d. Gong., 1st. sess., H. Doc. 103, vol. 2, pp. 800-801.

«Daly, R. A., Geology of the North American Cordillera at the 49th parallel: Qeol. Survey Canada, 

Mem. 38,1912.

1" Gibbs, George, Physical geography of the northwestern boundary of the United States: Jour. Am. 

Geog. Soc., vol. 3, pp. 147, 156, 157, 378-382, 387-388, 1873.

11 Calkins, F. C., A geological reconnaissance in northern Idaho and northwestern Montana: II. S. Geol. 

Survey Bull. 384,112 pp., 1909.

" Davis, W. M.,Features of glacial origin in Montana and Idaho: Assoc. Am. Geographers Annals, vol. 

10, pp. 97-104 [19201.

" Gibson, Russell, Geology and ore deposits of the Libby quadrangle, Mont., with descriptions of the 

glaciation by W. C. Alden and the physiography by 3. T. Pardee: U. S. Geol. Survey Bull. 

(in preparation).
INTRODUCTION O

tries are lumbering, agriculture, and railroading; Troy, Mont., a local 

mining center, with a population of 869; and Libby, Mont., which has 

a population of 2,947 and whose principal industries are mining and 

lumbering. Leonia, Idaho, a small mining community on the State 

line, is about midway between Bonners Ferry and Troy. Other than 

the railroad and Leonia, no development exists in the valley bottom 

between Bonners Ferry and Troy. North of the river, on the broad, 

high bench that flanks the base of the Purcell Kange, are some small, 

partly forested farms.

Failure of a high dam at any point on the river above Bonners 

Ferry and Troy would probably destroy both towns. Such a disaster 

would also flood the railroad and its small stations. The track level 

is so near the surface of the river that it has been flooded twice, once 

in 1894 and again in 1916. In 1894 the water was so high that boats 

were used in the streets of Bonners Ferry, which is 1,787 feet above 

sea level. In the spring of 1916, 4 feet of water flowed through tunnel 

No. 8 for 4 days. Even in normal years spring flood waters come 

within a few feet of the ties at many places. The natural constrictions of the river develop high backwater during flood periods, 

and, as the sites under consideration are the most economical sites 

available for dams, improvement of flood conditions could not be 

expected by the construction of low movable dams, however fine and 

delicate their control.

A cursory examination does not reveal any feasible possibility of 

rerouting the railroad out of the inner gorge below Troy. The altitude of Troy is 1,889 feet above sea level, and the altitude of the river 

surface is about 1,870 feet at ordinary stage. An alternative route 

from Troy would cross the river at or near the town, ascend to the 

bench at the base of the Purcell Kange, and then parallel United States 

Highway No. 2 to Moyie Falls, where connection with the Spokane 

International Railway into Bonners Ferry could be made, the main 

line of the Great Northern Railway being resumed below Bonners 

Ferry.

CLIMATE

The following summary of climatological data is based on records 

of the United States Weather Bureau at Libby, Mont.

Summary of climatological data, Libby, Mont., 1895-1936

Annual precipitation, mean____________________.inches._ 19. 22

Annual snowfall-____________________________inches__ 50. 75

Mean temperature______-_____-_______________-_°F__ 44. 6

Highest temperature___..___._____________°F__ 109

Lowest temperature-___._-_----.---______-_-___._°F_. 46
6 DlAM SITES ON TRIBUTARIES' OF1 COLUMBIA; RIVER 

TOPOGRAPHY AND DRAINAGE

Northwestern Montana and northern Idaho (see pi. 1) are occupied 

by several irregular groups of mountains and two conspicuous linear 

depressions. These depressed areas and the major streams form the 

geographic and, in some places, the geologic boundaries of the mountain ranges. The eastern depression is known, in the structural sense, 

as the Rocky Mountain trench. 14 It is about 800 miles long, and about 

160 miles of its length is in Montana. It trends to the northwest, 

the axis crossing the international boundary at about 115° 10' west 

longitude. The width varies, narrowing northward, and between 

Gateway, Mont., and Golden, British Columbia, averages about 5 

miles. The floor of this trough is much aggraded and contains parts 

of the Columbia, Kootenai, Tobacco, Stillwater, and Flathead Rivers 

and Flathead Lake.

The axis of a similar depression, called the Purcell Trench,15 crosses 

the international boundary at 116° 30' west longitude, parallel to and 

about 60 miles west of the Rocky Mountain Trench. The floor of the 

Purcell trench also is aggraded and contains Lake Pend Oreille, the 

Kootenai River below Bonners Ferry, Idaho, and Kootenai Lake, in 

British Columbia. At the international boundary, the Rocky Mountain trench is flanked on the east by the Whitefish Range, known in 

Canada as the Galton Range, and the Purcell trench is flanked on the 

west by the Selkirk Range.

The Purcell Mountains extend into the United States between the 

trenches as far south as the transverse valley of the Kootenai River. 

The part in British Columbia has been described by Schofield,16 the 

part along the international boundary by Daly,17 and the part in the 

United States by Calkins.18 The Cabinet Mountains are bounded on 

the north, downstream from Libby, by the Kootenai River; on the 

west by the Purcell trench; on the south, from Lake Pend Oreille to 

the town of Perma, by the Clark Fork River; and on the east and 

northeast by the Little Bitterroot and Fisher Rivers. They have been 

mentioned briefly by Calkins,19 but their geologic features outside of 

the Libby quadrangle, which has been mapped recently by Gibson,20 

afe not known in detail. Another irregular mountain mass lies east 

of the Purcell Range, from which it is separated by the Kootenai River. 

It has been known as the Flathead Mountains, although Clapp 21 in

14 Daly, R. A., The nomenclature of the North American Cordillera between the 47th and 53d parallels 

of latitude: Geog. Jour., vol. 27, p. 596, London, 1906.

"Daly, R. A., op. cit, p. 597.

18 Schofield, S. J., Geology of Cranbrook map area, B. C.: Canada Geol. Survey, Mem. 76,1915.

" Daly, R. A., Geology of the North American Cordillera at the 49th parallel: Geol. Survey Canada, 

Mem. 38, vol. 1, pp. 119-137,1912.

18 Calkins, F. C., op cit., p. 16,1909.

" Calkins, F. C., op. cit., pp. 14,15,16.

M Gibson, Russell, op. cit.

11 Clapp, C. H., Geology of a portion of the Rocky Mountains of northwestern Montana: Montana Bur. 

Mines and Geol., Mem. 4, p. 14,1932.
INTRODUCTION 7

1932 suggested the name Selish Range,22 which has not otherwise 

been used.

KOOTENAI RIVER

All the waters that rise in the mountainous areas described above 

form the headwaters of the Columbia River. The Kootenai River 

rises in the Rocky Mountain Trench, near Golden, British Columbia, 

where a narrow divide separates it from the headwaters of the main 

Columbia River. The river follows the trench southward to Rexford, Mont., which is a few miles south of the international boundary, 

and then leaves the trough and flows southwestward along the east 

flank of the Purcell Range to Jennings, at the mouth of the Fisher 

River, 12 miles east of Libby. From Jennings to Bonners Ferryr 

Idaho, where it enters the Purcell Trench, the river flows directly 

through the mountains. After entering the Purcell Trench, the river 

flows northward, crossing the international boundary at Port Hill, 

Idaho, and then widens out into Kootenai Lake, 16 miles north of the 

boundary. Thus along the international boundary the river forms 

a loop about 60 miles wide, which at its southernmost point, swings 

43 miles into the United States. (See pi. 1.)

DISCHARGE AND DRAINAGE AREA

The size of the Kootenai River may be indicated by the following 

data on the mean monthly flow for 1932: 23 Rexford, Mont., 10,900 

second-feet; Libby,, Mont., 11,900 second-feet; and Copeland, Idaho, 

15,700 second-feet. The maximum discharge between these points 

ranges from 61,000 to 75,000 second-feet, and the high-water months 

are May, June, and July. In 1932 the mean accession within the 

United States was about 4,800 second-feet, which was contributed 

chiefly by the Tobacco, Fisher, Yaak, and Moyie Rivers and numerous 

small streams. (See pi. 1.) The drainage area in British Columbia, 

above Rexford, Mont., is about 8,420 square miles; above Libby, 

Mont., the area is 11,000 square miles; and at Copeland, Idaho, the 

outgoing international gaging station, it is 13,400 square miles. 

Most of this area is forested, and consequently the river is free from 

silt, except in time of flood. The color of the water is a translucent 

bluish-green.

The chemical character of the water during the low-water stage is 

shown by the following analysis 24 of a sample taken at Kootenai 

Falls in October 1934.

22 The spelling Salish, not Selish, is used for the Indian tribe in Handbook of the American Indians: Bur. 

Am. Ethnology, Bull. 30, pt. 2, pp. 415-418,1910.

83 Surface water supply of the United States, 1932, part 12, North Pacific slope basins, A, Pacific slope 

basins in Washington and upper Columbia River Basin: U. S. Geol. Survey Water-Supply Paper 737, pp.. 

72-81,1934.

" Analysis by J. G. Crawford, U. S. Geol. Survey Lab., Midwest, Wyo., Lab. No. 35-W47, Oct. 17, 1934-
8 DiAM SITES ON TRIBUTARIES OF COLUMBIA RIVER

Reacting values

Sulfate . -- -_ _ 

Chloride ___________ _________ ________

Parts per 

million

16

37

g

31

5

148

Reacting 

value

0.71

1.85

.66

.65

.14

2.43

Value in percent

11.02

28.73

10.25

10.10

2.17

37.73

Properties of reaction

Percent 

Primary salinity_--_--______--_____________----__---__- 22. 04

Secondary salinity__-_-_-_-___-___--____-__-_-_-_-_-_-_ 2. 50

Primary alkalinity__-_-_-_____--.-----.--_-----_-_--_--__ 0

Secondary alkalinity____________--___-____-______-_-_-_ 75. 46

Chloride salinity ___ ____________ _ __ _ _________ _ _ 17. 68

Sulphate salinity_______. ________ __ _-_--_-_-_-----_-_ 82. 32

m . ^ TJ Parts per Total sohds million

By evaporation __ ___________-_-__-___--_-_-____--__--__ 178

After ignition. __________________________________________ 163

_____-_________ -_----__-_-_-_----_-__---_-__ 170

VALIJBY PROFTLE

The cross-sectional profile of the Kootenai Valley between Troy 

and the mouth of the Moyie Kiver is asymmetric. Within distances 

of 4 to 8 miles the slopes of the left, or south bank, rise from the 

water surface, whose altitude ranges from 1,800 to 1,860 feet, to the 

summit of the Cabinet Range, which stands at altitudes of about 

6,400 feet. The bottom of the valley is narrow, and the river is 

closely confined by the lower walls, its width seldom being more than 

600 feet. The right, or north bank, rises abruptly to altitudes of 

2,400 to 2,600 feet and then flattens to a slope that within 2 to 4 

miles rises by small steps to an altitude of about 2,800 feet, the base 

of the Purcell Range, and then ascends sharply to the regional 

summit level. This broad bench narrows upstream and seems to 

disappear at the mouth of Kootenai Falls gorge. The inner trench 

of the river, from 200 to 600 feet deep, follows closely the left wall 

of the old valley. (See topographic map of the Priest Lake quadrangle.)

