Late Cenozoic Geology and Lacustrine 

History of Searles Valley, Inyo and 

San Bernardino Counties, California

Professional Paper 1727

U.S. Department of the Interior

U.S. Geological Survey
This page left blank intentionally.
Late Cenozoic Geology and Lacustrine History of Searles 

Valley, Inyo and San Bernardino Counties, California

By George I. Smith

Professional Paper 1727

U.S. Department of the Interior

U.S. Geological Survey

Detailed geologic maps of Searles Valley document a late Cenozoic, primarily Quaternary, sedimentation history. The Quaternary sediments prominently include the 150-2 ka Searles Lake Formation, described and named herein. The Searles Lake 

Formation is divided into seven, dominantly lacustrine units, which can be correlated with subsurface units known from drill 

cores in now-dry Searles Lake, in the center of the valley. Together, these surface and subsurface sediments help chart the 

region’s complex recent climatic history.
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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FRONT COVER

False-color satellite image (Landsat Thematic Mapper) of Searles Valley, California. North is at the top. The valley is 

flanked by the Slate Range on the east and the Argus Range and Spangler Hills on the west. The linear feature trending 

east-northeast from southwest corner of image is the Garlock Fault. Scale: widest part of valley near middle of Searles 

Lake is 15 km; vertical dark line north of lake is 1,800-m-long airport runway. Image is a band-ratio composite, in which 

blue indicates Fe3+ in the reflecting material, green indicates Fe2+, and red reflects clay, CO3

, and vegetation. Yellow 

is produced by mixtures of red and green. Searles Lake (left center) is largely magenta and dark blue, colors caused 

by differing mixtures of Fe3+-bearing clays and CO3

 (straight lines on the lake surface are roads and evaporating-pond 

dikes). Alluvial fan surfaces east and north of the lake are mostly green because of the abundance of Fe2+ in detritus from 

metamorphic rocks from the Slate Range (note erosional shorelines northeast of lake and curved offshore bars north of 

lake); fans west and south are also green but have areas of blue (more Fe3+-bearing volcanic rocks and desert varnish) 

and red (CO3

- and clay-rich lacustrine sediments). Orange bands on the flanks of the Argus Range and Spangler Hills are 

caused by the impure CO3

 in massive tufa deposits near the highest lake shoreline (carbonate bedrock in mountain areas 

in northeast part of image also shows orange hues). Photograph courtesy of Ronald Blom, Jet Propulsion Laboratory, 

California Institute of Technology, Pasadena, California. For geographic reference, see figure 1; for geology, see plates.

Suggested citation:

Smith, G.I., 2009, Late Cenozoic geology and lacustrine history of Searles Valley, Inyo and San Bernardino Counties, 

California: U.S. Geological Survey Professional Paper 1727, 115 p., 4 plates.
iii

Foreword

George I. Smith received a Bachelor of Science Degree in chemistry from Colby College, Maine, 

in 1949 and a Ph.D. in geology from the California Institute of Technology in 1956. He joined 

the U.S. Geological Survey (USGS) full time in 1952, and after a short period of geologic mapping and drilling for saline minerals in the northern Mojave Desert and Death Valley, he began 

a career-long interest in the sediments, saline mineral assemblages, and paleoclimatic significance of Searles (dry) Lake, California. After 1960, he was the USGS commodity specialist for 

several commercially produced saline minerals.

After recognizing the role that past climate change played in the accumulation of sediments and 

saline minerals, Smith broadened his investigations to determine the magnitudes, timing, and 

meteorological causes of past climate and consequent hydrologic changes evidenced in many 

of the continental saline deposits of the southwestern United States. Much of the understanding of the climate record in Searles Valley has been based on studies of a 930-m drill core 

through the sediments beneath the dry lake, which provided a 3.2-million-year climate history 

to compare to the deep-sea record. The present study integrates that subsurface work with the 

deposits that crop out on the surface of the valley, from which Smith defines the Searles Lake 

Formation to include those deposits of the past 150,000 years. During his many years of studying 

the outcrops in Searles Valley and adjacent areas, Smith frequently complemented traditional 

fieldwork with aerial reconnaissance from a small plane he piloted himself. He also provided the 

leadership for drilling and studying a 323-m core hole in Owens Lake that provided an 800,000-

year climate record. During pluvial (wet) periods in the Pleistocene, Owens Lake was the first 

lake in a chain that included Searles Lake and ultimately emptied into Death Valley.

George Smith served as Chief of the Light Metals and Industrial Minerals Branch of the USGS 

between 1966 and 1969. In 1978, he organized the USGS Climate Change Program, and he then 

served as its coordinator for its first 3 years and as the Department of the Interior representative 

to the Climate Research Board of the National Research Council. He patiently explained the importance of geologic studies of past climates as an aid to understanding climate change and for 

the modeling of future climate. Smith received the Meritorious Service Award of the Department 

of the Interior in 1983. He is an elected fellow of the Geological Society of America and of the 

Mineralogical Society of America. After retiring from the USGS in 1995, Smith received a Pecora 

Fellowship for 1995 and continued working as an Emeritus USGS scientist until 2005.

The original manuscript and geologic maps for this work received colleague review in 1992 and 

1993 and approval from the USGS Volcano Hazards Team in 1996. They were edited by the then 

Western Publications Group in 1999 and 2000 and returned to the author. Various revisions were 

made to the edited manuscript over the next several years. In 2004, George Smith had a stroke 

and further work on the manuscript was undertaken with the assistance of his stepdaughter Michelle Ono. In 2005, the manuscript was returned to the Volcano Hazards Team for publication. 

Careful review of the 2000 and 2005 versions by USGS editor Peter Stauffer indicated that the 

earlier version was more internally consistent, and consequently this published version is largely 

based on the 2000 version, with some updates and additions from the 2005 version.
 

The final editing of the manuscript was done by Peter Stauffer, and final editing of the geologic 

map plates was done by Jan Zigler. Joel Robinson took the commercially scanned digital versions of Smith’s original hand-drafted geologic maps and processed them to finalized versions 

for production. Throughout these final stages, Manuel Nathenson of the Volcano Hazards Team 

served as author’s representative. Some degree of judgment was required in the process of 

transforming the supplied materials to the final version presented here, and those involved in it 

have made every effort to be faithful to the author’s original work.

Suzette M. Kimball 

Acting Director
 v

Contents

Foreword ........................................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................3

Acknowledgments.........................................................................................................................................6

Field and laboratory methods ......................................................................................................................6

Stratigraphy and lithologies of mapped units ...........................................................................................8

Tertiary units ..........................................................................................................................................8

Siltstone and sandstone .............................................................................................................8

Bedrock Spring Formation .......................................................................................................10

Volcanic rock..............................................................................................................................10

Tertiary or Quaternary units ..............................................................................................................10

Sandstone and siltstone ...........................................................................................................10

Older tufa.....................................................................................................................................11

Older gravel.................................................................................................................................12

Christmas Canyon Formation............................................................................................................13

Searles Lake Formation .....................................................................................................................14

Criteria for correlating outcropping units..............................................................................17

Criteria for correlating outcropping units with subsurface units ......................................22

Criteria for identifying disconformities...................................................................................24

Radiometric ages of exposed units ........................................................................................26

Fossils .........................................................................................................................................33

Lithologies of exposed units ....................................................................................................34

Unit A ................................................................................................................................36

Unit AB...............................................................................................................................39

Unit B ................................................................................................................................40

Unit BC ...............................................................................................................................42

Unit C ................................................................................................................................45

Unit CD...............................................................................................................................45

Unit D ................................................................................................................................47

Tufa ................................................................................................................................50

Undifferentiated gravels..................................................................................................55

Middle and late Holocene units .......................................................................................................55

Older alluvium.............................................................................................................................55

Playa silt and clay......................................................................................................................57

Windblown sand and colluvium ..............................................................................................57

Windblown dune sand ..............................................................................................................57

Active alluvium...........................................................................................................................57

Geomorphology............................................................................................................................................57

Neotectonics ................................................................................................................................................62

Paleolimnology.............................................................................................................................................67

Lake-water chemistry and density stratification...........................................................................67

Low-energy environments ................................................................................................................68
vi 

High-energy environments................................................................................................................69

Bar-gravel transport directions........................................................................................................71

Reconstructed history of Searles Lake....................................................................................................74

Units AB to D.......................................................................................................................................74

Unit A ..................................................................................................................................................77

Reconstructed paleohydrology of lakes in the Owens River system..................................................79

Comparison of the Owens River system with the reconstructed 

paleohydrologies of other areas in the western United States...................................82

Paleohydrologic records for the period between 150 and 35 ka ................................................84

Paleohydrologic records for the period between 35 ka and the present..................................85

Comparison with history of high-latitude glaciation..............................................................................87

References....................................................................................................................................................88

Appendix 1. Measured sections................................................................................................................96

Appendix 2. Sediment studies..................................................................................................................108

Appendix 3. Evidence and reasons used for determining slopes, 

 elevation ranges, and ages of segments of lake-history diagrams 

 (figures 39C and 40C) .........................................................................................................114

Plates

[In pocket]

 1. Geologic Map of Searles Valley, Inyo and San Bernardino Counties, California

 2. Geologic Maps of Valley Wells Wash and Randsburg Wash

 2A—Valley Wells Wash

 2B—Randsburg Wash

 3. Geologic Maps of Poison Canyon and Salt Wells Valley

 3A—Poison Canyon

 3B—Salt Wells Valley

4. Geologic Map of The Pinnacles Area

Figures

1. Geographic and stratigraphic setting of Searles Valley and its 

late Cenozoic deposits ....................................................................................................................5

2-5 Photographs showing:

2. Deformed Tertiary siltstone and sandstone beds ..............................................................9

3. Hills composed of older tufa................................................................................................11

4. Outcrop of gravel facies of the Christmas Canyon Formation.......................................13

5. Type section of the Searles Lake Formation.....................................................................17

6. Stratigraphic column for the type section of the Searles Lake Formation...........................18

7-13 Photographs showing:

7. Outcropping subunits sb1 through sb2 and unit BC of the Searles 

 Lake Formation....................................................................................................................19

8. Exposure of Searles Lake Formation unit CD ..................................................................20
 vii

9. Exposure of subunits sa1, sa3, and sa4 of Searles Lake Formation..........................20

10. Laminated sediments of subunit sc1 of Searles Lake Formation .................................21

11. Horizontal contact between units B and C of the Searles Lake Formation................22

12. Older fossil soils of the Searles Valley area .....................................................................23

13. Younger fossil soils of the Searles Valley area ................................................................24

14. Diagrams showing inferred depositional history recorded by a marl-sand-marl 

sequence of outcropping deposits from a lake of varying level ............................................26

15. Photograph of lacustrine sand facies of unit BC of the Searles Lake Formation...............27

16. Photograph and diagram of outcrop showing sublacustrine angular 

unconformity within Searles Lake Formation............................................................................28

17. Plot of radiometric ages against elevations of sampled outcrops ........................................32

18-21 Photographs showing:

18. Gravel and tufa formed in the time of deposition of unit A of the 

Searles Lake Formation........................................................................................................38

19. Extensively weathered and pitted boulders in alluvial gravels 

mapped as part of unit A of the Searles lake Formation ................................................39

20. Eroded and filled channels formed during the time of deposition 

of unit AB of the Searles Lake Formation .........................................................................41

21. Two outcrops that include thick sections of unit C of the 

Searles Lake Formation........................................................................................................46

22. Field sketch of exposures of Searles Lake Formation showing 

soft-sediment deformation ..........................................................................................................48

23-31 Photographs showing:

23. Vertical aerial view of two alluvial fans composed of unit CD of 

the Searles Lake formation..................................................................................................49

24. Characteristic appearance of the gravel and sand facies of unit D of the 

Searles Lake Formation on the surface of Searles Lake................................................50

25. Oblique aerial view of The Pinnacles and surrounding areas.......................................52

26. Vertical aerial view showing en echelon alignment of The Pinnacles ........................53

27. Outcrop and thin-section views of tufa .............................................................................54

28. Typical lithology and surface of older alluvium unit........................................................56

29. Oblique aerial view of depositional shorelines ................................................................59

30. Oblique aerial view of remnants of lake deposits, east edge of Searles Valley.........60

31. Oblique aerial view of lacustrine bars, Valley Wells Wash area ..................................61

32. Diagram showing major climatic regimes in southeastern California, 

3.2 Ma to present............................................................................................................................63

33. Oblique aerial photograph showing normal-fault scarp, west edge of Slate Range..........64

34. Diagrams showing plan view and cross-section view of faults in unit B or C

of the Searles Lake Formation, west edge of Slate Range .....................................................65

35. Oblique aerial photograph and map of graben, west edge of Slate Range .........................66

36. Diagrams showing lithologic and compositional data 

of Parting Mud in core GS-16.......................................................................................................70

37. Photograph showing defluidization structures, unit AB

of the Searles Lake Formation .....................................................................................................72

38-42 Diagrams showing:

38. Locations of lacustrine bars and inferred current directions at 

various lake levels in Searles Lake ....................................................................................73
viii 

39. Inferred lake-level history of Searles Lake, 35 ka to present ........................................76

40. Inferred lake-level history of Searles Lake, 170 ka to 30 ka...........................................78

41. Diagrammatic representation of climatic regimes in the region 

of the Owens River system, 3.2 Ma to present.................................................................80

42. Estimated flow volumes of Owens River required to offset evaporation 

from Searles Lake and other lakes, 150 ka to present ....................................................83

Tables

1. Criteria used in Searles Valley to differentiate between outcropping 

lacustrine and alluvial deposits .....................................................................................................7

2. Stratigraphic correlations between units and subunits of Searles Lake Formation 

shown on plates 1-4.......................................................................................................................15

3. Subsurface stratigraphy of Searles lake, inferred lake character, and correlative 

outcrop units ...................................................................................................................................16

4. Generalized field characteristics of units of Searles Lake Formation ..................................25

5. Radiometric ages of deposits assigned to the Searles Lake Formation...............................29

6. Mollusca described by Hanna (1963) from Searles and Panamint Valleys ..........................34

7. Fossil mollusks and ostracodes from lacustrine sediments 

of Searles Lake Formation ............................................................................................................35

8. Distribution and characteristics of major lacustrine bars in Searles Valley........................37

9. Highest and lowest elevations of lacustrine and alluvial units and subunits of 

Searles Lake Formation.................................................................................................................43

10. Areas and volumes of historic and Pleistocene-maxima lakes 

in the Owens River system ...........................................................................................................81

11. Distribution of drainage-area elevations for five lake basins in the 

Owens River system.......................................................................................................................82

12. Distribution of clast sizes in sediments from Searles Valley ................................................110

13. Statistical parameters for 27 sediment samples, based on sieve analyses 

listed in table 12............................................................................................................................113
Late Cenozoic Geology and Lacustrine History of Searles 

Valley, Inyo and San Bernardino Counties, California

By George I. Smith

Abstract

Searles Valley is an arid, closed basin lying 70 km 

east of the south end of the Sierra Nevada, California. It is 

bounded on the east and northeast by the Slate Range, on 

the west by the Argus Range and Spangler Hills, and on the 

south by the Lava Mountains; Searles (dry) Lake occupies 

the north-central part of the valley. During those parts of late 

Pliocene and Pleistocene time when precipitation and runoff 

from the east side of the Sierra Nevada into the Owens River 

were much greater than at present, a chain of as many as five 

large lakes was created, of which Searles Lake was third. 

The stratigraphic record left in Searles Valley when that lake 

expanded, contracted, or desiccated, is fully revealed by cores 

from beneath the surface of Searles (dry) Lake and partly 

recorded by sediments cropping out around the edge of the 

valley. The subsurface record is described elsewhere. This 

volume includes six geologic maps (scales: 1:50,000 and 

1:10,000) and a text that describes the outcrop record, most of 

which represents sedimentation since 150 ka. Although this 

outcrop record is discontinuous, it provides evidence indicating the lake’s water depths during each expansion, which the 

subsurface record does not. Maximum-depth lakes rose to the 

2,280-ft (695 m) contour, the level of the spillway that led 

overflowing waters to Panamint Valley; that spillway is about 

660 ft (200 m) above the present dry-lake surface.

Several rock units of Tertiary and early Quaternary ages 

crop out in Searles Valley. Siltstone and sandstone of Tertiary 

age, mostly lacustrine in nature and locally deformed to nearvertical dips, are exposed in the southern part of the valley, as 

is the younger(?) upper Miocene Bedrock Spring Formation. 

Unnamed, mostly mafic volcanic rocks of probable Miocene 

or Pliocene age are exposed along the north and south edges 

of the basin. Slightly deformed lacustrine sandstones are 

mapped in the central-southwestern and southern parts of the 

study area.

The Christmas Canyon Formation and deposits mapped 

as older gravel and older tufa are extensively exposed over 

much of the basin floor. The older gravel unit and the gravel 

facies of the Christmas Canyon Formation are boulder alluvial 

gravels; parts of these units are probably correlative. The 

lacustrine facies of the Christmas Canyon Formation includes 

the Lava Creek ash, which is dated at 0.64 Ma; the older tufa 

deposits may be equivalent in age to those sediments.

Most of this study concerns sediments of the newly 

described Searles Lake Formation, whose deposition spanned 

the period between about 150 ka and 2 ka. Most of this formation is lacustrine in origin, but it includes interbedded alluvium. To extract as much geologic detail as possible, criteria 

were developed that permitted (1) intrabasin correlation of 

some thin outcrop units representative of only a few thousand 

years (or less), (2) identification of unconformities produced 

by subaerial erosion, (3) identification of unconformities produced by sublacustrine erosion, and (4) correlation of outcrop 

units with subsurface units.

The Searles Lake Formation is divided into seven main 

units, many of which are subdivided on the five larger scale 

geologic maps. Units A (oldest), B, C, and D are dominantly 

lacustrine in origin. The Pleistocene-Holocene boundary is 

placed at the top of unit C. In areas that were a kilometer or 

more from shore at the time of deposition, deposits of units 

A,B, and C consist of fine, highly calcareous sand, silt, or 

clay; nearer to shore they consist of well-sorted coarse sand 

and gravel. Unit A has been locally subdivided into as many 

as four subunits, unit B into six subunits, and unit C into six 

subunits. The finer facies of units A, B, and C contain such 

high percentages of CaCO3 that they are best described as 

marl. Sediments of unit C, and to a lesser extent those of 

unit B, are laminated with light- to white-colored layers of 

aragonite, calcite, or dolomite(?) that may represent seasonal 

deposits. Unit D, which is divided into two facies, is a pinkish 

silt with halite efflorescences that is locally overlain by a thin 

lacustrine gravel.

Units AB, BC, and CD, which are interbedded between 

the two single-letter units that make up their names, include 

both alluvial and lacustrine deposits. Unit AB is divided into 

as many as seven subunits, unit BC into two subunits, and 

unit CD is undivided. Where these units are alluvial, their 

lithologies range from pebble sand to boulder gravel that is 

poorly sorted and bedded. Soils developed on each unit are 

distinctive, and in most instances they serve as a basis for 

tentatively identifying each unit throughout the basin (as well 

as constraining the possible ages of overlying and underlying 

lacustrine sediments). Where these units are lacustrine, they 

are most commonly shallow water, well sorted sand.

The depositional intervals of the units that make up the 

Searles Lake Formation are estimated to be as follows (all estimated ages are in “uncorrected 14C years”): unit A, 150 ka to 
32 ka; unit AB, 32 ka to 24 ka; unit B, 24 ka to 15 ka; unit BC, 

15 ka to 13.5 ka; unit C, 13.5 ka to 10.5 ka; unit CD, 10.5 ka 

to 6.0 ka; unit D, 6.0 ka to 2.0 ka. These ages are determined 

primarily by correlation with subsurface deposits that are dated 

by 14C dates on organic carbon and U-series dates on salts.

Late Holocene deposits are mapped as (1) older alluvium, 

(2) playa silt, (3) windblown sand and colluvium, (4) windblown dune sand, and (5) active alluvium.

Tufa, deposited by a combination of organic and inorganic processes, is widespread. Major periods of growth of the 

relatively structureless “lithoid” variety of tufa occurred early 

during deposition of unit A, and deposition of the nodular, 

tubular, or lobate “nodose” variety of tufa occurred near the 

end of unit B time and the beginning of unit C time. Volumetrically, most of the tufa grew near the 1,800-ft (550 m) 

and just below the 2,280-ft (695 m) levels; the largest masses 

occur along the west side of the basin (see cover image) and 

in an area named The Pinnacles, where towers as high as 30 m 

are found.

Fossil snails, clams, and ostracods are found in many 

parts of the Searles Lake Formation, but they are especially 

abundant near the paleoinlet area. The snails and clams indicate fresh water conditions, which occurred most commonly in 

the inlet area. Ostracods tolerate a wider range of salinities and 

occur more widely. Vertebrate fossils were not found.

Shorelines, the most obvious geologic expressions of 

former lakes, are abundant around Searles Valley. Erosional 

shorelines have cut as much as 100 m into brecciated bedrock; 

depositional shorelines (beaches or tufa benches) are common, 

but their deposits tend to be thin. Gracefully curving offshore 

bars and spits, 2 to 10 m high, are prominent in the north and 

south ends of Searles Valley and near the middle of its west 

side. They were deposited subparallel to the shoreline, but 

their crests vary in elevation by as much as 10 m and it is clear 

that they were not deposited a uniform distance from shore. 

Most bars are asymmetrical, having slopes as steep as 25° on 

the uphill side but no more than 5° on the downhill side.

Several faults are mapped as having displacements of late 

Cenozoic age. The left-lateral Garlock Fault, 250 km long, 

bounds Searles Valley on the south and is the most geologically significant fault in the area. It displaces several of the 

mapped units of late Quaternary age but does not displace 

active or older alluvium deposits of late Holocene age. A 

prominent graben along the east side of the valley, and normalfault extensions of it to the north and south, also represent 

Holocene displacements; alluvial deposits of the early Holocene unit CD are displaced, but late Holocene older alluvium 

deposits are not.

Certain paleolimnological aspects of the lakes that deposited the Searles Lake Formation can be reconstructed. Lakewater chemistry and pH are approximated from subsurface 

data on the mineralogies of salt layers, from outcrop data such 

as the mineralogy of salt efflorescences, and from the reconstructed salinities indicated by ostracod or mollusk suites. 

Laminated sediments are believed to indicate salinity stratification in the depositing lake; this requires the lower saline 

layer to be sufficiently dense to keep the stratification stable. 

Even when the lake was stratified, however, large amounts of 

CaCO3 were deposited near the paleoinlet, where Ca-bearing 

inflow waters soon mixed with the high-pH, CO3-rich lake 

waters, creating a “chemical delta.”

Nearshore high-energy environments of deposition in 

Searles Valley lakes produced beaches and bars composed of 

coarse sand and gravel. Many of these deposits are now well 

cemented by calcite. During deposition of the Searles Lake 

Formation, the deposits of unit A were composed of larger 

fragments than were the later deposits of unit B, which, in 

turn, were coarser than those of unit C, apparently indicating 

a long-term decrease in storm-wind intensities. Storm-current 

directions, reconstructed from the fragment composition of 

offshore bars, also indicate differences in storm-wind directions at different times and lake levels.

Combining the subsurface evidence of lake history with 

the evidence described herein allows the history of lake fluctuations to be reconstructed for the period between about 150 

ka and the present. Between 150 ka and 140 ka, Searles Lake 

rose from a depth below the present dry-lake surface to its 

spillway level, now approximately at elevation 2,280 ft (695 

m), 780 ft (235 m) above its floor at that time. From then until 

about 118 ka, it overflowed into Panamint Valley. Following 

this period of overflow, lake level lowered and fluctuated at 

intermediate levels until 35 ka. There was possibly a brief 

period of overflow at about 50 ka. These intermediate- to highlevel stands were separated by brief lower level stands that are 

estimated to have occurred at periods centered at 107 ka, 79 

ka, 69 ka, and 45 ka. Between about 35 ka and 23 ka, Searles 

Lake fluctuated every 1 to 2 thousand years between intermediate depths (when silt and clay were deposited) and shallow 

depths (when it deposited salts); it desiccated briefly at about 

28 ka. This low- to intermediate-depth stage was followed by 

one of increased inflow, culminating in a period of overflow 

at about 16 ka. After falling to a low level between 15 ka and 

13.5 ka, the lake again rose twice to overflow levels, then 

fell to desiccation levels at about 10.5 ka. Searles Lake has 

remained mostly dry since its desiccation at 10.5 ka, except for 

a period centered at about 3.5 ka when the lake surface rose to 

a level of about 1,800 ft (550 m).

Translating this record of lake fluctuations into paleohydrologic and paleoclimatic histories is complicated by 

uncertainties as to which of the several components of climate affected runoff volumes and lake-surface evaporation. A 

simplified model, however, suggests that the flow of the Owens 

River stayed between 2.5 and 4.5 times its present flow volume 

for most of the past 150 k.y. Its flow exceeded this range only 

about 14 percent of the time, and it fell below this range only 

4 percent of the time—which includes the present. In fact, the 

past 10 k.y. is clearly the driest part of the past 150 k.y.

