University of Nevada Revo Environmental Geology Problems of Pyramid Lake Basin. a Thesis Submitted in Partial Fulfillmen

University of Nevada

Revo

Environmental Geology Problems of

Pyramid Lake Basin.

A thesis submitted in partial fulfillmen

'of che requirements for the degree of

Master of Science in Geology.

by

Raymond Russell Waggoner

■Mines Library University of Nevada Reno, Nevada 89507

May 1975 /

The thesis of Raymond Russell Waggoner is approved:

University of Nevada

Reno

May 1975

i 'ACKNOWLEDGEMENTS

The writer wishes to extend his gratitude, to the following people

and organizations for their support during this project. Members of the

Pyramid Lake Paiute Indian Tribe for their permission to work within

the reservation. Professors D. B . Slemmons, Mackay School of Mines,

G. F. Cochran and G. B. Maxey, Desert Research Institute (DRI), and

F. F. Peterson, Fleischmann School of Agriculture, for their time, advice,

interest, discussions, and for their objectivity in evaluating the results.

Additional thanks are given to Dr. Cochran for providing, through the

Center for Water Resources Research, DRI, financial, support. Appreciation

is also extended no Messrs. D. Koch and D. Schulke for their assistance

in the initial phases of this study.

The study was also partly supported by the Geologic Society of

America under Penrose Research Grant number 1936-74.

ii ABSTRACT

The study investigates faults, earthquake potential and problems, mass wasting, sanitary landfill site locations, and reviews selected water

resources literature as they affect future development of the Pyramid

Lake Indian Reservation, Nevada.

Faults are mapped and their activity and zone of influence deter­

mined. Piedmont-shoreline faults, developed in cha Holocene, are clas­

sified as active. Bedrock faults are. classified, tentatively, as

inactive. Age determinations for piedmont-shoreline faults axe from

radleasetrically dated shoreline features. Bedrock faults are evaluated

from stratigraphic relationships. The zone of influence for piedmont-

shoreline dip-slip and strike-slip faults is fifteen to twenty-five and twenty to fifty feet, respectively. Bedrock dip-slip faults effect

a zone fifty to one hundred feet wide.

The Pyramid Lake Basin is in a structural trough within the Walker

Lane fault zone. Epicenter distribution, earthquake, and fault history imply a high probability of future activity in this area. The shoreline has a high potential cor differential settlement, tilting, liquefaction, and inundation by seieh waves, or other mechanically produced water wove fronts.

Mass wasting by rockslides, rockfalls, soil.falls , mudflows and shoreline slumping is abundant, The Fair Rah Range and Virginia Mountains have the greatest amount of mass wasting. The piedmont -shoreline c£ these mountains has a high potentrial for involvement in future mass wasting activity. Rockfa'Lls and deltaic failure may produce mechanical

iii water-wave propagation, which could inundate east and west shoreline areas. Rockslid.es, assessed by radiometric dating of shoreline features are pre-Holocene. Rockfails, soilfalls, mudflows, and slumps, are partly historic.

Thirteen sanitary landfill sites were investigated relating to geology, hydrology, economics, and convenience. Eight are suitable for trench-type landfill sites; and five are unsuitable for use.

The water resources appraisal consists of a summary of selected reports which are concerned, to varying degrees, with the Pyramid Lake

Basin. Recommendations to be included in a complete hydrologic evalu­ ation. of this basin are: a) bank storage, b) groundwater-lake water interface determination, c) groundwater replenishment, d) groundwater storage, and e) springflow determinations.

A young volcanic ash-flow is discussed as its occurrence relates to future lake developments.

iv * TABLE OF CONTENTS

INTRODUCTION ...... 3

LIST OF FI G U R E S ...... 4

LIST OFTA B L E S ...... 4

LIST OF PLATES ...... 4

I. FAULTING ...... 7

A. Region 1 - Pah Rah R a n g e ...... 7

B. Region 2 - Virginia Mountains ...... 9

C. Region 3 -- Terraced H i l l s ...... II

D. Region A - Lake R a n g e ...... 12

E. Region 5 - Nixon floodplain ...... 13

II. FAULT A C T I V I T Y ...... 3 5

A. A.ge of A c t i v i t y ...... 1C

1. Pali Rah Range and v i c i n i t y ...... 1/

2. Virginia Mountains and vicinity ...... 18

3. Terraced Hills and vicinity ...... 20

A. Lake. Range and v i c i n i t y ...... 2'J

B. A s s e s s m e n t s ...... 23.

III. ZONE OF INFLUENCE OF F A U L T S ...... 22

A. Mountain B l o c k ...... 23

B . . Piedmont end paleo-shorelina ...... 23

IV. E A R T H Q U A K E S ...... ?5

A. Piedmont-and puieo-shoreline ...... 26

B. Earthquake epicenters ...... 29

C. S e i s m i c i t y ...... 29

i). Earthquake effects 32

v 1. Lake shore and subaqueous slumping ......

2. Liquefaction ...... , 35

3. Differential settlement ...... 35

4. Embankment and pre-existing deltas j « ; 36

5. Seiching and delta f a i l u r e ...... 37

V, MASS W A S T I N G ...... 40

A. Rockslides ...... 40

B, Kockfalls andSo i l f a l l s ...... 40

C. M u d f l o w s ...... 41

D. Potential Failures ...... 41

E. Activity of Slide Ma s s e s ...... 42

F. Age. R e l a t i o n ...... 4 3

VI. SANITARY LANDFILL ...... 46

A. Geology ...... 46

B. Hydrology ...... 46

G. Economics 48

D. A e s t h e t i c s ...... 48

E. General Investigative Information . 48

1. Depth to seasonal water table and soil drainage classes 4 8 2. P e r m e a b i l i t y ...... 48

3. Slope Conditions ...... 4 9

4. Subjacent stratigraphy ...... 49

5. Texture and water holding capacity ...... 49

6 . Groundwater ...... 49

?. Exposed r o c k ...... 50

F . Site Locations . . . 50

1. Locations 7, 8 > 9, & 1 0 ...... 50

vi 2. Location 12 51 3. Location 5 51

4. Locations 1, 2 52

5. Locations 4, 3. 3. 52

6. Locations 6, 11 53

G. Problems Arising From Site O p e r a t i o n ...... 53

VII. WATER RESOURCES APPRAISAL ...... 55

A. Synopsis of Selected Reports ...... 55

1. Wilsey and E a r n ...... ' ...... 55

2. Born Report ...... 58

3. Water Resources Reconnaissance and Pyramid Lake Task Force Reports ...... 58

4. Pyramid Lake Task Forcer Betterment Studies Work G r o u p ...... 59

5. Simulation Theory Applied to Water Resources Man­ agement, Phases I, II and I I I ...... 60

6 . Arid Basin Management Model with Concurrent Quality and Flow Constraints, Phase I ...... 61

7. Lower Truckee-Carson Hydrology Studies .... 61

8. Alternate Plans for Wafer Resources Use: Carson- Truckee River Basin ...... 62

9. California-Nevada Water Controversy .1955-1563 . . 63

10. 100-Year Record cf Truckee River Runoff Estimations 64

B. Recommendations ...... 66

3.. Bank S t o r a g e ...... 66

2 . Groundwater-Lake water Interface ...... 65

i. Groundwater Replenishment ...... 67

4, Groundwater Storage ...... 58

5. Spring!low ...... 73

vii C. Otlier Conditions - 74

1. G r o u n d w a t e r ...... 74

2. Truckee River Delta...... 75

3. Truckee River Floodplain ...... 76

4. Ephemeral Streams ...... 7 9

VIII. V O L C M I S f t ...... 81

BIBLIOGRAPHY AND REFERENCES ...... 83

GLOSSARY . . ' ...... 92

> i

INTRODUCTION

The Pyramid Lake depression (see index map) was formed during Plio-

Pleistocene, time coincident with uplift of the Virginia Mountains and the

Lake Range (Bonham, 1969). The present lake is a remnant of pluvial-

Lake Lahontan. The bounding mountain ranges have moderate to high re­ lief and include the Pah Rah Range, Virginia Mountains, Terraced Hills and the Lake Range (Figure 1).

Pyramid Lake is bounded on the southwest by the Tertiary volcanic and sedimentary rocks of the Pah Rah Range. The west and northwest shore, is bounded by similar age and type rocks of the Virginia Mountains. To

the north it is bounded, in part, by the Tertiary volcanic rocks of the

Terraced Hills. The east shore is closely bounded by the Tertiary voiean ic rocks of the Lake Range. At the south end of .the lake stands au ex­ posed part of the I.ahontan Lake plain which has been dissected by the pcs glacial Truckee River.

I chose to study Pyramid Lake because of the variety of environment­ al geology problems and e. desire to present these problems to the people v?ho are affected. The boundaries of this study area are indicated on the index map and enclose about 386 square miles. This preliminary study should be. used as a planning tool. More detailed information must be

gathered for future development.

Aerial photographs at scales of 1 :1 2 ,0 0 0 , 1:32,000, 1:40,000 and

1:62,500 were used for the initial examination and later as base maps

for field mapping. Original field work included mapping the faults, determining boundar­ ies of mass wasting features, examination of potential sanitary landfill site locations and evaluating stratigraphic and radiometric age determin­ ations as they apply to faults. Field work was completed during the sprin and summer of 1974 and the final information 'was transferred to a

1:24,000 scale topographic base map (Plates I-IV). A literature review of earthquake, and hydrology information is included as it applies to the area.

Earthquakes and associated faulting are the most significant and potentially detrimental problem. Numerous potential secondary effects are related to earthquakes and faulting: a) tilting of the ground sur­ face, b) horst and graben development, c) mass wasting, d) seiehing, e.) differential settlement, and f) liquefaction. The Pyramid Lake Basin is a structural trough within the Walker Lane fault zone. Expected principal movement along faults is right-lateral however, dip-slip and minor left-lateral displacement are present on conjugate east-vest- trending faults.'

Mass wasting features have been mapped because of their prevalence and nearness to or occurrence on the lake shoreline, and their influence on areas of future development. Several rocks!ides cover extensive areas and those which occur in canyons might cause debris flood problems if they slide into and temporarily dam these canyons, For example, the

Rodero Greek slide (T23N R72E), which covers about seven square miles and fronts part of the west shore, is inherently unstable and should ex­ clude this shore area from major structural development. 3

Sanitary landfills are considered necessary as the population increases. These refuse disposal sites do not create the health hazard of open dumping and burning which are presently used. I have located and evaluated several potential landfill sites.

Although having received previous consideration the surface, water and ground water system lacks the appraisal required for future devel­ opment. Certain published reports are summarized, additional informa­ tion is included as a supplement to these reports, and 1 have recommend­ ed investigating other hydrologic situations. Lateral erosion, terrac­ ing, floodplain encroachment, and the delta environment of a part of the

Truckee River is discussed. Flooding problems of ephemeral, streams, both dammed and undammed Is presented. Finally, a brief appraisal of potential volcanic problems is included. LIST OF FIGURES

page

Figure 1. Index Map 6

2. Generalized Cross Section showing Major Landforms . . 8

3. Sketch Map of the Sutcliffe area showing well locations in relation to diatomaceous earth deposit and faults ...... 19

4. Gilbert’s diagrams of fault scarps and secondary fractures in alluvium ...... 22

5. Log plot of displacement on main fault trace and the associated earthquake magnitude ...... 27

6 . Log plot of length of the surface rupture on the main fault trace and the associated earthquake magnitude ...... 27

7. Epicenter May; of N e v a d a ...... 30

8 . Seismic Regionalization Map of Pyramid Lake Basin . . 33

9. Modified Mercalli intensity scale ...... 34

10. Location Map of Sanitary Landfill Sites .... 47

11. Elevations of Pyramid and Winnemucca Lakes . . . 65

LIST OF TABLES

Table 1. List of earthquakes from 1838-1959 for western Nevada and California-Nevada a r e a ...... 31

2. Groundwater in storage available for pumping . . . 69

3. Estimated annual potential re-charge to the ground- water sys tem t

LIST OF PLAXES

Plat e I. Southwest part OX study area (in pocket)

II. Northwest p cl 1' t of s tudy area (in pocket)

III. North eas t part of study area (in pocket)

IV. South eas t part of s tudy area (in pocket) V. Master legend for plates I-I.V (in pocket)

LIST OF EQUATIONS

Equation 1. Water budget for determining specific yield . . . 6 7 a/,.,,

SCALE 1 :2 5 0 ,0 0 0

\ \ J J v . X A W x v V s > t j N X

/ X, f \ f . S /V*

■%*,/ X r X . K E N O 3v« mi. ( W " PKRAMJ5 UtXS X, ! Q x, UU \ X

\

\l.'.S VSGAS

\r FIGURE 1. INDEX MAP FAULTS

Five areas in the Pyramid Lake Basin each, displaying different types of faulting, and diverse structural and geologic conditions are described. Clockwise around the lake, from the southwest discussion of the area is divided into: 1) the east side of the Pah Rah Range, its alluvial fan piedmont and adjoining lake shore (Plates I & IV),

2) the east side of the Virginia Mountains, its alluvial fan piedmont and adjoining lake shore (Plate II), 3) the southern part of the Terraced

Kills, its lake shore, and the North Beach area eastward, 4) the west side of the Lake Range, its alluvial fan piedmont and adjoining lake shore (Plates III 4 IV), and 5) the Lahontan Lake plain and Truekee

River floodplain extending from the south end of the Lake Range to

Marble Bluff and southward surrounding Nixon. (Plate IV),

A. Region 1: Pah Rah Range

Faults form a linear northwest-southeast zone along the floodplain and pre-Lahontan boundary (Plate J.V) . In this location the zone of rupture is up to 1.5 miles wide, with the narrowest part 0.5 miles wide.