The gorge between Libby and Troy is about 9 miles long. Its 

cross section is a wide, flat U rather than the broad V of a valley formed 

by normal stream erosion. In the middle and upper parts of the 

gorge the floor is flat and narrow, and the steep walls flare outward 

to altitudes of about 2,400 feet. The slopes to higher altitudes are 

gentler. The hanging tributaries, somewhat modified by recent 

erosion at the mouths of Burrell, China, and Koot Creeks, once 

may have been accordant with their trunk stream at an altitude of
INTRODUCTION 9

about 2,500 feet, the approximate average altitude of the downstream 

bench. At the head of Kootenai Falls, the altitude of the valley 

floor is about 1,975 feet, which indicates an overdeepening of about 

525 feet. Alden 25 has shown that the 2,500-foot constructional terraces 

on the major streams in the Libby quadrangle are related to the 

2,500-foot stage of the waning glacial Lake Missoula, a comparatively 

recent geologic event. Pardee 26 has suggested that the silt fill at this 

level in the valley below Kootenai Falls may be referred to the same 

cause. If the hanging tributaries are related to this fill, however, 

erosion must have proceeded with extraordinary rapidity to reduce 

the valley floor to its present elevation. Valley glaciation offers an 

alternative explanation for the presence of these features. Below 

the head of Kootenai Falls, the valley floor has been incised by the 

stream to a depth of about 85 feet; above the falls it is intact. Upstream from Libby, the valley broadens and opens again and is different 

in character from the two sections just described.

GRADIENT

The profile of the part of the Kootenai River under discussion is 

shown on sheets H and I of the river maps,27 adjustment being made 

for ordinary low water stage. Both above and below Kootenai Falls, 

the stream flows smoothly over alluvium for long distances. From 

mile 4.5, \% miles downstream from Katka dam site, to mile 13.5, 

just below Tunnel No. 8 dam site, the river surface drops 40 feet, or 

4.4 feet per mile. Through Tunnel No. 8 dam site (mile 14) the gradient is about 3.5 feet per mile. From here to the foot of the Kootenai 

Falls section, at mile 31.75, the average gradient is 4.3 feet per mile. 

Upstream from Libby also the gradient is low, and a slope of 4 feet 

per mile may be considered as normal for the river. These stretches 

contrast markedly with the character of the stream in the gorge, 

which is entered just below the mouth of Bobtail Creek, 4 miles 

west of Libby. The gradient is normal, or a little less than normal, 

to the mouth of Dad Creek; then it increases to 11 feet per mile 

from here to Burrell Creek, a distance of 1 mile. Rapids also occur 

in the next \% miles. In the mile stretch just above the head of the 

falls, however, the river surface drops only 3 feet.

The Kootenai Falls consist of a series of short falls or rapids, 

that make a total drop of about 85 feet in 1.85 miles. The upper falls 

are the highest and drop about 30 feet in a distance of 600 feet over 

a series of ledges that dip upstream. A middle rapid that extends

25 Alden, W. C., Pleistocene glaciation, in Gibson, Russell, Geology and ore deposits of the Libby 

quadrangle, Mont.: U. S. Geol. Survey Bull. (in preparation).

28 Pardee, J. T., Personal communication.

27 Plan and profile of the Kootenai River from a point 1 mile below Moyie River, Idaho, to the international 

boundary, Mont., scale, 1:31,680, contour intervals, 20 feet and 5 feet, 9 sheets, U. S. Geol. Survey, Washington, 1937.
10 DiAM SITES OF TBIBUITARIES OF COLUMBIA KIVEft

1,000 feet upstream from the mouth of Koot Creek has a drop of 

about 15 feet. The lower rapids begin about 500 feet below the cable 

bridge and continue downstream to the lower dam site, making a 

drop of about 15 feet over a distance of 1,200 feet. These three 

rapids account for 60 feet of the fall. The remainder of the stream, 

which is by no means quiet, drops 25 feet in a total distance of 4,200 

feet. The lower end of the falls section occurs at mile 31.75, and the 

northward projection of the Savage Lake fault crosses the river at 

approximately the same place.

GEOLOGY 

STRATIGRAPHY

The rock formations exposed in the Kootenai Valley between 

Kootenai Falls and Katka are of widely divergent ages. The old, 

hard rocks consist chiefly of a thick assemblage of pre-Cambrian 

strata that have been invaded locally by tabular masses of basic 

igneous rock. Soft, unconsolidated deposits of Pleistocene silt and 

Recent alluvium rest unconformably upon them in the valley and on 

the benches.

PRE-CAMBRIAN ROCKS (BELT SERIES)

The Belt series is subdivided into a number of formations or 

mappable units, chiefly on the basis of lithology. The lower and 

middle parts of the series are present along the river, and, from oldest 

to youngest, the formations are Prichard, Ravalli, and Wallace. 

The Wallace is overlain by the Striped Peak formation, which is not 

involved in any of the dam-site areas.

In their original state these rocks were composed of well-bedded 

deposits of fine-grained sandstone, clayey sandstone and siltstone, 

and clayey magnesian limestone. Over wide areas, toward the end 

of the deposition of the Wallace formation, they were invaded by 

basic igneous rock, and the surface of the Wallace, or its equivalent, 

was covered by a sheet of this material. In their present condition, 

the rocks of the series are now described as quartzite, argillite, metaargillite, and siliceous dolomitic limestone. The igneous rocks 

approach amphibolites in character.

With the exception of argillite and meta-argillite, these terms are 

more or less familiar to the engineer, as they define rock types encountered frequently. An argillite may be defined as the derivative of 

mudstone, siltstone, or shale by incipient static metamorphism. It 

is less thoroughly altered than a slate, which is a product of dynamic 

metamorphism. A meta-argillite is more or less thoroughly recrystallized, but retains its original structures and does not show marked 

evidence of schistosity or slaty cleavage.
GEOLOGY 11 

TERTIARY AND QUATERNARY DEPOSITS

The lake beds, laid down in the Kootenai Valley when ponding 

occurred, are not present in any of the dam or reservoir sites. Small 

amounts of Kecent alluvium are present, but no deposits of glacial 

drift.

IGNEOUS BOCKS 

MOYIE SHJL.S

The steeply inclined pre-Cambrian strata between Bonners Ferry 

and a point about a mile east of Leonia, Mont., have been invaded 

by tabular masses of basic igneous rock, which, for the most part, are 

accordant with the bedding. This attitude, certain internal characteristics, and the relations of veins emanating from them into the 

country rock, indicate that these rock masses are sills. The sedimentary rocks must have been nearly horizontal when the intrusions 

occurred.

Three large Moyie sills and two minor intrusives, a sill and a dike, 

occur in the Katka district. The sills are shown in plate 2, but the 

dike occurs outside of the area mapped. The most important sill is 

the massive one whose resistance to erosion causes a notable restriction 

in the width of the gorge at the Katka dam site. This sill crosses the 

river at right angles, 4,500 feet upstream from the Katka station. 

Both its width at the surface and its thickness are about 700 feet. 

The enclosing beds are quartzites of the Prichard formation. The 

beds at the base of the sill dip 52° to 56° NE., and those at the top 

dip locally as much as 73° NE. These variations in dip give the mass 

a wedge-shaped cross section and suggest that it may disappear with 

depth. It also seems to decrease slightly in thickness from south to 

north. These differences are probably local and are due to crumpling 

or minor variations in the dip of the quartzite.

The rock of the sill is tougher and more resistant than the quartzite 

and makes even more of a ridge than is indicated by the topographic 

map. At first sight it appears to be fairly uniform throughout, but 

the dull, gray-green, weathered surface conceals some important differences in texture and composition. Examination of fresh surfaces 

shows that the rock is a dark-green hornblendite or hornblende gabbro. 

The grain at both the base and the top is fine, and the texture is 

dense and compact. Hornblende is the most conspicuous mineral, 

then plagioclase feldspar. Small amounts of metallic minerals present 

appear to be magnetite, chalcopyrite, and, possibly, pyrrhotite. The 

upper part of the sill shows more feldspar than the other parts and is 

cut by numerous quartz veins that have altered the sill rock adjoining 

them to a compact, medium-grained amphibolite. At a few places 

where these veins persist into the quartzite they have been prospected. 

The quartz varies in color from nearly white to a light gray and has a

250583 41 3
12 DlAM SITES ON TRiIBUITARIES OF COLUMBIA RIVER,

translucent luster. The only mineralization noted was a sparse scattering of pyrite and some malachite stain.

The internal portion of the sill, which forms both abutments of the 

dam site, is a coarse-grained hornblendite containing minor amounts 

of feldspar. Some of the individual laths of hornblende are half an 

inch long. The rock is strong, tough, and insoluble, and makes an 

excellent foundation for a dam.

According to Daly 28 the mineralogical composition of the dominant gabbroid type of the Moyie sills is:

Percent 

by weight

Hornblende__________________ 58. 7

Percent 

by weight

Biotite______________________ 0. 9

Apatite. ______________________ .2

100.0

Na2O__--_____-----__-_

K2O-_ - _-_

H2Oat 110° C . .--_

H2O above 110° ____.__

P2 0, _ 

CO2 ..______---_---_____

Percent 

______ 1.38

______ .47

______ .10

______ 1.07

______ .04

______ .06

99. 78

Labradorite-_----__-__-----_-_- 34. 8

Quartz___________-_--_-___-___ 4.0

Titanite and magnetite________ 1.4

A chemical analysis of the rock follows:

Percent

SiO2---~-~---~ -------- 51. 92

TiO2 __ .83

M2O3 .----------------------- 14. 13

Fe2O»__ _ _______ 2. 97

FeO-.. 6. 92

__-_____-___________._ .14

__--____-_--___-.__._- 8.22

CaO___.__-__-_____-_-_____-_ 11. 53

Specific gravity of the rock, 2.99.