Over the full 3.2-m.y. period known from subsurface 

data, the climatic record is influenced by a geologic factor: the 

ever-increasing “rain shadow” produced by continuing uplift 

of the Sierra Nevada. Meteorological principles and subsurface evidence from Searles Valley and elsewhere support the 

2 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California
Introduction 3

existence of this climatic trend toward aridity, yet the longest 

sustained period of desiccation of Searles Lake was in the 

first third of that 3.2-m.y. period, as was the longest period of 

continuous perennial-lake deposition. This and many other 

lines of evidence show that the lake oscillations in Searles 

Valley have been products of climatic changes that exceed the 

impact of geologic and topographic changes. The durations 

of the most persistent and extreme climatic regimes in the 

Searles Valley area resemble phenomena found in the deepsea record that have a 413-k.y. cycle length, which can be 

attributed to the Earth’s orbital perturbations. During “intermediate” climatic regimes, however, the shorter duration, less 

extreme climatic changes in the Searles Lake record appear 

to reflect the orbital perturbations of shorter cycles that may 

have controlled the timing of high-latitude glacial events. It 

remains to be seen whether the glacial history of the east slope 

of the Sierra Nevada followed a timetable dictated by cooler 

temperatures related to high-latitude glaciation, or one that followed the 413-k.y. precipitation cycles recorded downstream 

by Searles Lake.

Introduction

Searles Valley is in southeastern California, about 200 km 

north-northeast of Los Angeles and 160 km east of Bakersfield. It lies near the southwest corner of the Basin and Range 

Province just north of the Mojave Desert and about halfway 

between the south ends of the Sierra Nevada and Death Valley 

(fig. 1A). The valley is crescent shaped and has an axial length 

of about 65 km and a maximum width of about 15 km. Searles 

Lake, a normally dry salt lake, occupies the widest part of the 

valley. The former towns of Pioneer Point, Trona, Argus, and 

Westend lie along its west edge (fig. 1B); in the early 1990s, 

the limits of Trona were expanded to include all four.

The climate in Searles Valley is arid. Annual temperatures 

during the period 1951 to 1980 averaged 19.0°C (66.2°F), but 

seasonal variation is great. Average temperature maxima and 

minima in July were 40.9°C and 22.4°C (105.6°F and 72.3°F); 

these extremes in January were 14.9°C and -0.2°C (58.9°F and 

31.7°F). Mean annual precipitation was 100.3 mm (3.95 in), 

more than half of that amount falling in the first three months 

of the calendar year (National Oceanic and Atmospheric 

Administration, 1982). Interannual precipitation variability 

ranged from 43 mm (1.7 in) to 246 mm (9.7 in). Except during 

rain days, relative humidity varies diurnally from near 20 to 40 

percent in early evening to 70 to 90 percent in early morning 

(G.F. Moulton, written commun., 1987).

Vegetation is sparse in Searles Valley; typical plants are 

those characterizing much of the Mojave Desert region, such 

as creosote bush (Larrea tridenta), hop sage (Grayia spinosa), 

desert holly (Atriplex hymenelytra), and burro bush (Franseria 

dumosa). In the adjoining mountain ranges, at elevations near 

or above 2,000 m (6,500 ft), Pinyon pine (Pinus monophylla) 

and joshua trees (Yucca brevifolia) grow locally.

The native fauna are numerous, but a brief list includes 

coyotes, rabbits, various rodents, tarantulas, quail, lizards, 

and snakes (rattlesnakes, gopher snakes, and other varieties). The wild burros that are commonly seen in these areas 

are not native but were introduced by early prospectors and 

travelers who brought them from the Middle East in the late 

1700s and 1800s.

Mining of evaporite minerals from the deposits beneath 

the surface of dry Searles Lake has been an important part 

of the area’s history. Since the late 1800s, individuals and 

small companies have owned or occupied land on the lake 

and produced selected industrial minerals. The first mineral 

having known value, borax (Na2B4O7•10 H20), was discovered 

in 1872 by the brothers John and Dennis Searles. They started 

production of borax from the west side of the lake in 1874 and 

prospered from it for 21 years, but in 1895 the operation was 

sold to the Pacific Coast Borax Company, who closed it. In 

1908, soda ash (Na2CO3) production was attempted by the new 

California Trona Company, but it went into receivership the 

following year. Soon after, the company, revived under a new 

name (American Trona Company) built a small plant that was 

also designed to produce soda ash. First, however, they built 

a 35-mile-long railroad that connected the site of their future 

plant with the Southern Pacific Railroad at the southwestern 

tip of Searles Valley; the railroad was a success but the plant 

never produced any soda ash!

 In 1913 the unowned parts of Searles Lake were withdrawn from prospecting and designated a potash reserve by 

the U.S. Government, which “discovered” potash (KCl) in 

Searles Lake brines, although its presence there had been 

known and discussed for several years (Gale, 1914, p. 309-

312). As anticipated in the Government’s action, after World 

War I started in 1914, the global price of potash increased 

tenfold (except in Germany, where it was produced). At that 

time, two California plants flourished: the one at Trona, built 

by the American Trona Co., and another one at Borosolvay, 5 

km south of Trona, built by the Pacific Coast Borax Co. and 

the Solvay Process Co.

By 1920, however, World War I had been over for more 

than a year and the potash price had returned to prewar 

levels. The plant at Borosolvay was closed; the American 

Trona Co. plant at Trona managed to survive and undertook 

a long-term program of basic research. Within the next few 

years, many of the technical problems were solved and the 

plant was taken over and renamed by the American Potash & 

Chemical Co. (AP&CC).

Over the next few decades, lithium (Li), phosphate (PO4), 

and bromine (Br) were added to AP&CC’s list of products, 

although production of these stopped later during the late 

1900s. At the Westend Chemical Co. plant, 6 km south of 

Trona and adjacent to the West End settlement, production 

of borax and potash was started in the early 1920s, but the 

process was found to be inadequate. However, engineering 

improvements to the plant put soda ash back into production 

by 1927, borax was added in 1930, and salt cake (sodium 

sulfate) was in production by 1955.
4 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Since those times, several changes in ownership and 

procedures at both plants have taken place. In the late 1900s, 

another plant was built by AP&CC just southwest of Trona, 

the ownership of much of the land on the lake was consolidated, and many changes in the operational processes were put 

into effect (Smith, 1979, p. 5). By the late 1980s, three large 

industrial-chemical plants, owned by the North American 

Chemical Co., were pumping brines from beneath the surface of the dry lake and extracting soda ash, potash, borates, 

and salt cake. Production in 1986 was valued at $172 million 

(Kerr-McGee Corporation, 1986, p. 24); total production since 

1872 exceeds $3 billion (Smith, 1990).

The geologic origin of Searles Valley was as a product of 

downwarping during late Cenozoic time. Seismic and gravity studies provide evidence of a bedrock floor that is in the 

form of a synclinelike trough, oriented north-south beneath the 

Cenozoic sediments (Mabey, 1956, fig. 5). The basin is asymmetrical, and the deepest part is estimated to be about 1,000 m 

below the east-central part of the present lake surface (in secs. 

F25 and G30—see pl. 1 for locations). Core KM-3, drilled 

at the common corner between secs. F22, 23, 26, and 27, 

penetrated bedrock at 915 m (Smith and others, 1983, table 2), 

a depth that compares favorably with the geophysical estimate 

of bedrock depth of about 800 m at that site (Mabey, 1956, fig. 

5). There is also evidence of presently active synclinal folding 

in the basin (Smith and Church, 1980, p. 528-529; Smith and 

others, 1983, p. 16).

Furthermore, known late Cenozoic faults in the area fail 

to provide an explanation for the valley’s existence. With the 

exception of the Garlock Fault, a left-lateral fault that trends 

east-northeast along the valley’s south edge, major high-angle 

faults of late Cenozoic age do not bound the valley. No frontal 

faults are known in the Argus Range, on the west side of the 

northern valley (pl. 1). Frontal faults in the Slate Range, on 

the east side of the valley, are mostly of early Cenozoic or 

pre-Cenozoic age, except for fault displacements of a few 

meters that have created a graben, which extends northward as 

a normal fault (Smith and others, 1968, pl. 1). Normal faults of 

Quaternary age along the southeast side of the Spangler Hills 

extend only about half the mapped length of that side (pl. 1), 

and they do not appear responsible for major displacements. 

Uplift of the Lava Mountains, south of Searles Valley, may be 

partly a result of Tertiary activity along the left-lateral Garlock 

Fault (pl. 1), but its late Quaternary deformation is expressed 

as upwarping that formed—and is still forming—the northeast-trending Christmas Canyon anticline (Smith, 1964, p. 

51-52; Smith, 1991a, fig. 3). The history of earlier geologic 

studies, as well as the economic development of the area and 

additional details of the geologic and climatic setting of Searles Valley, are available elsewhere (Smith, 1979, p. 2-8).

Searles Valley has long been recognized as a basin that 

was filled one or more times by large lakes. Fairbanks (1896, 

p. 69) first reported shorelines, and Gale (1914) reconstructed 

the late Pleistocene chain of as many as five lakes, of which 

Searles was the third (fig. 1A). The first lake in the chain was 

Owens Lake, which received the flow of the Owens River 

that drained much of the east side of the high south half of the 

Sierra Nevada, including Mount Whitney (14,495 ft; 4,418 

m). Under the present climatic regime, but before irrigation in 

Owens Valley, Owens Lake was about 13 m deep and covered 

about half its maximum possible area. During wetter periods 

of late Pleistocene time, Owens Lake filled and overflowed to 

the south into Indian Wells Valley to form China Lake. China 

Lake, in turn, spilled east into Searles Valley, and the two 

lakes coalesced into one at a level just below that reached by 

Searles Lake when it filled. In the even more intensely wet 

periods, Searles Lake overflowed into Panamint Valley, and 

Panamint, in turn, overflowed into Death Valley. Dramatic 

climatic fluctuations were responsible for the variations in the 

numbers and sizes of lakes in this chain, and reconstructing 

the history of Searles Lake, which was the most sensitive of 

the basins because it was a perennial but fluctuating lake much 

of the past 150,000 years, provides a valuable source of paleoclimatic data that is probably applicable to a large region.

As a start in evaluating the history of Searles Lake, an 

existing 150-ft core hole (L-W), which had previously been 

drilled by the American Potash & Chemical Corp., was reactivated in 1953 under U.S. Geological Survey (USGS) direction. 

The core hole was deepened to 875 ft (267 m) and renamed 

L-W-D. The log of core hole L-W-D was reported in Smith 

and Pratt (1957). It was also decided that additional shallow 

coring and a more complete evaluation of all of the upper two 

saline bodies beneath the surface of the lake were needed.

The additional coring was undertaken during 1954 and 

1955 by the USGS in collaboration with the American Potash 

& Chemical Corp., San Bernardino Borax Mining Co., Ltd., 

Searles Lake Chemical Corp., and the West End Chemical 

Co., all of whom permitted additional drilling on their properties. Forty-one core holes, ranging in depth from 29.8 ft (9.1 

m) to 143.3 ft (43.7 m), were consequently drilled and logged 

(Haines, 1959).

In 1967, the Kerr-McGee Chemical Corp., which had 

absorbed the holdings of the American Potash & Chemical 

Corp. in 1963, started an exploratory well, KM-3, which was 

finished in July 1968. Well KM-3 was located at the junction 

of the four midlake sections 22, 23, 26, & 27, all within T. 25 

S., R. 43 E. (township F on plate 1). The core hole recovered 

lacustrine sediments to a depth of 2,275 ft (693.4 m), alluvial 

sediments from there to a depth of 3,003 ft (915.3 m), and 

finally bedrock to a depth of 3,050.2 ft (929.6 m). In September 1968, D.A. McGee, Chairman of the Kerr-McGee Corporation, granted the USGS permission to study these core logs 

and publish the results (Smith and others, 1983).

The study described in this report is a continuation of 

these earlier investigations of the subsurface geology of Searles Lake (Smith, 1979; Smith and others, 1983). Those papers 

document the stratigraphy beneath the surface of the lake as a 

series of alternating saline layers (indicative of shallow saline 

or dry lakes) and silts, clays, and marls (indicative of deeper 

perennial lakes); such sediments constitute the upper 693 m 

of deposits and represent the past 3.2 m.y. (see fig. 1C). Much 

of the emphasis in the above-cited reports was on the paleocli-
matic significance of the fluctuations recorded by the subsurface sediments, but the depths of water in Searles Valley could 

only be estimated from criteria that allow the salinity of the 

lake to be inferred.

The present study attempts to reconstruct actual lake levels 

by tracing lacustrine sediments deposited in lakes of known 

succession (and approximated ages) to their highest levels in 

the valley. Conversely, intervening periods of lake recession or 

0 50 MI

36°

119° 118° 117°

37°

38°

0 50 KM

A

S I E R R A N E V A D A

White Mountains

Inyo Mountains

Coso Range

Argus Range

Panamint Range

Mono

Lake

Adobe

Lake

Owens

Lake

Panamint

Lake

China

Lake

Searles

Lake

Lake Manley

(Death Valley)

CA

Present playas or lakes

Pleistocene lakes

Present river

Pleistocene rivers. Arrows 

 show flow direction

EXPLANATION

Bishop

NEVADA

CALIFORNIA

Owens

River

Map B

Map A

Panamint Range

Panamint Valley

Slate Range

Searles Lake

(dry)

Pioneer Point

Wilson

Cyn

Poison Cyn

and Wash

The Pinnacles

Plate 1 area

Pleistocene

overlfow from

Searles Lake

Pleistocene

overflow from

China Lake

Trona

Argus

Westend

Searles Lake

(dry)

U.S. Naval Weapons Center

Randsburg Wash Test Range

Spangler Hills

Lava Mountains

Argus

Range

Salt Wells Valley

Valley Wells Wash

S e a r l e s

 V a l l e y

Teagle Wash

Randsburg Wash

B

0 10 MI

0 10 KM

178

 

Searles

Lake

Formation

This paper

Previous

terminology

0

5

10

15

20

25

30

50

150

Surficial

deposits

Unit

D

Unit

CD

Unit

B

Unit

AB

Unit

C

Unit BC

Christmas

Canyon

Formation

Siltstone

and

Sandstone

unit

Bedrock

Spring

Formation

Volcanic rock Older tufa

Older gravels

Overburden

Mud

Upper

Salt

Lower

Salt

Unit

A

CCF

Bottom

Mud

Mixed Layer

Parting

Mud

Tufa (nodose) Tufa (lithoid)

Sandstone

unit

Gravels (undifferentiated) ?

Age, in thousands of years B.P

Miocene Pliocene (?) Pleistocene Holocene

Lower Upper

TERTIARY —— ? —— QUATERNARY

C

Figure 1. Geographic and stratigraphic setting of Searles Valley and its late Cenozoic deposits. A, Map showing locations of 

Pleistocene and present lakes, playas, and rivers in the northern part of the Great Basin within California. Major mountain ranges 

are also shown. B, Map of the Searles Valley area, showing mountains, canyons, main washes, towns (black squares), and the 

area of geological mapping on plate 1 (within heavy line). C, Generalized stratigraphic column for the late Cenozoic deposits of the 

Searles Valley area, with expanded columns for the Searles Lake Formation, showing unit names used or defined in this work and 

equivalent older terminology based on drill cores beneath the surface of Searles (dry) Lake (see Smith, 1979).

Introduction 5
desiccation are reconstructed by determining the lowest elevations of interbedded alluvial deposits and fossil soils that are 

indicative of subaerial conditions. Although the prime emphasis 

of this study has been placed on the late Quaternary deposits 

exposed in Searles Valley, studies have also been made of the 

older Quaternary and Tertiary sediments and rocks exposed near 

the valley. Pre-Tertiary rocks are not differentiated.

Acknowledgments

I would like to thank the many U.S. Geological Survey 

(USGS) employees who helped during so many stages of this 

project. I am particularly grateful to Robert J. McLaughlin for 

his full-time help in the field and laboratory during the early 

stages of this study, to Gloria Harris for her nearly full time 

assistance in the laboratory and office for so many months 

during the later stages, and to Michele Ono for her careful 

typing of the final draft of this report. Stacey Andrews, David 

Aquino, Diane Cheney, Joshua Delgado, Daniel Dilling, 

Susan Howell, Peter Irish, Michele Ono, Susan Orr, Tammy 

Parker, Glendora Payton, Jacqueline Richy, Jose Rivera, Rossana Torres, and Ron Valine also assisted in X-ray diffraction, sediment-size analysis, map coloring, table compilation, 

manuscript preparation, and other tasks. The managers and 

assistants of the 14C and U-series dating laboratories deserve 

special thanks for their essential contributions.

Discussions with Charles B. Hunt and Roger B. Morrison 

during the early stages of this work and with Larry Benson 

and Richard L. Hay during later stages were helpful in bringing this project to a successful conclusion. Joseph P. Smoot 

and Robert S. Thompson provided helpful reviews. At the 

time, all but Hay were with the USGS.

Ronald G. Blom, of the Jet Propulsion Laboratory, Pasadena, California, arranged for access to the false-color satellite 

photograph of the Searles Valley area that is used for the cover 

of this volume. Several employees of the chemical companies 

operating in Searles Valley assisted me in various ways when 

I was doing field work, especially D.S. Arnold, C.F. Cowie, P. 

Cortessis, L.J. Czel, F. Dluzak, W.A. Gale, D.E. Garrett, D.A. 

Holmes, L.E. Mannion, and J.F. Phillips.

USGS editorial assistance and map preparation were 

provided by Richard Koch, Joel Robinson, Sue Mayfield, Julia 

Thomas, Jan Zigler, and Peter Stauffer. Manuel Nathenson provided guidance and editorial assistance during final production.

 Finally, I would like to thank the 300-or-so participants 

of two Friends-of-the-Pleistocene field trips, plus several 

smaller groups who joined me in Searles Valley. They offered 

critical scrutiny of, and asked probing questions about, my 

interpretations of the field evidence.

Field and Laboratory Methods

Approximately 600 days were spent in the field compiling the six geologic maps that are the primary basis for this 

report (pls. 1-4). The first period of field work extended from 

1961 to 1970, the second from 1983 to 1996. Mapping was 

originally compiled on prints or enlargements of black-andwhite aerial photographs selected from six sets, none of which 

covered the entire area or were at the same scale. The mapping 

on photographs was transferred, using a projector, to enlargements of the topographic base taken from the appropriate 

15-minute topographic map.

The base map covering most of Searles Valley (pl. 1) was 

made by joining four 15-minute quadrangles (Trona, 1949; 

Manly Peak, 1950; Searles Lake, 1949; and Wingate Pass, 

1950) along the edges and then enlarging the combined map 

from the original 1:62,500 scale to 1:50,000 scale. For the 

detailed maps (pls. 2-4), these topographic bases were enlarged 

to 1:10,000 scale. For convenience, the area covered by each 

of these five detailed maps has been named after included (or 

nearby) geographic features: Valley Wells Wash (an informal 

name) (pl. 2A), Randsburg Wash (pl. 2B), Poison Canyon (pl. 

3A), Salt Wells Valley (pl. 3B), and The Pinnacles (pl. 4). 

The extreme enlargement required to make these five 

detailed maps has reduced the accuracy and topographic detail 

far below normal levels for base maps. In transferring the 

geology from photographs to the topography of plates 2 to 4, 

therefore, compromises were made. In some instances, the 

geology plotted on photographs was adjusted so its geometry 

correctly fit the contours as represented by the enlarged maps. 

In other instances, however, where details of the actual geologic configurations are important to the correct interpretation 

or would aid another field observer to locate and identify certain outcrops, the generalized contours were ignored and the 

more detailed field relations, as mapped on the photographs, 

were plotted.

Many of the units plotted on the geologic maps are too thin 

or small to be shown accurately, even on the large-scale maps. 

No minimum thickness was established for mapping, and in 

some areas, units less than a meter thick were plotted because 

they are relevant to the interpretation of the lacustrine and 

nonlacustrine depositional history of the valley fill. Besides the 

large number of relatively thin units, many of the best exposures 

and significant relations are observed on steep slopes where 

even thick units are difficult to plot accurately. The geologic 

maps in these areas, therefore, are diagrammatic, and future 

observers in the field will need to adapt to these portrayals.

As the contours on these base maps indicate feet above 

sea level, all references to elevations in the text are in feet, 

sometimes followed by appropriate metric equivalents. Horizontal distances, however, are mostly in kilometers, thicknesses of units or stratigraphic sections are in meters, and all 

other dimensions are in the convenient metric unit.

With the exception of the volcanic rock unit, all of the 

mapped units of Cenozoic age are chemical or clastic deposits. 

Because a central focus of this study has been to reconstruct 

past climates, chemical and clastic deposits indicating lacustrine deposition, which required a wet (“pluvial”) climate 

relative to the present, are generally noted and separated from 

deposits indicating subaerial deposition, which required a dry 

6 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California
(“interpluvial”) climate. Criteria for separating the two environments of deposition are many. Discussions and summaries 

by Clifton (1973) and by Rigby and Hamblin (1972) include 

many of the criteria used in this study. These and other criteria 

developed during this study are summarized in table 1.

To simplify the process of describing localities that offer 

especially good exposures, complete sections, or definitive 

geologic relations, the townships that are partially or entirely 

included on the map of Searles Valley (pl. 1) have been 

assigned capital letters, A through P, as shown on plate 1. 

Townships L, M, O, and P are actually unsurveyed, but their 

boundaries have been projected from surrounding grids and 

hypothetical sections plotted within them. The northernmost 

partial township, A, is T. 23 S., R. 43 E.; the southeasternmost 

partial projected township, P, is T. 28 S., R. 44 E. (Mount 

Diablo Base and Meridian). Sections retain their normal numbers. Thus a locality in section 27, T. 27 S., R. 42 E. would 

be referred to as “sec. K27.” For more precise identifications 

of locations, especially on the large-scale maps (pls. 2-4), 

each section is subdivided into sixteenths, which are assigned 

lower-case letters, as also shown on plate 1 (lower-case i and o 

are omitted). A locality in the southeast corner of section K27, 

therefore, is designated “K27-r.”

Stratigraphic sections (appendix 1) were measured by a 

combination of hand-leveling methods and visual estimates 

of each component bed. Rock and sediment descriptions used 

in these tabulations and in the text were based on megascopic 

properties plus hand-lens study; a few thin sections were 

studied with a petrographic microscope, but they added little 

information that was useful. Reported occurrences of megascopic crystals of halite, gypsum, and gaylussite were visually identified in the field; identifications of the fine-grained 

minerals such as calcite, aragonite, dolomite, thenardite, 

thermonatrite, ulexite, halite, and analcime are based on X-ray 

diffraction data. Numerical data on sediment sizes (appendix 

2) are based on field measurements and laboratory analyses 

using standard-mesh sieves. Clastic size terminology follows 

Wentworth (1922). Colors indicated by alphanumeric expressions are based on the Rock Color Chart of Goddard (1951). 

All carbon-14 (14C) dates are reported without any corrections 

Table 1. Criteria used in Searles Valley to differentiate between outcropping lacustrine and alluvial deposits.

Characteristic Lacustrine Deposits Alluvial Deposits

Bedding Persistent; if horizontal, usually for more than 10 m Lenticular, rarely persist for more than 3 m

Sorting 

(gravel)

Well sorted, largest fragments commonly about 2x 

average fragment, none much larger; matrix commonly half sand, half open space, rare clay-size 

material

Poorly sorted, large fragments may be 100x average size, commonly one or two fragments in a 

given outcrop even larger, matrix is nearly 100 percent sand and silt, always some clay-size material

Sorting (sand) Well sorted, some deposits have small percentage 

of similarly sized pebbles, none large, rare clay-size 

material

Poor to fair sorting, usually some pebbles having 

diverse sizes, common clay-size material

Sorting 

(silt and clay)

Well sorted Rarely found

Rounding 

(coarse deposits)

Subangular to well rounded, but individual deposits 

mostly composed of similarly rounded fragments

Mixture of angular to well-rounded fragments derived mostly from older coarse lacustrine deposits

Fabric 

(coarse deposits)

Tabular or elongate fragments commonly aligned in 

persistent “shingle-structure” zones

Tabular or elongate fragments locally aligned in 

“shingle-structure” zones, more commonly randomly oriented

Fossils Common, locally abundant, especially in Poison 

Canyon area

None (except reworked specimens) 

Porosity 

(apparent)

High (little fine material in matrix) Low

Color (fresh surface) Fine-grained deposits are light shades of green, gray, 

or tan; coarse deposits may be gray to very dark gray

Fine deposits mostly tan; coarse deposits dark 

brown or gray

Color 

(weathered surface)

Very light tan to tan orange if fine; dark browns to 

gray if gravel

Tan to dark brown or orange brown 

Carbonate content High throughout High in soil zones; low elsewhere

Resistance to erosion Fine-grained deposits with high percentage of 

CaCO3 very resistant, coarser deposits less resistant, 

form steep to intermediate slopes

Variable, but generally form intermediate slopes

Field and Laboratory Methods 7
8 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

for initial nonequilibrium conditions in the lake water or for 

past variations in cosmic ray intensity.