The most prominant. geomorphic feature of the zone is a graben about 40no yards wide. Tire most recent surface fault displacment, of this zone, is along the graben. Fault scarps which bound the graben are covered mainly by boulder:; and cobbles with a minor amount of finer material, sags and terminated drainage define, its interior. Westward, multiple episodes of faulting are discemable in the pre-I.ahontan sediments., and the: apparent dip of these normal faults is to the east. The sequence of rupture is confined mostly to these sediments and faults in the ad­ jacent volcanic rocks are not common. The faults, discussed above, 8

are exposed from Secret Canyon northward :o Big Mouth Canyon where most of the zone is truncated by a pronounced southwest-northeast dip-slip fault. The fault which forms the eastern edge of the giaben is semi- continuous to the lake.

Another zone of rupture (see figure 2 for location of major laxid- fonns) extends north from Big Mouth Canyon within the piedmont and paleo- shoreline area. East of this zone another fault system, branching and semi-continuous, can be traced up to the Mullen Creek drainage, VJ1/4,

T24N R22E; (Plates I & IV). Fault displacement at this location suggests at least two periods of movement. According to Russell (1885), faulting in this general area has displaced the lake sediments. The main trace

fau3 t scarps reach heights of five to six feet and are the most recent

faults in this area.

FIGURE 2 . GENERALIZED CROSS SECTION SHOWING MAJOR IANDEORMS Near the alluvial-bedrock contact by Big.Mouth Canyon, a group of fault traces are continuous to south of Tom Anderson Canyon (Plate IV).

In this area there are a number of southeast-northwest faults in the bed­ rock that terminate near the alluvial-bedrock contact. The faults extend

up to, and beyond, the main drainage divide. North of Tom Anderson

Canyon all of these fault traces are vague or indestinguishable due to the S.odero Creek Rockslide, ’Within the slide there are lineaments which suggest possible post-slide faulting. Many rockslide features occur in

the Pah Rah Range and are discussed under the topic "Mass Wasting".

South of Quail Canyon two southwest-northeast trending fault traces

terminate near the highest paleo-shoreline. Faults in "region one" are principally dip-slip and discussion of relative displacements is pre­ sented under the topic "Earthquakes". The present beach area displays many features which are linear and suggest: faults, but in part many are due to differential settlement.

Is. Region 2: Virginia Mountains

North of Mu3.1en Pass the piedmont and paleo-shcreline faults, re­ cognisable to the south, are nor. evident (Plates I & II). Debris slough­ ing on the side slopes of the stream gulley 0.5 miles north of the inter­ section of Nevada highway 33 and 34 prevent recognizing possible displaced lake sediments. Major faulting is, for the most part, restricted to the exposed bedrock of those mountains. Near Sutcliffe (N1./2. T2AN, R21E), and adjacent to Hardscrabble Creek faults are obvious, but they are not as continuous, or as easily identifiable as southward. Relative displace- merit Indicated by well log data is considerable, The apparent: vertical offset of a diatomaceous earth denosit is 220 feet. (This is discussed under the topic "Fault Activity'1.) This displacement is on the southern part of a major alluvium-bedrock fault, which to the north vertically offsets volcanic stratigraphy by about 300 to 350 feet. In both locations the mountain block has been down dropped. Which is in contrast, with pied­ mont and paleo-shoreline faults southward which elevate the mountain block.

West of Sutcliffe faults are more complex, and display both vertical and lateral offsets. Exposed volcanic stratigraphy allow, in most cases, recognition of the offset that has occurred. Northwest of Sutcliffe faults are essentially parallel to the axis of the mountains, with pied­ mont and paleo-shoreline faults not evident until in the vicinity of

Water Hole Canyon (W1/2IT25N R21E). Here there is a fault in the lake sediments. The southern part of this fault has an apparent reversal of relative movement compared with its probable continuation one mile north.

A fault is indicated by the abrupt transition from the gently sloping piedmont to a cross-cutting scarp surface covered with cobble sized clasts with most of the finer material removed. This contrast is not present over the entire piedmont surface but the apparent drainage and divide alignment, and truncation of older erosion surfaces suggests structural influence due to faulting. All of the major faults transact

Water Hole. Canyon and with the exception of one other apparently reversed fault, the mountains have been elevated relative to the lake basin.

The reversed faults bounding a rotated block about 2.9 x 0.5 miles, are singular along the west shore, hut exemplify the rotation and tilting which accompanies fault, movement. 11

North of Wood Canyon and vest of Warrior Point (NE1/4. T25N. R20E), faults, which to the south are confined to bedrock, converge on and inter­ sect the piedmont and paleo-shoreline area. This is due primarily to the physiographic change in the shoreline configuration, rather than a change in direction of the fault traces. Faults intersecting this alluvial area from the mountain block lack surface expression.

In the Big Canyon area (Si/2. T26N. R20E), north-south trending faults are again developed. However, further north within two miles of this canyon, these faults are concealed where they intersect the piedmont and paleo-shoreline. area. Along the alluvium-bedrock contact of this paleo-shoreline salient (Nl/4. T26N. K20E), there is a linear alignment of springs and a fault is implied. Northward this implied fault is recogniz­ able by displaced volcanic stratigraphy and a linear north-south geomorphi trend, that cuts the northern end of the Virginia Mountains. Again, the mountain block has been elevated.

The piedmont and paleo-shcreline area of these mountains dees not reveal significant faults, with the exceptions noted at Sutcliffe and

Water Hole Canyon. However, within the present beach linear features are recognizable and in some instances they truncate shoreline features such as sand bars, and in some, instances small grabens are developed.

C. Region 3: Terraced Hills - North Beach

In Aster Pass (SWl/4. T27N. R20E). separating the Virginia Mountain from the Terraced Hills, at least two faults are inferred (Plate II).

Evidence includes young-linear shoreline and the linear character of a mid-pass tufa deposit approximately 300 yards long, that has a good align­ 12

ment with a north-south trending fault which dies out in young lake sed­ iments immediately northward. Rotational block faulting in the Terraced

Kills is north-south trending and the. majority of the longest fault

traces mark the upthrown western edge of these blocks. Branching faults in the eastern salient of the hills have produced the same structural

conditions,, but are. northeast-southwest trending. Where the branching and major faults emerge from the bedrock they are concealed by lake sed­

iments. It is probable that they are present in the concealed, bedrock.

There is an inferred fault along the eastern margin of the hills (NWi/4

T27N SW1/4 T28N R21K), its influence is suggested by the. shoreline con­

figuration which appears to be structurally controlled (Dr. Y. Takehisa, personal communication, 1974).

The North Beach displays extensive right-lateral displacement along faults and is the exception to the type of faulting in other pied­ mont and paleo-shoreline areas. Its north edge is bounded by faulted volcanic, bedrock and pre-Lahontan sediments. Alignment of linear features in bedrock suggests the continuation of some bedrock faults lakeward

through the littoral sediments. Although establishing any continuous

fault traces from this stratigraphy is not possible, there are linear

features implying faults which are conspicuous in this shore area. The

lateral displacement is recognized in the truncation of strandline

trends, us an altering of strandline direction and in the formation of

fault-line scarps (?) over a long distance.

D. Region 4: Lake Range

The eastern edge of the North Beach area and the. east shoreline are bounded by the Lake Range. (Plates III & IV). Frontal faulting has 13

elevated the mountain block, but this fault system is difficult to rec­ ognise because only short and isolated fault scarps are obvious, in contrast with the west side of the lake, lack of physical features of this side requires inferences to be made of fault location.

Bedrock faults at the north end of this range, trending northeast- southwest, are dominated by two major faults (El/2. T27N R22E), which subdivide it into three sections. This faulting has depressed the south­ east edge of each section. Further south this main fault trend is north- south and in most cases the mountain block has been elevated. Landslides have occurred, but not in the same abundance as along the vest side of the lake. They are discussed under the topic. "Mass Wasting", The pied- mont and paleo-shoreline fault system, trends across the major- lake salients cn this side. This interpretation is from the shorte path followed between two points which display north-south trending, fault- inferred features. From the south edge, of the middle section (SEl/4

12.7N R22E), the number of faults increases and they have developed a series of rotated blocks, east edge up.

The area of the greatest number of faults is in the large drainage basin east of Ana’no Island (SW1/4, T25N, NW1/4 T24N, R23E) .

North-trending faults influence drainage patterns and are offset by northeast-southwest faults that displace them in a left-lateral senc.e.

South of this area the Lake Range is covered by the southeast lake shore, and faults are concealed.

E. Region 5:__Paieo-1ake plain-floodplain

This region is composed of the Lahontan Lake plain and the Truckee River floodplain (Plate IV), It is an area of low relief and physical features are generally not preserved because of pronounced erosion. The lack of evidence for existing faults does not imply that they are not present, As noted, fault traces abruptly cease where the Lake Range contacts this area; and in the Truck.ee Range to the southeast, fault traces also terminate at the alluvial-bedrock contact. The ephemeral nature of the floodplain prevents recognizing older features suggesting faults, and no recent features were found. However the evidence indicates that faults exist and thus their presence, especially near bounding bedrock faults, should he considered. FAULT ACTIVITY

The. classification of a fault is based on determining its activity, or if it may be considered active or inactive. A number of definitions

concerning fault activity have been proposed (Louderback, 1950; Bonilla,

1969; Wentworth, 1970; Wesson, 1972). The main objective of any defin­

ition concerns the time limits in which previous activity may be observed

to have occurred. Faults are considered active if movement has occurred

in the past 10,000 to 12,000 years (least amount of time), or between

35,000 to 500,000 years b.p,(greatest amount of time). For this study because of previous work (Broecker, Orr,Kaufman, Morrison, Frye and Born),

littoral features and sedimentary deposits have been radiometrically or stratigraphically dated serving as indicators of the absolute and relative ages of movement. Based on this information, which doss not apply to the boundary mountain block, a classification of faults is presented. Where fault movements have developed during the past 12,000 years, the faults are classified as active.

The best criteria for estimating the activity of a region would be to use recurrence intervals or strain accumulation measurements, but

these are not available. Therefore, the age of fault displacement must be used as an indication of activity. Seismicity has not been used with

this report, but is available and can also provide information on the areas potential, for generating ground rupture. In the study area age evaluation is a direct one arrived at from evidence which provides initial limits on the time span in which movement occurred.

Absolute dates of features preserved in the lake basin have been made using isotopes (Broecker, 1953, 1965). However, the use of these 16

isotopic dates is limited to features within the paleo-shprelina area.

Faults in the bounding mountain blocks are assigned a relative age based on: 1) the completeness of the existing geologic record along the. fault trace, 2) the quality of age control of the disrupted stratigraphy, and

3) interpreting the geologic relationships froia exposures.

Inconspicuous or minor faults in the lake chore areas Blight not have been recognized or might have been confused with other shoreline features. In the shoreline areas it is assumed that fault scarps much cider than the Lahontan shorelines were obliterated by Lahontan age erosion and deposition.

A. Age of Activity

The. last high lake stand, at about 3,990 feet above mean sea level, was about 3,000 years ago; while the highest lake stand at 4,400 feet, was about 12,000 years ago (Broecker &0rr, 1958; Broecker & Kauffman,

1965; Morrison & Frye, 1965). Since 8,000 years ago there has been a general lake level decline, but it has not always been constant.

According to Bona (1972, after Morrison & Frye, 1965), during the past 4,000 years at least five lake fluctuations, between 3,850 and

3,950 feet, and at least one desiccation can be recognized. Three of these have been recorded in the past 2,000 years and the lake has under­ gone a decline to the present level during the past 1,000 years. During the past 100 years this decline has been especially rapid due to man's influence.

Information on lake level elevations for the past. 2,000 and pos-- slbly 4,000 years is inconsistent. Within the past 4,000 years Pyramid 17

and Winnemucca Lakes were connected by a channel. Mud Lake Slough

(NE1/4 T23N, R23E), elevation 3,863 feet, is the most recent and does not necessarily represent the paleo-channel configuration. A paleo- channel implies a stilistand at the elevation of that channel. The stillstand elevation during the past 4,000 years would be lower than

3,900 feet and implies that lake surface elevations above 3,900 feet in. the past 4,000 years may not be accurate. Implying that age dates col­ lected of higher lake stands of this period are questionable. Although the age data is perhaps unreliable it will be used to make initial age. evaluations on faults in the piedmont and paleo-shoreline areas.

1. Pah Rah Range anu vicinity

The faults system along the Pah Rah Range has been modified or removed completely by shoreline erosion. This suggests an age, based on lake level decline, of older than 12,000 years for the faults in the most southwest part of the area (El/2 T22H R23E). The adjacent graben was formed during the past 12,000 years as faults cross strandlines of this age. The east bounding fault of this graben continues northward, cuts younger strandlines, and is younger still.

Faults near the Rodero Creek rockslide (T23N R22E), are also datable. The rockslide toe is covered by littoral sediments at least

10,000 years old. These faults are within reasonable age correlation to those noted above. There are two fault traces crossing the mouths of

Quail Canyon and Mullen Creek (NW1/4 T23N, SW1/4 T24N R22E), and their elevation indicates an age range between 1,200 and 7,500 years b.p.

The western most fault trace of this pair suggest an older age which 18 is consistant with: 1) those fault traces to the south, and 2) older faults toward the mountain block. Two fault traces parallel to and south of Quail Canyon intersect, but do not disrupt the highest shoreline thus, suggesting an age older than 12,000 years b.p.. Another fault trace crosses Mullen Creek, displaces littoral sediments and is at least 10,000 years old.

The linear features within the present beach are termed secondary fractures and are much younger than any of the faults. Because of their location relating them to specific earthquakes and associated faults is difficult. However, due to the cohesionless and unconsolidated condi­ tion of the sediments these fractures probably formed because of dif­ ferential settlement. Based on their elevation and preservation of low relief features they are probably less than 1,000 years old. These small zones are generally of minor concern unless sufficiently numerous to affect the strength or permeability of the ground for future devel­ opment.

Some fault scarps in the shoreline area suggest more than one event for their formation, this is indicated by a levelled upper surface and a lower steeper face. If this represents two faulting events during the past 10,000 years, as an average it indicates one event ever}7 5,000 years.