In the other sills in the Prichard formation the character of the 

rocks is essentially the same as that of the rocks in the sill at the dam 

site. The thinner sills are slightly more uniform in composition. The 

sill in the Wallace (?) rocks is, however, finer-grained and does not 

show marked development of hornblende, except in its upper part, 

where plagioclase feldspar is also more abundant.

The dike rock consists of a small, badly weathered mass, in a fault 

about five-eighths of a mile above Katka dam site, on the left bank of 

the stream. It consists of innumerable small euhedral needles of 

black hornblende about 0.3 inch long, embedded in a dense, graygreen groundmass. Gibson w also observed dikes in similar situations 

in the Libby quadrangle, where they are associated with stocks thought 

to be late Mesozoic in age and related to the Idaho batholith.

GEOLOGIC STRUCTURE

Although the Kootenai River forms the geographic boundary between the Purcell and Cabinet Mountains from Troy, Mont., northwest to the Purcell Trench, these ranges are also separated structurally

as Daly, R. A., Geology of the North American Cordillera at the 49th parallel: Geol. Survey Canada, 

Mem. 38, p. 224, 1912. 

29 Gibson, Russell, op. cit.
GEOLOGY 13

in this region by the Leonia fault. Between Troy and Libby the Purcell and Cabinet Mountains are an unbroken geologic unit. The damsite areas are thus involved in two distinct types of geologic structure, 

the Leonia and subsidiary faults and the mountain folds at Kootenai 

Falls gorge.

UEONIA FATJI/T »»

The Leonia fault is a high-angle overthrust fault, with downthrow 

to the east and dip to the west. In addition to the pioneer observation of Calkins, the fault has also been studied by Kirkham31 and 

Gibson.32 The displacement is greatest near the north end, where the 

fault crosses the Kootenai River east of Cranbrook, British Columbia. 

According to Kirkham 33

The actual vertical displacement here reaches through at least 35,000 feet of 

Belt series alone, as well as 10,000 feet of interbedded basic sills in the AldridgePrichard and Creston-Ravalli formations and an unknown thickness of Purcell 

lavas interleaved with the Siyeh formation. As one goes southward to Moyie 

Lakes, the stratigraphic displacement becomes progressively less.

Gibson reports a displacement of "at least 26,000 feet" in the northwestern part of the Libby quadrangle. Thus, by interpolation, the 

displacement on the fault in the vicinity of Katka dam site is about 

30,000 feet.

The Leonia fault leaves the bed of the Kootenai River about 1,500 

feet upstream from the Katka dam site and passes into the north or 

right bank. The fault cannot be seen, owing to alluvium and slump 

of the Pleistocene silt from the higher benches. However, the position 

of the trace can probably be located within 400 feet. The strata dip 

toward it on either side, the dip of the Prichard formation on the west 

being 65° N. 60° E., and that of the younger beds on the east being 

85° S. 60° W.

A fault of unknown displacement, probably directly related to the 

Leonia fault that lies 300 feet northeast, is exposed in a railroad cut 

on the left bank of the river, half a mile upstream from the dam site. 

The strike, as determined from the single exposure, is approximately 

north, which may account for its nonappearance west of the Leonia 

fault on the north side of the river. The beds on the east or upstream 

side strike N. 35° W. and dip 68° S.; those on the west side strike N. 

30° W. and dip 58° N. On the west side, a short distance above the 

cut to the southeast, the beds strike N. 27° W. and dip 74° N. The 

dip of this fault could not be determined.

30 This fault was named by Calkins (U. S. Geol. Survey Bull. 384, p. 53) for the railway station of Leonia, 

Idaho, near which it passes. The spelling "Lenia," now well established, is probably due to a-typographical 

error. It seems advisable, however, if the fault is to be named for the town, to follow the spelling of the town 

name.

» Kirkham, V. R. D., The Moyie-Lenia overthrust fault: Jour. Geol., vol. 38, No. 4, pp. 364-374, 1930, 

1 map and 3 cross sections.

32 Gibson, Russell, op. cit.

SB Kirkham, V. R. D., op. cit., p. 371.
14 1MM SITES ON TTtlBUffARlES 6,F COLUMBIA.

Another fault of unknown displacement cuts the Prichard formation 

about 1,700 feet west of the Katka dam axis. (See pi. 2, section C-D.) 

This fault, also essentially parallel to the Leonia fault, strikes about 

N. 15° W., but the dip could not be observed accurately. It is probably nearly vertical, as the beds on the west side at a point 350 feet 

east of the bench mark that indicates an altitude of 1,809 feet are 

vertical, whereas those on the east side strike N. 18° W. and dip 66° E. 

On the right bank of the river the dips along the fault are opposed; 

those on the west side strike N. 26° W., and dip 58° E., and those on 

the east side strike N. 26° W. and dip 85° W. This zone of vertical 

or steep west dips is about 300 feet wide, and east of the zone the 

normal east dips are resumed at high angles.

TUNNEL NO. 8 FAULT

The fault at Tunnel No. 8 strikes west and dips 43° S. Its strike 

forms an angle of about 60° with the strike of the Leonia fault, which 

passes 1% miles to the south. The Wallace formation is present on 

both sides, so the displacement cannot be greater than its thickness, 

which is about 12,000 feet. This fault is characterized by a 3-foot 

zone of soft clayey gouge. The beds adjacent to the north side of the 

fault strike N. 33° W. and dip 59° W; those on the south side strike 

N. 31° W. and dip 65° W.

SAVAGE LAKE FAULT

The Savage Lake fault, named by Gibson,34 crosses the Kootenai 

River about a mile west of the mouth of Koot Creek, which enters the 

river at approximately the center of the Kootenai Falls dam-site area. 

The fault thus does not occur within the area mapped in plate 5. The 

following statements have been summarized from the work of Gibson, 

who observed the fault at the Crater prospect, 1 mile east of Savage 

Lake:

The fault zone is at least 40 feet wide and the downthrow is on the west * * * 

A persistent metadiorite dike, which in places is not very deeply buried in the 

till, probably follows the Savage Lake fault.

Along the mountain front east and southeast of Savage Lake there are slight 

depressions and small swamps, possibly indicating recent downward movement 

of the depressed block near the mountains.

The Kootenai Falls have also been interpreted by Pardee 35

as evidence of a very recent upward movement of the mountain block. The falls, 

a scenic feature of the gorge which Kootenai River has cut between the Libby and 

Troy basins are at the head of an inner gorge about 3 miles long. They appear 

entirely unrelated to any of the glacial features and are therefore assumed to have 

been initiated by uplift along the fault near the entrance to the gorge. Con34 Gibson, Russell, op. cit.

3J Pardee, J. T., Physiography of the Libby quadrangle, in Gibson, Russell, Geology and ore deposits of 

the Libby quadrangle, Mont.: U. S. Geol. Survey Bull. (in preparation).
GEOLOGY 15

sidering the vigor of the river and the fact that the rock is not particularly resistant, the upstream migration of the falls may easily have been accomplished since 

the Pleistocene.

MOUNTAIN FCXLDS

The geologic structure in the Kootenai Falls gorge is related to the 

Savage Lake fault and to an anticline that plunges to the northwest 

just east of the fault and whose west limb is cut off by the fault. The 

structure in the gorge thus consists of the east limb of the anticline 

and the floor of the syncline adjacent to it on the east. The axis of 

this syncline crosses the river about 5 miles downstream from Libby.

A complete view of the left wall of the gorge below the lower dam 

site at Kootenai Falls shows that the east limb of the great anticline 

descends into the syncline to the east by a series of sharp steplike 

structural terraces that are characterized by short, steep "risers" and 

narrow "treads." An entire unit, from base to head of riser, is shown 

in plate 5, section A-B. Another similar unit occurs high up on the 

left wall of the valley, downstream from the dam-site area, and probably others exist.

Between point A, plate 5, and section E-D, structural details of 

the base of the riser are well exposed in the new road cut. The beds 

involved are the massive argillites of the lower member of the Kootenai 

Falls section of the Wallace formation. A series of bedding faults are 

present, the first fault appearing along the road 525 feet southwest 

of the point where a small culvert cuts through the narrow rock ridge 

between the highway and the railroad. This fault strikes N. 30° W. 

and dips 47° E. The shear zone is about 15 inches thick; the upper 

6 inches consists of clay and gouge, and the basal part is a breccia. 

A bedding fault occurs at 553 feet, the hanging wall dipping 50° N. 

62° E. The beds in the footwall dip 36° in the same direction. A 

fault at 558 feet strikes S. 20° E. and dips 65° W., and the gray argillite on the west side dips 27° N. 79° E. Some evidence of movement 

exists along this zone, the gouge being 6 inches thick. At 690 feet 

there is a zone similar to that at 558 feet; the strike is S. 68° E., dip 

71° W. Another fault, at 990 feet, strikes S. 30° E. and dips 50° E.; 

the beds below the faults (west) are thin gray argillites that strike 

S. 30° E. and dip 51° E. Somewhat similar features appear along 

the road cut northeast of the culvert, and continue as far as the 

crumpled zone that forms the ten-ace or tread in the middle part of 

area shown on the map.