Some abbreviations are used in this report. Dates and 

geologic ages are expressed in years (yr), thousands of years 

(ka), or millions of years (Ma); the “ago” and “B.P.” suffixes 

are omitted. Periods lasting thousands or millions of years 

are abbreviated k.y and m.y. Abbreviations used for metric 

and English measurement systems are the conventional ones. 

Sections (sec.) refer to the land-grid system discussed above. 

Measured sections (meas. sec.) refers to the stratigraphic 

descriptions in appendix 1.

Stratigraphy and Lithologies of 

Mapped Units

Three of the rock units discussed herein and shown on the 

geologic maps (pls. 1-4) are formally designated formations; 

the Bedrock Spring and Christmas Canyon Formations were 

established and described elsewhere (Smith, 1964, p. 15-23, 

40-42), and the new Searles Lake Formation is described 

herein. All three of these formations contain a variety of rock 

types representing both sublacustrine and subaerial sedimentation, and one also contains volcanic deposits; formal stratigraphic terminology would now designate each of them as an 

“alloformation,” to emphasize their diversity. However, the 

first two were published before the introduction of that term, 

and the third is no less diverse, so the term “Searles Lake Formation” is used herein. The other rock units are informal units 

whose lithologies, stratigraphic positions, or surface morphologies generally allow them to be identified and differentiated 

with little difficulty.

Detailed stratigraphic study was limited to the late Quaternary lacustrine (and interbedded alluvial) sediments of the 

Searles Lake Formation of late Pleistocene to late Holocene 

ages. These lacustrine sediments have limited elevation ranges, 

from the floor of the valley (1,616 ft) to about 2,280 ft; geologic relations among late Cenozoic deposits exposed above 

this latter elevation were studied less carefully. Similarly, 

sediments assigned to the Christmas Canyon Formation and to 

units that are contemporaneous or older were also studied in 

less detail because of their ages, but descriptions and observations of stratigraphic successions of these older sediments 

were made in sufficient detail to determine the environment 

of deposition and the areal extent of the unit. Subdivision of 

these older units into members or subunits was generally not 

attempted, but the Christmas Canyon Formation of middle 

Pleistocene age is divided into lacustrine and alluvial facies. 

The Searles Lake Formation was divided into 12 units on 

plate 1 and as many as 27 units and subunits on plates 2 to 4. 

Younger deposits of middle and late Holocene ages are subdivided into five units.

Rocks assigned to Tertiary units are mostly deformed. In 

areas along the Garlock Fault, rocks assigned to the siltstone 

and sandstone map unit dip steeply and may be locally overturned, but the other two Tertiary rock units are not as extensively deformed within the mapped area. Some of the sediments 

assigned to the Tertiary or Quaternary units are deformed, but 

typical dips are between 10° and 20°. Sediments assigned to the 

middle Pleistocene Christmas Canyon Formation are slightly 

deformed, dips being mostly in the range of 2° to 5°. The Searles Lake Formation may have undergone regional uplift of a few 

meters, but tectonic tilting is not measurable.

The regions covered by plates 2 through 4 required about 

300 days of field work. The areas on plate 1 not covered by 

those more detailed maps required several hundred additional 

days. The major difficulties in mapping such a large area over a 

period of more than 30 years were (1) applying uniform criteria 

to the identification, correlation, and mapping of units and (2) 

making retroactive adjustments to existing mapping as new 

units were identified or old units redefined. Some errors were 

undoubtedly introduced or not eliminated as a result this process, but every effort was made to reduce those to a minimum.

Three areas on plate 1 represent significantly less detailed 

geologic mapping, and two areas are based largely on previously published mapping. Except for the area shown on plate 

2B, the region within the Randsburg Wash Test Range (part 

of the Naval Weapons Center, fig. 1B), near and southeast 

of the Garlock Fault and east of Christmas Canyon, reflects 

only a few days of reconnaissance mapping. Units shown 

as mapped on the U.S. Naval Weapons Center near the west 

edge of plate 1, west of Searles Lake and north of Salt Wells 

Valley (fig. 1B), are based on photogeology. The geology of 

the floor of northern Searles Valley above 2,280 ft is based on 

reconnaissance mapping. The geology of the west edge of the 

Slate Range is modified from Smith and others (1968, pl. 1); 

the geology of the northern Lava Mountains is modified from 

Smith (1964, pl. 1).

Tertiary Units

Three rock units in the Searles Valley area are known or 

assumed to be of Tertiary age. Vertebrate fossils in the Bedrock Spring Formation (Smith, 1964, p. 15-23) are of Hemphillian age (C.A. Repenning, oral commun., 1985), which is 

presently considered to be latest Miocene. Stratigraphic evidence shows most volcanic rocks in the Lava Mountains to be 

younger than the Bedrock Spring Formation, but the volcanic 

rocks in the Argus and Slate Ranges could be older or younger 

than that formation. The siltstone and sandstone unit, which 

crops out near the Garlock Fault, as shown in the southern part 

of plate 1, is probably older than the Bedrock Spring Formation inasmuch as it is somewhat more indurated and much 

more intensely deformed, but the two units are not known to 

be in stratigraphic contact.

Siltstone and Sandstone

Rocks of this (unit Ts) were described briefly by Noble 

(1931) and by Smith and others (1968, p. 14), who concluded 
that they had a lacustrine origin and tentatively correlated them 

with the Christmas Canyon Formation, following the suggestion of Smith (1964, p. 41, fig. 17). During the present study, 

more detailed mapping of the relations east of the type section of the middle Pleistocene Christmas Canyon Formation, 

which is mostly of lacustrine facies, shows that the sediments 

constituting the type section rest unconformably on the finegrained lacustrine deposits of the early Miocene(?) siltstone and 

sandstone unit (pl. 1). The lithologies of the two units here are 

similar and the contact between them is not exposed, but in outcrops less than 100 m apart, contrasts in the degree of induration 

and the steepness of their dips leave little question that they are 

different. Furthermore, in many areas the gravel and sand facies 

of the Christmas Canyon Formation rests unequivocally on the 

deformed lacustrine deposits of the siltstone and sandstone unit.

Within the area of plate 1, the rocks of this unit (Ts) are 

restricted to areas just north and south of the Garlock Fault. 

Most are well-bedded siltstone and sandstone, commonly 

containing thin layers of well-sorted gravel, characteristics that 

support a lacustrine origin. Beds, typically 0.5 to 1.0 m thick, 

dip at angles as high as 90°. Colors of well-exposed sections 

are grayish yellow (5Y7-8/2-4), although coarser facies just 

east of the mapped area are characterized by darker shades of 

tan and brown. Noble (1931, p. 10-13) reports gypsum and 

traces of nitrates in these deposits, possibly an explanation for 

the fact that little vegetation grows on outcrops of the finer 

grained facies of this unit. Several tuff beds were noted.

Beds of unit Ts are deformed in almost every exposure, 

with dips exceeding 45° being common (fig. 2). No pattern of 

fold axes or faults was determined, nor were any stratigraphic 

sections measured. However, much more extensive sections 

crop out to the east of the area of plate 1, along the south edge 

of the Slate Range (Smith and others, 1968, pl. 1), where the 

rocks of this group could have thicknesses that exceed 500 m. 

Deposits in other areas that are similar and possibly correlative 

are not known.

No fossils have been found in this unit, and none of the 

volcanic ash layers have been correlated with dated ash layers. 

Its age, therefore, is not known, but it is reasonable to assign it 

a Miocene(?) age.

Figure 2. Deformed Tertiary siltstone and sandstone beds (unit Ts) unconformably overlain by 

horizontal beds of unit A of the Quaternary Searles Lake Formation. The tilted lacustrine deposits, of 

possible early Miocene age, here dip about 55° (apparent dip in photograph about 40°). Sublacustrine 

erosion formed a flat, unchanneled surface before deposition of unit A lacustrine beds. View toward 

west; location: plate 1, sec. M19-k.

Stratigraphy and Lithologies of Mapped Units 9
10 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Bedrock Spring Formation

Outcrops of the Bedrock Spring Formation (unit Tbs; 

Smith, 1964, p. 15-23) are all south of the Garlock Fault. Its 

clastic rocks are chiefly arkosic alluvial sandstone and conglomerate that are light pinkish tan. In the 1,500-m-thick type 

section, which is about 3-6 km south of the southwest corner 

of the mapped area of plate 1, lacustrine layers are found 

in the lower quarter and near the top, as well as scattered in 

other parts of the formation. Alluvial gravels make up most of 

the rest. The debris was largely derived from plutonic terrain 

to the south, although volcanic rock fragments are found in 

nearly all exposures and volcanic breccia layers are prominent 

locally. Reconstruction of the depositional basin for this formation suggests that its north edge was parallel to the Garlock 

Fault and just north of the outcrops shown on plate 1 (Smith, 

1964, p. 19, fig. 9).

Vertebrate fossils, which include six identifiable genera 

from 24 sites, indicate a Hemphillian age, which was once 

considered early to middle Pliocene (Smith, 1964, p. 21) but is 

now considered to be of uppermost Miocene age (C.A. Repenning, oral commun., May 1985).

Volcanic Rock

Volcanic rock (unit Tv) crops out in two areas shown on 

plate 1. Near the north tip of the mapped area, flows of black to 

dark gray basalt rest on the flanks of the Argus and Slate Ranges 

(Smith and others, 1968, p. 14; Smith and Church, 1980, fig. 4). 

Augite-olivine basalt dominates these rocks, but basaltic andesite is also reported (Moore, 1976, p. 68, 69). Flow thicknesses 

within the area of plate 1 are most commonly between 30 m and 

60 m. Ages of these volcanic rocks are uncertain. The nearest 

radiometric age on similar rock, 5 km west of the northwest corner of the area shown on the plate 1 base map, is 1.75±0.10 Ma 

(Duffield and Bacon, 1981, loc. 60). The basaltic rocks shown 

on the northern part of plate 1, however, are believed to be older 

because of the evidence that they predate development of the 

Argus-Slate Range Syncline and Slate Range Anticline (Smith 

and Church, 1980, p. 528-529, figs. 1 and 4). That syncline has 

since been recognized as the probable cause of Searles Valley 

and as extending southward to near the Pleistocene outlet of 

Searles Lake, so it was renamed the Searles Valley Syncline 

(Smith, 1991a, p. 615). Alluvial sedimentation in Searles Valley 

is known to have begun well before deposition of the first lake 

deposits at 3.2 Ma (Smith and others, 1983, p. 16). Radiometric 

ages of basaltic rocks on the crest and east flank of the northern 

Argus Range, in the vicinity of Rainbow Canyon, which is 40 

km north of the area of plate 1, range from 7.7 to 2.5 Ma (Schweig, 1984, table 1); the older half of this age range seems more 

reasonable for these flows.

The majority of the volcanic rocks that crop out near the 

south edge of the area shown in plate 1 are well indurated, 

massive lapilli tuff and tuff that form variegated, steep-sided 

hills (Smith, 1964, pl. 1, p. 39-40, 42). They appear to rest on 

Bedrock Spring Formation, but relations are obscure. Included 

in this unit on plate 1 are several younger northeast-trending 

basalt dikes and small flows; they appear to intrude the Christmas Canyon Formation, which would make them Quaternary in 

age, but the field relations are also obscure.

Tertiary or Quaternary Units

Sandstone and Siltstone

Most of the rocks assigned to the sandstone and siltstone (unit QTs) crop out in two parts of the area of plate 1, 

but there is no stratigraphic evidence that they are correlative. The rocks cropping out in the Spangler Hills, which are 

found at elevations as much as 140 ft (43 m) higher than any 

deposits of the Searles Lake Formation, are poorly exposed 

but characteristically form very light gray outcrops. They 

are uniformly arkosic and include both alluvial and lacustrine deposits. Fragments range from angular to round and 

their sizes vary from medium sand to pebble gravel. Granitic 

rocks, like those in the Spangler Hills, make up most of the 

coarser detritus. Many outcrops have a well-developed layer 

of caliche near or at the surface, and a pronounced lag gravel 

characterizes most surfaces.

Ages for these rocks are uncertain. They appear to 

underlie the older gravel (unit og) of Pliocene or early to 

middle Pleistocene age (defined below), although contacts 

are poorly exposed. A greater age is also suggested by the 

caliche development, which is more extensive than in the older 

gravel. Where these deposits are in contact with the sediments 

mapped in the Spangler Hills as early units of the Searles Lake 

Formation, the greater concentrations of caliche distinguish 

the older deposits. If the deposits represent a very much earlier 

stand of Searles Lake than the younger stands discussed in this 

report, that lake’s surface and the lake’s outlet would have had 

to be higher than during late Pleistocene time or the Spangler 

Hills lower.

Rocks assigned to this unit that crop out near the southeast corner of the area of plate 1 are also both lacustrine and 

alluvial in origin. North of the Garlock Fault, virtually all 

rocks assigned to this unit are lacustrine. South of the fault, 

most of the rocks assigned to this unit are alluvial; an interbedded facies that may be lacustrine is not similar to the lacustrine 

deposits included in this unit just north of the fault.

The lacustrine deposits just north of the Garlock Fault are 

mostly well bedded, coarse to fine sand with interbedded silt. 

Characteristically, these rocks are well indurated and beds are 

2-10 cm thick. A typical sand layer is composed of mediumto fine-grained angular sand containing some angular pebbles; 

about 80 percent of the grains are granitic debris and 20 percent are volcanic debris. Colors of fresh surfaces of sandstone 

outcrops are commonly olive-yellow hues in the range 5Y4-

7/1-2. Siltstone outcrops are slightly lighter. Good outcrops 

of these rocks can be found in sections L26-p and L25-q (pl. 

1) and M19-l (pl. 2B). Geologic relations consistently show 

that these rocks unconformably underlie sediments of the 
Christmas Canyon Formation and unconformably overlie the 

siltstone and sandstone of Tertiary age.

The alluvial and lacustrine deposits assigned to this unit 

south of the Garlock Fault were not carefully mapped or studied. Most good exposures are close to the Garlock Fault, where 

the beds are tilted and deformed. A kilometer or more south 

of the fault, they are poorly exposed except along the sides of 

Randsburg Wash; there (sec. P5-f), 3-5 m of exposed sediments 

consist of moderately indurated, pebbly arkosic sand that is pale 

brown (5YR5-7/2). Poorly sorted, subangular to subrounded 

volcanic rocks constitute the coarser fragments. Another 

well-exposed surface (sec. M33-c) consists of grayish orange 

(10YR7/4) pebbly arkosic sandstone that is faintly bedded.

These rocks are similar to the sandstones and conglomerates of the upper Miocene Bedrock Spring Formation in the 

Lava Mountains (Smith, 1964, p. 17-18), and the possibility exists that the rocks of this sandstone unit in this area are 

extensions of that formation. The rocks south of the Garlock 

Fault assigned to this sandstone unit are clearly overlain by the 

gravels and lacustrine facies of the Christmas Canyon Formation, and they are underlain by the Tertiary siltstone and sandstone unit. These rocks are not correlated with the Bedrock 

Spring Formation, however, because they are less deformed 

and indurated than the rocks of that formation.

Sediments questionably assigned to this unit crop out 

unconformably beneath gravels of the Christmas Canyon 

Formation along the south edge of the Spangler Hills (secs. 

K31-p and N6-c). They are composed mostly of tan sand that 

contains many calcareous pods and gypsum crystals (altered to 

bassanite). Several interbedded gravel lenses, about 1 m thick, 

are composed of light-purple or banded light-tan volcanic 

lavas and greenish or white pyroclastic rocks, components 

known from their mineralogy and petrographic textures to 

have been derived from the Lava Mountains and Summit 

Range 10 km to the south and southwest (Smith, 1964, pl.1, p. 

27-40). This suggests their deposition in a north-sloping fan at 

some time prior to uplift of the Spangler Hills.

Older Tufa

Ten or more large tufa mounds (unit ot) crop out in the 

south quarter of Searles Valley; two small masses were tentatively identified in the northern valley (secs. C5 and C8). In 

the southern part of the valley, the largest tufa mound covers 

an area of 0.2 km2

 and the highest extends 37 m above its base 

(fig. 3). This massive lithoid tufa, following the terminology of 

Scholl (1960, p. 418-419, figs. 3c and 10), is lithologically distinct from the light tan to brown, porous tufa masses deposited 

during the time represented by the Searles Lake Formation, 

although most outcrops of massive lithoid tufa have coatings 

of younger tufa on their outer surfaces.

The massive lithoid tufa consists of dense calcite that has 

weathered with the development of sharp ridges and points 

that are attributed to solution by rain. Exposed surfaces are 

Figure 3. Two dark hills, about 1.5 and 3 km from camera, are mostly composed of older tufa, with 

tufa of Searles Lake Formation locally coating the older deposits. Nearest large hill is about 37 m high 

and 0.5 km wide; note shorelines eroded into surface. Railroad tracks visible on near side of hill. Symmetrical flat-top peak on skyline is Pilot Knob, about 35 km from camera. View to southeast; location 

of largest tufa mass: plate 1, sec. K24-c.

Stratigraphy and Lithologies of Mapped Units 11
12 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

light olive gray (5Y6/1) to medium gray (N5-6); fresh surfaces 

are yellowish gray (5Y7-8/1-2) to pinkish gray (5YR7-8/1-2). 

Locally, medium to coarse sand is embedded in the calcite 

matrix, but some samples are virtually pure calcite. Cavities 

and drusy fillings are present, but they are much less abundant 

than in the tufa types associated with the Searles Lake Formation. Scholl (1960, p. 419) reports the bulk density of this 

massive lithoid tufa as 1.9. Pure calcite has a density of 2.7, 

indicating that the measured samples of this older tufa have 

about 30 percent porosity.

The restriction of massive lithoid tufa to about the same 

elevation range as the lacustrine sediments of the Searles 

Lake Formation suggests a sublacustrine origin. The domelike shapes and the alignment of three groups of these masses 

(secs. K14, K24, L19, and L29 on pl. 1) suggest an origin 

related to springs aligned along a buried fault at right angles to 

the mapped faults in this area. Springs could have introduced 

Ca- and HCO3-rich water into the slightly alkaline lake, causing precipitation of calcite inorganically when the two waters 

mixed and the solubility product of calcite was exceeded. 

The other tufa masses are not aligned with each other or with 

known faults; the characteristic they have in common is that 

they lie at or near the highest shorelines of the later lakes, arguing for an organic process that included the action of algae in 

shallow water, where the penetration of sunlight was strongest.

Sediments and tufas associated with the Searles Lake 

Formation are all stratigraphically younger than the older tufa. 

That both these map units are restricted to the same elevation 

range implies that there was not sufficient geologic time for 

tectonic forces to have greatly altered the basin configuration 

and suggests that the older tufa deposits are not much older. 

A U-series age of “greater than 300,000 ka” (J.L. Bischoff, 

written commun., March 28, 1984, lab. no. 84-19a), however, 

indicates that the older tufa deposits are at least twice a old as 

the Searles Lake Formation.

Older Gravel

North of the area where the Searles Lake Formation is 

underlain by the gravel facies of the Christmas Canyon Formation, essentially the latitude of The Pinnacles (pls. 1 and 4), 

all alluvial gravels that underlie that formation are included in 

the older gravel unit (og). In most places, they are cobble to 

boulder gravels with poorly sorted, gray to tan sand constituting 50 to 80 percent of the sediment and angular to subangular pebbles, cobbles, and boulders constituting the balance. 

Locally, within a kilometer of the edges of the Argus and Slate 

Ranges, boulders a meter or more across are incorporated. 

Bedding is generally poor and discontinuous; some cross-bedding was observed. Most outcrops along the sides of canyons 

are very well cemented with calcite.

Deposits in separate areas may differ significantly in age. 

Even deposits that are physically overlain by tufa or sediments assigned to the Searles Lake Formation appear in some 

instances to be demonstrably older than the base of that formation; prior to deposition of the younger sediments, channels 

were cut into some of the top surface of the older gravel, and 

moderate to strong soils as much as 2 m thick were developed. 

The channels may only document a limited depositional gap, 

but the soils probably document exposure to weathering for 

tens of thousands of years after gravel deposition ceased. 

Slight angular discordances are observed but are uncommon.

Deposits mapped as part of this unit near the west edge 

of the area of plate 1, in and near the areas of plates 3A and 

3B, are also angular cobble and boulder gravels. Plutonic and 

hypabyssal rocks are the most abundant fragment types in these 

areas. The gravels are not as indurated as are gravels in some 

other parts of the valley, and the cobbles and boulders mostly 

have a heavy coat of desert varnish. In the Poison Canyon 

area (pl. 3A), the older gravel unit has been separated into two 

facies on the basis of stratigraphic position and the intensity 

of varnish and soil development. The older facies is a boulder 

gravel that is very dark gray to brown and heavily varnished, 

and a strong calcareous soil has been developed on its surface. 

The younger facies is a pebble gravel that is dark orange-brown 

and less heavily varnished, and its angular fragments in a sandy 

matrix suggest a colluvial or debris-flow origin. Inasmuch as 

both facies extend to the ridge of this part of the Spangler Hills, 

and are therefore considered to be of approximately the same 

age, some process has apparently retarded the varnish process 

on the lighter colored facies, even though both include the same 

rock types. Field study did not resolve this question.

The older gravel that rests on bedrock in the Slate Range, 

northeast of Searles Lake, was described by Smith and others 

(1968, p. 14) as having a thickness of as much as 120 m. Its 

lithology is similar to those described above, and it forms a 

discontinuous cover over Manly Pass, a broad saddle in the 

Slate Range having a maximum elevation of nearly 2,900 ft 

(885 m). In an area east of the north edge of Searles Lake, the 

older gravel can be traced down to elevations where it is cut by 

shorelines and overlain by sediments of the Searles Lake Formation. The great thickness of gravel included in this unit in 

the Slate Range, and its position on the crest of the range, suggest that a substantial amount of time is represented, and the 

lower part—or all—of this section could be of Tertiary age.

Exposures of older gravel along two canyons in the Slate 

Range (secs. G10-n, G15-c,d,e,g,l, and G16-h) reveal three 

or four thin zones of lacustrine sands and gravels. One zone, 

1 to 2 m thick, is near the top of the section and is composed 

mostly of angular gravel (sec. G15-l). The middle zone 

generally consists of two beds of lacustrine gravel, each 1 to 

2 m thick and separated by 1 to 2 m of alluvium; another bed 

lies lower in the section (measured sec. G10-n). Some layers are very coarse sand, but most are gravels that are dark 

gray, poorly sorted, and composed mostly of subrounded to 

rounded, cobble-size fragments, with foreset and backset bedding locally prominent. A discontinuous volcanic ash layer 

(sec. G16-h) is approximately at the level of these beds, but 

it proved unsuitable for K/Ar dating. Study by Ray Wilcox 

of the USGS found it to be unlike the Lava Creek or Bishop 

ashes, and he was unable to correlate it with other ashes of 

known age (written commun., August 1967).
The older gravel map unit is probably correlative in part 

with the Christmas Canyon Formation. The two units are 

as similar as the rocks in their diverse source terrains allow, 

implying a similar climate at the times of their deposition. 

Both contain a lacustrine facies, and both have strong calcic 

soils, 1 to 2 m thick, developed on their upper surfaces. My 

inclusion of the deposits on the crest of the northern Slate 

Range in this map unit, as well as the numerous coarse gravel 

outcrops elsewhere in the mapped area that lack stratigraphic 

control, is responsible for the expansion of the suggested age 

for this unit from Pleistocene down into the Pleistocene-orPliocene age bracket (see pl. 1, Description of Map Units).

Christmas Canyon Formation

The Christmas Canyon Formation was established by 

Smith (1964, p. 40-42) on the basis of outcrops in the Lava 

Mountains to the south of Searles Valley. Two facies, one a 

lacustrine sandstone facies and the other an alluvial boulder 

conglomerate facies, were described. The type section (sec. 

O8-e) is about 45 m thick. It is composed predominantly of 

nearshore lacustrine siltstone, sandstone, gravel, and breccia, 

although the alluvial boulder conglomerate facies accounts 

for the uppermost 6 m and a 10-m bed of gravel within the 

lacustrine facies may be alluvial in part. The Lava Creek B 

ash (0.64 Ma) lies 1 m below the top of the lacustrine facies 

(Izett and Wilcox, 1982; Izett and others, 1992; Lanphere and 

others, 2002). On plate 1 of this report, the lacustrine facies 

of this formation is mapped as sand and silt (ccs), and the 

alluvial facies is mapped as gravel and sand (ccg).