2. Virginia Mountains and vicinity

The shoreline area of the Virginia Mountains and Pah Rah Range is similar. South of Sutcliffe lineaments observed in the topography are suspected faults. If these are fault traces they disrupt shoreline features and are younger than 10,000 years old. 19

•The lower reach of Hardscrabble Creek (SE1/4, NW1/4 T24N, R21E) is offset by faults (Figure 3). Diatomaceous earth deposits north of the creek, have ar. age of 17,200 + 250 years b.p. (C-^a date of contemporan­ eous deposit in Astor Pass (SW1/4 T27M R20E), Broecker & 0rr,1958).

Well log data shows a vertical separation of about 220 feet between diatomaceous sediments north and south of the creek. Without knowledge of depositional and present attitudes for the southern sediments, it is

Figure 3. Sketch map of Sutcliffe area, showing well locations with respect to diatomaceous earth deposit and faults. 20

difficult to determine the influence of faulting. However, if the ver­ tical offset is due to faulting, and displacement for Basin and Range faults generated by a strong earthquake is 5 to 20 feet it implies:

1) at least eleven separate events have been generated on this fault trace in the past 17.000 to 18,000 years, and 2) on the average one event has occurred every 1,600 to 1,700 years. Where this fault trace enters the mountains (NW.l/2 T24N R21E), the stratigraphy has an apparent ver­ tical displacement of 300 to 350 feet. This agrees with the offset above, and suggests this fault has been active in both areas. Branching of the fault trace north of this location prevents determining which trace is more active.

In the Water Hole Canyon drainage (SW1/4 T25N R21E), there is an apparent fault scarp. Its elevation and lack of obvious littoral erosion, indicate it is less than 10,000 years old.

3. Terraced Hills and vicinity

The present beach areas south and east of the Terraced Hills, have the largest extent of Holocene faults in the lake basin. The faults are recent, but determining the exact period cf activity is difficult.

The area from Fox Beach (T27N El/2 R21E, Wl/2 R22E), north displays the most recent and best preserved fault traces. Right-lateral displacement

'is the most obvious type of movement. The littoral sediments range from the most recent to at least 3,000 years old.

4, Lake Range and vicinity

A piedmont and paleo-shoreiine fault system along this entire range is probable. However, the only exposure of this type of fault 21

system is in the Hells Kitchen Canyon alluvial fan (NE1/4 T26N R22E).

All three fault scarps are modified by erosion, which is in part lit­ toral. Elevation of the highest fault scarp is about 4,100 feet, the lowest near 3,900 feet. Therefore a minimum age for the higher fault scarp is greater than 8,000 years old, and the lower scarp could be slightly older than 1,000 years b.p.

A fault scarp 1.5 miles long at the north end of this range off­ sets shoreline features older than 8,000 years. Near the southern end of the range lineaments in the present beach area appear to truncate shoreline features.- These lineations can be grouped with similar features in the present beach area and dated at less than 1,000 years old.

B ■ Assessment

Since piedmont and paleo-shoreline faults transect Holocene features movement can be expected in the near geologic future with a high probability of recurrence in the immediate future.

Faults within the surrounding mountains cannot be adequately dated, with the exception at Sutcliffe. The problem is lack of age correlation for the volcanic stratigraphy, and at best the faults range from several hundred thousand to several million years old. 22

ZONE OF INFLUENCE OF FAULTS

Faults in alluvium can produce secondary features which may increase the width of the zone of rupture. These features result from the gravity collapse of either the foot or hanging wall or as subsidence along a belt parallel to the fault trace (Figure 4). Inability to recognize these secondary features should not be confused with their

Figure 4. Secondary features produced b}’ gravity failure along a fault. 1. Simple fault scarp produced by fracturing.

2. Subsidence zone parallel to the fault trace.

3. Gravity failure in the hanging wall parallel to the fault trace.

4. Gravity failure in the foot wall parallel to the fault trace. lack of formation. Fault scarps and the topographic expression within

the fault zone of secondary features, is typical in the Basin and Range province. The secondary features are termed gravity failure because

their formation is the result of gravitational instead of tectonic forces. Future movement along these faults can lengthen fault traces and increase the height of fault scarps.

A . Mountain Blocks

Faults confined to the mountain blocks can be more variable in

form, relative movement, zone of influence, and branching features

chan faults in alluvium. Faults within and extensions out from the. mountains, are related to tectonic deformation. Relative displacement increases toward the central part of some fault traces, while others do not show this relationship. Measured and estimated vertical dispiac ments on the faults range from about 70 feet to more than 300 feet.

Horizontal (lateral) movement is indicated as a component of net dis­

placement on slickensided surfaces and is minor in comparison.

Faults within the Virginia Mountains are more variable in char­ acter than in other areas, and branching and rejoining along major

fault traces is common. The relative width of the disturbed zone is about 50 to 100 feet, and in some cases much narrower. These limits apply to bedrock faults in other mountain blocks, too.

B, Piedmont and pa.l eo-shorel ine

Major piedmont and paleo-shoreline faults display a relative vertical displacement of five to six feet, and in one case suggest at least two periods of movement. These faults have an apparent zone of 24 rupture fifteen to twenty-five feet wide.

Lateral displacement is observed on the faults in the shore area near the Terraced Hills. The displacement ranges from 50 feet to more

than 2,000 feet and is confined to a narrow zone about 20 to 50 feet wide. 25

EARTHQUAKES

The Walker Lane fault zone involves Pyramid Lake and has been partly investigated (Albers, 1967; Bonham, 1969; Nielson, 1965; Profett,

1972; Sales, 1966; Shawe, 1965; Slemmons, 1967; and Stewart, 1968).

This fault zone will not be discussed except to say that since 1932,

the northern part including Pyramid Lake has had a high degree of seis­ mic activity (Slemmons, 1965). Further, Nevada had the highest in­ cidence of earthquakes from .1932 to 1960, of any of the conterminous

United States (Slemmons & Gimlett, 1965).

The main bedrock faults indicate a tectonic origin and this implies they have been associated with earthquakes. Main fault scarps in the piedmont and paleo-shoreline area probably reflect the prop­ agation of bedrock faults through the overlying alluvium. However, this mechanism may not apply to those secondary fractures preserved in the present beach area. Bedrock faults in the mountain block are being excluded from any earthquake related evaluation, because of the lack of control and measurement concerning their displacement, history and age significance. A]so there is no recent movement and their locations with respect to the active piedmont and paleo-shoreline system, suggests that the strain energy presently being developed will cause future rupture along the alluvial bedrock contact. This evaluation agrees with Ziony (1973), where those faults with the most recent displace­ ment are more likely to be active and have a higher rate of movement".

The historical record also shows a greater probability for each new earthquake fauic breaking at the most recent traces rather than along older breaks (Slemmons, 1972). 26

A. Piedmont and paleo-shoreline

Piedmont and paleo-shoreline faults have been produced by the most recent earthquakes, and there is one area, cut of four separate and apparently unrelated ones, which can be evaluated. This evaluation assesses the nature of an earthquake which might be the cause of move­ ment at that location. The data collection is based on widely scattered and sometimes incomplete information. Its extrapolation into usuable information to establish guidelines for design., urbanization and gener­ al future development must be carefully assessed.

The fault traces fronting the Pah Rah Range offer the most com­ plete record for number of events, relative amounts of displacement for these events, and the most clearly defined and semi-continuous traces.

At least two events totaling five to six feet of vertical displacement can be recognized. The greatest vertical offset of approximately four feet is the most recent. The total length of this fault system is ap­ proximately sixteen miles. With this information a tentative assessment of earthquake magnitude and intensity can be made.

Earthquakes producing displacements of about two and four feet, were of Richter magnitude from 6.0 to 6 . A and 6.5 to 6.9 respectively

(Figure 5). These values are in apparent disagreement with other data, and emphasize the need for judgement in terms of their reliability.

According to Cordova (1969), surface ground ruptures of five to twenty feet imply an associated earthquake of 6.5 to 7.75 Richter magnitude.

However, Browrn. (1967), reports ground rupture of a few inches laterally, over several miles, was produced by a series of shocks where the larg­ est magnitude was 5.5. According to Allen and Brune (1967), minor Maximun surface displacement on main fault (ft) v , •r4 S3 a « a S d 20 rhquak agnitude M ke a u q arth E ~ T 5 1 1 5 ICO 50 10 5 1 .5 0 2 ' - 7' fc- gure 6 o aio of engt surf upt e wih earth­ h t r a e ith w re tu p ru e c fa r u s f o th g n le f o parison Com 6 e r u ig F quake m ag n itu d e . Symbol (+ ) re p re s e n ts p ie d m o n t-la k e sh o re re o sh e k t-la n o m d ie p ts n e s re p re ) (+ Symbol . e d itu n ag m quake t tace l h. agonal i s bv (after Bonila,1970) , lla i n o B r e t f a ( above as e lin l a n o g ia D . th g n le e c tra lt u a f egh surace r ur man t ( i) (m lt u a f ain m , re tu p ru e c rfa u s f o Length _ . ____ ■ / x r a a , - u dipl ement r mai aul lt u fa - in a m or. t n e m ce la isp d mua re u ig F _ ~ i la, 1970). 0 7 9 1 n , io s re illa g n e r o B are s e lin l a n o g ia D Symbol (-:•) re p re s e n ts peidmonc - peidmonc ts n e s re p re (-:•) Symbol her ye of ts (after r e t f a ( from s lt u ata a d f f t o i f t s types e b r e f th o o s e rv u c la k e sh o re f a u lt d isp la ce m e n t. t. n e m ce la isp d lt u a f agnitude. m re o sh ke a u q e k la arth e ith w e c tra j ___ — V i - a . j h . - / 5 -- Com parison o f m axi- axi- m f o parison Com / / -■ - / -L - 500 l - a 2 .7 displacement on surface faults (those already established) was from a swarm of earthquakes, centered in a small area, with a maximum 3.6

Richter magnitude.

Probable magnitude can also be related to the length of a sur­ face rupture (Figure 6 ). For a fault trace approximately sixteen miles long, a magnitude of 4.75 is indicated; or conversely, using the pre­ vious value, a 6.4 magnitude earthquake should generate a surface rupture much longer than sixteen miles. According to Otsuka (1964), the fault length depends on various factors, such as the earthquakes \ energy, focal depth, mechanism at the origin, and the strength of the medium from which it was generated. The lack of sufficient and accurate information about a fault producing earthquake and length of the surface rupture may account for the contradiction. Another problem is recog­ nizing modified features which could lengthen and/or elevate the fault traces, thus making a better correlation of data.

Intensity evaluations are even more arbitrary due to the method of data accumulation. The intensity of shaking, with time, depends upon the smoothness of the surface rupture and on the observer's position relative to the rupture. Earthquake evaluation of the other three areas will not be attempted, because of the difficulty in assessing fault trace features which are more clearly evident near the Pah Rah

Range. 29

B , Earthquake epicenters

Fourteen earthquakes ranging from 4.0 to 4.9 and twenty-two earth­

quakes ranging from 5.0 to 5,9 Richter magnitude have occurred within

thirty miles of Pyramid Lake since 1932 (Figure 7). The epicenter map

reflects expected magnitudes, the probable epicenters of future earth­

quakes, and indicates the intensity which they may develop. It also

shows the potential Pyramid Lake Basin has for realizing a damaging

earthquake in the near future.

A partial list of earthquakes dating from 1838 to 1959 with their

associated magnitudes and intensities is contained in Table 1. The table

includes only those earthquakes greater than 5.0 Richter magnitude which were in the western Nevada and California-Nevada area. According to

Slemmons (1965), a cycle of earthquakes with a twenty year frequency, with peaks at about 1852, 1372, 1S94, 1916, 1932 and 1954, is evident

for this area. Therefore, the 1975 to 1980 period is one of high prob­

ability for producing earthquakes of potentially damaging magnitudes.

C . Seismicity

The Pyramid Lake area was seismicallv active during the late

Quaternary (Slemmons, 1967). The northern part of the Walker Lane fault

zone, which involves Pyramid Lake, has been especially active since 1932

(Slemmons, 1965). Seismologicai studies indicate zones of non-activity surrounded by active areas and implies the probability of future activity

in these non-active areas (Ryall, et ai, 1966).

A seismic regionalization map reflecting intensity, or ground vibration associated with varying geologic conditions, was prepared for ‘ *c **t« • 3>;.-«?4n **5*»t*« # ^ O «->•« O » O c* W4WYiiof 6 4 .r--a C . • .C**.v .5 SCAI.C + 9 HGURE 7. fCME MAP EfiCLMtER (at'tAr SIEMMONS, «. \ \ e* «l, 1965 e* «l, \ \ *©(-' i ) - 4s- T e ? ? vs$ + \ \ r \ {■ 7 o ! I I 4 f I i i tfw.* f’37' «i' 31

Table 1. List of Earthquakes from 1833 to 1959 in the northwestern Nevada and California-Nevada region (after Wood, 1966).

Geographic Location Date Magnitude Intensity Earthquake (Richter) ■ (Modified Major/Minor ' ' Mercalli) or ' Intermed.