This zone begins abruptly with a small, steep fault, along which 

the footwall has been dragged upward by the development of two 

small, sharp, compressional, chevron folds. The fault strikes N. 46° 

W. and dips 81° W. Adjacent to the fault on the east is a j 3-foot 

shear zone in which the thin, dense bluish-gray argillites above algal 

bed D are greatly mashed and squeezed, but no gouge exists. These
16 BAM SITES ON TRIBUTARIES OF COLUMBIA RIVER

beds strike S. 52° E. and dip 87° W. This zone is crossed diagonally 

by cleavage planes that strike N. 42° W. and dip 53° W., the planes 

being spaced a foot or so apart. Normal to them is another set of 

more closely spaced cleavage planes that strike N. 36° W. and dip 

86° E. Striae on the surface of the fault show that the direction of 

movement along this fault is parallel to the dip. The throw is about 

25 feet. The two small folds adjoining the fault on the east are 

together 200 feet across at the base. The beds just west of the axis 

strike N. 48°-50° W. and dip about 40° E.; about 30 feet farther west 

the dip increases to 55°. The fracture cleavage at the base of the 

massive bed near the axis strikes N. 43° W. and dips 65° E. East of 

the axis of this flexure the strata are nearly horizontal and extend into 

a rather flat-floored syncline, about 400 feet wide, that has a small 

saddle near its center. The east limb of the flat syncline gradually 

rises into an anticline, about 400 feet in width, whose flat top has been 

slightly crumpled. This fold breaks down by steps into a narrow 

syncline that forms the west limit of the major anticlinal fold on the 

east side of the crumpled zone. This fold has the appearance of an 

inverted V. It is 300 feet across at the base and about 150 feet high. 

One more minor open flexure occurs, and then the top of the algal 

zone dips below the surface of the river and does not reappear within 

the dam-site area. The total length of this deformed area is about 

1,600 feet, and the amplitude of the folds, with the exception of the 

stronger folds at each end, is such as to confine them wholly to the 

algal zone.

The deformation of this structural terrace is probably due to the 

compression and shear of a relatively incompetent zone, the algal 

beds being the principal yielding members, between massive, rigid 

argillite members near the trough of a syncline. The deformed area, 

which shows some interesting features of structural symmetry, 

probably portrays in miniature the geologic structure of the Cabinet 

and Purcell Ranges. At the head of the structural terrace the small, 

sharp anticline east of the fault would have its counterpart in the 

mountain-forming anticline that lies to the east of the Savage Lake 

fault zone. The stairlike character of the limbs of the open folds 

and the flat-floored synclines are present on both a large and small 

scale.

The age of this deformation is difficult to determine, for the present 

attitude of the strata is the algebraic sum of all previous movements 

and, as has been explained, no strata later than pre-Cambrian, by 

which such movements could be separated, are present. The greater 

part of the deformation is credited commonly to the Rocky Mountain revolution in the late Mesozoic, but it is likely that some deformation accompanied the injection of the Moyie sills.
GEOLOGY 17

Gibson 36 determined that in the Libby quadrangle the folding preceded the major faulting, of which three periods may be distinguished. 

At some places the movements are continuing to the present day.

EARTHQUAKE PROBABILITY

Evaluation of the geologic stability of this region and the probability of future movement along these faults indicates that faults of 

the overthrust type and of the high-angle thrust or upthrust type 

would seem to be definitely quiescent, as the antecedent conditions 

that led to their development were dissipated by this same movement. 

Furthermore, no evidence of regeneration of stress exists.

This is not true, however, of old reverse faults on which the character of movement has changed, such as the Hope fault, or of normal 

faults, such as the Savage Lake fault. The post-glacial movement 

along the Savage Lake fault is of serious concern at the Kootenai 

Falls dam site, which is situated in the rising block a short distance 

east of the fault.

The apparent absence of activity along the old thrust faults and 

the lack of a historic record of seriously destructive shocks does not 

guarantee future immunity from earthquakes in this region. The 

length of the historic record for Idaho and Montana is so short, 

beginning in 1872 for Montana and in 1905 for Idaho, that insufficient 

time has elapsed to determine whether the few earthquakes that have 

been recorded are related to the existing faults or whether they have 

taken place elsewhere and are perhaps indicative of stress accumulation along new or incipient lines. Considering the geologic history 

and structure of northern Idaho and northwestern Montana, the 

earthquake activity seems small indeed.

From 1905 to 1927 only 12 earthquakes have been recorded for 

Idaho, and half of these took place during the years 1916 to 1918. 37 

None occurred within the region under consideration and only two 

near it. These were of medium intensity, and the small areas affected 

suggest that the foci lay at shallow depths. If earthquakes occur along 

the Kootenai River in the United States, they will probably be of this 

character. The most serious danger from such shocks would probably 

be secondary effects, such as landslides and collapse of tunnels. 

Nevertheless, the design of all dams should be made as nearly earthquake-proof as possible.

The earthquake frequency of the entire Rocky Mountain region 

has been investigated recently by Freeman,38 who states:

By reason of the scant records and the rugged topography, notwithstanding 

the distance from the ocean, it seems only prudent for an insurance company to

36 Gihson, Russell, op cit.

" Heck, H. N., Earthquake history of the United States: U. S. Coast and Qeod. Survey, Special Pub. 

149, p. 6,1928. 

«8 Freeman, J. R., Earthquake damage and earthquake insurance, p. 160, New York, 1932.
18 DAM SITES ON TEIBTJITARIES OF COLUMBIA ItlVEB,

base its premium rates for this Rocky Mountain-Wasatch region on the basis 

of expecting that at one place or another there may be an average of four serious 

earthquakes per century within this vast area of 1,120,000 square miles.

Freeman 39 also predicts that these four earthquakes will be of intensity IX or X, the intensity of the earthquake in Montana in 1925, 

and that

the resulting hazard of an occurrence of a destructive earthquake at any one 

city or area of 25 by 100 miles in any particular year is 1 to 11,200.

Inasmuch as the Rocky Mountain region, as defined by Freeman, 

includes the eastern margin of the Snake River lava plain, and other 

fairly active seismic areas, it is probable that an apparently quiescent 

area, such as that along the Kootenai River, is less active than his 

figures for the entire region would indicate.

KATKA DAM SITE

(See pis. 1 and 2)

Location. NK sec. 31, T. 62 N., R. 3 E., Boundary County, 

Idaho, about a mile upstream from Katka station on the Great 

Northern Railway.

Stream gradient. The gradient above the dam site is about 4 feet 

to the mile, but it is steeper between the axis of the proposed dam and 

Katka station.

Catchment area. The drainage area above the Geological Survey 

stream-gaging station at Katka covers 11,860 square miles. No 

upstream diversion is made.

Purpose oj dam. Power and flood control.

Valley profile. The width of the ancient high-level valley is near 

its maximum. The character of the inner gorge, in which the site 

is located, is shown in plate 2, section A-B.

Apparent possible height of dam. The general topographic character 

of the site is such that it would be suitable for a 430-foot dam.

Character and depth of valley fill. Owing to the force with which 

the river sweeps through the narrow gorge, only a small amount of 

alluvium is present in the channel at the axis of the dam. Above 

and below the axis of the dam there are considerable deposits of 

alluvium that consist chiefly of unconsolidated sand and gravel.

Country rock. The rocks in the dam-site area are the Prichard 

formation and some younger rocks, which are thought to be Wallace 

but which may be Ravalli. Both the Prichard and the Wallace (?) 

formations have been invaded by a series of sills of basic igneous 

rock. These are the famous Moyie sills described briefly in a preceding 

section.

« Freeman, J. R., op. cit., p. 630.
GEOLOGICAL SURVEY WATER-SUPPLY PAPER 866 PLATE 2

w . 

OK

-; ;.-RANCH ; ;.;.-.>>,;.;.-.

EXPLANATION

SAND AND GRAVEL

. PLEISTOCENE ? SILT

QUARTZITE TALUS BRECCIA 

CEMENTED BY CALCAREOUS 

TUFA

IGNEOUS TALUS

SEDIMENTARY TALUS

INFERRED POSITION OF 

MOYIE SILLS

MOYIE SILLS (DIORITE 

AND AMPHIBOLITE)

WALLACEC?! FORMATION 

PRICHARD FORMATION 

CONTOUR INTERVAL IOO FEET

STRIKE AND DIP

STRIKE OF 

VERTICAL STRATA

DEPTH OF WATER 9-25-34. 

050 WATER SURFACE 27'BELOW 

RAILROAD TRACK.

K PROSPECT

* SPRING 

30|29

3I32 SECTION CORNER

X 1803.7 U.S.C.4G.S.

BENCH MARK

2400

2200 

2100 

2000 

1900 

1600 

1700 

1600 

1500 

Pleistocene ? 

silt-.

IWM»W: r i ' >A

Prichard formation f

ray quartzite and 

reen argillite

Prichard formation 

gray quartzite

y quartzite 

Wallace (?) form.

SECTION ALONG LINE C-D

500

F I I I

1,000 Feet

Contour interval IOO feet

GEOLOGIC MAP OF KATKA DAM SITE, NH SEC. 31, T. 62 N., R. 3 E., BOUNDARY COUNTY, IDAHO.

^7?Xv *

Pleistocene ? silt

SILL * ,, *>Tr 

Dionte and am - * » / * *V *

phibotite > **

*.--.*«,-^Truedip 

23° NE 

Gray quartzite

Prl chard 

formation

SECTION ALONG LINE A-B COAM AXIS) 

LOOKING DOWNSTREAM

 2200

 2100

 2000

 1900

 1900

 1700

 1600

 I5OO

KATKA DAM SITE 19

The dam site itself is situated in one of these thick sills, which is 

now in a nearly vertical position. This sill is about 700 feet thick 

and is included in gray quartzite of the Prichard formation. The 

top of the sill dips about 73° E., and the beds at the base dip 52° to 

57° E. The general strike is N. 25°-30° W. The rock is a fine- to 

coarse-grained, dark-green hornblendite or hornblende gabbro. The 

top is cut by thin quartz veins. Subsequent to cooling some recrystallization occurred, with alteration of the character of the hornblende 

from the magmatic type to a more fibrous type.

The rock is strong, tough, and more elastic than the quartzite. 

Tests of the ultimate crushing strength are not available, but flawless 

fresh specimens would probably resist pressures of 25,000 pounds to 

the square inch. The specific gravity of the fresh rock is close to 3. 

Permeability, porosity, and absorption through the fresh rock are 

probably negligible. The rock minerals are difficultly soluble under 

under present climatic conditions. Under prolonged exposure some 

of the accessory sulphide minerals would break down, but they are 

present in such relatively, small amounts that the quantity of acid 

radicles developed would not be important or affect normal weathering. 

These processes would remove some iron from the hornblende and 

break down the plagioclase. However, as a whole, the rock of the 

sill is very fresh.

Dips. The attitude of the country rock is indicated in plate 2, and 

that of the beds enclosing the dam-site sill has just been described. 