The lacustrine facies grades rapidly from silt and sand in 

the most northerly exposures (secs. O5-n,p and L23-f) to the 

interfingering fine-and-coarse lithologies of the type section 

(Smith, 1964, figs. 14 and 15). Most of the finer facies are tan 

to grayish yellow sandstone and siltstone, with pebble stringers in some zones. A lacustrine origin for all of these sediments is based on (1) their high content of CaCO3, (2) the persistence of bedding planes, (3) the general lack of fragments 

that are several times larger than the average sizes in that layer 

or that exceed 10 cm in maximum dimension, (4) the absence 

of channels, and (5) the continuity of bedding between 

unquestioned fine lacustrine layers and the interbedded coarser 

lacustrine layers. Several zones composed of calcareous tubes 

and nodules resemble fossil soils, but the absence of channeling of other beds at these levels supports the earlier conclusion 

that these features are more likely to be zones of calcified 

water-plant roots (Smith, 1964, p. 42).

The gravel and sand facies of the Christmas Canyon 

Formation represents more than 90 percent of the exposures 

of this formation shown on plate 1. In well-exposed sections, 

which may be as much as 15 m thick, poorly sorted, coarse to 

very coarse sand constitutes the moderately indurated matrix. 

This matrix is found in two colors—the more abundant is 

yellowish brown (10YR6-8/2-4), the less abundant is pale red 

(10R5-6/2-4). Conflicting evidence was noted as to their stratigraphic sequence; there may be more than one layer of each. 

Angular to subrounded pebbles, cobbles, and boulders make 

up 5-50 percent of these rocks (fig. 4). Most pebbles and some 

cobbles are angular to subangular, but boulders are generally 

more rounded. A strongly developed calcic soil is found on 

both exposed and buried surfaces of this unit. It consists of a 

reticulated network of calcite veins, 2-5 cm thick, that extends 

downward as much as 2 m. The matrix material is extensively 

altered to clay. Samples of this clay, from an exposure of the 

soil where it is overlain by basal beds of the Searles Lake 

Formation (sec. I32-r), were studied by R.L. Hay, who writes 

(written commun., March 1989):

The clay is a green (5GY4/2) illite that meets most 

of the criteria for glauconite * * *. The tetrahedral 

sheet in the green illite is almost at the boundary 

between celadonite and glauconite. The (060) d 

spacing is 1.514Å, which falls in the range 1.510-

1.517 accepted for glauconite, but the Fe/Al ratio 

is too low. It can be called a glauconitic illite. * * * 

The green illite is presumably the reaction product 

of pedogenic clay, most likely montmorillonite, with 

alkaline pore fluid from overlying sediments [that 

are lateral equivalents] of the Bottom Mud. Much of 

the Fe in glauconite is very likely from the isovolumetric alteration of magnetite to porous hematite, 

which releases considerable Fe to solution.

Additional data on the implications of the δ18O in these 

clays was later presented by Hay and others (1991, p. 90).

A diagnostic fragment type in the Christmas Canyon 

Formation is vesicular basalt that was derived from the Black 

Hills, 5 to 15 km south of the area of plate 1, and the presence 

of these fragments was the criterion used in identifying this 

Figure 4. Outcrop of gravel facies of the Christmas Canyon 

Formation. Cobbles and boulders, composed of vesicular basalt 

and more felsic volcanic rocks, were derived from outcrops 20 

km southeast of this locality, which is in sec. L5-r (pl. 1). Geologic 

pick is 28 cm long.

Stratigraphy and Lithologies of Mapped Units 13
14 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

formation in most areas of plates 1, 2B, and 4. Andesitic and 

dacitic fragments of the types found in the same area further 

indicate this direction of sediment transport to be correct. This 

formation, however, has since been deformed into a series of 

broad folds that trend N. 50° E. and display as much as 100 

m of structural relief. This deformation must have occurred 

during the period since 0.64 Ma, the age of the Lava Creek ash 

(Smith, 1991a, p. 617-621; Izett and others, 1992; Lanphere 

and others, 2002), which lies about 1 m below the basalt-rich 

gravel facies of this formation. The basaltic fragments are 

characteristically 0.1 to 0.5 m across and concentrated in the 

lag gravels on outcrops. In southern Searles Valley, gravels of 

this formation contain basalt fragments throughout an area that 

extends from the south edge of the area of plate 1 to a line that 

is a few hundred meters northwest of Teagle Wash. On plates 1, 

2B, and 4, however, the formation has been extended into two 

areas where basalt fragments are not included. One extension 

is on the flanks of the Slate Range east of Randsburg Wash, 

which appeared justified because both the top and base of those 

gravels lie on grade with the easternmost basalt-bearing gravels 

of this formation. The second area is on the southeast side of 

the Spangler Hills, where the elevations of the top surfaces of 

the gravels included in this formation can be projected to the 

same grades as gravels containing basalt fragments.

The lacustrine facies has been correlated with unit D+E

in the subsurface section beneath Searles Lake (Smith and 

others, 1983, p. 17). That unit is a 61-m-thick body composed 

mostly of calcareous silt and clay representing perennial lakes, 

but it also includes several salt layers that represent desiccation. The correlation is based in part on the similarity in the 

radiometrically and paleomagnetically estimated age of 0.57 

Ma for the top of that subsurface unit and the 0.64 Ma age 

of the Lava Creek B ash near the top of the lacustrine facies 

of the Christmas Canyon Formation at its type section. That 

correlation allows the gravel and sand facies of the Christmas 

Canyon Formation, which overlies the sand and silt facies at 

the type section, to be correlated with the subsurface deposits 

of unit C of Smith and others (1983), a mostly saline layer 

representing desiccation of the lake and alluviation throughout 

the surrounding valley.

Searles Lake Formation

The Searles Lake Formation, a new formation described 

herein (see table 2 for units and subunits of the formation and their correlation), is the outcropping record of the 

uppermost 50 to 70 m of sediments known from numerous 

cores from beneath the surface of Searles Lake, the longest 

of which is 930 m and extends to bedrock. On the basis of 

those cores, lacustrine histories have been interpreted for the 

past 150 k.y. (Smith, 1979, p. 108-112) to 3.2 m.y. (Smith 

and others, 1983, p. 20-22). It is axiomatic that the history of 

lake sedimentation based on the subsurface record must be 

compatible with the history of lake fluctuations derived from 

the outcropping record.

In selecting the stratigraphic limits of this formation, in 

an area that has been the site of a lake during much of the past 

3.2 m.y., I wished to restrict its time frame to a period that was 

dominantly lacustrine and young enough for much of its record 

to be preserved in outcrop. The extensive alluvial gravel of the 

Christmas Canyon Formation and the older gravel unit clearly 

represent a long period of low lake levels. The base of the Bottom Mud, which appears to be the product of a deep perennial 

lake that started filling the basin at 150 ka, is interpreted to 

be the approximate equivalent of the earliest beds of the wellpreserved lacustrine sediments exposed in Searles Valley. The 

lakes responsible for the sediments immediately beneath the 

Bottom Mud, units A and B of the Mixed Layer (Smith, 1979, 

p. 13-15), which represent the interval between about 350 ka 

and 150 ka, are interpreted to have had depths that fluctuated 

between about 130 and 170 ft (Smith, 1979, fig. 32, p. 86). A 

170-ft-deep lake in Searles Valley, whose floor at that time was 

near 1,400 ft elevation, would have deposited all of its highest 

sediments well below the present dry surface of Searles Lake, 

meaning that none could now be exposed.

The top of the youngest of the perennial-lake sediments 

in the valley defines the top of the Searles Lake Formation. 

Correlations between the informally named subsurface units 

and the formally named units and subunits of the outcropping formation are shown in table 3. As discussed in detail 

later, most of those correlations are supported by 14C dates, 

but the most compelling physical evidence is provided by the 

mapped stratigraphy.

The Searles Lake Formation therefore includes all of 

the perennial-lake deposits in Searles Valley that overlie the 

Christmas Canyon Formation and equivalent or older units. 

Alluvial deposits that are interbedded with these lacustrine 

deposits, and inferred upslope correlatives of them, are also 

included in the formation. This formation is divided into seven 

main units, but in no one place are all of them preserved and 

exposed. The type section is designated as the outcrops in the 

Poison Canyon area (pl. 3A) that are south of California Highway 178, in section H24-f (figs. 5 and 6). The 11 undeformed 

beds of the Searles Lake Formation in this 25-m ridge are subunits of only three of the seven mapped units in the formation 

(Smith, 1987, p. 138-141). Supplemental reference sections 

are designated as (1) the southwest-facing outcrops in the 

central part of section H14-r (pl. 3A, fig. 7) and the laterally 

correlative outcrops in the northwest part of section H23-a; (2) 

the deposits exposed in section I8-n (pl. 3A); (3) the sediments 

exposed in the vicinity of section I30-c (pl. 4, fig. 8); and (4) 

the western part of section I32-r (pl. 4, fig. 9). These additional 

sections are described in appendix 1. Together, these five areas 

provide well-exposed strata representing all of the formation’s 

seven units and many of their subunits.

The seven main units of the Searles Lake Formation were 

deposited successively; the undifferentiated gravel unit and 

tufa unit span the formation’s entire depositional period. Four 

of the seven successive units represent times when lakes in the 

valley expanded significantly, and these are named unit A (the 

oldest), unit B, unit C, and unit D. Units representing the three 
Stratigraphy and Lithologies of Mapped Units 15

Table 2. Stratigraphic correlations between units and subunits of Searles Lake Formation shown 

on plates 1-4.

Units and subunits on plate 1 and larger scale maps

Units of 

Searles 

Lake Formation

Searles 

Valley 

(pl.1)

Valley 

Wells 

wash 

(pl. 2A)

Randsburg 

Wash 

(pl. 2B)

Poison

Canyon 

(pl. 3A)

Salt 

Wells 

Valley 

(pl. 3B)

The

Pinnacles 

(pl. 4)

D sd sd

CD scd scd scd

C sc sc sc4

sc3c

sc3 sc3 sc3b sc3

sc3a

sc2 sc2 sc2

sc1d sc1 sc1 sc1

sc1c

sc1b

sc1a

BC sbc sbc2 sbc sbc sbc

sbc1

B sb sb sb62 sb sb6

sb21 sb5 sb5

sb4 sb4

sb1 sb3 sb3

sb2 sb2

sb1 sb1

AB sab sab7 sab sab7 sab

sab6 sab6

sab5 sab53

sab4

sab3

sab2

sab1

A sa sa sa sa4

sa3

sa sa sa2

sa1

1

Subdivision of unit B on plate 2A not correlated with individual subunits in other areas.

2 Only the six subunits in the southeast part of plate 3A are correlated with subunits in plate 4.

3

Subunits sab1 to sab5 in plate 3A are correlated with subunit sab5 in plate 2A.
16 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

intervening periods when the lake underwent partial or complete recession are named with letters assigned to the preceding and succeeding lacustral expansions, namely unit AB, unit 

BC, and unit CD. With two exceptions, these units represent 

the maximum practical subdivision of the Searles Lake Formation where mapped at 1:50,000 scale (pl. 1); the exceptions are 

units A and D, which are divided into two facies on that map. 

In areas mapped in more detail (pls. 2-4), individual units 

have been subdivided into as many as seven subunits, using 

numbers and lower-case letters for successive subdivisions (for 

example, subunit sc3a). The inferred correlations between 

subunits in different areas are complex. Some map units 

assigned the same subunit label are considered correlative, 

some are not; table 2 indicates which correlations are intended.

The thickness of the Searles Lake Formation varies 

greatly. Some of the thickest accumulations of individual 

Table 3. Subsurface stratigraphy of Searles Lake, inferred lake character, and 

correlative outcrop units.

[Data from Smith, 1979, p. 108-112; Smith, and others, 1983, p. 16-18]

Subsurface unit Age1 (ka) Inferred character of lake Outcrop units and

subunits (pl. 1)

Overburden Mud 6.0 (?) Perennial, shallow and saline Unit D (sd, sdg, sds)

Upper Salt 10.5 Desiccating or dry Unit CD (scd)

Parting Mud 24.02 Perennial and deep, followed 

by a shallow stand, then several 

more brief deep stands

Units C, BC, B (sc, sbc, sb)

Lower Salt 32.02 Alternating deep perennial 

lakes and small shallow lakes

Unit AB (sab)

Bottom Mud 1503 Perennial and deep, brief(?) 

periods of intermediate lakes

Unit A (sa, saa)

Unit A + B 3104 Perennial, intermediate to 

shallow depths

ccg, og

Unit C 570 Dry, briefly perennial ccg, og

Unit D+E 1,000 Mostly perennial, intermediate 

depths

ccs, ot (?)

Unit F 1,280 Perennial, deep ccs, ot (?)

Unit G 2,040 Perennial, intermediate depths, 

periodically desiccated

?

Unit H 2,560 Dry, playa ?

Unit I 3,180 Perennial, deep QTs (?)

1

Age is for base of unit.

2

Stuiver and Smith (1979, p.74) estimated these horizons, using 14C methods, to be 24.0 ka 

and 32.5 ka; Peng and others (1978, table 5) determined average corrected 230Th ages for these 

horizons of 24.5 ka and 32.0 ka.

3

Estimated by Smith (1979), by extrapolation of 14C-determined sedimentation rates, to be about 

130 ka. U-series age determined by Bischoff and others (1985, fig. 2) may confirm that estimate, 

but considerations described in text favor the 150 ka age.

4 Bischoff and others (1985, fig. 2) date this horizon as greater than 0.33 Ma.

units or subunits occur where bars formed. Where blanket 

sedimentation took place, however, the thickest deposits occur 

in the area of the paleolake that bordered the inlet, where 

the main volume of water entered Searles Valley from China 

and Owens Lakes and the Owens River (fig. 1B). This region 

extends from Salt Wells Valley (pl. 3B), through Poison 

Canyon into the area to its east (pl. 3A). It was both a “clastic 

delta,” as sediment from upstream drainages flowed into the 

quiet body of water and settled, and a “chemical delta,” as 

dissolved Ca and HCO3 entered the basin, mixed with highpH water of the lake, and precipitated as calcite, aragonite, 

and possibly dolomite. Parts of the paleolake that received 

water from major local drainages in the northern and southern 

parts of Searles Valley (fig. 1B) had smaller deltas, and some 

evidence of more calcareous deposits in these areas is found. 

Parts of the paleolake that received drainages from single, 
Figure 5. Type section of the Searles Lake Formation along south side of Poison Canyon Amphitheater 

(pl. 1, sec. H24-f; see also pl. 3A). The lower 18 m of the section described in figure 6 is along right side 

of reentrant in lower slope (right arrow); remaining section shown in figure 6 is exposed below skyline 

in left quarter of photograph (left arrow). View toward south.

on older alluvial gravel, where available wave energy removed 

all fragments smaller than a certain size, the observed minimum sizes of the remaining fragments decrease progressively 

with decreasing age. For example, in the same part of the 

basin, erosional shorelines correlative with unit A may include 

no clasts smaller than 30 cm, those correlative with unit B will 

have no clasts smaller than 15 cm, and those correlative with 

unit C will have no clasts smaller than 5 cm. This progression 

allows the ages of lacustrine gravels and shorelines that cannot 

be traced directly into a recognizable stratigraphic sequence to 

be tentatively correlated with one unit.

The most reliable criteria for correlating sediments 

between separate areas are related to lake-water chemistry, 

which generally is a basinwide characteristic. Studies of 

circulation and mixing rates of dissimilar waters in lakes show 

them to be generally sufficiently rapid for a lake, or each layer 

in a stratified lake, to approach compositional homogeneity 

more rapidly than evaporation or other processes can produce 

compositional diversity (Hutchinson, 1957, p. 282-289, 297; 

Friedman and others, 1976, p. 506). In lakes the size of Searles 

Lake, when they are full, one to three weeks would have been 

adequate for a water mass to traverse the entire periphery 

of the main body of the lake, a distance of 100 to 150 km. 

Hutchinson (1957, p. 227, table 21), using one of many available models, calculates current velocities in an unstratified 

lake by assuming a 100-m-deep lake and wind velocities of 

30 and 75 km/hr. Respective current velocities at the surface 

would be about 15 and 32 km/day, and at the bottom 5 and 

12 km/day. The slowest of these would require only 20 days 

to travel 100 km within a lake, mixing with other lake waters 

along the entire route.

short canyons have markedly less chemical component 

in their sediments, which are composed primarily of 

sediment from those and nearby canyons.

Criteria for Correlating Outcropping Units

Many outcrops of lacustrine sediments look 

similar to each other. The sizes of clastic fragments 

deposited at any one site primarily reflect the intensity 

of the wind-driven bottom currents in that part of the 

lake. Fragments that were too large (or heavy) for a 

given current strength were not transported into that 

area, and fragments that were too small (or light) continued being transported to other areas characterized by 

lower current strengths. Inasmuch as all ancient lakes 

of significant size and depth in this basin had areas 

somewhere on their floors that were characterized by 

any given bottom-current strength, it is not surprising 

that lacustrine clastic sediments deposited during one 

lake cycle are similar to clastic sediments deposited 

during other lake cycles.

In Searles Valley, however, there is evidence that 

the maximum wind energy during the times of most 

intense erosion of shorelines, and rapid transport of 

material to gravel bars, changed with time. Where 

lacustrine gravels representing two or more map units 

coexist, the older unit contains larger fragments than 

the younger unit. This applies to any combination of 

units A, B, C, and D. Study of erosional shorelines 

leads to the same conclusion. Along shorelines carved 

Stratigraphy and Lithologies of Mapped Units 17
18 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

sab6

 Pebbly sand, tan, top surface covered by scattered lag gravel and an incipient 

soil; fair to poor sorting, beds locally well developed; basal contact sharp

 UNCONFORMITY—caused by subaerial erosion

 Silt, mostly laminated or thinly bedded with as much as 1 m of very fine sand at 

base; basal contact sharp

 Sand, fine to coarse, tan or pinkish-tan; locally contains orange-stained pebbles 

reworked from subunit sab7, fragments of nodose tufa and older lacustrine 

clay; a few molluscs; basal contact gradational

 Clay and silt, mostly laminated, weather to buff-colored surfaces; 1 m above 

base is a 3-cm-thick pinkish-tan layer of nodose tufa; about 2 m above the base 

is a discontinuous thin layer of orange-weathering tuff(?); gypsum crystals 

locally common; basal contact sharp

 DISCONFORMITY—caused by sublacustrine erosion

 Sand, generally coarse to very coarse, mostly poorly sorted, especially in upper 

part, contains pebbles 2–3 cm in diameter, locally includes 1-m bed of 

calcareous silt near middle of unit; in this area, sand is tan to slightly orange, 

but in area just west and south, unit is conspicuously orange and its uppermost 

zone is characterized by conspicuous lag gravel; basal contact gradational

 Silty sand and sand, lower 0.5–1 m is fine grained more calcareous, and lighter 

colored; unit characterized by discontinuous beds 5–50 cm thick; tan to very 

pale orange, weathers with puffy surface; in this area has sink holes as much 

as 3 m deep; a small number of snails and clams noted; contact with underlying 

unit generally sharp

 Sand, fine in lower part and coarse in upper part; pebbles 2–3 cm across locally 

common, including fragments of nodose tufa; bedding locally deltaic; molluscs 

scattered throughout, abundant at top; basal contact gradational in most places

 Silt and very fine sand , calcareous, basal 0.5 m is white laminated marl grading 

up into light-tan, less well bedded silt and very fine sand; about 1 m up from 

base is a thin layer of white nodose tufa; gypsum crystals locally abundant; 

basal contact generally sharp

 Sand, medium to very coarse, local layers of pebbles 2–3 cm in diameter and clay 

fragments as large as 10 cm; generally horizontally bedded but locally cross 

bedded, especially in lower half; tan orange to orange; notable concentrations of 

molluscs in upper 0–2 m; basal contact gradational

 Silt to very fine sand, some clay; faintly bedded; weathers to light tan-green 

puffy surface, contains a few molluscs; basal contact sharp, locally thins to a 

single white layer

 Silt and sand; lower half silt and very fine sand, calcareous, faintly bedded, 

weathers to light-tan puffy surfaces; upper half medium to very coarse sand 

containing pebbles 2–3 cm in diameter, cross bedded, with a 2-cm orangestained zone at the top; in places, top of unit represented by a conspicuous lag 

gravel composed of dark angular fragments of hypabyssal rocks; base not 

exposed

4

3

2

1

5

6

7

25

20

15

THICKNESS, IN METERS

10

5

0

BC

B

8

9

10

BREAK IN SECTION (see fig.5)

Unit and

 subunit Description

CD

scd

C

sc3

sc2

sc1

AB

sab7

sab5

sab4

sab3

sab2

sab1

scd

sc3

sc2

sc1

sab7

sab6

sab5

sab4

sab3

sab2

sab1

Figure 6. Stratigraphic column for the type section of the Searles Lake Formation (location: south side of Poison Canyon 

Amphitheater, pl. 1, sec. H24-f; see also pl. 3A), showing units and subunits and their lithologies. Numbers refer to fossil-collection horizons (table 7).
In Searles Lake, two aspects of lake-water chemistry 

became expressed in the sedimentary record. The first of these 

is that the lake water was notably alkaline most of the time, an 

inference based on the composition of the salt layers and their 

interstitial brines (Smith, 1979, tables 4, 9, 14, and 16). When 

voluminous inflow brought large amounts of Ca into the basin, 

all deposited sediments contained notable concentrations of 

calcite or aragonite. When inflow was reduced, allowing the 

salinity to increase, the calcareous sediments had pore waters 

containing higher percentages of Na, SO4, or Cl; those sediments now contain trace to moderate amounts of gypsum, 

thenardite, or halite. Gypsum may have extracted some of its 

Ca from the enclosing sediments; thenardite and halite probably crystallized after burial from the trapped interstitial brine.

The second indicator of lake-water chemistry stems 

from the creation of a stratified lake, which happens when a 

body of saline, relatively dense lake water becomes covered 

with a layer of fresh, less dense water resulting from seasonal 

precipitation, melting of glacial ice, or longer term climatic 

changes (Smith, 1966b, p. 173-174). This structure requires 

that a seasonal or climatic succession first produced a lakecontraction stage that concentrated the dissolved solids to 

form a relatively dense water body; this stage then had to be 

followed by lake expansion caused by an increased fresh-water 

inflow volume sufficient to create the stratified lake’s upper 

layer. Although some carbonate crystallization also occurred 

as a result of evaporation, most crystallization probably 

resulted where mixing took place along the plane between the 

two parts of the stratified water body. This process, however, 

would soon deplete those waters of the crystallized components unless circulation were maintained in both layers. While 

circulation velocities and mixing rates in the lower layers of 

stratified lakes are difficult to determine, studies show that 

such circulation does occur. Several models and calculations 

(Hutchinson, 1957, p. 282-285) conclude that winds produce 

a sloping of the plane separating two stratified layers and that 

the “bottom” currents of the upper layer produce drag on the 

“surface” of the lower layer, causing circulation throughout 

the lower water body as well.

Stratification of this type is likely to be a basinwide 

phenomenon, and it provides a mechanism to account for 

several types of observed evidence that are otherwise difficult to explain. First, the mineralogy of the subsurface saline 

layers indicates that the dissolved components of the enlarged 

lakes included substantial percentages of Na and CO3 (Smith, 

1979, p. 84-96), so a lake-water pH of at least 9 is likely for 

all except the most dilute stages. When more Ca was introduced with each annual influx of fresh water, most of it should 

have precipitated as aragonite or calcite near the inlet, where 

the fresh water first mixed with the high-pH water, to make a 

“chemical delta.” Some stratigraphic units, however, have a 

high CaCO3 content over most of the basin, raising questions 

as to how the Ca avoided precipitation at the inlet. Postulating a stratified lake, with a layer of fresh, Ca-bearing water 

sbc

sb4

sb3

sb2

sb1

Figure 7. Outcropping subunits sb1 through sb4 and unit BC (sbc) of the Searles Lake Formation. Unit BC

here consists of windblown sand; the subunits below it are lacustrine deposits. View toward north; location: 

plate 1, sec. H14-r.

Stratigraphy and Lithologies of Mapped Units 19
20 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

that could spread throughout the basin, solves this problem. 

Later, the Ca in the surface layer precipitated when that layer 

warmed, evaporated, or mixed with the underlying layer along 

the chemocline. Postulating a stratified layer also explains the 

apparent cycles of carbonate deposition, expressed as alternating layers of white and greenish laminae in both subsurface and outcrop samples (fig. 10). Smith (1979, p. 79-80) 

calculates the amount of annual CaCO3 deposition required 

to produce the amounts reported by analyses of subsurface 

laminated sediments and finds the amounts plausible. These 

laminae could have been caused by the seasonal nature of 

either the snowpack melting in early summer or the evaporative removal of the surface-water layer during summer and 

autumn. The fresh upper layer of a stratified lake would 

provide protection over much of its floor from strong winddriven currents that the preservation of fine—sometimes 

paper-thin—laminae requires, and a saline lower layer would 

tend to exclude burrowing organisms that would also disrupt 

the laminae.

Stratification was not, however, an ever-present feature 

of the lake structure. Many outcrop units are unlaminated, and 

other units, in areas away from the inlet, are characteristically 

less calcareous, a property that is expressed by darker outcrop 

colors and orange or tan hues. The evidence for or against stratification, therefore, becomes a basinwide criterion that helps 

identify the unit to which isolated outcrops should be assigned. 