1. San Francisco, CA 1838 3.3 X #/ 2 . Olinghouse, NV 1369 6 .5-7.5 IX-X #/ 3. Owens Valley, CA 1872 8.3 X--XI it/ 4. San Francisco, CA 1906 8.2 XI if/ 5. Pleasant Valley, NV 1915 7.6 X H 6 . Cedar Mtns., NV 1932 7.3 X it/ 7. Dixie Valley, NV 1954 7.1 X it! 8 . Western NV 1860 ? V /it 9. CA-NV 1868 1 Destructive f« HI 10. CA-NV 1869 ? /it ? 11. Western NV 1872 Violent a t ij 12. Carson City, NV 1887 VI IN /it 13. Nevada City, CA 1883 ? Felt in W. NV /# '? 14. Vacaville, CA 1892 VI1+ /it 15. Virginia City, NV 1894 VI-1 /it (100+ shocks) 16. Carson City, NV 1894 2 VI a t 9 17. Honey Lake, CA 1908 VII /it 18. Eureka, NV 1908 2 VII HI TT-r- .19. Reno, NV 1914 O V J. lit 20. Western NV 1916 2 V /it 21. Fernley, NV 1930 2 VI HI 22. Wabusca, NV 1933 2 VI 7 it 23. SE of Hawthorne, NV 1934 6 15 VII /if 24. SE of Minden, MV 1939 5.5 VII Hi 25. NE of Mina, NV 1939 5,5 V HI 26. W of Wadsworth, NV 1942 5.5 2 Hi 27. Excelsior Mts., NV 1943 6.3 VIII HI 28. Verdi, NV 1948 6.0 VI / it 29. CA-NV 1952 2 9 lit 30. CA-NV 1953 5.2 7 H 31. Rainbow Mts. , NY 1954 6 . S VIII Ht 32. E of Fallon, NV 1934 6.6 IX lit 33. SE of Fallon, NV 1954 6.4 2 Ht 34. E of Fallon, NV 1954 6.8 IX fit 35. Dixie Valley, NV 1954 5.8 2 HI 36. SE of Lovelock, NV 1955 6.0 VII HI 37. Hawthorne, NV 1955 5.0 2 lit 38. Hawthorne, NV 1956 5.0 2 H 39. Dixie Valley, NV 1959 6,3 VI HI 40. Schurz, NV 1959 6.1 VI HI the Pyramid Lake Basin (Figure 8). Boundaries between intensity levels

(see Figure 9), is subject to change in position depending on its near­ ness to these varying conditions. Generally ground vibration (intensity) for a particular geographic area is primarily dependent on local ground „ conditions and secondly to faulting (Richter, 195S). Therefore, due to liquifaction influences and nearby faults the shore area is assigned a

Modified-Mercal11 intensity rating of IX* (Figure 9). The mountain block are assigned a rating of VII (actually VI to VI I'*') . The pre-Lahontan sediments in the north and southwest are assigned a rating of VIII. The rating of VIII is consistant with Richter's interpretation of a similar type deposit in the Los Angeles Basin.

Earthquake damage depends cm several variables such as, epicentre! location, intensity of shaking, near surface soil and geologic conditions and structural types ana design (duff, 1971). The resulting damage can occur in several ways, therefore, consideration of the faults is importan in order to delineate hazardous areas, and the above information is pro­ vided for this purpose.

D. Earthguake effect;;

Earthquake damage may result in four ways: 1) surface rupture,

2) strong ground motion (shaking), 3) ground failure (mass wasting, liquifaction, differential settlement and tilting), and 4) seiching

(periodic oscillation of water in a basin). This section deals in gen­ eral with the effects under (3) and (4) and specifically with their in­ fluence on those areas peripheral to the lake. 32> 34

MODIFIED - MERC AL U INTENSITY SCALE OF 1931

1 Not fct by people, except under especially favorable circumstance's However, dizziness or nausea may be experienced. Sometimes birds and animals are uneasy or disturbed. Trees, structures, liquids, bodies of water may sway gently, and doors may swing very slowly. i! Felt indoors by ?. few people, especially on upper floors of multi-story buildings, and by sensitive or nervous pftrww. As in Grade 1, birds ?rid animal;* are disturbed, and trees, structures, liquids and bodies of water may sway. Hanging objects swing, especially if they are delicately suspended ili Fekindoors by several people, usually as; 2 rapid vibration that may not be recognize ?! an eart!.quake ct ftr-.t Vibration it sc mix' 10 that of a light, or lightly loaded trucks, or heavy trucks some distance away. DuraUonmay be estimated in soot ec sues. Movements may be appreciable on upper levels of tail structures. Standing motor can may rock slightly. IV l*el*, indoors by many, outdoor* by few. Awakens a few individuals, particularly light sleepers, but frighten# no o*ve except thcw« apprehensive from previous expeoence. Vibration like th at due Jo paxring of heavy, or heavily loaded track.*. Sensation lik-: s heavy body striking building, or ihe f riling of heavy objects inside. Dishes, windows and coots rattle; glassware and crockery clink and clash. Walls and house frames creak, especially if intensity is in the upper range of this grade. Hanging objects often swing. Liquids in open vessels ere disturbed slightly. Stationary automobiles rock noticeable.. V Felt indoors by practically everyone, outdoors by most people. Direction can often be estimate*.! by fho2-e. outdoors. Awakens many, 01 most sleepers brightens a. few people, with* slight exdten eni; some persons run outdoors. BuiKhngs tremble throughout, Dishes and g,-as&v are break to some extent. Windows crack in some cases, but not ^encr- ally. Vases and small 01 unstable objects overturn in many instances, and ? few fall. Hanging objects and doers swirg generally or considerable. Pictures knock against walls, or swing out of place. Dcors and abutters open o; clos? abruptly" Pendulum docks stop, or run fast or slow. Small objects move, and furnishings may shift to a slight extent. Small amounts of liquid; spill from weli-fiited open containers. Trees and bushes shake slightly. VI FslS by everyone, b. doers am! cu 'doors. Awaken? all sleeper.. PrighUn.3 m v y peootc; gancril fcxciterae&t, surid some-pcrc>.K* run outdoors. Persons move unsteadily. Trees and oushes shake slightly to moderately. Liquids arc set in strong motion. Small’bells In churches and schools ring. Poorly built buildings may be damaged. Piaster falls in small amounts Oth rr p’hst"* cracks >vmewhat. Many dishes and classes, and a few windows, break, Knick-knacks, books and pictures faii- FurrJ&tue overturns in many instances. Heavy furnishings move. VH Frightens everyone. General alarm, and everyone runs ourdoooc People find it difficult to stand. Persons driving ia.r$ notice shaking. T c<*v and bushes :'ha';s moderately to strongly. Waves form cn pon.lv, lakes and streams. Water is muddied. Grew-: or sar.d stream banks cave in. Large church re f; ring. Suspended objects quiver. D ane's is negligible in budding’- of good design and construction; slight to nv>denIs in ■ •vell-b' f t ordinary buildings; considerable in r ooriy built or badly de*‘VTned fe.rildir.gs adobe Louses, old w..R: {:?re ci- ahy where Lrid up without mortar), spires, etc. Pb?!er and some stucco fall. Many windows and some furrcbvti r.Tfel:. ijyosat'td brickwork and tiles shake down. Weak chimneys breek at the roofline. Cornices fall from towers and bb;h buildings. Bricks and stones are disiod&ed. Heavy fu-niture overturns. Concrete irrigation ditches are con-vidcitibly damaged. V71I General fright, sr/i alarm approaches panic. Persons driving ecus are disturbed. Trees sl:?ke strongly, and benches'and trunks break off (especially palm tm*o). Sand ztvi mud erupts in small amounts. Flow cf springs and wells is temporarily and sometimes permanently charged. Dry wells renew flow. Temperatures of spring and well waters varies. Damage slight in bricx structures built especially lo withstand e-arrhqu&kes;considerable in ordinary substantia] buildings, with some partial collapse; heavy In conic vreodrn houses, v-.ith seme tumbling down. Panel walls break ?way in frame r. true lures. Decayed pilings c-resV. off, VV.rib fall. Solid stone walls crack and break seriously. Wet grounds and steep slopes crack to some extent. Chimneys,columns, mciiuments and factory stacks and towers twist and f3li. Very heavy furniture moves conspicuously or overturns. IX Prrjc fc gaiuTul. Ground, crack.- conspicuously. Damage is considerable in masonry structures built especially to vdthstnrrri earthquakes; groit in other masonry buildings • • some collapse in Luge part. Some wood frame houses built especially io withstand earthquakes are thrown out c f plumb, others are. shifted wholly o il foundations. Reservoirs ure seriously damaged and underground pipes sometimes break. X Panic is gcn'xal. Ground, especially when loose and wet, cracks up to widths of several inches; fissures up to a yard in width run parade! to can' I and stream bank.*. Landsliding is considerable from river banks and steep coasts. Sand and mud shifts horizon- tally or. beach S3 and tint lard. Water level changes in wells. Water is thrown on banks of conais, lakes, rivers, etc. Dams, dikes, • rubankriicnh axe seijoi'.ily damaged. Wdbbuiit wooden structures and bridges are severely damaged, and some collapse. J>x.n,?iTou‘ cracks develop in excellent brick walls. Most masonry and frame struct*.ires, and their foundations, are destroyed. Railroad sails tend slightly. Pipe tines buried in earth tear apart or are crushed end-vise. Open cracks and broad wavy folds open in cement pavements and asphalt road surfaces. XI Panic b geiwraL Disturbs rices in ground are many and widespread, varyirr with the ground material. Broad fissure*:, earth slumps, and land slips develop in soft, we? ground. Water charged with sand and mud is ejected in large amounts. Sea waves of signi­ ficant magnitude may develop. Damage i$ severe to wood fn n v i.tructures, especially near shock, centers, great to dame, dikes arid embankineixls, even at long distances. Few it" any masonry structures remain standing. Supporting pio.es or pillars of large, weLFbuiU 0ridges are. wrecked. Wooden bridges that “give’ are less affected. Railroad rails bend greatly and some thrust endwise. Pipe lines buried in earth aie put completely out of .sendee. X!1 Panic is general. Damage is total, and practically all works of construction are damaged greatly or destroyed. Disturbances in the ground ar« great and varied, and numerous shearing cracks develop. Landslides, rock fails, and slumps in river banks etc numer­ ous and extensive. Large rock masses are wrenches} loose and torn off. Fault slips develop in firm rock, and horizontal and vertical offset displacements are notable. Water channels, both surface and underground, are disturbed and mo allied greatly. Lakes are dammed, new water fails are produced, livers are deflected, etc. Surface waves are seer, on ground sur­ faces. Lines of sight and level are distorted. Objects are thrown upward into the air. Figure 9. (after Cluff end Bolt, 1969). .1., Lake - shore and .subaqueous_slumping.

Subsurface or subaqueous slumping can result in the. destruction of

shoreline facilities due to their nearness co this failure. Slumping

in shore areas can be common on slopes of one to three degrees (Youd.

1971;. Mechanically the failure might progress away from the headwall

toward the tee, or in contrast to this be retrogressive headward and

involve a potentially greater area as the headwall failure repeatedly

establishes a new equilibrium. A retrogressive type failure may exist

over a large area along the shoreline fronting theVJbi.ttey Ranch (NE1/4

T25N R20K).

Vibration associated with an earthquake may cvclicy load and pro­

duce failure in loose subaqueous sands by causing their structural break­

down. This is accompanied by a reduction of the sands bearing capacity

causing spontaneous liquefaction (Anderson, 1967). Other mechanisms

can 'induce a similar type of slumping. Most commonly slumping results

from an over-steep slope, and this steepness can be accomplished by either

fault Induced tilting or by eroding water currents (Morgenstern, 196?).

Areas marginal to the lake consisting of sandy and silty sediments which

transgress lakeward, have the potential for failure as described above.

Slumping is particularly common at the mouth of large rivers, but this

is more restrictive In time and place because it corresponds to those

times when the river has deposited its greatest sediment load (Morgenstern

1967). This is discussed under the topic "Embankment and Deltaic Failure"

2 . Liquefacfcion

liquefaction -is related to the mechanics of subaqueous slumping.

However, liquefaction is not. restricted to a subaqueous environment. 36

Liquefaction may be explained as the .condition that results from the

compaction of a saturated material, which decreases its volume while

increasing the pore-water pressure when the water pressure becomes equal

to the overburden pressure or intergranular stress the material develops

a liquefied state (Seed, 1966; Anderson, 1967; Youd, 1971). Liquefaction

can be prevented if drainage is concurrent with the compaction. Accord­

ing to Youd (1973), liquefaction alone poses no particular hazard. In

fact a liquefied layer at depth may actually be an insulator reducing vibratory energy (Ambraseys, 1973).

In the liquefied state water migration is both horizontal and verti­

cal, with the latter causing the biggest problem. Upward migration either

liquifies the overburden, or moves directly on to the surface. Flooding along shore areas results where wTater table and geologic conditions per­ mit. The upward flow may also cause settlement or tilting, and buoying up of lightweight buried structures (Seed, 1966, 1967).

3. Differential Settlement

Differential settlement accompanies liquefaction due to compaction by vibration. In the situations of liquefaction where surface water is rapidly removed, the most detrimental long terra problem is a random low­ ering of the ground surface. Along the shoreline, where relief is very low, this might generate water-filled depressions.

Differential settling without liquefaction is also possible, thus, one does not necessarily imply the other.

4. Embankmen t and pre-existing deltas

The conditions noted in 2 and 3 above, are those which can occur 37

in fiat lying areas but, the problem can be greater along slopes or em­ bankments. Shoreline deposits of loose sands and silts, may translate laterally because of the induced vibratory effect while liquified. If liquefaction occurs in or under a sloping soil mass the mass will move toward the unsupported sides. This type of failure is referred to as progressive slope deterioration (Seed, 1966). Seed (1970), has shown that relatively flat or gently sloping areas may fail by earthquake in­ duced shaking. Natural slope failures during the Alaska 1964 earthquake occurred on banks with an extensive horizontal surface behind the crest and. a flat or slightly sloping boundary near the toe (Idriss, 1966) -.

These parameters apply to soils with uniform as well as those with variable vertical and horizontal properties.

Three conditions commonly associated with liquefaction on slopes are: 1) flow slides, 2) limited displacement landslides, and 3) quick condition failures (Youd, 1973). The most common occurrence of this type

(1-3 above), of situation is in areas of pre-existing deltas (Seed, 1964;

Born, 1973). The pre-existing deltas at Tom Anderson (Sec. 14 T23N R22E),

Rodero (Sec, 10 T23N R22E), Quail (Sec. 4 T23N R22E), Mullen (Sec. 30

T24N R22E), Hardscrabble (Sec. 9 T24N R21E), Water Hole (Sec. 23 T25N

R21E), Wood (Sec. 18 T25N R21E), Jigger Bob, Poison-Thunderbolt-Sharp

(Sec. 1 T25N R20E), and Big Canyon (Sec. 25 & 36 T26N R20E) are potential areas of failure.