Insofar as the dam site is concerned, the sill is so thick and massive 

that the question of dip does not enter, in a practical manner, into 

the considerations of the structure at this site. Any dam that may 

ever be built at this locality will probably have both abutments and 

foundation wholly within the limits of the upturned sill.

Joints. The following joints were observed in the right (north) 

abutment:

Strike

N. 68° W.

N. 28° W.

N. 64° E.

N. 80° E.

N. 47° E.

Dip

62° W.

62° E. 88°-90° S.

64° S.

67° N.

Character

Major

Other joints were also observed, including some that are nearly 

horizontal now but that were probably nearly vertical when the sill 

was in its initial position. All of the joints are spaced closely, being 

1 to 4 feet apart.
20 DlAM SITES O1ST TRIBUTARIES 0,E COLUMBIA RTVE'R

The joints in the left (south) abutment are as follows:

Strike

N. 42° W.

N. 65° E.

N. 58° E.

Dip

48° W.

Vertical

69° N.

Character

Strong;

spaced at

20-foot

intervals.

The intervening areas are thoroughly jointed by fractures that dip 

principally to the northwest and west at low angles; these are probably 

the older joints.

Examination of the joints in both abutments indicates that there 

are two sets of master points, one striking about N. 42° W. and dipping 

48° W. The strike of this set is normal to the direction of stream flow 

and unfavorable to percolation, but the direction of dip favors leakage. 

These joints are not closely spaced, and percolation through them 

would probably not be as effective as it would along the joints of the 

other set, which are more closely spaced and are approximately parallel to the direction of stream flow. This sill and the latter set of 

joints are probably responsible for the abrupt bend of the river just 

above the sill.

Faults. Several faults are present in the Katka district. The 

principal one, the Leonia fault, is about 1,500 feet east of the dam 

site and strikes to the northwest. It is probably of the high-angle 

thrust or upthrust type. Another fault that may be of some significance cuts the Prichard formation about 1,700 feet west of the 

axis of the dam.

Ground-water conditions. The ground-water table on each side of 

the river in the Katka district is high, particularly upstream from the 

dam site. Many springs issue from the silt overlying the pre-Cambrian rocks, which apparently have their sources in lakes and ponds 

on the broad high-level bench. Several large perennial springs 

occur at the Glass ranch, and another series appears on top of the 

bench, 800 feet north of the dam site. The ground is boggy and gives 

forth a resonant sound when struck, suggesting the presence of small 

open pockets or channels close to the surface. Travertine from these 

springs has cemented some of the talus in the river gorge to a breccia, 

and the surface of the deposit was wet with seepage water where 

observed. A rather large stream flows into the river from the northeast, where it has exposed the Wallace (?) strata. The gorge is steep 

and rocky and contains several falls. Dry ponds were noted on top 

of the bench on the left bank upstream from the axis of the dam.

Permeability. The question of permeability at the Katka dam site 

involves only the dam-site sill. Percolation through the rock is
KATKA DAM SITE 21

probably negligible. Tests on this particular type of crystalline rock 

do not seem to be available, but tests on granites have yielded a permeability coefficient as low as 2 to 10 X 1CT 12 . Any percolation that 

takes place probably occurs along the joints, particularly along those 

that parallel the course of the river and those that are normal to the 

course but that dip downstream. Assuming one crack to be 0.001 

foot wide per unit cubic foot of rock and to have a head of 300 feet 

and a path of percolation of 700 feet, or a crack to be 0.001 foot wide, 

1 foot high, and 700 feet long under a 300-foot head, the permeability 

coefficient per unit area of the foundations and lower abutments would 

be about 250 X 10~7 , which is probably about 10 times too high, owing 

to the excessive width of crack selected. On the same basis as the 

flawless granite specimen cited above, this would be 25,000,000 

X 10~12 .

As has been mentioned, the passage of water through the rock would 

not result in solution or other weakness. Furthermore, the cracks 

in the sill are probably amenable to pressure grouting. Permeability 

should not cause any difficulty at this site.

Dam section. Only one section is available. (See pi. 2, A-B, and 

pi. 3, A.) The width of the gorge at the water surface in September 

1934 was 280 feet, and the maximum depth of the water in the axis 

of the dam was 50 feet. A short distance upstream, where the bottom 

was probably of bedrock, the depth was 60 feet. The altitude of the 

bottom of the valley is about 1,720 feet If a masonry dam were 

built, the foundation would thus have to be about 60 feet deep. If a 

dam were raised to 1,800 feet, the crest would be about 20 feet above 

the water surface and only 7 feet below th<

The length of crest would be 300 feet, 

are presented in the following table:

level of the railroad track. 

Data on other heights of dam

Height 

above 

foundation

Feet

130

180

250

Altitude of 

crest

Feet

1,850

1,900

1,970

Le ngth of 

crest

Feet

385]

590

760|

good 

and

Abutments and foundation. The abutments 

and rugged, equal in bearing power, give 

and the rock is relatively impermeable 

true of the foundation.

Height and length of possible dam. 

suited for a dam, the railroad grade is 

height of any possible structure under present 

the high-water mark was only 18 feet be 

years of high water the approach is much

at this site are strong 

security against sliding, 

insoluble. The same is

tie

Although the site is admirably 

factor that controls the 

conditions. In 1934 

ow the track level, and in 

closer. In times of flood
22 DIAM SITES. ON TR'IBUITARIES OF COLUMBIA EIVE'R

the track is submerged. No spillway section is available (except 

tunnels, which would have to be of considerable diameter) for dams 

less than 250 feet in height, and any dam below track level obviously 

would render the situation of the railroad even more precarious than 

it is now. Furthermore, the depth of the foundation is such that, 

to obtain a 10- or 15-foot head, it would be necessary to build 70 to 

75 feet above the foundation, which would not be economical.

Appurtenant works, The great volume of the river makes the spillway the most important accessory work. A natural spillway section 

does not exist below an altitude of 1,970 feet. Up to that altitude 

tunnels or an overflow type of dam would have to be used. A bench 

250 feet wide occurs in the left abutment at an altitude of 1,970. 

This is hardly an adequate width for the flood requirement, but it 

might be adapted to the design. The peculiarity of this site is that 

the higher and longer the dam the better the spillway section, the 

section over the right abutment being best for the maximum possible 

height. As the height of the dam is increased the storage capacity 

of the reservoir increases. At its best, however, the reservoir would 

probably not contain enough reserve storage capacity to remove the 

crest from a large Kootenai flood. Consequently, the spillway requirement remains a maximum and cannot be reduced greatly by raising 

the dam to provide for flood storage.

Reservoir area. The reservoir of the Katka dam site is the inner 

gorge of the Kootenai River. (See pi. 3, B.) A dam 100 feet above 

bedrock (altitude crest 1,820 feet) would back up water beyond 

Leonia. A 180-foot dam (altitude crest 1,900 feet) would back up 

water to within a few miles of the base of Kootenai Falls (altitude 

1,885 feet), and a 280-foot dam (altitude crest 2,000 feet) would back 

up water a little beyond the head of Kootenai Falls (altitude 1,975 

feet). To preserve the Kootenai Falls site, the water should not be 

raised higher than an altitude of 1,885 feet, although the maximum 

possibilities of the site are greater.

The geology of the valley floor is relatively simple. A few small 

mines and prospects are present in the vicinity of Leonia and Troy. 

They have been described in the reports by Calkins and Gibson, to 

which reference has been made. The bottom lands are timbered, 

but the stands are small and generally of second growth. Most of 

the good timber has been logged off. Ground water moves toward 

the reservoir, from which no leakage is possible, except a negligable 

amount at the dam site. Little or no silting would occur.

Conclusions and recommendations. The Katka site is suitable for 

a masonry or concrete dam up to an altitude of 2,150 feet. This 

would require a structure having a maximum height above foundation 

of 430 feet and a maximum crest length of 1,820 feet. Such a dam
TUNNEL. NO. 8 DAM SITE 23

would provide the maximum possible attainment in power and flood 

control on the Kootenai River in the United States.

A 430-foot dam would, however, back up water beyond Libby, 

which is 37 miles upstream, and inundate the town site. The river 

surface at Libby has a normal altitude of 2,050 feet at the bridge, 

and the altitude of the town ranges from 2,060 to 2,100 feet. A dam 

of this height would also deeply flood the town of Troy and would 

effectively block the passage of the Great Northern Railway between 

Libby and Bonners Ferry.

The crest of a dam 180 feet above foundation would stand at an 

altitude of 1,900 feet. Water at this level would flood the lower end 

of Kootenai Falls, and the level is the maximum possible if that 

power site is to be preserved. It would cause considerable flooding 

in the vicinity of Troy, which is at an altitude of 1,889 feet, and force 

the Great Northern Railway to reroute its trucks over the bench 

along the south flank of the Purcell Mountains. As has been pointed 

out, such a dam would have an available head of only 100 feet, and 

the spillway section would be inadequate.

The contingencies of a dam with a crest below the track level at 

the dam site have been examined, and the conclusions have been 

reached that the proportion of available head to depth of foundation 

is far from economical, that the spillway requirement increases with 

reduction of head, and that the peril to the present track level will be 

much increased by floods and ice if any obstruction is placed across 

the stream.

The ultimate conclusion is that although the Katka dam site is 

topographically and geologically the most attractive of any in the 

southern loop of the Kootenai River, the cultural development in the 

valley indefinitely precludes consideration of the site for actual 

construction.

TUNNEL NO. 8 DAM SITE

(See pi. 1 and fig. 1)

Location. EK NW# sec. 28. T. 33 N., R. 34 W., Lincoln County, 

Mont., about \% miles east of the Montana-Idaho boundary and 2 

miles upstream from Leonia, Idaho.

Stream gradient. The gradient through the dam site is about 3% 

feet to the mile.

Catchment area. The entire drainage area of the Kootenai River 

above Leonia covers 11,740 square miles, and the catchment area at 

the dam site is slightly less.

Purpose of dam. Power.

Valley profile. The width of the ancient high-level valley is less in the 

vicinity of tunnel No. 8 than at Katka. The lower slopes of the inner 

gorge show a series of minor rock-cut benches, and a steplike group is
24 BAM SITES ON TRIBUTARIES OF COLUMBIA RIVER

especially well defined above the north abutment of the dam site. 

(See pi. 4, A)

Apparent possible height of dam. The rail elevation at Tunnel No. 

8 is about 1,831 feet. During normal water stages the altitude of the 

river surface is about 1,815 feet, which allows the railroad a freeboard 

of 15 feet.