Where sequences of units are present, sequences of paleolimnological reconstructions help test alternative correlations.

Another criterion used to identify units in the field is the 

type and abundance of tufa found as fragments, interbedded 

layers, or buried where attached to a substrate. As noted in the 

section on tufa of the Searles Lake Formation, Scholl (1960, 

p. 416-421) divided the tufa types in Searles Valley into seven 

CD

C

Figure 8. Exposure of Searles Lake Formation unit CD (about 75 

cm thick, with moderately developed calcareous soil on top), here 

underlain by unit C (about 40 cm of laminated lacustrine sediment) 

and overlain by 10 cm of windblown sand and colluvium. Location: 

plate 1, sec. I30-c.

Tufa

ccg

sa4

sa3

sa2

sa1

Figure 9. Exposure of subunits sa1, sa3, and sa4 of Searles 

Lake Formation totaling 8.6 m in thickness, resting on Christmas 

Canyon Formation unit (ccg), and overlain by tufa (see appendix 

1, reference section I32-r). Subunit sa2, as much as 0.5 m thick 

elsewhere in this wash, is here represented only by a very thin 

layer. Tufa above subunit sa4 (dark gravel) 14C dated as 13,700±50 

yr B.P.; two 14C dates on marl immediately under sa4 gravel and 50 

m to left of photograph area, which are considered erroneous, are 

21,910±100 yr and 21,330±80 yr.
groups, which have been combined in this report into two 

types, the relatively dense and structureless “lithoid” variety 

and the nodular or lobate “nodose” variety. The period of most 

intense growth of nodose tufa was at the end of deposition of 

unit B, and unit BC in many areas is identifiable because it is 

a lag gravel composed almost entirely of fragmented nodose 

tufa (fig. 11). Apparently, large quantities of this recently 

formed tufa were eroded and spread by strong currents over 

much of the south third of Searles Valley, making this horizon 

into a time line.

Fossil soils, along with stratigraphy, are used to identify 

certain alluvial units. These soils were developed on four 

units in the Searles Lake Formation—on an alluvial layer 

within unit A and on the tops of units AB, BC, and CD. The 

soil within unit A characteristically has a densely reticulated 

calcite zone as much as 1 m thick and a 10- to 20-cm-thick 

zone of gray-orange coloration at its top (fig. 12A); except 

for the grey-orange zone, it is similar to the soil developed on 

the Christmas Canyon Formation and older gravel. Although 

not always a “soil” in the pedogenic-profile sense, a zone 

believed to represent a fossil desert varnish on the top of unit 

AB indicates a period of subaerial exposure as does a soil; the 

original iron oxide component of the desert varnish has now 

mostly hydrated to produce limonite or geothite, minerals with 

distinctive orange to brown colors that now characterize this 

horizon. However, pedogenic calcareous concentrations are 

locally found in this zone (fig. 12B), thus supporting its designation throughout the region as a fossil soil. The soils on units 

BC and CD characteristically consist of a zone of dispersed 

calcareous pods, 1-2 cm in diameter, and both the pods and 

matrix material are infiltrated by a network of hairline, pale 

red (10R5-6/2-4) marks of indeterminate origin. The soil on 

unit BC, however, is more extensively developed, contains a 

small amount of clay, and generally extends downward about 

Figure 10. Laminated sediments of subunit sc1 of Searles Lake Formation (knife is 9 cm long). Thin 

white layers are aragonite laminae, interbedded with dark gray silt and clay (top and bottom). Location: plate 1, sec. I23-r.

Stratigraphy and Lithologies of Mapped Units 21
22 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

B

C

30 cm (fig. 13A), whereas the soil on unit CD contains 

virtually no clay and most commonly extends downward 

about 20 cm (fig. 13B).

The lithologic characteristics used in the field to identify 

the major units of this formation are summarized in table

4. During mapping, outcrops that were small or isolated 

from areas having convincing stratigraphic sequences 

were assigned to units on the basis of these criteria. A few 

sedimentary units with apparently reliable 14C dates were 

assigned to the appropriate map unit on that basis, providing the lithologic and stratigraphic evidence did not contradict that assignment. As discussed later, 14C ages on these 

sediments were used cautiously. Only where two or more 

dates on different materials from the same unit were substantially the same, and where lithologic and stratigraphic 

criteria were not diagnostic, were stratigraphic assignments 

based on dates.

Criteria for Correlating Outcropping Units with 

Subsurface Units

Correlations between outcrop and subsurface deposits 

are based on four types of physical evidence, supplemented 

by radiometric ages. The physical evidence:

(1) When tracing outcropping units toward Searles 

Lake, each unit reaches a point where it becomes covered 

by younger deposits, which themselves eventually disappear 

beneath the dry-lake surface. The succession of outcrop units 

can then be correlated with the succession of subsurface units. 

For example, along the northeast, south, and southwest edges 

of the now-dry lake, the sediments of units C and CD can be 

traced to the edges of the lake and can be seen disappearing 

under sediments of unit D which, in the valley center, is the 

Overburden Mud in subsurface stratigraphic terms (table 3). 

Around the flanks of the basin, all units older than unit C are 

observed being covered by successively younger units when 

traveling lakeward.

(2) The lithologies of the outcrop units help verify these 

correlations by being geologically reasonable equivalents of 

the subsurface deposits. For example, alluvial gravels must be 

the upslope lateral equivalents of shallow- or dry-lake stages. 

Similarly, greenish-hued, high carbonate or laminated lake 

deposits found at high levels around Searles Valley are reasonably correlated with mud layers having similar characteristics 

in subsurface records, as both indicate perennial-lake depositional environments.

(3) The apparent stability in the levels of lakes responsible for a succession of sediments also provides a basis for 

their correlation. For example, outcrops of thick perenniallake deposits are reasonable correlatives of thick subsurface 

Figure 11. Outcrop showing horizontal contact between units B and C of the Searles Lake Formation. 

Units B and C together are here about 3 m thick. Unit BC is represented by a thin lag gravel bed (arrow) 

composed of white nodose tufa fragments. Many tufa masses, which were formed near the close of unit 

B deposition, were fragmented and spread by waves of the retreating lake responsible for unit B or the 

advancing lake responsible for unit C. View to south; location: plate 1, sec. L5-j.
A

B

Figure 12. Older fossil soils of the Searles Valley area. A, Exposure of two fossil soils. Lower calcareous 

soil (below sharp end of pick) is on Christmas Canyon Formation; it is about 1 m thick and characterized 

by white pods (plus horizontal and vertical stringers) of calcite-rich material and a gray-green matrix. 

Upper calcareous soil (below top of exposure) is on alluvial unit sa2 of the Searles Lake Formation; it is 

similar in thickness, mineralogy, and structure to lower soil, except that the matrix of top 50 cm is reddish 

brown, a characteristic of this soil. Pick handle is 28 cm long. B, Detailed view of fossil soil on top of unit 

AB of Searles Lake Formation. This soil is very commonly characterized by a strong orange or orangebrown zone (here, 5 cm thick) at the top, less commonly also by white calcareous pods as seen here. 

Ruler is 12 cm long.

Stratigraphy and Lithologies of Mapped Units 23
24 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

A

BB

A

B

Figure 13. Younger fossil soils of the Searles Valley area. 

A, Fossil BC soil showing white calcareous pods with pink 

coloration on them as well as on pebbles and matrix. Soil 

here is about 40 cm thick; top is at undissected surface, 5 cm 

above upper end of 30-cm-long ruler. Some pedogenic clay is 

present in upper 30 cm of the soil. B, Fossil CD soil showing 

small calcareous pods in lower part of preserved soil profile, 

which is here about 20 cm deep (ruler is 15 cm long). Several 

characteristics of CD soil are similar to those of the BC soil, 

except that the younger CD soil is thinner, the calcareous 

pods are smaller, the pink coloration is less intense, and 

pedogenic clay is present only in very small amounts.

units composed of marl or fine clastics, as both indicate long 

periods of deposition in a deep lake. Outcrops of alternating, relatively thin, fine- and coarse-clastic subunits are 

reasonable correlatives of subsurface sequences made up of 

alternating thin layers of marl and salt, as both indicate a 

fluctuating lake history.

(4) As noted earlier, the abundance of carbonate in deposits far from the inlet and the presence or absence of laminae in 

these deposits are interpreted to be evidence of the presence or 

absence of stratification in the lake. Because outcrop units B

and C both display laminae, the deposits of units B, BC, and 

C are correlated with the subsurface Parting Mud, the upper 

part of which is prominently laminated (Smith and Haines, 

1964, fig. 14). Deposits of subunits sc1 and sc3 of unit C are 

consistently characterized by fine, light-colored or white (aragonite) laminae, whereas deposits of unit B and its subunits 

may be finely or coarsely laminated or unlaminated, and the 

laminae may be white, gray, light orange, or various shades 

of green. Fine laminae couplets in outcrops are typically 1 to 

5 mm thick (fig. 10), and coarse laminae couplets may be as 

thick as 10 to 40 mm. Further corroboration of the proposal 

that the presence, absence, and character of laminae represents 

a reliable basis for making correlations between exposures 

and subsurface deposits is presented later in the section on 

Paleolimnology, Low-Energy Environments, where their use 

in reconstructing changes in lake levels is also explored.

Criteria for Identifying Disconformities

As a result of the numerous oscillations in lake level 

during the period that the Searles Lake Formation was being 

deposited, both alluvial and lacustrine deposition was interrupted many times, each time introducing the potential for 

a disconformity accompanied by a loss of section. A disconformity is clear where one or more units or subunits are 

found to be missing. Where no units are lost, however, only 

differences in thickness would document a loss of section, 

but lacustrine sediments around the edge of a basin vary 

greatly in thickness over short distances, making that test 

unreliable. Other evidence, such as angular discordance of 

superimposed beds or channeling of the underlying sediment, 

is locally observed.

In mapping units and subunits of the Searles Lake 

Formation, several sequences composed solely of lacustrine 

sediments, which initially appeared to represent “layer cake” 

stratigraphy, were eventually found to include major hiatuses 

that were overlooked at first because they were not accompanied by any geological criteria of erosion. These were 

suspected of being the result of sublacustrine erosion. The 

mechanism inferred for this process is as follows (fig. 14): 

During the retreating stage of the lake, when the deep-water 

sedimentation ceased, nearshore processes began depositing 

a sandy layer that covered the deeper water sediments. As the 

lake continued to retreat, wind-driven currents reworked these 

unconsolidated shallow-water sediments, producing structures 

characteristic of that environment. At any given time, the 
Fine facies Coarse facies

Unit Lithologic

character

Color range

(outcrop dry)

Tufa type and form

D Silt, massive, “puffy” 

surface on outcrop, 

cemented by halite 

in fresh exposures, 

white efflorescence, 

lacustrine

Light brown (5YR6/4)

to grayish orange (10YR7/4)

Angular pebbles, grayish orange 

mixed with silt, lacustrine and alluvial

None

CD Pebbly sand, soft, 

alluvial

Dusky yellow (5Y6/1) 

to grayish orange pink (5YR7/4)

Pebble, cobble, to small-boulder 

gravel, fine- to medium- sand matrix, 

massive, soft, alluvial, fossil soil on 

top 20 cm thick

None

C Silt, very calcareous 

and gypsiferous, thinly 

laminated, well indurated, lacustrine

Dusky yellow (5Y6/2)

to moderate greenish yellow 

(10Y7/2)

Pebble gravel, rounded to subrounded,

lacustrine, moderate varnish

Nodose tufa, as 

growths and fragments, tufa layer near 

base

BC Sand, subangular, 

fairly well sorted and 

cemented, cross-bedded, lacustrine

Grayish orange pink (5YR7/2) 

to grayish orange (10YR7/4)

Angular alluvial rubble near bedrock 

outcrops, gray to dark brown, fossil 

soil 30 cm thick with calcareous pods 

1-2 cm in diameter

Abundant fragments of 

nodose tufa

B Silt to sand, moderately well sorted, less 

calcareous than unit 

C, coarsely laminated 

or unlaminated, high 

percentage of greenish 

mica, lacustrine

Light olive gray (5Y5/1) 

to moderate greenish yellow 

(10Y7/2)

Pebble to cobble lacustrine gravel, 

very calcareous, rounded, heavy 

varnish

Abundant growths of 

nodose tufa, medium 

to dark brown

AB Alternating silt and 

sand, silt locally 

calcareous near base, 

sand commonly crossbedded

Pale brown (5YR5/4) 

to grayish orange (10YR7/6), 

distinctly orange at top of unit

Angular alluvial rubble near bedrock 

outcrops, very dark brown varnish 

with orange hues, fossil “soil” most 

commonly an orange zone 5-30 cm 

thick (weathered desert varnish?), locally contains pedogenic calcite

Rare, thin layers, both 

lithoid and nodose 

types

A Silt to coarse sand, 

silt is very calcareous, coarse sand well 

cemented by calcite, 

indistinct bedding

Moderate yellow (5Y7/1) 

to pale greenish yellow (10Y8/2)

Cobble to boulder gravel, lacustrine, 

angular to slightly rounded, heavy 

varnish; fragments in alluvial bed(s) 

angular to slightly rounded; calcareous 

soil, about 1 m thick, present within 

unit, with orange zone at its top

Lithoid tufa, massive 

deposits, forms bulk 

of The Pinnacles and 

tufa concentrations 

near highest shoreline, 

grayish orange

Table 4. Generalized field characteristics of major units of Searles Lake Formation, primarily in the Poison Canyon area (pl. 3A) 

and The Pinnacles area (pl. 4).

strength of bottom currents was fairly uniform over areas that 

lie at about the same depth, and this produced a shallow-water 

erosion-and-redeposition surface that was notably planar. 

If the lake retreated below the level of the outcrop being 

observed, subaerial erosion processes began to alter this planar 

surface. Later, when the lake again expanded and its waters 

readvanced, a second episode of shallow-water erosion-anddeposition took place, reworking the upper part of the soft, 

subaerially eroded older beach sediment, usually obliterating 

any small channels on its upper surface that had developed 

subaerially. As the lake deepened and lake-floor currents 

diminished, shallow-water sand began to accumulate on this 

planar surface. Later, deep-water sedimentation returned.

The most distinguishing characteristics of sublacustrine erosion are planar horizons at the base of the sediments 

representing the return of lacustrine deposition and an absence 

of subaerial channel structures. These planar surfaces may be 

conformable or uncomformable relative to the dips of beds 

deposited during the previous cycle. In either case, the uncomformity represents the zone of interrupted deposition and possibly missing sediments. If it is comformable, the uncomformity generally lies within the coarse-grained units composed 

Stratigraphy and Lithologies of Mapped Units 25
26 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

of shallow-water sand or gravel rather than at the boundaries 

between fine- and coarse-grained lithologies (fig. 15). Many of 

the sand units in the Searles Lake Formation display a change 

in bedding, color, or fragment size near the middle of the bed, 

and this probably represents the actual hiatus (fig. 15). Where 

the planar sublacustrine erosion surface is disconformable, the 

sand that represented the retreating lake is lost.

Good examples of sublacustrine unconformities are found 

in the Poison Canyon area (pl. 3A). One is found where unit C

rests disconformably on subunit sab7 of unit AB at the type 

section for the Searles Lake Formation (fig. 6), on the south 

side of the amphitheater. Two more unconformities are found 

on the north side of the amphitheater—one is where subunits 

sb1, sb2, sb3, and sb4 of unit B are truncated by a planar 

surface that was created by the readvance that led to the deposition of unit C (sec. H14-r); the other is where subunits sab4, 

sab5, sab6, and sab7 of unit AB are missing because they 

were truncated by the readvancing lake that deposited subunit 

sb5 of unit B (sec. H23-c, f). In a broad area between the east 

end of the Spangler Hills and the railroad tracks (pls. 3A and 

4), deposits of unit D rest directly on an originally near-planar 

surface cut on units B and C. On the east edge of Teagle Wash 

(sec. L8-k), erosion has exposed a vertical cross section clearly 

Marl Sand Marl

Outcrop level

ELEVATION

TIME (AND STRATIGRAPHIC SEQUENCE)

ELEVATION

TIME (AND STRATIGRAPHIC SEQUENCE)

Alluvial

deposition

(or erosion)

Lacustrine

deposition

Lacustrine deposition only

Lacustrine

deposition

Outcrop Lithology

Lake level

Lake level

Marl Sand Marl

Outcrop level

Depth of 

chemocline or

wind-driven 

currents

Outcrop Lithology

Lake level

Lake level

A

B

Depth of chemocline 

or wind-driven currents

Figure 14 Diagrams showing inferred depositional history recorded by a marl-sand-marl sequence of outcropping 

deposits from a lake of varying level. Time and stratigraphic 

sequence progress toward the right. Both A and B start and 

end with deposition of marl in water lacking bottom currents 

strong enough to transport sand. This condition could result 

from (1) the water depth being or becoming great enough to 

reduce wind-driven bottom currents to negligible velocities or 

(2) the chemocline in a stratified lake being or rising above the 

outcrop elevation, effectively insulating the bottom sediments 

from the effect of winds. A lithologic contact resulting from a 

rising chemocline would be a sharp one; a contact resulting 

from depth change in an unstratified lake would be a gradational one, because bottom currents would vary in strength 

as storms came and went. A, The inferred sequence as the 

lake level falls, eventually below the elevation of the outcrop, 

and then again rises to become a deep, possibly stratified, 

lake. This makes the resulting sand bed a potential record of 

three successive events: (1) lacustrine sand deposition in the 

shallow water around the edge of a falling lake, (2) subaerial 

alluvial deposition or subaerial erosion, and (3) lacustrine sand 

deposition in the shallow water around the edge of a rising 

lake. If the alluvial deposits or subaerial erosion channels of 

step 2 were removed by sublacustrine erosion as the lake 

reexpanded, the sand layer would only record lacustrine deposition, with a hiatus in deposition occurring somewhere near 

its middle. B, Sequence as in A, except that lake level does 

not fall below outcrop level, so the resulting deposit is entirely 

lacustrine. The low point of the lake-level oscillation would, 

however, again be near the middle of the sand layer.

showing the unconformable relations and the planar surface 

cut by this sublacustrine-erosion process (fig. 16, pl. 4).

Radiometric Ages of Exposed Units

The estimated ages of stratigraphic units in the Searles 

Lake Formation are primarily based on correlations between 

each unit or subunit and the equivalent subsurface deposit, 

which includes the Bottom Mud and all overlying units. These 

subsurface deposits are the sources of 30 U-series dates on 

salts and more than 50 finite 14C dates (that is, not open-ended 

minimum ages) on lacustrine organic carbon that I consider to 

be less susceptible to large errors than are radiometric dates on 

inorganic carbonates and many other outcrop materials. The 

stratigraphy of the subsurface deposits is also more straightforward than that of the outcropping sediments. Confidence 

in the subsurface age control also stems from the observations 

that subsurface dates on organic carbon from one core closely 

resemble dates from carbon in the same unit or horizon in 

another core obtained several kilometers away and that the ages 

become younger moving stratigraphically up through the section and rarely show reversals of more than a few hundred years.
Figure 15. Lacustrine sand facies of unit BC of the Searles Lake Formation (dark, partly cross-bedded 

interval), here exposed between lighter colored, finer sediments of subunits sb6 (below) and sc1

(above). Lower half or two-thirds of sand bed is attributed to sedimentation during the retreat of lake that 

deposited unit B, and upper part of sand bed is attributed to sedimentation as lake was readvancing, 

eventually to deposit sediments of unit C (see fig. 14). Alluvial deposits mapped as part of unit BC are 

present 40 ft (12 m) below the elevation of this outcrop, so a break in lacustrine deposition had to occur 

at this level. This break is inferred to be either at top of uniform zone of foreset beds making up lower half 

of sand unit, or at the higher horizon (aligned with 18-cm white scale) where horizontal bedding begins. 

Searles (dry) Lake is to the left; location: plate 1, sec. I19-f.

The base of the oldest outcrop unit included in the Searles Lake Formation is correlated with the base of the Bottom 

Mud, which is now considered to have an age of about 150 

ka. The earlier age estimate of about 130 ka for this contact 

(Stuiver and Smith, 1979, p. 75) has been revised in view 

of two studies of Searles Lake cores, the U-series dating by 

Bischoff and others (1985, fig. 2) and the combined radiometric-date and sedimentation-rate estimates by Jannik (1989, 

figs. 25, 26). This revised age is about 10 k.y. older than the 

midpoint age of a major climatic change indicated by a U/

Th-dated isotopic study of calcite veins in an area about 50 

km east of Death Valley (Winograd and others, 1988, fig. 4; 

Winograd and others, 1992, p. 257, fig. 4) and the Vostok ice 

core from Antarctica (as interpreted by Winograd and others, 

1992, p. 257, fig. 4, and footnote 14).

Radiocarbon dates were determined on various types of 

material from outcrops in Searles Valley (table 5; fig. 17). The 

samples were collected from below the weathered zone and 

carefully checked with a hand lens for secondary carbonate. 

Samples of marl were collected from zones far enough in from 

the outcrop face to be free of any weathering cracks, veins, or 

other signs of penetration by postdepositional waters. In the 

laboratory, all 36 tufa samples, 10 of which were examined in 

thin section and confirmed to be free of recrystallized carbonate, were crushed until the fragments were 3 to 5 mm in 

diameter. Most were also studied using X-ray diffraction; contaminated tufa samples composed of aragonite can be identified 

by the presence of detectable percentages of calcite, which is 

almost always the secondary carbonate. These, as well as samples containing oolites, mollusks, or ostracodes, were soaked 

and disaggregated in water (using an ultrasonic bath if needed), 

placed in screens finer than the material being purified, and 

washed with a high-velocity water spray until all attached 

sediment was removed. After drying at room temperature, the 

sample material was hand picked until believed to be pure. 

Organic carbon was recovered by digesting the carbonaceous 

marl or tufa in HCl until no carbonate remained. All carbonate 

samples, except marl, were partially dissolved in acid before 

the carbonate used for analysis was extracted. Neither wood 

nor charcoal suitable for 14C dating was found in outcrops.

Stratigraphy and Lithologies of Mapped Units 27
28 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Figure 16. Photograph and diagram of outcrop showing sublacustrine angular uncomformity within Searles Lake Formation. (Note: In 

the early 1980’s, this outcrop was severely eroded by flood waters that moved the face of the lacustrine deposits away from the camera 

position as much as 3 m, so that present outcrop appears different.) A, View of outcrop looking northeast; unconformity is along top of 

beds having orange hues. Note planar form of unconformity surface and lack of channels; outcrop about 10 m high. Location: plate 1, 

sec. L8-k. B, Identification of units exposed in outcrop photograph; see measured section L8-k in appendix 1 for lithologies.

Panamint Range

(Telescope Peak, 3,368 m) Slate Range

BC

sc1 sc2 sc3

B

sab7

sab6

sab5

sab3

Christmas Canyon Formation

Searles

Lake

Formation

Active alluvium

Older alluvium

Sublacustrine unconformity

(lag gravel, orange)

A

B
Stratigraphy and Lithologies of Mapped Units 29

Table 5. Radiometric ages of deposits assigned to the Searles Lake Formation.

[Listed in descending stratigraphic order of unit, within unit by decreasing elevation. Precision of locations indicated by significant figures in latitude and 

longitude estimated when sample was obtained.]