5. Scichlng and delta failure

Local surface waves can be generated when embankments slump suddenly into lakes, and are a potential hazard to shoreline facilities. According to McCulloch (1966), slide induced waves and seiching can be produced by failure of deltaic and littoral sediments, Wiegel (1970), states that

rockfalls and slope failure can also produce problems by wave generation.

However this vravc development depends on several variables: 1) height

of the. fall, 2) mass of material, 3) total elevation or depression of the water surface (h), in response to the impact, 4) distance over which

item 3 occurs (A), and 5) water depth (d), Certain combinations of

h and d can produce waves which have little decrease in wave height at

long distances from the source area. This implies that such failures

across the lake from inhabited areas could produce significant run-up height on the far shore.

Only the eastern shoreline is bounded by steep slopes which are potentially hazardous in terms of mass wasting produced water waves.

These propagated waves could cause damage to the present Warrior Point

and Sutcliffe areas. Waves might also be developed from slumping in the

present Truckee River delta (McCulloch, 1966). The wave generation problem, in this regard is two-fold: 1 ) backfill waves, and 2) far-shore waves. Waves developing from slumping in the Truckee River delta probably would not affect rhe Terraced Hills-North Beach area but, would involve most of the west and east shoreline. Although the wave point of generation,

is in effect perpendicular to these shores, due to refraction conformity will occur and inundation can be as complete as if the source were immedi­ ately lakeward.

Back-fill waves are formed by water rushing in toward the delta to

fill the void left by slumping. The inshore distance of inundation and run-up height relate directly to the. mass of debris released during one period of wave generation. McCulloch reports back-fill waves running 39

urc to 30 *ect and inland 300 feet, while run-up height reached along lake facing cliffs exceeded 70 feet for far-shore waves. (McCulloch’s investigation was concerned with a lake whose dimensions approximated

Pyramid's). The size of the deltaic failures is related to the mag­ nitude of the earthquake which triggers them and should not be confused with slope failure resulting from normal progressive delta building.

Saiching can also be damage producing. If; is a periodic oscillation produced by a surface disruption, or lake basin tilting and relates to the physical dimensions of the lake. This oscillation continues after the initiating force ceases and is usually dominant in the direction of the lake’s longest direction. The problem, in either case of seiching or wave generation by slope failure, is the same in areas of abrupt shallowing. The west shore from the Truckee. River delta to Warrior

Point is fronted by shallow water. Run-up will be higher in rapidly shallowing water and is due to the wave energy relationship to water depth. Seiching also causes general surface elevation changes which can promote bank failure by the rapid dewatering of exposed subaqueous dedimen r.s. 40

HASS WASTING

The Pah Rah Range and Virginia Mountains are the most actively involved in mass wasting. The Lake Range and in general the entire peripheral shoreline are also subject to mass wasting but, not to the same degree. live types of mass wasting are recognizable within the lake basin (Plates I-V). They are: 1) rockslides, 2) rockfalls,

3) soilfalls, mudflow, and 5) shoreline slumping. Item (5) is dis­ cussed under the topic "Earthquake Effects".

A . I

The rockslide is the largest mass wasting event both in areal extent and number of occurrences, Tills type of landslide involves the rapid sliding of bedrock during which the material is greatly deformed and fragmented (Pashley, 1971; Van Horn, 1971). Movement is generally closely related to and controlled by surfaces of weakness. These sur­ faces of weakness are inherent in the involved stratigraphy, such as bedding planes, variation in the strength of different lithologies, and the attitude of the stratigraphy at the time of failure (Komarnitskii,

1968). Another sufrace of weakness is faulting either as the plane of failure, or the triggering mechanism which disrupts the equilibrium of the. slope..

3. Rockfall and Soilfall

The second most common slope failure is the rockfall. The soil- foil relatable to the rockfall by the mechanism involved (i.e. gravity) is the third most common. Both are of relatively small areal extent tut, develop and proceed to a new equilibrium position at a much faster rate than the rockslide. This is primarily due to their freer falling 41

movement. There is little interaction between moving materials, in

contrast to the rockslide where the interaction is partly responsible

foi a slower rate of movement. The rockfails and soilfalls are less numerous and involve much smaller areas than the rockslides. However, rockslides are partly restricted to, and within the boundary mountains, whereas the rockfails .and soilfalls are presently confined to the shore­

line area.

C, Mudflow

Mudflows are recognizable in only two locations. This preserva­

tion does not preclude the occurrence of previous flows which have been removed or modified beyond recognition. The young flow in the

Lake Range (Sec. 27 T25N R22E), and the older flow in the Pah Rah Range

(Sec. 27 I23k R22E) have a close affinity with rockslides. The rock- slide has reworked this highly permeable material and affords the great­ est potential for their development. Essentially the mudflow is a viscous fluid, unconsolidated, with a high water content, and moves down slope as a slurry. Due to the high viscosity they have the ability for transporting large rock masses long distances. The mudflow in the

Lake Range carried boulders, two to three feet in the longest dimension, some 200 to 300 feet in front of the canyon mouth but, measured only a few tens of feet wide and approximately one foot thick at. this location.

D. Potential Fai1 ores

Areas which have not failed but, have physical conditions which indicate their inherent instability have been delineated. In all cases

they arc associated with rockslides as a peripheral feature. Faults 42

which might-have been the - causal mechanism of past failure intersect steep severely cracked slopes which are unstable. The poor stability-

is because of the ease of surface water entry and the location near a

fault which has been active in the past (Plates I & II).

E. Activity of_ Slide Masses

Rockslides were examined to determine the cause of failure, the

feasibility of detering future slope failure and the probability of future movement. Tu all cases examined a fault trace or traces inter­ sect the slide mass or defines at least one peripheral boundary. In the

Rodero Creek (T23N R22E), Quail Canyon (NWl/4 T23N R22E), and Hardscrabble

Creek (NW1/4 T24N R21E) rockslides it appears that post-slide movement is occurring (Plates I & II), Thus, the probability of further dis­ equilibrium within the slide mass should be expected (Van Horn, 1971:

Varnes, 135S). Due to the restricted location and/or the large areal extent: of the slide, masses, and the limited type of development prefer­

red for this area, deterring further movement is not a viable consideration.

The slides whose boundaries are delineated should be completely avoided in terms of structural development. This includes areas considered for development which are fronting canyons or hillsides with mass wasting close to the lake shore.

Rockfalls and soilfalls, because of their limited areal extent, do not present che same kind of problems stated above (Plates I-1V).

The northeast shoreline cliffs have the greatest potential for rockfa11s as indicated by their past failure. Soilfalls are active along any shoreline embankment where erosion, due to wave action and long-shore currents continually produces over steep banks that achieve-equilibrium

by failure. Inis applies to any of the littoral-sediment shoreline

embankments peripheral to the lake (Plates I-IV). Mudflows are also

limited in areal extent, but because of their affinity for rockslides

they will develop on slopes and the same restrictions pertaining to

rockslides, noted above, are required of mudflows.

The mass wasting examples discussed above, are on moderate to near vertical slopes. However, sliding may also develop on shallow slopes as mentioned under the topic "Earthquake Effects". This shallow

slope failure would involve lake sediments, consisting of sands and gravels, silts and clays which more common],y occur in deltaic sediments and includes those areas fronting the major drainages along the west and east. shores. The unconsolidated, cohesionless nature of some sediments and the relatively shallow groundwater table can also result in the problem of liquefaction. Liquefaction can effectively reduce shear strength thus allowing gravity to perpetuate, lakeward slumping (Youd,

1971). This condition is observable along the shoreline embankment near the Whittey Ranch (NE1/4 T25N R20E) and extends 100 to 200 yards inland and 400 to 500 yards along the lake shore.

F. Age Relations

Age determinations for possible correlation to historic earth­ quakes and faults and an evaluation of the present state of equilibrium were made. The rockslides have developed a soil profile and a. complete vegetation cover with the exception of those areas undergoing erosion.

Soil profile development can take several thousand years and is a better indication of apparent long term stability than vegetation. The Rodero Creek (T23N -K22-E) and Quail Canyon (NW1/4 T22N R22E) slides, the slide

in the canyon north of Coal Creek (SW1/4 T25N R22E) are the only rock-

slides that have been modified by littoral erosion and an approximate

age can be assigned to their movement.

Covering the toe of the Rodero Creek, the unnamed canyon slide,

ana the east of Pyramid slide are lacustrine sediment with a high lake

strandline near 4,400 feet. This implies a minimum age of greater than

12,000 years b.p. since any major movement. The Quail Canyon slide has been disrupted by faults which do not cut older shorelines, and is

also greater than 12,000 years old.

Surface investigation of the Rodero and Hardscrabble Creek (NE1/4

T24N R20L) slides reveals small localized movement resulting from equil­ ibrium adjustments. However, no indication of this readjustment was observed over large areas. According to McMahon (1967, Colorado School of Mines), constant slope movement prior to the time of failure cannot be used as a measure of slope stability, as some slopes are known to have continued movement for years while others fail suddenly without a pre­ vious history of movement. This re-emphaszies the necessity to avoid structural development in areas on or peripheral to any slide mass.

The slide in Quail Canyon has abundant ground cracking indicating pres­ ent activity and a lack of equilibrium. The transecting faults indicate recent movement toward the east, end and west from this segment of the trace Lhey lack physical evidence of movement. All of the other rock- slides may be subjectively dated as having developed during the. same time period as the Rodero Creek, Quail Canyon, unnamed canyon and the east of Pyramid slides. This evaluation is made by assuming a similarity in the strength of the volcanic, stratigraphy in the boundary mountains and the strong influence exerted by the earthquake which triggered trie large Rodero Creek slide.

The rockfalls, soilfslls and mudflows are assumed to have been partly developed during historic time. This is especially true for soilfalis and mudflows because of their ephemeral nature. Rockfalls because of their more permanent preservation are more difficult tc evaluate. The unstable condition of the region where rockfalls have developed suggests that their failure could have been caused by any one of the larger earthquakes listed in Table 1. It can be assumed that if a larger earthquake is generated, further mass wasting of this type can result.

In general the reactivation of mass wasting and the gross distri­ bution of it, ir. controlled by the intensity of ground shaking, with local variation in occurrence reflecting variation in character and structural integrity of local geology (Korton, 1971). The various mass wasting features discussed and mapped have a multiple causal history, involving their contained stratigraphy, weathering and erosion. Earth­ quakes and faulting have been the triggering mechanism. 4 6

SANITARY l a n d f i l l

Open doping and uncontrolled incineration are the two types of waste disposal presently used on the reservation. Both disposal practices could adversely affect the water resources and should be dis­ continued.

Thirteen areas were examined for potential use as sanitary land­ fill sites (Figure 10). Considering the probable useage, geographic location and optimum benefit, it is recommended that trench-type land­ fills be implemented. A detailed account concerning use, preDaration and maintenance of such disposal trenches is presented in a "Guide for

Interpreting Engineering Uses of Soils" (1971).

The areas investigated were evaluated considering: 1) geology,

2) hydrology, 3) economics, and 4) aesthetics as discussed below.

A. Geology

Depth to bedrock and the character of surficial. material regarding its use as an intermediate and final site covering are the geologic con­ siderations. Presently no soils investigation of the total lake basin exists. Two reports by the United States Department of Agriculture

(Reno, 1970; Carson City, 1973), deal with part of the basin but, the reports are restricted to adjacent areas and upper slope (mountain) soils

B. Hydrology

Depth to the groundwater table was the only hydrologic considerable

However, information on permeability, infiltration rates, runoff, and rainfall arc necessary, but chat data is beyond the scope of this study. 41 48

C. Economics

Haulage distance was the only economic consideration measured

(cost of ton/mile, Anon. Rept. If39, 1950). However, the evaluation considers the type of terrain, the. condition of this terrain regarding its surficial deposits and prevailing wind conditions, availability of existing roads, and cost for site preparation. Haulage costs were as- sinned equal for tonage, thus the distance from existing and potential population sites was the main consideration.

D, Aesthetics

Aesthetics are partly influenced by the prospective site location in relation to regions of existing and potential lake use, plus the site location in relation to the total lake shore.

E. General Investlgat.l ve Information

This study is preliminary and more complete data must be gathered at the area selected for a disposal site. The criteria listed below are essential in determining site suitability and cost (USDA, SCS, 1971).

1. Depth to teasonal high-water table and soil drainage classes

These factors effect the soils wetness and must be evaluated when considering the influence on earth moving operations. The borrow site soil material must also be assessed for probable contamination of groundwater at the landfill site. The site itself requires examination as to the effects of long term usage on the existing groundwater system.

?■. Permeability

Permeability is closely related to the effects cn the groundwater 49 system and soils with low permeability are more desirable because cf

their limitation on subsurface water migration.

3. Slope conditions

ihe slope conditions require assessment because or the necessity of constructing access roads and the problem of adequate diversion of surface runoff from higher ground. This is a special problem for trench- type landfills and the facility must be contoured parallel to existing slope conditions.

4. Subjacent stratigraphy

Inplace bedrock requires examination because, depending on its depth and condition, it may significantly influence the construction cost. The main consideration is the depth below the surface and relates to the volume which must be removed. Examination should also reveal the groundwater conditions relating to the stratigraphy to assess pos­ sible contamination by leachates.

5. Texture and water hoiding capacity

The texture cf surficial deposits is an important consideration as preparation, daily usage, and final covering require investigation to determine the soil utility in wet and dry conditions and the rate of leachate movement. Water retardation is desirable for the. migration of the leachate thus allowing time for removing bacteriological contami­ nants, The present surface material should he stockpiled for final covering as it is suitable for promoting plant growth.

6. Groun dwa ter

The groundwater conditions are determined empirically for each 50

site and involve depth measurement of the static water level and deter­

mination of seasonal fluctuations. Knowledge of the groundwater situation

for the site allows determination of: design criteria to minimize contamin­

ation.

7. Exposed rock

Exposed rock is called stoniness or rockiness and refers to the

detached-rock or bedrock, respectively. Construction costs vary depend­

ing on the amount and condition of rock which requires removal and

selecting a site with minimal stoniness or rockiness is preferable.