The width of the stream along the axis of the dam is 360 feet, owing 

to the projection of the spur through which the tunnel passes into the 

river. This is about half of the normal width of the river, and the 

constriction causes the stream to rise rapidly during flood periods. 

In the ordinary year high water comes in June, and the water rises to 

within 2 feet of the ties, or to about 1,828 feet. The local trackwalker 

reports that during the flood of 1916 the depth of the water in the 

tunnel was about 4 feet and that this depth was maintained for 4 or 5 

days. Even a movable dam with a 10-foot head would aggravate this 

condition to a considerable degree. Another difficulty is that the 

proportion of available head to foundation depth is about 1 to 4.

Character and depth of valley fill. Owing to the force with which the 

river sweeps through the narrow gorge, only small amounts of alluvium 

are present in the active channel. The cutting is now against the 

north bank, and the depth of the water there on October 1, 1934, was 

about 30 feet. The depth to bedrock is probably not much more than 

40 feet, which would make the altitude of the bottom of the channel 

about 1,780 feet. From this point the floor probably shelves gradually 

toward the left bank.

The fill is chiefly gravel and silt, with the silt particularly abundant 

at the mouth of McCormick Creek and on the left bank below the 

tunnel and the gravel confined to the stream bed. The alluvium is 

probably reworked during each flood period and is too unstable to 

support a dam. If any structure is contemplated at this locality, it 

should be founded upon the bedrock, in spite of the added difficulty 

and expense.

Country rock. The country rock is the Wallace formation. It consists of thin-bedded, platy bluish-gray argillaceous limestone and contains a good deal more clay material than the same formation in the 

Swan Kange and other ranges farther east. The bedding surfaces are 

smooth and regular and open easily upon weathering. As a whole the 

rock is not very strong. The east end of the tunnel requires a timber 

support, and the west portal was being prepared for timbering in the 

fall of 1934, a large crack having developed above this entrance. A 

trackwalker reported that the rock in the tunnel tended to slake down 

when exposed to the air.

Crushing tests of the rock are not available, but its ultimate crushing strength is estimated to be 8,000 to 10,000 pounds to the square 

inch. An individual specimen containing no joints or bedding sur-
TUNNEL NO. 8 DAM SITE 25

faces would probably be more resistant. The hardness of the rock is 

about 4 or 5, and the specific gravity is about 2.7. Owing to incipient 

metamorphism, the absorption and porosity are probably small.

Dips. The strata dip steeply downstream. Although the downstream dip is unfavorable, it is compensated by the steepness of the 

dip, which in some places is nearly vertical. North of the fault the 

dip ranges from 69° to 79°. The strike ranges from N. 15° W. to N. 

27° W. South of the fault, on the spur about 300 feet above the tunnel, the dip is 52° W., and the strike N. 35° W.

Joints. The thin beds are well-jointed. The following observations were made on joints cutting the massive beds in the, tunnel:

Strike

S. 88° W.

S. 70° W.

S. 72° E.

S. 80° W.

Dip

66° S.

28° N.

75° S.

63° N.

Character

Good

Fair

------

These joints, at least those that strike strongly to the west, are 

probably related to the fault just south of the tunnel.

Faults. The fault just south of the tunnel strikes west and dips 

43° S. The gouge zone is 3 feet thick. Adjacent to the fault the 

beds on the north side strike N. 33° W. and dip 59° W., and those on 

the south side strike N. 31° W. and dip 65° W. This fault, with its 

thick zone of soft clayey gouge, is an element of weakness in the 

spur through which the tunnel passes and makes the spur unsuitable 

for the abutment of a high dam.

Ground-water conditions. The general attitude of the strata favors 

the quick return of ground water to the river and does not favor the 

reversal of the flow of any springs that may be present. McCormick 

Creek, which enters the river just above the axis of the dam, has 

built up a rather large deposit of calcareous tufa, which indicates that 

the flow is chiefly from springs. These springs are, however, probably 

near the top of the bench on the right bank, above the limits of any 

possible pool level.

Permeability. Movement of water through the bedrock is favored 

by the many smooth, even-bedding surfaces, but the attitude of the 

beds is against the direction of such flow; so the joints that cut across 

the beds principally affect the permeability of the formation. These 

joints would probably cause some leakage. In the north abutment, 

however, they are not closely spaced, and the path of percolation is 

about 300 feet long; so leakage would be small. In the south abutment 

some of the joints are closely spaced and are parallel to the fault. 

The path of percolation through the spur of the abutment is 200 feet 

or less, and that along the fault is 600 feet. The south abutment
26 DAM SITES ON TTHBUITABIES OF COLUMBIA RIVER

would probably leak more than the north, and, if the gouge zone should

become saturated, the abutment might have a tendency to move

toward the stream, though the direction of the dip is unfavorable to

a complete slide. 

The estimation of a permeability coefficient for this formation is

difficult. A rough estimate would be that 1£=10X10~ 7 . 

Dam section. Only one section is available. (See A-B, fig. 1.) 

The profile at the level of the lowest bench (1,900 feet) is suitable

for a dam 100 feet high, with a crest length of 640 feet. The details

for other economical sections are as follows:

Height 

above 

foundation

Feet

60

100

200

300

Altitude of 

crest

Feet

1,850

1,900

2,000

2,100

Length of 

crest

Feet

420

640

1,000

1,260

The profile of the lower part of the valley is obviously suitable for 

dams up to a height of about 300 feet.

Abutments. Both abutments are in the steeply dipping Wallace 

formation. The north abutment is more massive and stronger. Conditions in the south abutment are almost identical with those in the 

north, except that the base of the south abutment is cut off by a 

fault having a wide zone of weak gouge. The bearing power of the 

two abutments cannot, therefore, be considered equal.

Foundation. The character of the rock in the foundation is the 

same as that in the north abutment. It is sufficiently strong to resist 

crushing, and its attitude gives good security against sliding.

Appurtenant works. The spillway requirement at this site is large 

for a low dam, and the present channel of the river is inadequate to 

take care of the flood flow of the river witbont danger to the railroad. 

A dam high enough to provide storage capacity adequate to reduce 

the flood head would submerge the railroad for many miles upstream.

Reservoir area. The reservoir area consists of the Kootenai River 

trench (see pi. 4, B], which is probably underlain entirely by the 

Wallace formation. The trench contains only a small amount of 

alluvium, the banks are steep and forested, and it contains a minor 

amount of bottom land. The ground-water table on each side of the 

trench is high. Leakage from the reservoir is possible only in the 

vicinity of the dam site. Silting in any reservoir on the river would 

be negligible. The railroad is the principal cultural development 

within the reservoir area.
GEOLOGICAL SUBVEY WATEE-SUPPLY PAPEE 866 PLATE 3

A. VIEW UPSTREAM FROM A POINT 400 FEET EAST OF THE BENCH MARK THAT INDICATES 

AN ALTITUDE OF 1,809 FEET.

This view shows particularly well the profile of the left abutment of the Katka dam site; the right abutment 

is somewhat less distinct. The bench at the base of the Purcell Range is also visible, and in the distance 

are the mountains of the Purcell Range.

B. VIEW UP THE KOOTENAI RIVER FROM THE RIGHT BANK SOUTH OF THE GLASS RANCH

Shows the character of the inner gorge, which would form the reservoir area for the Katka Dam, and the 

route of the Great Northern Railway along the left bank. The Cabinet Range appears in the extreme 

distance.
GEOLOGICAL SURVEY WATER-SUPPLY PAPER 866 PLATE 4

A. VIEW DOWNSTREAM AT TUNNEL NO. 8 DAM SITE, SHOWING THE PROFILE OF THE

VALLEY. 

The east portal of the tunnel appears at the left center.

B. VIEW' UPSTREAM FROM ABOVE THE EAST END OF TUNNEL NO. 8.

Shows the grade of the Great Northern Railway and the character of the reservoir area of the proposed

dam site.
TUNNEL NO. 8 DAM SITE 27

Construction materials. None available except those required for 

a rock-fill dam. The limestone of the Wallace formation is probably 

not suitable for the production of cement.

Conclusions and recommendations. The gorge of the Kootenai 

River at tunnel No. 8 is so narrow that it is inadequate to pass the

EXPLANATION

This side of section 

is parallel to strike

 * Apparent change in-dip.due 

to curvature of section

FIGUBE 1. Geologic map and cross section of Tunnel No. 8 dam site, center

34 W., Lincoln County, Mont.

sec. 28, T. 33 N., R.

flood crest of the river without inundating the main line of the Great 

Northern Railway. The construction of even a low dam would 

aggravate this condition and unquestionably cause much damage. 

The geologic study shows that the left abutment rests against a 

fault having a thick zone of gouge that precludes the possibility of
28 DIAM SITES ON THIBUiTARIES OF COLUMBIA RIVER

building a dam higher than 20 feet. If a high dam were considered, 

the spur through which the tunnel passes should be removed, and the 

left end of the dam should be rested in the rock south of the fault; but 

even this procedure wouldvbe questionable, because the fault would 

still be present. The existence of a fault in the abutment of a dam 

warrants consideration of some flexible type of design; however, the 

large spillway requirement operates against such a design. Tunnel 

No. 8 site is, therefore, unsuitable for a dam from both economic and 

geologic points of view; the recommendation is made that it be given 

no further consideration.

KOOTENAI FALLS DAM SITES

(See pis. 1 and 5)

Location. In sees. 13 and 14, T. 31 N., R. 33 W., Lincoln County 

Mont. The upper site is about 500 feet and the lower site about 

4,500 feet downstream from the Kootenai Falls station.

Stream gradient. In the area of the sites the stream falls about 

85 feet in 1.85 miles.

Catchment area. The drainage area of the river at Libby, 12 miles 

upstream, is about 11,000 square miles, and the total area at the sites 

is slightly more than 11,200 square miles.

Purpose of dam. Power. The Kootenai Power Construction Co, 

once proposed to erect a dam at the lower site and core drilled the 

foundation of the section then selected. (See pi. 5, F-G.) The 

A-frames that suspended the drilling equipment still stand and are 

landmarks in the vicinity of the lower site. The company proposed 

to build a masonry dam 110 feet high and 2,110 feet long that would 

have occupied about 1.7 acres. The reservoir area at maximum flood 

level was to be 183.7 acres and 160 acres at spillway level, about 

112 acres of which would have lain in the Kootenai National Forest.