Unit Map location

code Latitude Longitude Elevation(ft )

Sample 

material1

Age2

(yr)

± 

(yr) Laboratory no.3

CD I18-a 35°40.62′ 117°23.06′ 1,690 S (16,200) 300 Y

C K22-e 35°34.68′ 117°27.34′ 2,260 L 17,000 1,000 B90-5 (U) 6

K22-e 35°34.68′ 117°27.34′ 2,2604 L 10,900 40 USGS-28456

M18-g 35°35.2′ 117°16.9′ 2,050 N 12,000 400 W-1317 

H28-d 35°39.4′ 117°28.3′ 2,030 O 11,730 350 W-1327 

L12-n 35°35.8′ 117°18.4′ 1,960 N 12,110 300 W-1325 

H28-f 35°39.2′ 117°28.0′ 1,940 N 12,700 60 USGS-2328A 

H28-f 35°39.2′ 117°28.0′ 1,9404 N 12,910 50 USGS-2328B 

L18-n 35°34.8′ 117°24.0′ 1,935 N 12,200 450 W-1318 

L18-n 35°34.8′ 117°24.0′ 1,9354 C5 11,720 500 W-1418 

C14-f 35°50.8′ 117°18.4′ 1,920 N 14,300 200 USGS-33A 

C14-f 35°50.8′ 117°18.4′ 1,9204 N 12,800 150 USGS-33B 

H23-l 35°39.92′ 117°25.90′ 1,875 S 11,700 160 Y

L7-p 35°35.67′ 117°23.75′ 1,870 O 11,020 400 W-1679 

L7-p 35°36.67′ 117°23.75′ 1,8704 O 11,820 400 W-1680 

H23-j 35°39.84′ 117°25.29′ 1,855 S 14,210 200 Y

C15-r 35°50.4′ 117°18.8′ 1,850 N 13,830 500 W-1893 

C15-r 35°50.4′ 117°18.8′ 1,8504 N 13,650 500 W-1890 

H23-j 35°39.89′ 117°25.27′ 1,845 N 10,430 100 Y

H23-f 35°39.96′ 117°25.85′ 1,840 C5 13,750 160 Y

H23-j 35°39.93′ 117°25.25′ 1,840 N 14,140 120 Y

H24-b 35°40.32′ 117°24.46′ 1,760 N 13,300 500 W-1201 

I32-r 35°37.4′ 117°22.0′ 1,750 N 13,700 350 W-1323 

I18-a 35°40.63′ 117°23.06′ 1,680 C5 13,200 200 Y

I18-a 35°40.63′ 117°23.08′ 1,670 C5 13,350 200 Y

B C3-a 35°52.7′ 117°18.8′ 2,110 Q (9,070) 300 W-1894 

C3-a 35°52.7′ 117°18.8′ 2,1104 M (7,700) 75 USGS-67 

M18-k 35°35.0′ 117°16.9′ 2,040 M 13,635 45 USGS-2521 

M18-c 35°35.3′ 117°17.1′ 2,030 L 21,160 +1,325 B86-38 (U) 

-1,075

M18-c 35°35.3′ 117°17.1′ 2,0304 L 21,000 +2,543 B-86-37 (Pr) 

-2,419

M18-g 35°35.1′ 117°16.8′ 2,020 N 13,520 120 USGS-2320 

H28-f 35°39.10′ 117°28.03′ 1,910 M 15,020 80 USGS-2424 

H28-g 35°39.1′ 117°27.9′ 1,910 M 15,220 100 USGS-2523 
30 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Table 5. Radiometric ages of deposits assigned to the Searles Lake Formation.—Continued

[Listed in descending stratigraphic order of unit, within unit by decreasing elevation. Precision of locations indicated by significant figures in latitude and 

longitude estimated when sample was obtained.]

L8-n 35°35.7′ 117°22.8′ 1,850 O 14,950 500 W-1904 

C15-q 35°50.4′ 117°19.2′ 1,850 N 15,250 60 USGS-2527 

H23-j 35°39.9′ 117°25.4′ 1,850 N 12,965 45 USGS-2526

 B H14-r 35°40.43′ 117°25.32′ 1,840 M 20,210 90 USGS-2321 

L8-n 35°35.6′ 117°22.9′ 1,840 C5 16,970 400 Y

H23-f 35°39.99′ 117°25.85′ 1,830 O 16,820 200 Y

H23-a 35°40.32′ 117°25.48′ 1,830 M 21,020 200 USGS-2425 

H14-r 35°40.39′ 117°25.35′ 1,810 N 22,500 600 W-1324 

I32-r 35°37.4′ 117°22.0′ 1,780 M 24,090 270 USGS-2525 

H23-b 35°40.28′ 117°25.48′ 1,780 M (30,510) 210 USGS-2102 

H23-b 35°40.28′ 117°25.48′ 1,7804 M (32,960) 420 USGS-2326 

H23-a 35°40.35′ 117°25.35′ 1,780 M 26,140 140 USGS-2423 

H23-g 35°40.07′ 117°25.52′ 1,760 S 17,750 140 USGS-2422 

H23-g 35°40.07′ 117°25.51′ 1,750 S 18,600 130 USGS-2103 

H23-g 35°40.07′ 117°25.51′ 1,750 M 18,560 210 USGS-2327 

I30-h 35°38.8′ 117°23.0′ 1,645 M 19,150 600 W-1905 

 AB H28-f 35°39.2′ 117°27.9′ 1,950 M (26,450) 140 USGS-2522 

 sab6 H23-c 35°40.25′ 117°25.77′ 1,820 M (29,960) 250 USGS-2106 

H23-h 35°39.96′ 117°25.29′ 1,765 O (32,100) 1,000 Y

H24-f 35°40.12′ 117°24.85′ 1,760 M 25,740 130 USGS-2104 

 sab4 H24-e 35°40.04′ 117°25.14′ 1,740 N 28,800 400 Y

H24-e 35°40.07′ 117°25.13′ 1,740 O 27,800 1,200 Y

H24-r 35°39.61′ 117°24.29′ 1,720 S 27,400 800 W-1922 

 sab3 H23-f 35°40.13′ 117°25.91′ 1,830 S 26,650 860 USGS-2105 

H23-c 35°40.15′ 117°25.75′ 1,790 M 29,130 160 USGS-2426 

H23-b 35°40.22′ 117°25.77′ 1,780 M 27,880 210 USGS-2322 

H24-f 35°40.11′ 117°24.86′ 1,735 S 29,200 2,000 W-1575 

H24-e 35°40.09′ 117°25.13′ 1,735 S (35,000) 1,600 Y

 sab2 C3-r 35°52.2′ 117°18.9′ 2,070 M (10,610) 50 USGS-2325 

 A N12-m 35°30.78′ 117°25.07′ 2,200 L (10,230) 300 W-1322 

K24-g 35°34.7′ 117°24.5′ 1,930 M (17,620) +549 B-84-18a (U) 

-376

L18-g 35°35.3′ 117°23.5′ 1,870 M (30,380) 280 USGS-2520 

L5-j 35°36.8′ 117°22.2′ 1,810 L (32,500) 2,000 W-1321 

H23-f 35°40.01′ 117°25.82′ 1,810 S 40,000 2,500 Y

L5-b 35°37.1′ 117°22.4′ 1,800 L > 36,000 -- GX-11935 

Unit Map location

code Latitude Longitude Elevation(ft )

Sample 

material1

Age2

(yr)

± 

(yr) Laboratory no.3
Stratigraphy and Lithologies of Mapped Units 31

L5-b 35°37.1′ 117°22.4′ 1,8004 L (31,700) +1,074 B-86-3 (U) 

A -800

H23-f 35°40.01′ 117°25.88′ 1,800 L (32,800) 390 USGS-2324A 

H23-f 35°40.01′ 117°25.88′ 1,8004 L (33,370) 330 USGS-2324B 

H23-f 35°40.07′ 117°25.84′ 1,780 M (30,900) 260 USGS-2323 

I32-r 35°37.3′ 117°22.1′ 1,750 M (21,910) 100 USGS-2329A 

I32-r 35°37.3′ 117°22.1′ 1,7504 M (21,330) 80 USGS-2329B 

I32-r 35°37.4′ 117°22.0′ 1,730 L (85,400) 4,000 B90-1 (U)6

I32-r 35°37.4′ 117°22.0′ 1,7304 L (25,400) 140 USGS-28416

I32-r 35°37.4′ 117°22.0′ 1,730 L (65,600) 3,000 B90-2 (U)6

I32-r 35°37.4′ 117°22.0′ 1,7304 L (29,100) 240 USGS-28426

I32-r 35°37.4′ 117°22.0′ 1,730 L (164,000) 9,000 B90-3 (U)6

I32-r 35°37.4′ 117°22.0′ 1,7304 L (32,300) 290 USGS-28436

I32-r 35°37.4′ 117°22.0′ 1,730 L (25,300) 1,000 B-90-4(U)6

I32-r 35°37.4′ 117°22.0′ 1,7304 L (18,000) 170 USGS-28446

1

Abbreviations for dated materials: C, organic carbon; L, lithoid tufa; M, marl or calcareous sandstone; N, nodose tufa; O, oolites; Q, ostracodes; S, mollusks.

2

Ages believed to be unreliable are enclosed by parentheses. They are judged to be unreliable because greatly different from ages believed to be correct for 

their stratigraphic assignment or greatly different from dates on more reliable material from nearby outcrops of the same unit.

3

Laboratory prefix codes and managers; 14C method except as noted: W-, M. Rubin, USGS, Washington, D.C., or Reston, Va.; USGS-, S. Robinson and D. 

Trimble, USGS, Menlo Park, Calif.; B- (U-series disequilibrium or Pr method), J.L. Bischoff, USGS, Menlo Park, Calif.; Y, M. Stuiver, Yale University, New 

Haven, Conn. (laboratory numbers not assigned); GX-, Kruger Enterprises, Inc., Cambridge, Mass.

4

Duplicate determination of preceding sample.

5

Sample W-1418 is organic carbon from nodose tufa; sample materials labeled C and having Y laboratory designations are organic carbon from marl.

6

Ten samples in this table are paired U-series dates followed by 14C ages on identical samples. See Garcia and others (1993) for details of sample locations. 

Three pairs are from subunits sa1 and sa3 collected from localities within a few meters of each other; the first two (B-90-1/USGS-2841 and B-90-2/USGS-2842) 

were believed to come from the same bed only 10 m away. The fourth locality (B-90-4/USGS-2844) is about 160 m south of the first three and may represent 

unit A or unit B; it is here placed under unit A. 

Table 5. Radiometric ages of deposits assigned to the Searles Lake Formation.—Continued

[Listed in descending stratigraphic order of unit, within unit by decreasing elevation. Precision of locations indicated by significant figures in latitude and 

longitude estimated when sample was obtained.]

Unit Map location

code Latitude Longitude Elevation(ft )

Sample 

material1

Age2

(yr)

± 

(yr) Laboratory no.3
32 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

abundant at the outcrop location, and the relatively contemporaneous, chemically precipitated carbonate provided most 

of the carbonate fraction in the sediments. Samples from 

0.5 m or more above the base of the marl bed yielded ages 

mostly consistent with their stratigraphic positions.

Thompson and others (1990, p. 31) observed that dates 

on dispersed organic matter deposited during shallow stands 

of Lake Bonneville, Utah, appeared 2 k.y. too old, and similar 

materials deposited during fresher water intervals provided 

apparently reasonable estimates. This may be another instance 

where contamination due to the contemporaneous erosion 

of nearby sediments, containing one or more forms of older 

carbon, altered 14C dates.

Dates on dense tufa from the top of unit B and base of 

unit C are generally consistent, but tufa that was vuggy, heavily weathered, or stratigraphically older produced dates that 

were somewhat (or a great deal) younger. One greatly contaminated date on ostracode shells from unit B was also too 

young, as was a date on the enclosing marl (table 5, laboratory 

nos. W-1894 and USGS-67, respectively).

Many or all of the dates on carbon derived from lake 

water, including organic carbon, shells, ostracodes, marl, 

and tufa, from both subsurface and exposed deposits, could 

be 1,000 or even 2,000 years too old because of the possibility that the CO2 dissolved in the lake water at the time 

of deposition was not in equilibrium with atmospheric CO2

(Broecker and Kaufman, 1965, p. 554; Stuiver and Smith, 

1979, p. 70-78). Peng and others (1978, p. 326, tables 3, 9) 

estimated the average error of this type in Searles Lake salts 

to be 900 years, based on calculations and comparisons of 

230Th and 14C ages from the same horizon in the Lower Salt, 

but the calculated age discrepancies range from about 400 to 

1,100 years, depending on lake area. The magnitude of CO2

disequilibrium in a lake, however, is also affected by factors 

such as depth, salinity, and stratification; these change continuously during a lake’s fluctuation, meaning that no single 

correction factor can be applied to dates from all parts of the 

sedimentary record.

Although one U-series age on the older tufa unit, reported 

as “greater than 300,000 years,” was consistent with its 

inferred stratigraphic position (described in the section on 

that unit), others were not. The earliest lithoid tufa deposits 

in the Searles Lake Formation appear to be stratigraphically 

equivalent to the basal layers of unit A, yet a sample of tufa 

from the innermost wall of a 5-m-long adit into one of the 

large pinnacles gave an age of 31,700 years (table 5, B-86-3). 

This sample was also dated by the 14C method and found to 

be “greater than 36,000 years,” an age that is compatible with 

(though not proof of) its correct stratigraphic assignment. 

Four additional samples of lithoid tufa from unit A that were 

dated by this method (Garcia and others, 1993) gave results 

that were not consistent with their stratigraphic position (table 

5). In using the U-series dating method on tufa, there appears 

to be a problem either with the amount of clastic impurities 

or with contamination or leaching of the original materials 

by subsequent lakes that repeatedly immersed these porous 

0 1,600

500

560

620

680

1,800

2,000

2,200

10 20

RADIOMETRIC AGE, IN THOUSANDS OF YEARS

Level of 

highest 

shoreline

ELEVATION, IN FEET

ELEVATION, IN METERS

30 40

Present

dry-lake

surface

Figure 17. Plot of radiometric ages of dated samples against 

elevation of sampled outcrop. Data from table 5; dates considered 

unreliable (enclosed by parentheses in that table) are not plotted. 

Dots represent sample material, such as tufa, shells, and oolites, 

that was probably deposited in shallow water; circles represent 

material, such as marl, that was probably deposited in deep water.

The 14C dates (table 5) from the exposed materials have 

an uneven record of internal consistency. The probable sources 

of most errors in such dates are noted by Broecker and Walton 

(1959, p. 16-18, 21-23), Benson (1978, p. 303-309), Stuiver 

and Smith (1979, p. 70-73), Benson and Thompson (1987b, p. 

243-244), and Benson and others (1990, p. 242-245); sources 

of large errors in a few dates on marl are discussed below. The 

most reliable dates on outcrop material from Searles Valley are 

believed to be those based on the 14C content in (1) organic carbon from sediments and tufas, (2) oolites, and (3) shell material 

from concentrations of fossil snails and clams that suggest an 

event that killed much of the living population at one time. A 

14C age obtained from a collection of widely scattered shells 

allows the inclusion of reworked fossils, as in one such sample 

(unit CD, table 5), introducing the concern that the resulting 

dates will be too old by an unknown amount.

Somewhat surprising is the finding that dates on disseminated CaCO3 in sediments (marl) appear fairly consistent with other criteria of age in the majority of instances. 

Dated marl samples as old as 29,000 years show that contamination by younger carbon can be minor. However, dates 

on marl that appear substantially too old were found when 

the samples were collected from near the base of a marl bed 

that overlies coarse sand or gravel. The explanation probably 

is that these lowermost marl layers were deposited shortly 

after the re-expanding lake first inundated the sample site. 

At that time, outcrops of older, unindurated, carbonate-rich 

marl (deposited during earlier lake stands) were undergoing 

intense erosion along the nearby readvancing lake shore, and 

these older calcareous sediments were being transported—

and redeposited—a short distance out into the lake. After the 

lake’s shoreline migrated to a more distant location, further 

up the side of the basin, older clastic carbonate became less 
Stratigraphy and Lithologies of Mapped Units 33

deposits in younger lake waters that contained new mixtures of 

the elements and isotopes being measured.

Three samples of altered silicic ash were found in the 

Upper Salt and Bottom Mud (table 3; Hay and Guldman, 

1987), subsurface units equivalent in age to parts of the Searles Lake Formation, but identifiable ash layers were not found 

in outcrops. This prevented intrabasin or interbasin correlations, as well as possible evaluation of the 14C chronology.

The dated samples listed in table 5 are grouped according to the stratigraphic units from which they come. Each 

group is interpreted to represent a population of dates that 

approximate the depositional period represented by a unit. 

Many of those dates may differ from the true ages of the 

samples by as much as 1,000—or even 2,000—years because 

of the error sources noted above; this amount of scatter and 

overlap in the age ranges of units is not considered significant. However, ages that lie much further outside of the age 

limits for the unit, as established from subsurface data, are 

suspect and therefore are enclosed by parentheses in table 5. 

These ages probably reflect the inclusion of large amounts of 

reworked carbon from older deposits, contamination of the 

dated material, or an error in the stratigraphic assignment of 

the outcrop bed.

A plot of the ages of these dated materials against the 

elevations of their sources (fig. 17) shows that the history of 

Searles Lake cannot be determined accurately or in any detail 

by this method. The highest elevation dates (all on tufa) come 

from localities where there are no nearby lacustrine sediments to provide stratigraphic context. Although porous tufa 

is abundant at these upper levels, almost all of it is unsuitable 

for dating because it contains visible secondary calcite. The 

best dates came from dense tufa, mollusk shells, or oolites at 

lower elevations in the basin when the water was shallower. 

Inasmuch as the remains of algae are found in all tufa samples, 

and mollusk shells presumably represent species that grazed 

on algae, deposits including these materials probably represent 

less than about 10 to 20 m of water, as this is about the maximum depth that the light required for algal growth reaches in 

most lakes (Ruttner, 1953, p. 12-23, fig. 5).

Figure 17 does show, however, that during the interval 

between about 15 ka and 10 ka, materials deposited in shallow water are found over an elevation range of about 630 ft 

(190 m); this aspect of the Searles Lake history is in agreement with the mapped stratigraphy. Prior to 15 ka, lower 

lake-surface elevations and a smaller range of fluctuations 

are indicated by the plotted positions of the shallow-water 

deposits (dots), but the number of dated deep-water deposits 

(open circles) means that the lake surface was at times also 

substantially higher.

In view of these uncertainties, the ages assigned in this 

paper to the timespans represented by the various units of the 

Searles Lake Formation are clearly approximations. Combining all of the radiometric data available from subsurface and 

outcrop studies, plus other considerations developed later in 

this paper, the ages assigned to the units of the Searles Lake 

formation, and used throughout this paper, are as follows:

Unit D 6.0 ka to ~2.0 ka

Unit CD 10.5 ka to 6.0 ka

Unit C 13.5 ka to 10.5 ka

Unit BC 15 ka to 13.5 ka

Unit B 24 ka to 15 ka

Unit AB 32 ka to 24 ka

Unit A 150 ka to 32 ka. 

Fossils

Lacustrine deposits of the Searles Lake Formation 

contain numerous fossil snails and clams, especially in the 

Poison Canyon and Salt Wells Valley areas (pls. 3A and 

3B). These regions were near the main source of inflowing 

fresh water at the times Searles Valley contained large lakes, 

and the genera and species of snails and clams all indicate 

low-salinity environments. Rare but widespread snails and 

clams in the deposits of unit A suggest that the lakes of that 

time were fresh throughout the valley, presumably a result of 

voluminous overflow into Panamint Valley. In units AB, B, 

and C, however, the near-absence of fossils in other parts of 

the basin seems to indicate that a horizontal salinity gradient 

existed much of the time.

The earliest published description of fossils from Searles 

Valley was by Hanna (1963, p. 1-14), although he reports 

that F.M. Anderson collected specimens from the area some 

30 years earlier. Species identified by Hanna came from 

two localities in Searles Valley (in H24-b and I18-a), and he 

collected samples containing many of the same species in 

Panamint Valley (fig. 1). Hanna (1963, p. 4) notes that both 

valleys contained freshwater lakes when these animals lived. 

His localities in Searles Valley probably included sediments 

of subunits sab7 (and sab5?), sc1, sc2, sc3, sc4, and unit 

CD of the Searles Lake Formation, but his locality data are not 

specific. For this reason, the identified species are only listed 

(table 6); to help reconstruct paleohydrologic connections, the 

species he found in Panamint Valley are also tabulated.

The genera and species of snails and clams found in the 

lacustrine sediments of Searles Valley after its stratigraphy 

was determined are listed in table 7. Of them, D.W. Taylor 

(written commun., July 28, 1966) writes: “All of these mollusks are freshwater forms * * * The snail Lymnaea kingii * 

* *, unknown so far in stratigraphically higher deposits [in 

Searles Valley] is known from Panamint Valley.” This snail’s 

presence in sediments assigned to unit A helps corroborate the 

stratigraphic and other evidence that Searles Lake overflowed 

into Panamint Valley during much of the time unit A was 

being deposited.

Ostracodes are more widespread in Searles Valley, 

and the genera and limited numbers of species suggest a 

brackish or saline environment for some collections. Of the 

abundant Lymnocythere, I.G. Sohn writes (written commun., June 22, 1966):
34 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Location and abundance

Mollusk species Searles Panamint

Lymnaea kingii Meek X C*

Lymnaea palustris (Müller) R* --

Physa humerosa Gould X X*

Paraphloyx effusa (Lea) C C*

Helisoma ammon (Gould) R* --

Gyraulus parvus (Say) C C*

Carinifex newberri (Lea) C C*

Amnicola longinqua Gould X C*

Valvata humeralis Say C* C*

Succinea rusticana Gould R* --

Anodonta cf. A. californiensis Lea R R

Pisidium sp. X X*

Sphaerium cf. S. striatinum (Lamarck) X* X*

Table 6. Mollusca described by Hanna (1963) from Searles and 

Panamint Valleys.

[Symbols as follows: C, common; X, present (or abundance not clearly indicated); R, rare; --, not reported; *, species illustrated in Hanna (1963).]

It is a crawler and burrower rather than a swimmer, and 

is restricted to nearshore mud and vegetation. * * * The 

presence of carapaces and growth stages as well as the 

hydrodynamic difference between the males and females 

indicate that they were not transported. This suggests no 

current action. I have no data on temperature. * * * The 

abundance of one species to the exclusion of other ostracodes is interpreted to indicate a hypersaline environment.

Concerning the ostracode species in samples from the 

type section of the Searles Lake Formation (figs. 5, 6, table 

7), R.M. Forester writes (written commun., Jan. 8, 1988):

Samples 3, 5, 6, 7, 8, and 10 contain fewer ostracodes 

and, in general, more poorly preserved ostracodes than is 

typical for life assemblages in open lacustrine sediments. 

My guess is that the ostracodes in these samples are most 

probably reworked from older lacustrine sediments in the 

basin. When these lakes become large, so that salinities are below 50 to 100 parts per thousand (ppt) and the 

bottom waters are oxygenated, ostracode productivity 

becomes enormous. The sand fraction of the sublittoral 

and profundal sediments is often nearly all ostracode 

valves. As the lake level falls, these older deposits may be 

redeposited in the lake by wind and streams. Reworked 

ostracodes are especially common in the littoral zone of 

western lakes. The ostracodes from samples 3, 5, 6, and 

8 are typical lacustrine taxa suggesting they are reworked 

from older lake sediments. Some of the taxa in samples 

7 and especially 10 are common to the “marsh” facies 

(ground-water discharge) that surround large lakes and 

thus suggest reworking from ‘marginal lacustrine’ facies.

Sample 2 contains abundant Limnocythere sappaensis

together with abundant brine shrimp pellets. This association is common in relatively saline lakes * * * The probable upper salinity tolerance of L. sappaensis is around 

75 to 80 ppt whereas the lower salinity tolerance of brine 

shrimp is around 25 to 30 ppt. These tolerances would 

therefore suggest the salinity was in this range. Limnocythere sappaensis is also restricted to carbonate enriched 

and calcium depleted waters. * * *

Sample 9 contains abundant Limnocythere sappaensis and 

no obvious brine shrimp pellets. Assuming the absence of 

brine shrimp pellets is a function of original hydrochemistry rather than diagenesis, then the salinity of this lake 

should be in the range of 5 to perhaps 30 ppt. and thus is 

lower than for sample 2, discussed above. The presence of 

pyrite may imply permanence of water and thus perhaps 

deeper water than would have existed for the lake represented by sample 2 above. The presence of Limnocythere 

sappaensis would, as indicated above, imply carbonate 

enriched water.

A number of samples from the Searles Lake Formation 

(as well as older lacustrine units) were examined for diatoms 

by K.E. Lohman and J.P. Bradbury. None were found. Samples 

from subsurface lacustrine deposits have also been examined 

and found barren of diatoms.

Terrestrial vertebrate fossils were sought throughout the 

study of exposed lake deposits, but none were found. This is 

in marked contrast with the abundance of vertebrate remains 

associated with the lacustrine sediments of China Lake 

(Fortsch, 1978), upstream from Searles Lake during pluvial 

periods. The relatively high salinity of Searles Lake during 

its low-level to intermediate-level stages could have discouraged vertebrate animals during those periods, but the absence 

of such forms in the high and presumably fresh stands, which 

are also indicated by the mollusks, is puzzling. The abundance 

of water during the wettest periods, and the relatively steep 

slopes around much of Searles Lake during its highest stages, 

might have precluded the development of marshy areas and 

adjoining grassy plains. These have been postulated (Davis 

and Panlaqui, 1978) as the favored habitats for animals at 

China Lake (as well as for early man—also represented by 

abundant artifacts in the China Lake area, but not in the Searles Lake area).

Lithologies of Exposed Units

The lithologies of the several units and subunits of the 

Searles Lake Formation vary greatly throughout Searles and 

Salt Wells Valleys. The following discussions provide a general description of each unit, indicate the inferred depositional 

environment, and outline the nature of any distinctive, unusual, 

or significant aspects of that unit’s lithologies. More local 

lithologic details of these units are identified in the explanations of plates 2 to 4. Still further details are provided by the 

series of measured stratigraphic sections presented in appendix 

1, and sedimentological size analyses and statistical param-
Stratigraphy and Lithologies of Mapped Units 35

Formation, unit, 

and subunit Location or number1 Faunal group2 Identification Other data

Searles Lake

Formation

Unit D I5-q C

S

S

Pisidium compressum (Prime)

Vorticifex effusus (Lea)

Helisoma newberryi (Lea)

Reworked?

Reworked?

Reworked?