F. Site Locations

The following information is presented concerning the sites examined:

1. Locations 7, 8, 9 & 10 (El/2, NW1/4 T26N R20E, El/2, SW1/4 T27N R20E, SW1/4 SE1/4 T27N R20E, SE.l/4 NE1/4 & NE1/4 SE1/4 T27N K20E)

All locations are determined to be adequately suited for landfill operation by; 1) Depth to bedrock is greater than 50 feet. The surficial soil material and subjacent stratigraphy have the recommended silt and clay content (approximately 40-60% sand with the balance having nearly equal amounts of silt and clay; ASCE Report #39, 1959), for covering operations; 2) Depth to the water table determined from well data

(Wilsey 6 Ham, 1971), is greater than 40 feet; 3) Existing roads are adequate and the crly road construction required would be access. The terrain and surficial deposits are well suited for site preparation.

Haulage costs are considered negligible because of the condition of the other criteria. The prevailing winds are northwesterly and landfill orientation would be no problem for locations 7 & 8 , nor sites 9 & 10 as these two are protected by surrounding bills; 4) Aesthetics as noted

j.n B above would not present a problem.

•). Location 12 (NW1/4 SE1/4 T24N R23E)

Twelve is the best southern area for a disposal site. Specifi­

cally: 1) The geologic conditions indicate a shallower depth to bed­

rock (less than 40 feet (?)), but as this area is in a natural depression

initial depth requirements are not as great. Surficial material is

adequate for covering operations; 2) Groundwater depth is approximated

(no well data available) at greater than 50 teat; 3) Econonieally this

location would only require the construction of access roads and as with the above locations this preparation would require minimal expense.

Site orientation to account for prevailing winds would not present a

problem. Haulage costs would be comparable to the northern sites (7, 8 ,

9 & 10), if this landfill is to serve the south and east shores; 4) The

aesthetics assessment conforms to the requirements as this site is

completely isolated from the lake front areas.

3. Location 5 (NEl/4 NE1/4 T25N R20E)

Area five would also suffice as a site location, but its pre­

ference is less than 7 through 10 or 12 because of the smaller area available for preparation. The criteria are: 1) Geologic conditions

indicate a shallow bedrock depth prevails (less than 30 to 40 feet), and the surficial deposits are more coarsely clastic than 7-10 or 12;

Groundwater deprh from well, data is estimated to be at least 50 feet

(Wilsey & Ham, 1971); 3) The site requires only minimal access road preparation and presents similar site construction costs. Haulage costs 52 would be less than for the. northerly locations (7-10);. 4) The aesthetic aspects are lower because of its nearness to the lake front, but are resolvable,

!>.^ L ocations 1 & 2, (SWl/4 NSi/4 &NE 1/4 NWl/4 T 2 4 N R21E)

Both of these locations must have permeability and runoff data assessed for the diatomaceous earth deposits. If acceptable area 1, because of its location and isolation is more practical chan area 2 , as follows: 1) Trie geologic conditions present no problem as depth to bedrock is greater than 100 feet, and surficial material is essentially a fine grained, clastic, sedimentary deposit; 2) The water table depth is greater than 50 feet (Wilsey & Ham, 1971); 3) This area is adjacent to the largest population center of the west shore and haulage costs would be lowest. Read construction is required for access to the site.

Site preparation costs are consistant with the other areas (7-10, 12, 5). because of the condition of the soils and subsurface material.

The remaining areas (3, 4, 6 , 11 4 13), have either been elimin­ ated entirely or pose, problems which warrant their being less desirable for economic reasons.

5. Locations 3, 4, & 13

All require the conjunctive operation of a borrow site because of the textural conditions of surficial deposits (3: NE1/4 SW1/4

T25N R21E; 13: NE1/4 SE1/4 T22N R23E), and lack of material (4: SWl/4 hivl/4 T25N R21E) . The borrow site, would provide covering material of the texture which meets engineering standards for site operation. 53

6. T.neation 6 & 11

Aesthetics (6 : SW1/4 SE1/4 T26N R20E), and shallow groundwater

(11: El/2 SW1/4 T28N R21E and NE1/4 NE1/4 T27N R21E), preclude these

sites. Area six xs situated between the Big Canyon and Whittey Ranch

and because of its relative nearness to sites 5 and 7 through 9 is 'not

considered satisfactory. Area eleven is located above a shallow water

table, ranging in depth from 7 to 17 feet (Wilsey & Ham, 1971), and is also uneconomical because of access road preparation and haulage costs.

The remaining areas around the lake, including Mullen Pass with­ in the study aiea, are assessed as not suitable for one or more of the following reasons: 1 ) location on an active or inactive floodplain providing easy access to the groundwater system, 2) located near poten­ tially active landslide(s) and/or fault(s), 3) non-aesthetic location by virtue of nearness to the lake shore or presently developed population center, and 4) uneconomical because of haulage costs, site preparation or available access.

G. Problems Arising From Site Operation

Because of the installation depth a complete investigation of potential pollution requires examination of surficial soil and rock formations which may become avenues for movement of leachates to aquifers, wells, water courses, and other water sources. Natural surface runoff must be. considered because of the elevation changes produced by site filling. The leachates from the disposal site also pose a problem as tafey contain chemical and bacteriological constituents that may be harm­ ful to the hydrologic system. Bacteria can be effectively removed by S4

percolating leachate through a sandy or silty soil, but the chemical

contaminants are in solution and can readily enter the groundwater

system. According to Anderson and Dornbush (1966), hardness may impair

groundwater quality. This is a constant problem of leaching, in that

organic matter undergoing aerobic decomposition produces C0 -> which is

soluble in water and forms carbonic acid. The acid can effectivelv

release Ca~ 2 from calcareous material (soil and rocks), causing a hard­

ness increase in the groundwater. The chloride iori(Cl~) may serve as

an indication of leaching, because: 1 ) easily measured, 2 ) not readily

absorbed by soils, 3) not altered by biological processes, and 4) con­ siderable quantities may be present in the refuse. 53

HATER RESOURCES APPRAISAL

This section consists partly of a summary of some, of the existing literature on surface and groundwater as it relates to the Pyramid Lake

Basin. During the period from 1963 to 1974 many reports have been written involving, to varying degrees, the hydrologic aspects of the reservation, hut few focus on conditions within the reservation boundar­ ies or the lake basin. Tire report of Hardman and Venstrom (1941), is included as ah historical evaluation of'flow rates and lake level fluctuation.

A , Syr f'j-'s i_; _o f Sc leer s ■1 Rene rts

The following is a brief summarization of those aspects in the reports specifically related to water resources. Where appropriate, and within the scope of this paper I have made supplemental recommend­ ations and additional data have been provided.

1. Wilsay and Ham Report

The Wilsey and Earn (1970), investigation concerns, itself with water resources and land use of the Pyramid Lake Indian Reservation.

The water resources portion of the report is subdivided into: a) Back­ ground Criteria, b) Water Sources, c) Water Requirements, d) Quality of

Water: and e) Projected Changes in Pyramid Lake. a. Background Critenia

This includes: a) the general conditions of Pyramid Lake,

6) those hydrologic aspects concerning inflow and outflow, e) water rights of record and their influence regarding the lake basin, and

°) the condition and extent of the surrounding agricultural lands. 56 b. Water Sources

This section is divided into the areas which presently contribute water to the basin. These are the Truck.ee River, ephemeral drainages, springs, and pumping. Other suggested methods of developing the avail­ able water are included. The purpose of this subdivision is to resolve, quantitatively, these contributions and appraise each as it relates to the overall system. c• Water Requirements

The intended and existing consumer sectors which include: a) municipal and domestic, b) industrial, c) recreational, and d) agricultural have been segregated. This is to project usage, based upon predicted growth, to formulate the effective sustained population which can be supported by an inter or intra basin supply. d. Quality of Water

The water usefulness is appraised and includes: a) water analysis b) water quality, and c) sewage disposal as having the most, immediate effect or. reservation usage. e, Pro.jected Changes in Pyramid Lake

These are presented as: a) control of Pyramid Lake character, b) stream depletion, c) water balance in the lake, d) projected changes in quality-quantity of water, and e) the lake future.

Hie water sources subsection is quite complete as far as it goes. However, its overall usefulness can be increased by including groundwater and storage evaluations, as accomplished here for the west .57

shore to the north and along tho east shore. Using the same method

outlined in Wilsey and Ham, further data have been generated for these

areas (Table 2 & 3)2./. Evaluation of the groundwater system may also

be supplemented by: .1 ) estimating the specific yield of the areas for

pumping (using the water budget method Eq. 1), and 2) estimating die

contribution of bank storage to the lake as a result of lake surface

lowering.

The report a]so discusses springs which are available for improve­ ment and which would contribute to the total water budget. However,

these are only assessed along the western margin. The investigation apparently overlooked some of the springs in this area, as the total of 29 is less than this writer's count. Fifty-four springs were counted within and adjacent to the. vest, north and ease boundaries of the basin, and the improvement of these could provide additional water to storage for use.

1/ The surface areas of the fans, were determined from U.S.O.S. topo­ graphic maps, with field observation to determine their boundaries. Ir was assumed that the water table would not be lowered below elevation 3,850 feet with the lake level at 3,800 feet. This places a lower limit of the usable aquifer. The upper limit was assumed to be the static water level, which well data Indicated at about 50 feet. Between tease two limits the aquifer would be a curved wedge, thin toward tho shoreline end thickest toward the mouth cf the canyons. As a rough approximation, the volume of the wedge was assumed to be the surface area times the depth (static water level to base of aquifer) times one-quarter (a shape coefficient). 58

2. The Born Report

Born's (1972), report deals with the delta complex at the mouth of the Truckee River. The purpose of the report was to study and doc­ ument the recently dissected, and previously undescribed late Quaternary delta exposure along the river between Nixon and the lake. A chronologic interpretation of paleo-lake fluctuations over the past 10,000 years follows this appraisal.

Hydrologic data have been accumulated for the Truckee River con­ cerning its historic flow rates, sediment load and influence on the surface elevation changes of the lake. Documentation of the rapid rate of aeration accompanying the lakes decline, of the modern delta sequence is provided and includes a description, history and formational mechan­ ism of mud-lump genesis. The report serves a dual purpose as: 1) to increase the understanding of deltaic sedimentation processes, and b) to specifically relate these processes of the delta as they apply to

Pyramid Lake. The report, although limited in its areal extent, contri­ butes useful data pertinent to lateral stream erosion and the ephemeral nature of the present delta, both of which are important to future development on the reservation.

3. Water Resources Reconnaissance and Pyramid Lake Task Force Report

Both reports deal with the various hydrologic aspects of the reservation as part of an overall appraisal of a larger region. In the Water Resources Reconnaissance report the area consists of the

'truckee River Basin; while the Task Force report extends this area and includes Washoe Valley, the Carson River, Lahontan Reservoir and the 59

Carson Sink. The Reconnaissance Report is a useful compilation of

hydrologic data in terms of the water budget (i.e. inflow and outflow) „

for the entire region. These data are presented in tabulated form

with additional information in the accompanying text.

The Task Force study was not intended to, and does not, provide

for the specifics stated in the report noted above. Its purpose is to

provide a broad scope investigation of the hydrologic system and to

suggest alternative solutions to existing and potential problems which

are inherent therein. It does provide insight to the interrelationship

between Pyramid Lake, Lahoatan Reservoir and the Carson Sink, hut does

this in a general sense thus its usefulness is limited.

/u Pyramid Lake Task Force: Betterment Studies Work Group

This study examined the areas of: a) Carson River Basin areas

other than wildlife management areas, b) Truckee River Basin areas

above Derby Dam other than wildlife management areas, and c) Wildlife management areas in the Carson and Truckee River Basins, to conserve water for the benefit of Pyramid Lake.

a. Study One

This study deals only with natural streamflow and precipitation

in the area, the presently irrigated lands and existing major structures,

ft does not evaluate additional water diversions into either the T7:uckee

or Carson Basins or discuss how salvaged water should be reallocated. h. Study Two

It examined possible alternative solutions of salvaging water

for Pyramid Lake from the Truckee River system above Derby Dam, and the estimated cost of these alternatives. conclusion an annual water

saving could be realized by: a) reducing exports from Echo Lake and

uo Sierra Valley, b) reducing consumptive use in the Truckoe Meadows,

Washoe Valley and Spanish Springs Valley, c) make changes in land management practices, and d) reduce snowpack evaporation. The total saving could amount to approximately 79,000 AF/Y. c. Study Three

The study examined alternate ways of managing lands and water conveyance to continue the operation of the Stillwater Wildlife Manage­ ment Area, in two phases. The first phase considered the. total water- fowl use of the. valley and determined approximately 77,000 acres are available. The. second phase evaluated the effect of reducing water supply to the wet.land areas to four different levels

5. Simulation Theory Applied to Water Resources Management Phases I,' IT. & III '

The purpose of this study was to develop criteria such that any reasonable constraints or demands which are placed on the actual system could be evaluated. Phase I examined the hydrology of the Truckee River system of California-Nevada defining inputs, hydrologic, interactions and outputs of this system in the form of a simulation model. Phase II defined the Carson River system as was done for the Truckee River system by extending the simulation model. This combination has provided a simulation modal for the complex two-river system. Phase III, the final phase of the project was to derive the most favorable operating conditions for the two-river system. The result-.s cf this project show that the simulation model is

a realistic approach for describing and examining water resource system

performance. Thus, its use as a valid planning and management tool has

been demonstrated.

6 , Arid Basin Management Model with Concurrent JJua1dty and Flow Constraints, Phase I

The simulation model developed for the Truckee-Carson. River

systems has been used in the Carson Basin for management purposes.

Inorganic water quality data, flow and reservoir storage constraints

are examined concurrently. Examination of the data indicates that

applying this type of inorganic quality-simulation model is valid.