Application for a final permit from the United States Department of 

Agriculture was made on January 20, 1913. The permit was granted 

by the Secretary of Agriculture on May 4, 1914, but was revoked on 

October 1, 1919, because the company failed to pay rental charges 

or begin construction.

During the period the permit was pending the feasibility of the 

project was investigated by E. W. Kramer, district engineer, United 

States Forest Service, Missoula, Mont. The following summary has 

been taken from Mr. Kramer's report.40

4° Kramer, E. W., District engineers' report on application of Kootenai Power Construction Company 

for a final water power permit on the Kootenai River near Litby, Mont., Kootenai National Forest, Missoula, Mont., Feb. 15, 1913 (manuscript report on file in the offices of the Forest Service in Washington, 

D. C., and Missoula and Libby, Mont.).
KOOTENAI (FALLS DAM SITES 29

Estimate of power capacity

Flood,. .. ........ ........... ----._-._----__ ___ ...

Maximum station capacity. . _______________________

Minimum (primary) flow ___ ----- __ _ -- ____ _____ __

Stream flow 

(second-feet)

80,000 

8,000 

2,000 

2,950

Head (feet)

Total

55 

87 

90 

89

Effective

50

85 

88 

87

Amount of water appropriated, 22,500 second-feet.

Theoretical horsepower at generator switchboard

Horsepower 

Maximum..._--_--_-_---____________..__.____--._.__ 58,000

Minimum.__________________________________________ 15, 000

Average.-.___..---_.__.__...._.._.._.__.._._..___.__ 22,000

It was proposed to transmit this power to Moscow, Idaho, 100 miles 

distant.

Valley profile. The profile of the valley at Kootenai Falls has the 

form of a wide flat U. (See pi. 6, A.) The floor is flat and narrow in 

the middle and upper parts, but the lower part has been trenched by 

the stream to a depth of about 85 feet.

Apparent possible height of dam. The general character of the lower 

site, section D-E, is such that it seems to be suitable for an 85-foot 

dam. The upper site, section H-I, might allow a 10-foot dam, but 

probably none higher.

Character and depth of valley Jill. Owing to the force of the current 

through the falls, little alluvium is present in the channel. Small 

gravel bars occur in protected areas. The bedrock floors at both sites 

are practically bare. Beginning about 500 feet below the area mapped 

the channel contains considerable amounts of gravel.

Country rock.-^-The bedrock formation at Kootenai Falls is the 

Wallace. Three members have been recognized and are shown in 

columnar section in plate 5. The lowermost member consists of dense 

massive gray argillite, and occasional zones of purplish material in 

beds ranging from 18 inches to 20 feet in thickness. This member is 

not involved in either of the sites. The middle member consists of 

about 255 feet of siliceous algal beds separated by massive layers of 

purplish and greenish-gray argillite. The lower part of this member 

is involved in the lower site. The uppermost member consists of 

thin-bedded, hard, dense, brittle, gray-green argillite. Ripple marks, 

mud cracks, and casts of salt crystals are common on the bedding surfaces. - This member is involved in the upper site.

The argillites and meta-argillites have a hardness of 4 or 5, and, 

although not as hard as quartzite, are tougher and less brittle. They 

fracture only when folded closely; the algal beds, as far as known,
30 DlAM SITES' ON TRIBUTARIES' OF COLUMBIA RIVER

always yield by folding. The rock is strong and durable in both an 

engineering and a geologic sense. Crushing tests are not available, 

but flawless specimens would probably withstand pressures of 15,000 

to 20,000 pounds to the square inch. The average specific gravity is 

about 2.7. Owing to incipient recrystallization, the absorption and 

porosity are probably low, and all of the rock is fresh. Practically all 

of the rock material is insoluble, and passage of water through it will 

not cause hydration or volume changes, nor enlargement of existing 

channels, nor weaken it in any other way. Pyrite is an uncommon 

accessory, and its oxidation will probably have no effect.

Dips. Structurally the Kootenai Falls area lies in a syncline, the 

axis of which is a short distance upstream from the upper site. All of 

the beds thus dip upstream. Those at the upper site range from 11° 

N. 65° E. in the right abutment to 28° N. 64° E. in the left abutment. 

The dips at the lower site are much steeper and range from about 21° 

N. 15° E. to 59° N. 44° E. The altitude of the beds in the intervening area is rather complicated, as shown in plate 5, section A-B. The 

folding and faulting are probably due to the crumpling of the incompetent algal zone between the massive, resistant argillite members as the 

area was compressed in the trough of the syncline.

Joints. The thin-bedded argillites are thoroughly jointed. At the 

upper site one set of joints strikes N. 4° W. and dips 80° W., the joints 

being spaced 8 to 10 inches apart. The associated set strikes N. 64° 

W. and dips 74° W., with the joints spaced 2 to 4 inches apart. The 

north-striking joints are earlier than those that strike to the northwest. 

Indications of movement on one joint striking N. 58° W. suggest that, 

with respect to the north side, the south side has moved to the northwest. The rock at the lower site is also jointed, and in addition fracture cleavage has developed in some of the sharper flexures. Just 

below the upstream A-frame on the left bank, the important closely 

spaced directions of jointing are strike, N. 41° W., dip, 66° W.; strike, 

N. 25° E., dip 84° S.

Faults and folds. Several small faults are present in the area of the 

sites, but their nature is such that they do not affect the stability of 

the region. They consist of bedding faults and shear zones developed 

in the argillite by gliding along the beds and of small vertical faults 

associated with the chevron folds in the algal zone. None of these 

features occur at the sites, and none are active.

Ground-water conditions. The ground-water level throughout the 

valley floor is low, owing to the thorough fracturing of the hard, 

dense rock. A few hillside seeps and springs wet the rock above the 

highway in the southwest end of the map area. A small stream 

flowing from the north enters the elbow a few hundred feet above the 

lower site. Koot Creek, the principal tributary to the river within 

the area of the sites, heads on the right bank, a little to the east of
KOOTENAI FALLS DAM SITES 31

the summit of King Mountain. No danger of reversal of flow of 

any of the tributary springs exists.

Permeability. The country rock is as hard and as dense as slate, 

and danger of percolation through the texture of the rock is negligible. 

The important seepage from any dam that may be built will be by 

way of the sheet openings, which consist of numerous bedding and 

jointing planes. This is particularly true of the rock at the upper 

site. A rough estimate of the permeability coefficient of the rock 

at the upper site would be: .K"=20X10~8 . On account of the thicker 

beds at the lower site and the less intense jointing, the permeability 

coefficient of the rock in these beds would probably be: .K"=15X10~8 .

Original section at lower dam site. Three dam sections are available, 

one at the head of the falls and two at the foot. The location of the 

original section at the lower site, F-G, is shown in plate 5.

The gorge section at F-G is 230 feet wide, from rim to rim, at the 

surface of the rock-cut bench. The banks are steep, nearly vertical 

in places, and have an average slope of about 60°. The width of the 

water surface is about 150 feet. A rock-cut bench, the top of which 

is just below the water surface, extends 50 feet outward from the base 

of the right bank. A narrower bench, about 10 feet wide, extends 

from the left bank. The surfaces of these benches are slightly more 

than 70 feet below the rim of the gorge. The midchannel, from the 

edge of one submerged bench to the other, is about 90 feet wide and 

probably 20 or 30 feet deep.

When the area was mapped, the altitude of the water surface at 

the axis of the dam was about 1,903 feet. Narrowness of the gorge 

causes the surface to fluctuate considerably with variations in river 

discharge. Just below the dam site a high watermark was found at 

1,920 feet. A few hundred feet upstream, just above the fault, the 

high watermark was 1,940 feet, or 30 feet above the river surface.

The current is swift through this section, and rapids occur 100 

feet upstream and 150 feet downstream. The water is a light applegreen color, owing to the presence of innumerable bubbles of escaping 

air. Near the water surface the sharp hiss of the air is audible above 

the roar of the rapids.

The right abutment of section F-G consists of the lower part of 

the algal zone, bed A cropping out 25 feet south of the downstream 

A-frame. The strata dip upstream 55° N. 42° E. The rock is hard, 

strong, tough, and durable. Owing to slight differences in thickness 

and composition, some layers are more resistant than others and impart 

a serrate character to the wall of the gorge. A considerable amount 

of jointing exists, especially in the thinner beds.

The left abutment is somewhat similar to the right in character, 

the strata included forming the middle part of the algal zone. The 

upstream A-frame rests on bed D, and the downstream A-frame rests
32 D!AM SITES ON TRIBUTARIES OF COLUMBIA RIVER

on bed C. At the water surface, just below the upstream A-frame, 

the dip is about 21° N. 15° E. Just below bed C is a 4-foot layer 

of dense, light reddish-brown argillite, which in turn is underlain by 

beds of dense, greenish-gray argillite that range in thickness from 

6 inches to 2 feet. Separating the algal beds is 10 to l&feet of thinbedded, gray-green argillite, the lower 3 feet being considerably 

fractured.

The intense fracturing at this locality results from a sharp, asymmetric flexure, the axis of which strikes to the northwest through the 

upstream A-frame. It flattens rapidly down dip to 15°, the beds 

abutting against the fault. To the southwest, or up dip, the beds 

steepen rapidly to a maximum of 67°. The brittle argillites have been 

particularly affected, and their shattered condition is the unfavorable 

feature of this abutment. The important directions are strike N. 

41° W. dip 66° W and strike N. 25° E. dip 84° S. They are closely 

spaced, and the removal of small blocks has resulted in the formation 

of a small cavern that extends into the bank toward the downstream 

A-frame and has the general form of a triangular pyramid, the mouth 

of the cavern forming the base of the pyramid. The length of the 

cavern is about 25 feet, and the width of the mouth is about 15 feet. 

The beds at the west corner of the mouth dip 54° N. 22° E.

If this abutment were used to support a dam, all of the shattered 

rock that surrounds the cavern should be removed; the abutment 

would then b£ essentially equal to the right abutment in bearing power, 

resistance to sliding, and permeability.

The rock foundation stands at an altitude of about 1,880 feet and 

is covered with little or no gravel. Structurally and stratigraphically 

its character is much like that of the right abutment, and any concern 

as to its strength is unwarranted.