Unit C G6-r

H28-f

H28-f

H28-f

C10-r

H23-f

10

9

8

O

O

O

O

O

O

O

O

O

Limnocythere

Limnocythere

Limnocythere

Candona

Candoniella

Limnocythere

Limnocythere,

 aff. L. inopinata (Baird)

Limnocythere, 

aff. L. inopinata (Baird)

Limnocythere sappaensis

Potamocypris n. sp.

Heterocypris n. sp.

Candona caudata

Limnocythere paraornata

Limnocythere sappaensis

Limnocythere sappaensis

Limnocythere ceriotuberosa

18 m above base

17 m above base

0.5 m above base

Fair preservation

Poor preservation

Dominant

Common

Rare

Rare

Rare

Very abundant, pyrite present

Reworked

Unit B C30-d

I7-k

L8-n

C3-h

S

C

C

S

S

S

S

S

S

O

O

Helisoma newberryi (Lea)

Sphaerium transversum (Say)

Pisidium compressum Prime

Valvata humeralis Say

Lymnaea proxima Lea(?)

Gyraulus parvus (Say)

Vorticifex effusa (Lea)

Planorbella subcrenata (Carpenter)

Physa virgata Gould(?)

Limnocythere sp., 

 aff. L. inopinata

Limnocythere sp., 

 aff. L. inopinata

Females dominant

Males dominant

Subunit sab7 7 O Limnocythere ceriotuberosa

Candona caudata

Limnocythere sappaensis

Heterocypris n. sp.

Cytherissa lacustris

Variable preservation

Some reworked?

Well preserved

Juveniles

Subunit sab6 6

5

O

O

Limnocythere ceriotuberosa

Candona caudata

Limnocythere sappaensis

Limnocythere ceriotuberosa

Candona patzcuara

Limnocythere sappaensis

Rare, well preserved

Juveniles, rare

Reworked

Rare

Juveniles, rare

Reworked

Subunit sab5 4 (barren)

Table 7. Fossil mollusks and ostracodes collected from identified stratigraphic units in lacustrine sediments, Searles Valley.

[Snails and clams identified by D.W. Taylor, USGS, Menlo Park, Calif., in May 1966. Ostracodes from localities other than type section of Searles 

Lake Formation identified by I.G. Sohn, USGS, Washington, D.C., in June and December 1966 and April 1972; ostracodes from type section identified 

by R.M. Forester, USGS, Denver, Colo., in March 1982 and January 1988.]
36 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

eters of samples collected from representative outcrops are 

presented in appendix 2.

Unit A (150 ka to 32 ka)

Unit A of the Searles Lake Formation is correlated 

with the Bottom Mud in subsurface (table 3), a unit that was 

interpreted as representing about 100,000 years of mostly deep 

lakes, with a few periods of intermediate-level lakes (Smith, 

1979, fig. 41). Outcrops of this unit are the least well preserved or exposed in the formation, but a few sections of silt, 

sand, and gravel extending to 2,280 ft elevation and exceeding 25 m in thickness (sec. M19-l, pl. 2B; sec. C36-h, pl. 1, 

and appendix 1) support the interpretation of long periods 

of deep-water deposition. Massive deposits of lithoid tufa at 

the highest shoreline along the west side of the valley (cover 

image and pl. 1) support this conclusion. Thinner sections of 

unit A are well exposed in most of the canyons along the edges 

of the Argus and Slate Ranges (pl. 1), especially in sec. H28-j 

(pl. 3B), in secs. H13-c and H26-e (pl. 3A), and in secs. I32-r, 

L8-m, n and K24-b (pl. 4). Many of those exposures, however, 

are at intermediate elevations where coarse, poorly sorted 

debris makes up much of the unit, and long periods characterized by intermediate-level lakes also seem confirmed. The 

huge volume of lithoid tufa near the 1,800-ft level in The Pinnacles area (pl. 4; fig. 18), a unit deposited in an intermediatedepth lake and in large part contemporaneously with the basal 

part of unit A, supports this inference.

Three types of gravels are included in unit A. The first 

type, near bedrock, consists of gravels that were transported by 

longshore currents. Many of these are interbedded with sand 

or silt, and they are identified as lacustrine deposits by their 

bedding continuity, fair to good sorting and rounding, absence 

of disproportionately large cobbles or boulders, and uncommonly low amounts of interstitial silt or fine sand. A variation in this type of gravel deposited by longshore currents is 

found in secs. K13, 14, 23, and 24 (pl. 1 and pl. 4). There, the 

fragments form a well-cemented veneer that consists of flaggy 

slabs eroded from nearby outcrops of older tufa.

The second type of gravel was deposited as lacustrine 

bars. The largest and best example is the southeast-trending 

bar that extends from the east end of the Spangler Hills 

toward The Pinnacles (secs. I31 and I32, pl. 4); it is 5 to 7 

m high and 2 km long (table 8; fig. 18). The fragments in it 

1

Location code as described in “Field and laboratory methods” section of text and in the Index Map on plate 1; numbers refer to horizons 

labeled on figure 6.

2

Abbreviations: C, clam; S, snail; O, ostracode.

Subunit sab4 3

2

O

O

Limnocythere ceriotuberosa

Limnocythere sappaensis

Candona caudata

Limnocythere sappaensis

Brine shrimp pellet coquina

Low abundance

Subunit sab3 1 O (barren)

Unit AB L8-k O Limnocythere sp.,

 aff. L. inopinata Beard

Females dominant

Unit A B25-h

C25-n

C36-e

S

O

O

Lymnea kingii Meek

Helisoma newberryi (Lea)

Vorticifex effusus

Limnocythere sp.,

 aff. L. inopinata (Baird)

Limnocythere sp.,

 aff. L. inopinata (Baird)

Females dominant

Females dominant

Christmas

Canyon

Formation

M33-d O Limnocythere camera (?)

Formation, unit, 

and subunit Location or number1 Faunal group2 Identification Other data

Searles Lake

Formation

Table 7. Fossil mollusks and ostracodes collected from identified stratigraphic units in lacustrine sediments, Searles Valley.—Continued

[Snails and clams identified by D.W. Taylor, USGS, Menlo Park, Calif., in May 1966. Ostracodes from localities other than type section of Searles Lake 

Formation identified by I.G. Sohn, USGS, Washington, D.C., in June and December 1966 and April 1972; ostracodes from type section identified by 

R.M. Forester, USGS, Denver, Colo., in March 1982 and January 1988.]
Stratigraphy and Lithologies of Mapped Units 37

Table 8. Distribution and characteristics of major lacustrine bars in Searles Valley.

Elevation1

(ft)

Location Length3

(km)

Direction of

fragment transport4

Stratigraphic

assignment5

Plate Section2

2,260 1 L22-g 2.9 E sa

2,260 1 N8-d 0.9 NW sc

2,260 2A A34-a 0.3 E sc3

2,260 2A A27-h 0.4 E sc3

2,255 2A A27-h 0.5 E sc3

2,250 2A A27-j 0.4 E sc3

2,235 2A A34-h 0.2 E sc3

2,100 2A C3-r 1.8 E sab6

2,100 1 L15-q 7.0 W sab

2,040 3B H21-r 1.4 W sa6

2,040 2B M18-k 0.1 W scg

2,010 1 L15-m 1.4 W sc

2,000 1 L19-m 1.6 NW sb

1,960 2A C10-r 2.7 W sc1b

1,960 1 L15-e 1.8 W sc

1,940 1 L18-p 10.1 W sc

1,920 2A C15-h 4.6 W sb1,sc1a

1,915 2A C15-j 2.8 W sb1,sc1a

1,850 2A C15-r 3.7 W sb1,st

1,790 4 I32-q 2.4 SE sa1,sa3,sa4

1,710 4 I33-q 0.4 SE(?) sdg

1

Elevations are nominal because bar crests vary in elevation by as much as 40 ft (12 m).

2

Section location indicates a representative segment of bar.

3

Length listed is for preserved remnant; most bars were originally longer.

4

Direction as determined at listed locality; some bars have some clastic contribution from opposite side of valley if bar extends 

that far. Abbreviations: NW, northwest; E, east; W, west; SE, southeast.

5

Abbreviations for stratigraphic unit(s) as explained on listed plate.

6

Original bar form apparently determined by underlying sediments of unit A, but horizontal, westerly transport of unit AB fragments that cover inferred sediments of unit A shows that a similar wind regime existed during that later period; deposits of units B

and C are also draped over original bar.

all come from the east slope of the Spangler Hills. This bar 

is very well exposed in both the railroad cut and where an 

unnamed wash to the southeast dissects it. These exposures 

show that the gravel facies and bar crest migrated southwestward during its growth. These medium to dark gray gravels 

are notable for what appears to be a near lack of fine-clastic 

matrix but abundant calcareous cement. Laboratory size analyses, however, show that many of these gravels have a slightly 

bimodal size distribution, with minimal coarse to medium 

sand but greater percentages of (windblown?) fine sand and 

silt (see appendix 2, table 12). Bedding, which generally dips 

5° to 10° northeast, is pronounced. The bar, which has been 

exhumed, is asymmetrical with a steep southwest side, more 

gradually sloping northeast side, and flat crest (fig. 18).

The third type of gravel included in unit A is, arguably, 

not a lake deposit because the fragments were not transported 

to their present site by the lake. These deposits consist of 

exposures of older gravels that have had shorelines carved 

on them by the waves associated with the lake responsible 

for unit A; gravel deposits assigned to unit A locally overlie 

them. Excellent examples are found in sections H26-c, L13-

L15, M5, and M8 (plates 1, 2B, and 3A). They are mapped 

as part of unit A because they document the existence of a 

lake at that time and at those levels. The processes of carving shorelines has removed the finer fraction of the original 

gravel, so that its present fragment-size distribution at the 

surface differs from that of the older gravels prior to their 

innundation by unit A lake waters.
38 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Sand and sandstone layers in unit A vary greatly in 

induration. One characteristic form is a very well cemented, 

or flaggy, sandstone. Most of the exposures of unit A along 

the Argus Range and Spangler Hills, where coarse-grained 

plutonic rocks crop out, consist of brownish (5-10YR4-8/2-4), 

coarse to very coarse granitic sand with angular to subangular fragments that are well sorted and have virtually no fine 

matrix. A few pebbles are commonly included. Elsewhere, the 

sands and sandstones of unit A are locally less well indurated, 

the fragments are mostly medium to coarse sizes, and the colors of some layers are more yellowish (5Y6-8/2-4).

Silt beds, which are not common, may be either very well 

or poorly bedded and have colors ranging from yellowish to 

greenish gray (5-10Y6-8/1-4). Silt beds deposited near the 

paleoinlet are highly calcareous (sec. H23-f, pl. 3A; H30-g, 

pl. 1) whereas those deposited in more remote parts of the 

valley, especially in the southern part (M18-k, pl. 2B), contain 

small percentages of carbonate.

The outcrop record of this unit is too discontinuous to 

reconstruct the temporal relation between these high- and 

intermediate-level stands. In some areas, however, an interbedded alluvial layer is preserved (subunit sa2, pls. 1 and 4); it 

is not known if these local layers are contemporaneous with 

each other and thus represent one lake recession, or if there are 

several layers that represent several recessions. Many examples of these alluvial layers, however, are truncated by a fossil 

soil that has similar properties (fig. 12A); it is a calcareous 

soil, similar to the one that truncates the Christmas Canyon 

Formation, but only about 1 m thick, and it commonly has a 

yellowish orange (10YR6/4-6) zone near its top (sec. K24-p, 

Figure 18. Gravel and tufa formed in the time of deposition of unit A of the Searles Lake Formation. 

Surface in foreground is the near-horizontal crest of The Pinnacles bar, a large lacustrine bar composed at its top of gravel belonging to subunit sa4. All younger, fine-grained sediments of unit B and 

younger ages have been removed by erosion. Note that bar-gravel lithologies and clast sizes are quite 

uniform and clasts are mostly angular to subangular. Tower-shaped pinnacles of tufa in background 

(one-half kilometer and more from the camera), began to grow at about 150 ka and reached elevations 

as much as 50 m or more above the gravel surfaces. The pinnacles were formed of the lithoid form of 

calcite (CaCO3), but starting about 30 ka, when deposition of the AB, B, BC, and C tufa members began, 

they were coated with hard crusts of nodose tufa composed of aragonite (also CaCO3); most of those 

layers are between 2 cm and 2 m thick.
Stratigraphy and Lithologies of Mapped Units 39

pl. 4). In one place (sec. I32-r, pl. 4), a 0.6-m lenticular bed of 

angular alluvial gravel correlated with this subunit and soil is 

orange-stained throughout.

Areally extensive outcrops of orange-hued boulder 

alluvial gravels, exposed northwest of Searles Lake, near the 

mouth of Wilson Canyon, are mapped as alluvial material 

that is interbedded in unit A. The best examples are exposed 

in secs. B25-a, C17-e,l,m,n, and C31-l. Local stratigraphic 

details appear to place them within unit A, but some of the 

evidence is equivocal. The boulders are commonly 1 to 2 m 

across, even though they are as much as 3 km from the mouth 

of the canyon from which they came. Many are also much 

more intensively weathered than boulders in other areas or 

from other units (fig. 19). This probably reflects their long and 

repeated exposure to the destructive forces of wave- and windborne, high-pH saline brines. When such brines penetrate 

cracks in rocks, some solution may occur as a result of the 

pH (Butler and Mount, 1986), and on drying, expansion and 

wedging may result from halite’s unusually large coefficient of 

thermal expansion (Skinner, 1966, table 6-1).

Unit AB (32 ka to 24 ka)

Unit AB is correlated with the Lower Salt in subsurface deposits (fig.1C), which is composed of seven salt layers 

separated by mud layers that represent perennial lakes, each of 

Figure 19. Large boulders in alluvial gravels mapped as part of unit A (subunit sa2?) are extensively 

weathered and pitted. The effects of various salts on chemical weathering processes are believed 

responsible for this morphology, with the salts being introduced by spray from waves of one or more 

moderately saline lakes when the shoreline was only a short distance away. Weathering as intense as 

documented by these boulders is not found in most other gravels within the part of Searles Valley once 

covered by lakes; it is not clear why this weathering product is so stratigraphically limited. Locality: 

plate 1, sec. C31, at an elevation of approximately 1,900 ft. Bushes in foreground are about 40 cm high.

which existed for hundreds of years to a few thousand years. 

Six of the salt layers represent partial desiccation, one (S-5) 

represents complete desiccation. These record a lake that fluctuated repeatedly between intermediate and low levels, and the 

relative thinness of unit AB subunits in all areas except near 

the main inlet (pl. 3A) is compatible with this interpretation.

In much of Searles Valley, unit AB is a coarse alluvial 

gravel, with its top-surface fragments exhibiting a characteristic light-brown hue (5-10YR3-5/2-6). The larger fragments are 

mostly angular to subangular; fragment sizes vary but are generally smaller than those in nearby outcrops of the Christmas 

Canyon Formation or older gravel map units and larger than 

those in unit BC. In cross section, gravels of this unit have 

similar hues but lighter values because of their poorly sorted 

sand matrix. Textures indicative of an alluvial origin include 

discontinuous and generally poor bedding, wide variation in 

fragment sizes, fine matrix material in gravel layers, local 

randomly oriented cross-bedding, and a lack of characteristics 

indicative of a lacustrine origin.

The lacustrine facies of unit AB all lie at elevations below 

2,120 ft. Lacustrine bar gravels, interpreted on stratigraphic 

grounds to be a part of this unit, are present at this elevation in 

the southern part of the valley (centered approximately in sec. 

L14, pl. 1); extensively cross-bedded lacustrine sand, mapped 

as part of this unit, extends up to about 2,100 ft in the north 

end of the valley (sec. C3-k,j, pl. 2A). The thickest exposed 
40 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

section of unit AB is in the Poison Canyon area (pl. 3A), which 

was near the main inlet of Pleistocene Lake Searles and thus 

part of its delta. The type section of the Searles Lake Formation (fig. 6) includes 15.7 m of sediments that are divided into 

seven separable subunits of unit AB, the maximum resolution 

of this unit that is possible in the valley. Most of these subunits 

can be traced about 1 km southeast. Subunits sab2, sab4, 

and sab6 are silt and fine sand that represent three expanded 

lakes, and subunits sab1, sab3, sab5, and sab7 represent 

shallower lakes that probably retreated one or more times until 

they deposited salines on the lake floor. Several more hiatuses must exist within these subunits of unit AB because its 

subsurface equivalent, the Lower Salt (table 3), contains seven 

separate salt layers, indicating that the lake fell to a lower 

elevation than these outcrops at least seven times.

Although several of the coarser beds in unit AB have 

orange hues, subunit sab7 is the most intensely colored, commonly approaching light brown (5YR 5/6). Even more intense 

orange stains are found on the upper 20-30 cm of this bed 

where it crops out to the west (sec. H23-h, pl. 3A) and south 

(south half of sec. H24-f, pl. 3A). The outcrop illustrated 

by figure 16 also displays this intense staining at the upper 

contact of unit AB, showing that the angular unconformity 

between units AB and B was caused by erosion during the 

retreat of the last deep-water stage during AB time; in subsurface, this stage is designated M-7 (Smith, 1979, fig. 4). That 

retreat allowed the orange stain to develop on the truncated 

surface during the short time before the readvance of the lake 

responsible for deposition of unit B. In the vicinity of The 

Pinnacles, at 1,720 ft and above, some of the thin gravel layers assigned to unit AB also have a calcareous soil developed 

on their upper surface (fig. 12B), supporting the conclusion 

that this orange-to-brown color zone is a product of subaerial 

processes. Development of a thick desert varnish remains as 

the most likely explanation for this characteristic color. However, the varnish would have had to develop rapidly because 

no reasonable correlation with dated subsurface sections 

permits more than about 1,000 years for deposition of S-7, 

the uppermost salt layer in the Lower Salt (Stuiver and Smith, 

1979, fig. 31) and the last episode during AB time when these 

sediments could have been exposed.

In the elevation range 1,980 ft to 2,080 ft, in the Valley Wells Wash area (pl. 2A), exposures reveal two layers of 

alluvial sediments assigned to unit AB that are separated by 

a very coarse, angular, well-sorted lacustrine sand. The lower 

alluvial layer, generally 1-4 m of very pale brown (10YR7/3), 

poorly sorted pebbly sand, is moderately indurated; it closely 

resembles the alluvial material in the modern wash. The upper 

layer is 1-2 m of grayish orange (10YR6-7/4-6), angular 

pebble gravel and sand that is poorly indurated and fills channels cut in the underlying unit. This contrasting pair of alluvial 

gravels suggests that the early episode of alluvial deposition of 

unit AB took place in a climatic setting much like the present, inasmuch as the modern alluvial sediment is so similar in 

color and occurs in a setting that promoted the development of 

a heavy desert varnish.

Channeling within unit AB is noted on both sides of a 

small ridge in one area southeast of the type section (sec. H24-k, 

pl. 3A). The channel, 1 to 2 m deep, is cut in subunit sab6 and 

filled with orange pebble sand of subunit sab7 (fig. 20A), and it 

aligns with prominent tufa-lined channels cut in gravels of unit 

A and plotted on plate 3A, about 200 m to the southwest (fig. 

20B). Those channels are thus well dated and appear indicative 

of a brief climatic episode that generated one or more intense 

debris flows within this very small drainage area, during deposition of subunit sab7 (see section on Geomorphology).

Because of this demonstrated tendency for unit AB to have 

notable concentrations of orange-stained fragments throughout, and even more so near its top, this color criterion has been 

widely used in identifying both lacustrine and alluvial sediments 

assigned to this unit. It is unfortunate that the process causing 

this widespread characteristic cannot be described more exactly 

than by postulating a climatic episode that rapidly produced a 

thick coating of Fe-rich desert varnish. The conversion of desert 

varnish to geothite or hematite, the apparent coloring agent, 

requires only a simple oxidation or hydration process.

Unit B (24 ka to 15 ka)

Unit B is the outcropping equivalent of the lower part 

of the Parting Mud (table 3) beneath the surface of Searles 

Lake. The Parting Mud, having a total thickness of 5.4 m in 

the core studied by Mankiewicz (1975), was subdivided by 

him into five subunits. The lower two, whose thicknesses 

account for 3.75 m (69 percent) of the Parting Mud, are here 

correlated with unit B of the Searles Lake Formation. Using 

the ages of contacts between the five subunits as estimated 

by Smith (1979, p. 111), the lower two would represent the 

span between 24.0 and 15 ka, a period nearly 9 k.y. long. 

These two subsurface units are characterized by closely 

spaced dolomite(?) layers, faint (or absent) aragonite laminations, and lighter colors. A shift in the hydrocarbon, terpene, 

and sterol characteristics at the boundary between these two 

units, attributed to changing ratios of fossil green algae, bluegreen algae, and vascular plant remains, suggests a period of 

vigorous inflow to the lake until about 17.1 ka, followed by a 

period of waning inflow (unit BC) until about 12.3 ka. Inflow 

then resumed, forming a stratified lake that deposited laminated muds (unit C) (Smith, 1979, p. 48, 53, 80). The sense 

of these reconstructed changes in inflow is notably similar to 

those inferred in a later section on the basis of changes in the 

lithologic character of the Parting Mud in core GS-16 and in 

its CaO and acid-insoluble components, although the inferred 

ages of the contacts are slightly different.

Outcrops of unit B are widespread in Searles Valley. Its 

coarser facies mostly consist of rounded to subangular gravel 

or sand, with common fragments of nodose tufa. The light to 

dark gray gravels are mostly well sorted and contain relatively 

little clastic material in their matrix, but they commonly are 

well cemented by massive calcite. Fragment sizes in bar and 

beach deposits include pebbles, cobbles, and small boulders. 

Extensive gravels composed of small, light-gray pebbles 
Stratigraphy and Lithologies of Mapped Units 41

A

B

Figure 20. Eroded and filled channels formed during the time of deposition of unit AB. A, Exposure of channel (outlined by dashed 

line) eroded in silt of subunit sab6 (light gray) and filled with sand of subunit sab7 (medium gray); channel width about 3 m, depth 1 to 

2 m. View to northeast; location: plate 1, sec. H24-k. B, Aerial view of two channels (arrows) on east end of Spangler Hills that are cut 

in shoreline gravels of unit A and align with filled channel shown in A. The small drainage collection area indicates that a very unusual 

weather event produced the volume of water required to erode these channels (see text). The channels, 3 to 5 m wide, are lined by 

levees, whose tops are about 2 m above the channel floor; the levees are built of boulder-size fragments. Channel floors are coated with 

nodose tufa, showing that no major amounts of water carrying coarse sediment have reoccupied them since the channels were formed 

during the interval between deposition of subunits sab6 and sab7. View to west; location: plate 1, sec. H24-q.

A

B

A

B

characterize deposits of this unit throughout a large region 

south and southwest of The Pinnacles (pl. 4). Gravel facies are 

mapped separately from silt and sand facies on plates 2 to 4.

Medium to coarse sands assigned to unit B tend to be 

greenish or tan and are well sorted with little finer matrix. 

Fine sand, silt, clay, and marl beds range in color from very 

light tan to greenish or slightly orange. Bedding, defined by 

color or grain-size change, is most commonly faint or absent; 

laminar bedding caused by color or mineralogic change is 

found locally, but white laminae are less common and are 

more widely spaced than in sediments of unit C. The calcareous component of the marl, silt, and clay consists of aragonite, 

calcite, and dolomite, but calcite dominates in most samples. 

Ulexite and gypsum occasionally are seen in this unit (sec. 

H23-g). In the Salt Wells Valley (pl. 3B) and Poison Canyon 

(pl. 3A) areas, most of the silt deposits assigned to unit B

contain conspicuous quantities of yellow-green mica flakes. 

Cauliflower-shaped growths of brown nodose tufa are abundant near the top contact of unit B in many areas, especially in 

the vicinity of Poison Canyon.

Unit B varies in thickness from a fraction of a meter to 

about 20 m. The thickest sections are on the north side of the 

Poison Canyon area (pl. 3A), although at the type section of 

the Searles Lake Formation, on the south side of this area, the 

entire unit was removed by sublacustrine erosion. Thicknesses 

of 2 to 3 m are common: In the southwestern part of Searles 

Valley, 2 to 3 m of pebble gravels and greenish silts assigned 

to unit B crop out over extensive areas; along the flanks of the 

Argus and Slate Ranges, 2 to 4 m of sand and pebble to cobble 

gravels represent the unit; east of The Pinnacles, 3 to 4 m of 

silt and sand are mapped as part of this unit; and along Randsburg Wash, 1 to 4 m of greenish sand and silt are exposed.

Although sediments assigned to unit B extend to the 

2,280-ft level, some evidence suggests that the lake responsible for unit B underwent considerable fluctuation. Exposures 

of sediments mapped as unit B along Randsburg Wash, near 

the 2,000-ft contour (pl. 2B), include layers of sand and gravel 

that appear to be alluvial but could be turbidites; exposures 

of silt near this elevation in the middle of the southwestern 

arm of this valley have several interbedded layers of sand. 