Modifications of the existing Truckee-Carson simulation model are

recommended and include: a) two additional stations on the Truckee

and one. on the Carson River, and b) measurement of flow after the

irrigation season in the Carson Basin.

The report is the first of a three phase, project. The end re­

sult is directed toward developing the most favorable operating regula­

tions for complex river systems when considering multiple influences and the actual characteristics of water quality and flow rates.

E. Lower Truekee-Carson River Hydrology Studies

The study reportedly has provided the Bureau of Indian Affairs with sufficient information on the Carson and Truckee Rivers to estab­ lish and protect the rights of the Pyramid Lake Indians in use of water and other interests by the government. 62

Thc-i lower Carson River area water consumption was computed.

Of the total amount of water consumed in the study area about one in five AF of water is consumed beneficially by agricultural crops. The remainder is incidental uses of surface and underground waste from the irrigated lands, and losses and spills from the storage reservoir.

Recommendations for: a) maximizing Carson River water use, b) increasing project efficiency in using water for the Newlands Project, c) delivering water to farmers only on demand and charging for all water ordered, and d) raising Lahontan Dam to increase the storage capacity, are included.

8_,_ _A1temate Plans for Water Resources Use: Carson-Truckee River Basin

The report on Area II, Carson-Truckee Planning Region is the second in a series of six state planning regions. The state plan is being developed in four phases: a) Phase I inventories the resources, b) Phase II is a forecast of future water ana related land resources requirements, c) Phase III is a formulation of alternative plans, and

(!) Phase IV is the formulation of a recommended plan.

The report which is Phase III for Area II, describes four alter­ native courses of action for the use of water and related land resources in the Carson-Truckee Planning Region. They are: a) without plan, b) economic efficiency plan, and c & d) two environmental quality alternatives. a^Without. Plan

This plan indicates conditions that are expected to prevail if 63

there is no plan or program designed to alter existing trends. It is

offered as a base for comparison in evaluating the other alternatives.

b. Economic Efficiency Alternative

The components of this plan are economically justified selected

projects. Each rs resigned to alleviate some problem associated with

•rater supplies. The projects include development of new supplies for

recreation, municipal, industrial use, power generation or irrigation.

Modification of runoff patterns to provide flood protection, enhance

water quality and/or maintenance of fish populations are also included.

c. Environmental Quality Alternative I

Emphasis is placed on maintaining Pyramid Lake at its present

size. Stabilization is suggested following Pyramid Lake Task Force

recommendations of improving the efficiency of the Carson and Truckee

River systems.

d. Environmental Qua.lt ty Alternative II

This alternative is not concerned with the stability of Pyramid

Lake. It allows development of both the Carson and Truckee Basins within certain environmental constraints.

9. Californta-Nevada Water Controversy 1955-1968

This is the second of a two part survey concerned with 100 years of the California-Nevada controversy. The survey is a general history of the California-Nevada Interstate Compact Commission from its form­ ation in 1935 through 1971. The commission's purpose wTas to produce a compact dividing surplus water from Lake Tahoe, and the Truckee, Carson 64

and Walker River s • Because of intervention Dy t’ne federal government

th e compact, has never taken effect.

As initial guidelines for drafting a compact the commission had accepted existing court decrees as the basis for determining the quantity of unappropriated water. However, the. federal government has put forth another water doctrine that conflicts with its earlier assumptions.

Their new position is established by the Winters v. United States, 207

U.S. 564 (1908) and Arizona v. California, 373 U.S. 546 (1963). These documents essentially support the contention that all waters from Lake

Tahoe and the Truckee River system other than those for the Newlands

Project and the 'water for third parties (i.e. United States v. Orr Water

Ditch Co. et al, Nev. Equity No. A-3 1944), are reserved for present and future development of Pyramid Lake.

12' 10Q~Yeer Record of Truckee River Runoff Estimations

The report covers the period from 1840 to 1939 and discusses the historical record of water-flow into Pyramid and Winnemucca Lakes.

Lake stillstand elevations for the earlier period are inferred from photographs and written documents. The past fluctuations in lake levels and volumes are a reflection of the variation in volume of water dis­ charged by the Truckee River. The study indicates both lakes were at a low level until about 1860, but increase rapidly between 1862 and

1871. The lakes were historically at their highest volume in 1890,

(Figure 11). 65 66

B. Recotmp^o Jafcl'cp <_s

V - to' vo further development of the reservation a complete and

co'.i' f t: 'r i v? - und -and surfacewater investigation is recommended.

•Re.cowa$ndatS ;.*• 1 through 5 are suggested as being an integral part of

the investigation that is needed.

. \ IV. „ * * 3- > ^ ’ • • 1. . Bank storage

During the historical decline of Pyramid Lake, frora 1909 to • -j*. • • I960, its surface has been lowered by about 75 feet. Well documentation *' * ‘e.indieates" this ami ants to dewatering the groundwater reservoir by about

-.1,500 AP/Y (Van Denburgh, 1973). The bank storage, decline represents

i t a significant quantity of groundwater depletion and a more precise

determinate oir of the actual quantity involved is recommended. This can

be accomplisVsc j use of mathamati cal models such as that developed by

Tbomj • ":»\ ^1 ; :cording to Coffin (197$, the necessary geologic

did i. to at rura .ely • aluate bank storage, need only be collected over

one • tarter of the re. ervoir length and within two miles of its shore­

line. The latter method may have limited application to Pyramid,

2. GroundwaLor-Lake water Interface

' Tr .( ccmi;-, i islw optimum well distribution mere knowledge of the

gre tt • . *.c tv interface is needed. Geophysical well logging

techniques can accomplish this (Keys, 1973). The geophysical invest-

igett ' in could be integrated with future water-well development, as

opposed to initiating c separate program. Long term groundwater

ae' Lopment can signi f ■ cantly effect the location of che interface and

enclvvger the longevity of wells.

v- 3, Groor.dwatar Rap 1 eri ishraen t

Artificial and natural recharge should be compared in an overall

appraisal of the groundwater system. Assessment of cost, need, conven­

ience, maintenance, availability and mechanics must be made. Areas

external to the Pyramid Lake Basin which are potential water supply

sources, include: Warm Springs, Honey Lake and Winnemucca Lake Valleys

and San Emidio and Smoke Creek Deserts (Task Force, 1971). Utilization

of the groundwater resources in these areas requires knowledge of the

present requirements on those systems and the projected interference

by additional usage. In view of the developmental considerations for

the basin and the complex retrieval, conveyance and distribution systems,

artificial recharge is not recommended.

Natural recharge of the groundwater system, if sufficient, is

preferable. However, a total evaluation should include such specifics

as projected well placement, and the possible interference effects

such as quality deterioration and hydraulic interference between adjacent

wells. Specific yield of the aquifers should be estimated and this

necessitates an assessment of springs for their contribution to the

groundwater system. According to Guisti (1971), specific yield deter­

minations can be accomplished using the water budget method by:

Eq. 1. os + V ‘ <°p+ V + °« + V * ** where: I inflow of surface water (recharge from rainfall and stream flow)

IgW - inflow of groundwater at the fan head.

0 r = outflow as runoff (this occurs in at least one area: kodero Creek has the only perennial stream reach- ing the lake).

Ogw = outflow of groundwater to the lake.

0 et = outflow as evapotranspiration.

0 p = pumpage from the fan.

& S = change in groundwater storage.

4. Groundwater Storage

Groundwater storage in the alluvium is estimated as a continua­ tion of work by Wilsey and Ham (1971), (Table 2 & 3). The tables con­ tain a list of areas which are tabulated for this study and those areas from the Wilsey and Ham report. The western and eastern alluvial fans are evaluated. The North Beach and Terraced Hills is eliminated from this evaluation due no the relationship of faults and the alluvial fan areas. The north end is peculiar because numerous faults cut these fans and depending on the vertical displacement, could cause a signif­ icant variation in the static water level.

In the areas assessed either existing well data, or springs were used to estimate the probable static groundwater level. The areas of

George Washington Rock (El/2 NW1/4 T26N R20E), (#12 & #13), and Hells

Kitchen Canyon (NW1/4 NE1/4 T26N R22E) fan (#15), were assumed to have a static water table elevation of fifty feet and Sweetwater Canyon

(SE1/4 NW1/4 T27N R22E) fan (#14), has a water table elevation of'twenty five feet. The former two (#’s 12, 13 & 15), were approximated from well data to the south, and the latter (#14). as an assumed probable level based on the occurrence of spings near the fan head in the main canyon and as an average depth for its occurrence. Well data for Big T a b l e Estimated groundwater storage in alluvium along the west and east lake shores.

1 2 3 4 5 6 7 Alluvial Area Area Elevation Depth of Volume of Total Estimated (ac.) (upper end/ usable usable yield of potential static water aquifer fan alluvium rechargej level) (feet) (AF) table 3 a / (feet) b7 c/ d/ (AF/Y) e/

1. Tom Anderson 160 4120/4070 220 8800 1320 200 Canyon

2. Rodero Creek 160 4180/4130 280 11200 1680 400

3. Mullen Creek 816 4100/4050 200 40800 6020 500

4. Quail Creek 240 4000/3950 100 6000 900 100

5. Hardscrabble 528 4100/4050 200 26400 3960 300 Creek A 5. North Sutcliffe 384 4120/4070 220 21120 3168 100

7. Water Hole 168 4000/3950 100 4200 630 200 Canyon

8 . Wood Canyon 138 4000/3950 100 3450 517 100

9. Jigger 3ob 128 4000/3950 100 3200 480 400 Canyon Table 2 (con t)

10. Poison-Sharps- 320 4100/4050 200 16000 2400 100 Th underbolt

11. Big Canyon 313 4200/4150 300 23460 3519 900

12. George Washing­ 701 4160/4110 260 45565 6835 ton Rock #1 (1+ 2 ) 100

13. George Washing­ 650 4110/4060 210 34125 5118 ton Rock #2

14. Sweet Water 484 4120/4095 245 29645 4446 100 Canyon

15. Hells Kitchen 402 4160/4110 210 21105 3166 200 Canyon

16. Big Basin 394 4090/4084 234 23049 3457 100

total 3800 a. areas 1 -1.1 abstra cted from Wilsey & Ham: areas 12-16 generated for this report. b . difference between the static water level and 3850 feet. c. Assumed to be column 2 times column 4 times 1/4. d. assumed specific yield as average from Todd (1959), for this type of aquifer, as 15% of column 5. e. from table 3, column 6 , as potential from natural recharge available for pumping. Items a, b, c, & d above are as used in the Wilsey & Ham (1970), report; item e is from table 3 this report.

o Table 3. Estimated annual potential recharge from drainages along the west and east sides of Pyramid Lake.

1 2 3 4 5 5 Drainage Basin Elevation Area, by zones Weighted Avg. Potential Recharge min/max 5-6, 6-7, 7-8 annual Ppt. recharge (AF/Y) (feet) 8+ (in.) % value (Rounded (1000 ac.) for zones to neare; of col. 3 100 AF)

a/ b/ c/ d/

1. Tom Anderson 4000/8000+ .79,. 74,.47, 10.0 3, 7, 15, 20 200 Canyon .02

2 . Rodero 4000/8000+ 1.950 , 2.030 11.5 do. 400 1.460 , .06

3. Mullen 4000/8000 4.94, 1.67, .18 11.8 do. 500

4. Quail 4000/7000 .8 6 , .52 10.2 do. 100

5. Hardscrabble 4000/8000 2.09, 2.18, .67 11.3 do. 300

6 . North Sut­ 4000/8000 1.04, .78, .11 10.3 do. 100 cliffe

7. Water Hole 4000/8000 1.13, .77, .29 11.2 do. 200

8 . Wood 4000/7000 .922, .20 10.5 do. 100

9. Jigger Bob 4000/8000 1.23, 1.605, 11.5 do. 400 1.408 Table 3 (con't)

10. Poison-Sharps 4000/8000 .608, .23, .017 10.5 do. 100 Thundergolt

11. Big Canyon 4000/8000+ 1.347, 2.694, 11.5 do; 900

12. George Wash­ 4000/7000 1.56, .869 10.3 do. 100 ington (1 &2 )

13. Sweet Water 4000/7000 1.292, .643 11.2 do. 100

14. Hells Kitchen 4000/8000 1.924, 1.251,.298 11.4 do. 200

15. Big Basin 4000/8000 1.970, .692, .044 10.8 do. .100

total 3800

a. assumed mir.umun elevation of 4000 feet for all drainage basins. b. subdivided basin into elevation zoxies (in 1000's of feet, e.g. 5000-6000) by acreage to facilitate use of recharge percentages. c. values for numbers 1-11 abstracted from Wilsey & Ham, values for numbers 12-15 assigned as values for comparable basins in other parts of the Pyramid Lake region. d. percentages for estimated potential recharge derived from Eakin and others (1949, 1951). B asin ($16 j NW1/4 NE1/4 125-.S R22E), is from one well that indicates the

s t a t i c water level is at six feet, but the influence of shallow bed­

ro ck i s unknown. Concern for the eastern area is to indicate the avail­ a b i l i t y of groundwater for whatever future interest involve this location.

The recharge values of column 7, Table 2 are considered more

realistic than the original values of Wiisey and Ham, because, their assumption of annual withdrawal a fifty percent of the specific yield

is not justified. The groundwater withdrawal volumes are based on the recharge estimates indicated in column 6 , Table 3. If pumping exceeded annual recharge, water would be removed from storage. The total annual withdrawal (column 7, Table 2), cannot be assessed as a single quantity.

Because of geographic separation of the groundwater reservoirs and areas of existing and future development it is not practical to consider the. east and west sides in the same perspective. Economically, development of the eastern reservoirs for purposes of transporting water, indicates the cost would probably be prohibitive compared to the derived benefits.

5. Assessment of Springflow

An evaluation of the total water system within the Pyramid Lake

Basin should include spring discharge data. Previous evaluations accounted for only twenty-nine springs along the west side of the lake.