Complete development of section F-G requires a dike from each 

abutment of the gorge section to the base of the main valley walls. 

The 110-foot dam that the Kootenai Power Construction Co. proposed 

to erect, assuming that height to have been above the foundation bottom, would have placed the crest of the structure at an altitude of 

about 1,990 feet and given the railroad track 5 feet of freeboard, the 

minimum allowable. A greater measure of safety would be afforded 

the railroad by allowing it 15 feet of freeboard. This would place 

the crest of the dam at 1,980 feet. At this altitude the crest length 

of the dike over the left abutment would be 310 feet and would follow 

the strike of the beds (S. 51° E.) from the A-frames. Half of this 

distance would be over bare rock and half over undifferentiated 

alluvium resting upon the rock. Unconsolidated material would 

have to be removed. The height of this dike at the A-frames would 

be about 20 feet, and no difficulty should be encountered in its 

construction.
KOOTENAI FAULS DAM SITES 33

The dike over the right abutment would have to extend only 110 

feet northwest before it encountered crest altitude. However, the 

gravel-covered embankment against which it abuts is a remnant of 

an alluvial fan. This fan was built out upon the rock floor of the 

valley by the small stream, which now divides it, before the river had 

attained its present course. At the time of fan building, the river 

was probably flowing along the center of the valley, directly across 

the salient projecting into the elbow, as is witnessed by the narrow, 

abandoned channel at its base and the abandoned falls on the right 

bank below the dam site. The strike of the steeply dipping beds in 

the vicinity of the fault would, however, tend to deflect the river to 

the northwest, where it probably met the fan-building stream and 

was again deflected sharply to the southwest, establishing its present 

course. As the river cut downward, the fan was dissected by its own 

stream, owing to its increased gradient and its inability to supply 

material as fast as it was removed by the undercutting river. The 

effect of this erosion is beautifully shown by the 10-foot contours on 

the topographic map, and the form of the remnants, as well as their 

composition, leaves no doubt as to their origin.

To obtain a rigid abutment for the right dike would probably 

necessitate trenching back into this fan for at least 200 feet, the rock 

wall of the valley probably lying about 250 feet north of the A-frames. 

The total length of the crest would be about 850 feet.

The spillway requirement for any dam in this valley is large, and 

the lack of room for a suitable section sugg.e$ts,that an overflow type 

of dam might be desirable. The shortest section would be over the 

left dike into the river, which would create a considerable fall and 

might necessitate paving part of the way to prevent quarrying out of 

joint blocks by the dynamic flow of the water. Other than this, 

probably little downstream erosion would occur. Another possible 

section is over the right dike and onto the old rock floor, the water 

returning to the river through one of the abandoned falls. This 

procedure would probably necessitate the removal of the entire 

southwest lobe of the dissected fan.

Relocated section at lower dam site. The location of this section, 

D-E, is shown on plate 5. The right abutment is about the same as 

that in section F-G, plate 6, B, the difference being that the axis of 

the dam of section D-E is more nearly parallel to the strike of the beds.

The left abutment (see pi. 7, A) has been shifted 150 feet downstream from the A-frames on the left bank. The axis of the dam thus 

crosses the river just above the head of the lower rapids. From rim 

to rim the gorge section is 245 feet wide. The top of the right bank 

has an altitude of 1,970 feet, and the top of the left bank an altitude 

of 1,950 feet. The width of the stream is 135 feet. The length of 

the right dike section to crest altitude of 1,980 feet is 125 feet, about
34 D|AM SITES ON TRIBUTARIES OF COLUMBIA B1VEK.

50 feet of which length is covered with an alluvial fan deposit. The 

length of this fan, from the outer margin to the base of the main valley 

wall, is about 210 feet. The total length of the right dike must thus 

be not less than 290 feet. The left dike section is about 225 feet long, 

the upper 100 feet resting on a superficial cover of undifferentiated 

alluvium and talus that must be removed. The total length of the 

section is thus about 760 feet. On account of the shallowness of the 

water at the head of the rapids, the height of the dam from foundation 

will probably not exceed 90 or 95 feet.

The strata included in the relocated abutment fall between algal 

beds A and B, which consist chiefly of dense, massive layers of graygreen and purplish argillite, ranging in thickness from a few inches 

to 3 or 4 feet.

The rapids are formed by an exceptionally hard, massive bed that 

occurs just above algal bed A. All of the beds dip steeply upstream, 

59° N. 44° E. (See pi. 7, A.) This new location avoids the shattered 

zone in the flexure at the old site, and the steeper dip is also a more 

favorable feature, equalizing the bearing power of the two abutments 

and reducing the permeability factor. Another advantage of the relocation is that the axis of the dam is essentially normal to the course 

of the main valley. The spillway conditions are the same as for 

section F-G.

Section at upper dam site. The location of this section, H-I, suggested as an alternative by W. C. G. Senkpiel, associate hydraulic 

engineer, Geological Survey, is also shown in plate 5. The section is 

at the head of Kootenai Falls, the axis crossing the river 650 feet downstream from Kootenai Falls station. (See pi. 7, B.} The altitude of 

the railroad grade just south of the left abutment is about 1,990 feet, 

and the crest of the dam should, therefore, not exceed 1,980 feet in 

altitude. The length of crest for this altitude is about 1,775 feet, 

except for a slightly deeper channel against the right bank. (See pi. 

6, A.) The height of the dam is thus limited to about 5 feet. It 

would probably be of the diversion type, either an overflow masonry 

dam or a roller dam. These designs would permit passage of large 

floods without creating a high and dangerous backwater and would 

also allow the passage of occasional log drives and ice. The diverted 

stream would be carried through pipes to the powerhouse at the foot 

of the falls, and the total available head would be the same as for the 

sections at the lower dam site.

The rock in the foundation and abutments consists of the hard, 

dense, thin-bedded, much-jointed, greenish-gray argillites of the member above the algal zone. In the right abutment the beds dip 11 ° N. 

65° E., and those in the left abutment, 28° N. 64° E. The low dip 

and the thorough jointing would necessitate excavation to sound rock 

to secure the foundation against sliding and to serve as a safeguard
GEOLOGICAL SURVEY WATER-SUPPLY PAPER 866 PLATE 6

A. UPSTREAM VIEW OF THE UPPER HALF OF KOOTENAI FALLS FROM THE RIGHT WALL 

OF THE GORGE AT AN ALTITUDE OF ABOUT 2,260 FEET.

Kootenai Falls station is the small shed at the right of the upper line of riffles. The mountain to the_right 

is Wm. Grambauer Mountain (altitude 7,385 feet) of the Cabinet Range, and the slope to the left is the 

south face of Flagstaff Mountain (altitude 6,078 feel) of the Purcell Range.

B. VIEW OF THE RIGHT (NORTH) ABUTMENT OF THE KOOTENAI FALLS DAM SITE, WHICH

IS JUST BELOW THE TWO A-FRAMES IN THE RIGHT CENTER.

Note the sharp flexure in the argillite in the wall of the gorge.
GEOLOGICAL SURVEY WATER-SUPPLY PAPER 866 PLATE 7

A. VIEW OF THE LEFT ABUTMENT OF THE KOOTENAI FALLS DAM SITE AS RELOCATED 

TO AVOID THE SHATTERED ZONE AT THE CREST OF THE FOLD DOWNSTREAM.

The new axis of the dam passes just above the head of the rapid in the foreground.

B. VIEW FROM THE RIGHT BANK SOUTHEAST ALONG THE STRIKE OF THE BEDS AT THE 

HEAD OF KOOTENAI FALLS.

The axis of the upper dam section strikes along the upper riffle.
KOOTKPTAI FALLS D'AM SITES 35

against percolation. The local head would be so low, however, that 

probably little leakage would occur through the rock.

Comparison oj sections. The only sections that are strictly comparable are the two at the lower site, D-E and F-G. These have equal 

advantages as to head, spillway conditions, and reservoir capacity. 

Section D-E has the following advantages over F-G:

It is normal to the strike of the main valley.

It is shorter by about 90 feet, because it is straight.

The foundation is probably a little shallower, which reduces the height to about 

90 feet.

It is parallel to the strike of the beds.

It has steeper upstream dips throughout, thus reducing permeability through 

the rock, affording more security against sliding, and equalizing the bearing power 

of the abutments.

It has a better left abutment.

Comparison of sections D-E and H-I is necessarily not so direct. 

The two sections have equal advantages as to length and storage 

capacity. The advantages of section H-I as compared with section 

D-E are:

A low height of 5 feet.

Shallow foundation.

Lack of gorge section.

Less excavation of rock and of unconsolidated material.

Less difficult stream diversion during construction.

Easier spillway conditions.

Less leakage and percolation as a result of small local head.

Section H-I is inferior to section D-E in the following respects:

A long pipe line will be required from the dam to the powerhouse at the foot of 

the falls.

The left abutment is low and may require a dike extending downstream parallel 

to the railroad to prevent the grade from washing.

The dip of the strata in the foundation is low, and greater danger from ice and 

sliding would exist than at the lower sites.

Choice of section. The upper and the two lower sections are safe 

for the construction of a dam. The upper section would be the most 

economical to build, but this saving would be partly offset by the cost 

and maintenance of the pipe line. The factors governing the final 

choice fall outside the domain of the geologist, and this decision must 

be made by the designing engineer.

Appurtenant works. The appurtenant works for the lower sections 

are the dikes, powerhouse, spillway, and tunnels for stream diversion. 

Those for the upper section comprise the powerhouse, the dike for 

railroad protection, and the pipe line.

Reservoir area. The reservoir area for each of the sections is small, 

the water being backed up for approximately a mile in each instance.
36 DAM SITES ON TRIBUITARIES OF COLUMBIA RIVER

The reservoir area for the lower sections will extend from the axis 

of the dam to the head of the falls. The geologic conditions of this 

area are shown in plate 5. The area is characterized chiefly by the 

crumpled exposures of the algal zone. Economic deposits and cultural development are nonexistent in the area. Ground-water conditions are tributary to the reservoir, in which a little silting will 

occur. Some leakage will probably develop through the rock of the 

dissected bench into the gorge downstream, but this can probably be 

controlled without difficulty inasmuch as both intake and outlet areas 

are accessible.

Conditions in the upper reservoir are even more simple. Less 

opportunity for leakage exists, and if silt or gravel should ever accumulate it can be swept downstream through the gates.

o
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