Fifty-four springs draining lakeward are within and adjacent to the boundaries of this study area. Estimating their discharge would supple­ ment the tota3. groundwater appraisal. The number which are perennial was not determined. q_ other__Conditions'Presently Existing

This section discusses certain presently existing conditions of groundwater, the Truckee River delta, Truckee River floodplain, and ephemeral streams.

1. Groundwater

Recharge and discharge are affected by: 1) discharge as evap­ oration, evapotranspiration, pumping and spring discharge, and 2 ) re­ charge which is dependent on precipitation and is variable depending on the elevation, exposure, vegetation and runoff. Runoff is also variable and is a function of temperature and rainfall and their dist­ ribution with time, factors such as soil moisture capacity and vegeta­ tion also effect this runoff (Thornthwaite, 1935). Cooley (1972), demonstrated that in semiarid regions such as Pyramid Lake Basin, sur­ face hardened caliche on interflow areas, gully-bed cementation and laminar layers in any physiographic position all severely reduce in­ filtration, Therefore because of runoff there is a reduction in poten­ tial natural recharge.

For discharge the two largest contributors are evaporation and evapotranspiration. Pumping is a minor contributor as the wells at

Nixon and Sutcliffe are siipporting local residents and the remainder within the basin are for stock supply and agriculture. Total well usage along the west side of the lake is approximated at S to 10 percent of the estimated total yield (i.e. recharge to alluvium and surface runoff) Wilsey & Ham, 1971). Spring discharge estimates are inaccurate as they occur within a localized area and evaporation loss is minor. 75

Subsidence due directly to groundwater withdrawal is nonexistant.

However, it may or already has manifested itself in conjunction with

the lake surface lowering (by dewatering occurring from 'bank-storage

depletion). Removing water from unconsolidated, cohesionless sediments,

results in compaction by pore-water pressure reduction. The problem may compound itself in not only compacting surficial sediments, but by

accompanying water table lowering resulting from earthquakes. The water table lowering was observed to result from secondary fracturing of bedrock (Robinson, 1971).

Lake water encroachment on the groundwater system is a potential problem. If adequate regulation of the pumping policy is not observed, water table lowering can result in the landward displacement of the groundwater-lake water interface. This relocation could C ci U 3 £‘. ci. \v t c X quality reduction and inhibit its use.

Effluent introduction is another groundwater problem. This can present itself by: 1 ) potentially improper future placement and instal­ lation of septic tanks, especially in the floodplain by Nixon, and

2) through the indiscriminant dumping procedures now used.

2. Truckee River Delta

The delta complex, formed where the present river enters Pyramid bake is very transitory. Historically the present location represents an approximate three mile shift, southward since 1835 (Born, 1972) , Be­ cause of the relatively steep frontal slope, subsurface failure is com- ffion (Mifflin, 1969: Bora, 1972). The slope failure is due to the unconsolidated, cohesionless and highly lubricated nature of the 76

sediments composing the delta.

As in less aqueous sediments the problem of liquefaction, from

cyclic loading, is real and can apparently impose itself over a large

area. Contorted bedding is common in the delta complex. The contortion

suggests liquefaction was followed by the expulsion of high pressure,

core, fluids (Born, 1S72). Large scale liquefaction features are trace­

able over distances of several hundred yards. During the liquefaction

process sediments on slopes will move down and outward and those on a

relatively horizontal surface will translate laterally (Seed, 1966).

Accompanying the unstable nature of the delta is the littoral

area which is one of high mechanical energy due to waves and long-shore

currents. The combination is not conducive to long term stability.

Prefrontal islands (inudlumps) have occurred from frontal slumping and

represent a hazard to lake users (Mifflin, 1969). Primarily because of

their surface size (30 to 100 yards in the longest dimension), and rapid

formation. The supporting surface area may be up to 40 acres, and at a relatively shallow depth (Born, 1972).

Physical features, such as swamps and stagnant water are not, at least historically, considered tc be a relevent problem and are not discussed,

3. Trucke.e River Floodplain

The floodplain and the alluvial-plain are. areas of large scale erosion. Significant changes have occurred to the floodplain during the past 45 years. Major floods, the most: recent in 1963, are the 77

primary contributors to those changes. However, when the dam and fish­

way are completed, erosion activity in the reach below the dam will be

reduced (Task Force, 1971).

The Truckee River in the vicinity of Nixon, has developed six

erosional terraces since 1910, standing from 10 to 35 feet above the

present stream (Born, 1970). Their .location ranges within one to six wiles of the present delta. The formation of these alluvial-plain

terraces can be attributed to one or more of the following: 1 ) read­

justment of the stream grade by removal of channel obstructions or

piracy in the lower reaches, 2 ) general crustal uplift, and 3 ) a broad

climatic variation (Hadley, 1960). In low runoff years main channels are incised to re-establish base level. While high runoff years involve the entire braided and meandering stream valley and produces valley widening by lateral erosion. Lateral erosion can destroy the meander belt and produce a steeper gradient stream with the force for pronounced downstream erosion. Frequency studies indicate that the floodplains of many streams of different sizes, flowing in different physiographic and climatic regions are subject to flooding about once a year (Wolman &

Leopold. 1957). This is not specific because any high discharge level, within approximately a one year period, falls within the limits of their parameters. The major flood-stage history of the Truckee, since 1910, shows four events in this 64 year period. This implies that future floods should be ejected to occur. However, their potential effects in the. lower reaches should not be as great because of improved upper reach stream and watershed management. 78

Stream channel widening occurs because of forces applied along

the channel boundary,, producing stresses greater than the bank can withstand (Burkham, 1972). Floods are a primary cause of channel widen­ ing, because the main flow-path is generally straight down the valley

(Burkham, 1972). Thus banks, bends, islands and other features are sub­ ject to degradation as the stream attempts to straighten its course.

The process of bank failure is common, and at these locations (generally at curved reaches), scouring triggers a subaqueous slump by oversteep­ ening. This slumping may or may not cause an upper bank failure. The frequency of occurrence indicates subaqueous failure is more numerous than upper bank failure (Turnbull, 1966). Failure is partly dependent on the condition and type of bank sediments. The failure of banks com­ posed of point bar deposits depends on their thickness and cohesiveness.

Thinner units will slough and shear and thicker ones can be expected to fail by flow (Turnbull, 196t). Consistent with this type of deposit, backswamps and swales also retard failure because of their composition and higher shear strength. The former due to pronounced thickness and c’ohesiveness which markedly retard failure.

A constancy can be applied to lateral erosion, with streams of constant length and discharge the rate of erosion varies directly as the rate of base level drop (Yoxail, 1969). Therefore, if the lake continues to decline, the base level will also, however, because of the large discharge variation lateral erosion will probably respond differentially.

The size of these failures is not predictable but there is some relation to the areas subjected to scour. Long radius curves suggest a higher probability for failure than those of short radius. Considering this 79

in terms of lateral erosion further development should avoid these

scour points in the lower reaches as the failure probability is high.

4; Ephemeral Streams

Rodero Creek is the only perennial stream to the lake. However, many spring fed streams become influent near the alluvial fan heads.

This discussion deals with a two-fold problem: 1) earthfill daws across drainages which ultimately discharge into the lake and which have the potential for failure either by cyclic loading or by hydraulic action, and 2) those undamir.ed streams whose drainage pattern allows the accum­ ulation of a sufficient quantity of water to produce debris flows of a large sice.

Dammed streams occur in at least four locations: a) Rodero Creek

(SSI/A Nb’i/t T22N R22E), b) Hardscrabble Creek (NE1/4 SW1/4 T24N R21E), and c) two in the Big Canyon drainage (NEl/4 NE1/4 T25N R20E). The earthfill dam on the Rodero Creek drainage, above the Monte Cristo Ranch, failed in 1973 discharging an estimated 25 to 39 acre feet of water

(A. Cunningham, personal communication, 1974). The debris flow included large boulders, tree trunks and assorted litter which moved down Rodero

Creek over three miles to the lake shore. Aggradation and degradation

Occurred along the entire channel and the final accumulation of debris blocked ftate Righwar 33 over a distance of 29) yards. The Hardscrabble

Creek drainage contains a storage pond of unknown capacity buttressed by an earth dam, and the Big Canyon drainage contains two dams on the. same channel, also of unknown capacity. Similar failure in these locations is possible and consideration should be given to the problem this poses. 80

The undammed drainage ways also have the potential for this debris

discharge. According to Marsell, (1971), rapid runoff and flooding

occur only when the precipitation rate greatly exceeds both the surface

retention and infiltration capacity of the plant soil mantle. Drainages

north of Sutcliffe all exhibit debris accumulations which vary according

to the stream channel si?,e. The debris is usually a mixture of mud,

rock, boulders and plant litter. The areas immediately west of Pelican

and Warrior Points are also prone to debris discharge. Thus, structural development near the lower reaches of these streams should be protected by construction of debris traps (bowl shaped basins) at the mouth of flood producing canyons. 81

VOLCANISM

A Holcene ash-fall is intercalated with a sequence of lake muds

and fine grained clastic materials. These exposures are immediately vest of the Truckee River Delta and along the shore near Sutcliffe, and h a v e been stratigraphically dated at within the last 1 ,0 0 0 years (Born,

1972). The significance of this occurrence is that the event is so

recent. The recency requires speculation as to a possible recurrence, and in that regard the impact of this problem.

All of the remaining volcanic rocks have been dated as early

Quaternary or older Tertiary age, and as such are not the source for this ash-fall. Areas of Holocene volcanic activity from south to north are: a) Mount Lassen, b) Mount Shasta, c) Medicine Lake Highlands, d) Crater Lake, and e) Newberry Volcano. The most recent event generated by Newberry Volcano has a Carbon-14 age (on basa.1 wood fragments) of

1,720 + 250 years b.'p. (Higgins, 1973). Of those volcanic locations listed only Mount Lassen and the Medicine Lake Highlands in California are known for producing silica-rich ash (of the type at Pyramid), during the Quaternary (Wilcox, 1 9 6 5 ) . With prevailing winds from the west and north, an eruption in northeastern California reaching the upper air patterns could reach Pyramid Lake.

The physical, character of the present ash consists of very fine fragments of glass (ash) with small unidentified phenocrysts. The glass due to its density could have been transported down the Truckee River as well as falling directly within the lake basin area. This could account for the 2.5 to 3 inch thickness this far from the probable source.

^8a The total area covered is unknown because of removal by erosion.

Although future volcanic events can be expected (as evidenced by th e activity in the Cascade Mountains of California, Oregon.and

Washington) prediction of such events is not possible in terms of s p e c i f i c time, place, or scale. The problem is that lack of identical conditions which may prevail significantly hamper predictive capability

(Crandell & Mullineaux, 1967).

A review of similar situations allows some insight into potential problems. The Mount Arenal eruption in Costa Rica (1967), involved quantities of ash which did substantial harm to surface water supplies; and regarding Pyramid Lake there may be harmful effects to the fisheries as well. The volcanic problem may for a short period of time produce harmful effects to the Pyramid Lake Basin, but considering the expected longevity of any given area within the basin, ignoring or neglecting a specific location under proposed threat of recurring volcanic problems is not warranted. S3

b l i o g r a f h y

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92

glossary*

1. ash fall. A deposit of airborne volcanic ash lying on the ground

surface.

2. hank storage. Water absorbed by the bed and banks of a stream and

returned in whole or in part as the ground-water level falls.

3. differential settlement. The uneven lowering of different areas of

the ground surface.

4. dip slip. The component of the slip in the direction of the true

dip of the fault plane.

5. earthquake. A local trembling, shaking, undulating, or sudden shock

of the surface of the earth, sometimes accompanied by fissuring or

by permanent change of level.

6. environmental geology. The collection, analysis, and application of

geologic data and principles to problems created by human occupancy

and use of the physical environment.

7. epicenter. Point on the earths surface directly above the focus of

an earthquake.

8. fault. A fracture or a fracture zone along which there has been dis­

placement of the two sides relative to one another parallel to the

fracture.

faulting. The movement which produces relative displacement of ad­

jacent rock masses along a fracture. 93

10. faultline scarp. A scarp which has been produced by differential

erosion along an old faultline.

11. floodplain. The flat ground along a stream, covered by water at

the flood stage.

12. footwall. The wall on the lower side of a fault.

13. geomorphic. Of or pertaining to the form of the earth or its

surface features.

14. graben. A depressed segment of the earth's crust bounded on at

least two sides by faults and generally of considerable length

compared to its width.

■5. hanging wall. The wall or rock on the upper side cf a fault plane.

6. headwall. The upper scarp of a slide block.

7. horst, A block of the earth's crust separated by faults from the

adjacent blocks that have been relatively1 depressed.

8. influent stream. A stream or the reach of a stream is influent with

respect to ground water if it contributes water to the zone of

saturation.

9- lateral displacement. The lateral movement of a point at the surface

may be to the left or the right. h mass-wasting. A general term for a variety of processes by which

large masses of earth material are moved byr gravity from one place

to another. 94

■ meander be.1 1 , That part of a f loodplain between two lines tangent

. 'to the onrer bends of all the meanders. *

■metasediment. A partly metamorphosed sedimentary rock.

metavolcajjic. Partly metamorphosed volcanic rock.

V - - • -* -

, physiogto. Involves a specific kind of structure on the

earth's surface.

* » pluvial. Of a geologic change resulting from the action of rain

or sometimes from the fluvial action of rainwater flowing in stream ' . * ' * ' 'channels,,

pre-Lahontan sediments. Sedimentary deposits which pre-date those

"deposi.ro ---n-f p~leo-Lake Lahontan.

- . * i » , i "*.r' ■ *; i ' * * ■ .l icking. hrationary oscillation of the water of a lake, bay or

marginal sea.

seismicity. Measure of frequency of earthquakes.

stillstand. A temporary or semipermanent water surface elevation

.-of a lake Requiting in the development of certain physical features

.-such -as- a? shacrtfclioe.

stratigraphy. That part of the descriptive geology of an area

which pertains to the descriminatior;, character, thickness, sequence,

age and correlation of the rocks of the area.

tectonic. Pertaining to rock structures and topographic features

resulting from deform tion of the earth's crust.