Exposures of unit B east and northeast of the Spangler Hills, 

between elevations of 1,630 ft and 1,720 ft, have been divided 

into six subunits (pls. 3A and 4), each of which is a bed of silt, 

as much as 2 m thick, overlain by a thinner sheet of lacustrine 

sand. This suggests deposition occurred during relatively long 

periods of deep lakes that were interrupted by brief periods 

characterized by shallow lakes whose surfaces were not much 

above the 1,720-ft contour level.
42 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Unit BC (15 ka to 13.5 ka)

Unit BC of the Searles Lake Formation is correlated 

with a 0.9 m section in the Parting Mud (table 3), as subdivided by Mankiewicz (1975). This section was interpreted by 

him to represent the period extending from 14.5 to 12.3 ka, 

a period 2.2 k.y. long; the ages used elsewhere in this paper 

reduce its duration to 1.5 k.y. The lithology of this part of 

the Parting Mud in cores is laminated marl, but the laminae 

are more widely spaced than in the overlying two subsurface 

units, and they are more frequently orange (dolomite?) than 

white (aragonite). The near absence of subsurface salines 

at this horizon suggests that while the depositing lake may 

have shrunk, its depth was always more than about 130 ft 

(40 m), the estimated maximum depth at which salts could 

have begun to precipitate in the winter from solutions having 

salinities near 13 percent (Smith, 1979, fig. 32). This would 

indicate lake levels near the 1,660 ft contour. However, 

alluvial, soil-bearing sediments assigned to unit BC can be 

traced locally down to the 1,630-ft level (table 9), meaning 

that for a period, some salts probably crystallized, as suggested by traces of trona and borax at about this horizon in a 

few cores (Smith, 1979, fig. 24), but that virtually all of those 

salts dissolved when the lake again expanded.

In many parts of Searles Valley, unit BC is an alluvial or 

colluvial gravel. The alluvial gravels have maximum fragment sizes that range from cobbles to boulders, with a matrix 

composed of poorly sorted pebbly sandstone. Bedding, when 

present, is discontinuous. Colors on fresh surfaces are tan 

or brownish orange; on weathered surfaces they are commonly moderate brown (5YR 4/4). Colluvial gravels, mostly 

0.3 to 1.0 m thick, are composed of pebbly sand or silt. In 

some areas, a high percentage of the pebbles are nodose 

tufa. It might appear that some of the deposits assigned to 

unit BC should be mapped as unit B, because lake waters 

were required to introduce some of the fragmental components that do not crop out uphill from the colluvial deposit 

and contacts between units B and BC are commonly gradational. However, in-place reworking of thin beds of unit BC

gravels that incorporated material from underlying deposits 

assigned to unit B would also be an adequate explanation 

for the anomalous fragment content of these sediments. In 

most areas, the unit separates lacustrine sediments that are 

assigned to units B and C.

At elevations below about 1,860 ft, unit BC is also commonly a lacustrine sand (fig. 15). Unit C once covered all 

of these deposits, but unit BC has been exhumed over large 

areas in the northwestern and eastern parts of the Poison Canyon area (pl. 3A), where the deposits of unit BC were uncharacteristically thick because they were deposited as a delta into 

the shrinking lake. Especially good exposures of this facies of 

unit BC occur where excavations were made for the railroad 

tracks adjoining the east edge of the area of plate 3A (I17-

d,e,m,n), and along the north side of the amphitheater (such 

as H14-r); outcrops interpreted to represent the transition 

from alluvial to lacustrine facies are found in secs. H22-a,h 

and H23-d,e. Away from outcropping bedrock, this lacustrine 

facies of unit BC most commonly consists of medium to very 

coarse sand, subangular to subrounded and fairly well sorted. 

Pebbles are locally common. Grayish orange hues (5-10YR5-

7/3-6) characterize most exposures, and some show deltaic 

bedding on a massive scale. Thicknesses of this facies vary 

from less than 10 cm to 2 m, and changes in thickness occur 

over short distances.

A distinctive and moderately well developed soil formed 

on the surface of unit BC (and older units exposed at the close 

of this time period). This soil was useful as a diagnostic criterion when mapping and is referred to herein as the BC soil. It 

consists of a zone about 30 cm thick, with semi-indurated pods 

of white calcite, 1-2 cm across and 2-5 cm apart, throughout 

the lower 25 cm of the soil (fig. 13A). Some profiles reveal a 

moderate concentration of clay, but others appear to be nearly 

clay-free. A diagnostic (and unexplained) characteristic of the 

soil is the presence of a network of very irregular, hairline-size, 

moderate red (5R4-6/6) streaks; they are visible on and within 

the calcite pods, form networks on the surfaces of pebbles, and 

can be traced through the silt or sand matrix material. These 

marks look like remnants of rootlets of some plant, but no remnants of roots were found attached to them. No plant was identified whose roots would produce this unusual color, although 

desert holly (Atriplex hymenelytra) flowers have colors near 

this hue (though not intensity), showing that the shrub contains 

the necessary components to produce the color. A similar, but 

thinner and less intensively developed, soil also formed on the 

surface of unit CD (fig. 13B), and care had to be exercised in 

using the BC soil as a correlation tool during mapping.

The soil on unit BC is remarkable because it appears 

that only about 1,500 years was available for both deposition 

of this unit and development of this soil; the lake’s recession 

period might have been at most 2,000 or 3,000 years, but even 

these lengths of time seem short for both steps to have taken 

place. Compounding the problem are exposures of this soil 

on exhumed surfaces of unit BC near the 1,640 ft contour, 

only 25 ft above the present dry lake surface (sec. F31-n); 

this would require the lake to have been below this level for a 

period long enough for the soil to develop. This one exposure 

might be an anomalous occurrence of the younger CD soil, but 

the BC soil is developed on many alluvial sediments below 

1,700 ft elevation that are tied to apparently reliable stratigraphy, meaning that the lake stood at levels below this elevation 

for a substantial period.

One reason that weak calcic soils could have developed 

rapidly in this region is the abundance of salty and calcareous 

sediment that was exposed to wind transport. Salt accelerates 

the fragmentation of mineral grains and thus increases the 

area exposed to rock-water reactions that can form pedogenic 

clays. Calcareous dust was—and still is—transported to all 

parts of the valley by wind, allowing rapid accumulation of 

the ingredients required for the observed calcareous horizon. 

Chadwick and Davis (1990, p. 243) present strong evidence of 

the importance of eolian dust as a source of fine materials and 

salts (which accelerate weathering rates) in late Pleistocene 
Stratigraphy and Lithologies of Mapped Units 43

Table 9. Elevations and representative locations of exposures mapped on plates 1 to 4 that document highest levels of 

lacustrine sedimentation (bold type) and lowest levels of alluvial sedimentation (light type), Searles Lake Formation.

 Elevations and locations on plates1

Unit Map 

label Pl. 12 Pl.2A Pl.2B Pl.3A Pl.3B Pl.4

D sdg 1,800 -- -- 1,800 -- 1,720

G6-c H24-k I30-k

sd 1,740 -- -- 1,810 -- 1,790

J28-n H23-f H31-h

CD scd 1,630 -- -- 1,645 -- 1,700

I8-a I8-f I34-e

C sc4 -- -- -- 1,700 -- --

I18-h

sc3 -- 2,280 -- 1,920 2,080 1,930

A28-e H23-e H21-m L18-l

sc2 -- 1,940 -- 1,870 2,080 --

C15-d H23-b H20-j

sc1 -- 2,2703 -- 1,920 2,030 1,940

A35-d H23-f H20-r L18-n

sc 2,280 -- 2,050 -- -- --

M17-p M18-k

scg -- -- 2,280 2,200 -- 2,280

M17-n H25-h K1-a

BC sbc 1,630 -- 1,850 1,910 -- 1,630

I6-j M6-l H23-e I28-a

sbcg -- -- -- 1,660 -- --

I8-e

sbc2 -- 2,020 -- -- -- --

C11-e

sbc1 -- 1,860 -- -- -- --

C15-l

B sb6 -- -- -- 1,880 -- 1,680

H23-c I19-p

sb5 -- -- -- 1,870 -- 1,675

H23-c I19-p

sb4 -- -- -- 1,840 1,670

H14-r I19-q

sb3 -- -- -- 1,820 -- 1,720

H14-r I32-e

sb2 -- 2,1504 -- 1,810 -- 1,670

A34-r H14-r I30-h

sb1 1,8204 -- 1,800 1,715

C23-e H14-r I32-e

sb 2,280 -- 2,060 1,960 2,030 1,970

C4-m M18-r H13-d H21-r L19-g

sbg -- 2,260 2,280 2,260

M19-f H26-h L6-d

AB sab7 -- 1,850 -- 1,970 -- --

C14-n H23-r
44 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Table 9. Elevations and representative locations of exposures mapped on plates 1 to 6 that document highest levels of lacustrine sedimentation (bold type) and lowest levels of alluvial sedimentation (light type), Searles Lake Formation.—Continued

AB sab6 -- 2,110 -- 1,960 -- --

C3-k H23-r

sab55 -- 1,840 -- 1,810 -- --

C-15p H24-c

sab4 -- -- -- 1,760 -- --

H24-e

sab3 -- -- 1,850 -- --

H23-c

sab2 -- -- 1,830 -- --

H23-c

sab1 -- -- 1,810 -- --

H23-c

sab6 2,100 -- 2,120 -- 2,010 1,840

L21-1 M18-m H28-e L8-k

sab7 1,700 -- 1,850 -- 1,920 1,710

I36-m M6-m H28-e I33-l

A sa4 -- -- -- 1,840

I31-h

sa3 -- -- -- -- 1,980

K13-p

sa2 -- -- -- -- 1,770

I32-r

sa1 -- -- -- -- 1,970

K24-f

sa 2,280 2,250 2,260 1,800 2,180 --

L24-a A27-r M30-n H23-f H28-8

sag -- -- 2,280 2,280 -- 2,280

M19-d H26-c L6-e

saa 1,660 -- -- -- -- --

F32-l

Tufa st 2,280 1,890 2,220 2,260 2,030 1,990

K22-e C15-k M19-l H26-b H28-l L19-h

1

Elevations in feet above mean sea level; section labels as explained on plate 1 and in text.

2

Locations cited on plate 1 are only those outside of areas shown on plates 2 to 4.

3

Includes map units scla, sc1b, sc1c, and sc1d

4

Subunits sb1 and sb2 on plate 2A not equivalent to subunits with same numbers on plates 3A and 4.

5

Subunit sab5 on plate 2A correlated with subunits sab1, sab2, sab3, sab4, and sab5 on plates 3A and 4 (see table 2).

6

Lacustrine sediments, undifferentiated.

7

Alluvial sediments, undifferentiated.

 Elevations and locations on plates1

Unit Map 

label Pl. 12 Pl.2A Pl.2B Pl.3A Pl.3B Pl.4
Stratigraphy and Lithologies of Mapped Units 45

soils that are imbedded in deposits of Lake Lahontan, Nevada; 

the eolian flux came largely from lake deposits that became 

exposed when the lake retreated, and the amount of dust was 

proportional to the percent of upwind area exposures, resulting in areally variable, but accelerated rates of soil formation 

during these dry periods. Machette (1985, p. 8) documents 

the amounts of aeolian carbonate accumulating and contributing to the soils in New Mexico, and he further notes the 

large amounts of dissolved Ca found in rainwater (which also 

contains dissolved CO2). In Searles Valley, where virtually all 

the fine lacustrine sediments exposed at the surface contain 5 

to 10 percent CaCO3, both mechanisms could have created an 

abnormal flux of both dissolved Ca and particulate CaCO3.

Unit C (13.5 ka to 10.5 ka)

Unit C is the outcropping equivalent of the upper two 

subdivisions of the subsurface Parting Mud as proposed by 

Mankiewicz (1975), plus a thin overlying third layer described 

by Smith (1979, p. 51). Mankiewicz’s two subdivisions, which 

together are 0.75 m thick, are finely laminated and contain 

large gaylussite and pirssonite crystals. They represent a 

period of time estimated by him to extend from 12.3 ka to 10.5 

ka (Smith, 1979, p. 73, 111-112), about 1.8 k.y.; the ages used 

in this paper (13.5 ka to 10.5 ka) increase the length of this 

period to 3.0 k.y.

Outcrops of unit C are found at elevations up to 2,280 

ft in Searles Valley. The gravel facies, deposited as beach 

deposits near bedrock, and as bars elsewhere, are similar to 

those of unit B, except finer in the same depositional setting. 

Gravel facies are mapped separately on plates 2 to 4. Most 

fragments are subangular to subround, and the deposit surfaces 

are dark gray except for brownish-orange bar and sheet gravels 

assigned to unit C at elevations between 1,840 and 1,960 ft 

(pl. 2A) in the Valley Wells Wash area. A bar of this age and at 

1,960 ft in the southern part of Searles Valley is light brown. 

Above about 1,960 ft, few gravel bars of this age are found.

Near the highest shoreline levels, the bar deposits mapped 

as parts of unit C are composed of sand. The best examples 

are in sec. A27-g,h,j (pl. 2A); less well developed bars at this 

elevation crop out in secs. N6-r and N8-d,e (pl. 1). The sand 

is moderately well sorted, subangular to subround, and most 

commonly in orange- or yellow-tan hues (5Y-10YR6-7/1-4). 

Bedding is fair to poor in most outcrops. Where not in the 

form of bars, sand layers assigned to unit C are mostly fine to 

coarse, well bedded, moderately indurated, calcareous, and tan 

to slightly orange or pink in color. Small mollusks are present 

in some beds.

Throughout virtually all of the Searles Lake basin, silt, 

clay, and marl deposits of unit C are thinly bedded and flatlying (figs. 21A and B), and virtually all are thinly laminated 

(fig. 10). Laminae are less distinct and sometimes missing in 

fine sediments exposed along the east side of Searles Valley, 

but elsewhere they are a reliable indicator of fine sediments 

belonging to unit C. Laminae are most commonly nearly 

white and range in thickness from paper-thin to about 3 mm, 

but 1-mm layers represent an approximate average. The layers 

separating these laminae are pale olive (10Y6/2) and typically 

several times thicker than the white laminae. Outcrop samples 

have high concentrations of aragonite in the white laminae, but 

calcite is detected. (In subsurface, white laminae are composed 

of pure aragonite; see Smith, 1979, p. 48, 51.) Dolomite is also 

a common constituent in outcrops of fine sediments from this 

unit, and megascopic gypsum crystals are present in subunit sc1

in many areas. Gaylussite crystals are present in outcrops at one 

place (sec. I23-p). The unlaminated subunit sc4 (pl. 3A) is typically dusky yellow green (5GY5/2), massive, and when moist 

(as it commonly is) has the plastic properties of modeling clay.

Nodose tufa deposits are found both at the base of, and 

within, sediments of unit C. Basal tufa deposits cannot be 

distinguished from those deposited during the late stages of 

deposition of unit B, so 14C dates on samples from this horizon 

mostly scatter between 15 ka and 12 ka. However, tufa coating 

the surface of a channel that appears to have been eroded just 

prior to deposition of 20 m of sediment correlated with unit 

C (H28-e,f, pl. 3B; fig. 21A) provided nearly identical dates 

(12,700±60 and 12,910±50 yrs) on carbonates. In the southern part of the basin (sec. L18-r, pl. 4), tufa whose carbonate 

and organic carbon content were dated at 12,200±450 yrs and 

11,720±500 yrs, respectively, preceded the construction of a 

prominent bar during unit C time. The carbonate in tufa 10 

km to the east (sec. L12-r), dated at 12,110±30 yrs, preceded 

deposition of the same bar. A thin bed of nodose tufa that lies 

about 1 m up from the base of unit C (fig. 21B) and persists 

throughout much of the Poison Canyon area (pl. 3A) is dated 

as 13,300±500 yrs. Unit C contains thin beds of tufa in many 

other areas, showing that lake chemistry during this period 

was favorable for tufa growth.

The sediments assigned to subunit sc4 appear to have 

acquired their plastic properties soon after deposition. Softsediment deformation of this unit, well exposed in sec. I18-a 

(pl. 3A; fig. 22), locally produced near-vertical attitudes of 

beds. The underlying deposits of subunit sc3 are scarcely 

deformed, although they were eroded subaerially prior to 

deposition of subunit sc4.

In spite of the small amount of time allocated to the deposition of unit C, it is widespread in Searles Valley. It undoubtedly once covered virtually the entire floor of Searles Valley 

below the 2,280 ft contour. Preserved thicknesses vary greatly, 

with 5 to 20 m exposed in the western part of the basin near 

the paleoinlet (pls. 3A and 3B), and 1 to 3 m in the south half 

of the basin. In the northern part of the Valley Wells Wash area 

(pl. 2A), bars assigned to subunits sc1 and sc3 are composed 

of 5 to 8 m of very coarse sand and pebbly sand that was 

largely derived from the weathering of plutonic rocks in Great 

Falls Basin (secs. B12, B13, C7, pl. 1).

Unit CD (10.5 ka to 6.0 ka)

Unit CD of the Searles Lake Formation is equivalent 

to the subsurface Upper Salt (table 3), and it is thus of early 

Holocene age. Whereas the Upper Salt is typically 15 m thick, 
46 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

A

B

sc2 sc1

sc2 sc3

Tufa sc1/sab7contact

CD

sab7

sc1

Tufa B sc3c sc3b sc3a

oal

al

Figure 21. Two outcrops that include thick sections of unit C of the Searles Lake Formation. A, View 

north from California Highway 178 of sediments exposed 1.6 km (1 mi) west of the upper end of Poison 

Canyon (pl. 3B; see also appendix 1, measured section H28-f); unit B and subunits sc1 to sc3c are 

labeled on the photograph. Unit BC is missing; units older than unit B are covered by older inactive 

alluvium (oal), and active alluvium (al). A thin bed of nodose tufa (labeled) covers an erosional 30° 

slope formed after deposition of subunit sc2 and before deposition of subunit sc3a. That tufa yielded 14C ages of 12,700±60 and 12,910±50 years B.P. B, Sediments exposed on south side of California Highway 178 at type section of Searles Lake Formation (see fig. 6). Deposits of unit C rest on flat erosional 

surface underlain by subunit sab7, which was exposed when sublacustrine erosion removed overlying deposits of units B and BC. Flat zone of nodose tufa (labeled), about 1 m up from base of subunit 

sc1, was traced 150 m northeast and sampled for 14C dating, yielding an age of 13,300±500 years B.P.
Stratigraphy and Lithologies of Mapped Units 47

unit CD in most of the areas shown on plates 1, 3A, 3B, and 4 

consists of only a few meters of sediment; locally, where units 

C and D are mapped as being in contact (sec. I16 and I21, pl. 

1), it is a sand layer as thin as 2 cm.

This alluvial unit was deposited at the time the last of the 

lakes responsible for unit C was retreating. In many areas, unit 

CD is perched on the tops of ridges, resting on very slightly 

eroded surfaces underlain by sediments of unit C. There, alluvial sediments must have followed the retreating lake, before 

the development of a network of alluvial channels at lower 

elevations diverted the remaining inflow and its sediment 

away from those abandoned surfaces. Most alluvial deposits 

of unit CD in the Poison Canyon area (pl. 3A) are pebbly sand 

or pebble gravel, 1 to 3 m thick. Outcrops are tan or slightly 

orange, and a thin pebbly lag gravel commonly is present on 

the top surface. Reworked mollusks are noted locally. A fossil 

soil, present in some areas, is similar to the BC soil, but this 

CD soil is generally thinner, the calcite nodules are smaller, 

the clay content is very small or missing, and the red root(?) 

marks are less prominent. In most of the Poison Canyon area, 

unit CD is 1 m to 3 m thick, but its base rests in part on a 

channeled surface, with channel depths ranging from less than 

1 m (fig. 6) to about 8 m (fig. 22); these channel depths are 

locally added to the more typical unit thickness. Erosion preceding deposition of unit CD in the channeled area extended 

to depths below that of the present wash, yet the smooth upper 

surface of unit CD in that area has a steeper gradient than the 

present alluvial surface and lies more than 10 m above it. This 

erosion could have been the result of a short (single?) episode 

of renewed overflow from China Lake after Searles Lake had 

nearly desiccated. Very shortly thereafter, more than 10 m 

of unit CD alluvium buried the channeled surface as Searles 

Lake continued to recede.

Deposition of unit CD is also responsible for a somewhat 

coarser, exhumed deltaic fan near the edge of Searles Lake 

and east of the railroad tracks (sec. I8, pl. 1). There, unit CD

is more than 2 m thick in places and rests on subunit sc4; silt 

and thin gravel mapped as unit D overlie its east edge. Along 

this contact to the southeast (sec. I16-c; pl. 1), unit CD thins to 

a sand layer only 2 to 20 cm thick.

On the east end of the Spangler Hills (secs. I19-p and 

I30-c,f,g, pl. 4), two fans composed of coarse boulder alluvium derived from the upstream canyons are mapped as unit 

CD (fig. 23). The alluvium rests on the nearly undissected 

beds of subunit sc1 and is overlain by both the fine and coarse 

facies of unit D. Although the lake responsible for unit D rose 

to the 1,800-ft contour, covering most of these fans, stillstands 

at that and lower levels must have been brief, because shorelines were not developed. Modern alluvium occupies channels 

cut about 1 m deep in these deposits of unit CD.

In areas 3 to 11 km east of The Pinnacles, remnants of 

unit CD are found as caps on as much as 5 m of dissected 

sediments mapped as units B and C. The gravels are alluvial, with maximum pebble sizes of about 2 cm; the CD

soil is present on some remnants. However, to the north and 

northeast of these dissected areas (starting at about sec. J29), 

and south nearly to the Garlock Fault, outcrops of unit CD 

descend nearly to the same grade as modern alluvium, and the 

gravels of this unit constitute most of the slightly dissected 

alluvial fan surface along the south half of the Slate Range. 

In these areas, the fragments are also angular but larger than 

those in modern alluvium; the largest are about 30 cm across 

and the average is near 5 cm. Most fans are medium dark 

gray, because the fragments are mostly metamorphic rocks 

and little desert varnish has developed on them. Below 1,800 

ft elevation, but not above it, many of the schistose fragments 

on the surface of the deposits mapped as unit CD are spalled, 

apparently the result of salt wedging during stands of the 

saline lake responsible for unit D. As on the fans of this age 

exposed east of the Spangler Hills (fig. 23), shorelines were 

not developed by that younger lake in these areas, and the CD

soil is preserved in only a few places. Downhill, the gravels 

of unit CD appear to be overlain by finer gravels mapped as 

the gravel and sand facies of unit D, although the stratigraphic 

relations along this contact are subtle.

Unit D (6.0 ka to ~2.0 ka)

Unit D, of middle Holocene age, occupies a larger percentage of the mapped area (pl. 1) than any other Cenozoic 

deposit. It is the lateral equivalent of the informally named 

Overburden Mud in subsurface studies (Smith, 1979, p. 

66-68), which core logs show to be composed of mud (moist, 

dark green, pirssonite-bearing clay, silt, or sand) beneath the 

edge of the dry lake and discontinuous beds of mud alternating with salines (halite and several other evaporite minerals) 

beneath its center. Core logs describe many of the saline 

layers as impure, poorly consolidated aggregates of euhedral 

to anhedral crystals, although some of these are interbedded with thin zones of pure, coherent crystal masses that are 

locally vuggy. A 14C date on wood from a depth of 2.4 m 

(Stuiver and Smith, 1979, p. 73) indicates its age at this level 

to be near 3,500 years.

This unit was deposited in a lake that rose to about the 

1,800-ft contour. Lacustrine silts and gravels identified as part 

of this unit are found in many areas, especially southwest of 

Searles Lake, and they are traced uphill to the 1,800-ft contour 

in two areas: In sec. I31-h (pl. 4), deposits of the sand and 

silt facies are preserved, and in sec. H24-k, q (pl. 3A), lacustrine gravels of the gravel and sand facies can be traced to 

the 1,800-ft contour, where they grade into angular-boulder 

alluvial gravels that extend almost to the 2,000-ft contour. 

These outcrops thus document a lake that was more than 200 

ft (60 m) deep when its floor was at an elevation near 1,600 ft. 

A nearshore bar, 1 to 2 m high and composed of sandy gravel, 

is found near the 1,720-ft contour in one area (I33-q, r, pl. 4).

Outcrops of unit D are divided on plate 1 into three facies 

and on plates 3A and 4 into two facies. Weathered surfaces of 

the sand and silt facies are characterized by loosely compacted 

clastic materials that weather with puffy surfaces, have thin 

halite efflorescences, and contain (rarely) small buried pods 

of ulexite. Their color systematically approximates grayish 
48 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

orange (10YR7/4). Fresh surfaces are commonly very well 

cemented by halite, as is much of the underlying 10 to 20 cm 

of sediment of units B and C. When outcrops of the sand and 

silt facies of unit D are traced from the outermost edges of 

Searles Lake toward its center, they become first a zone of 

moist, sticky, and soft mud on which it is impossible to drive 

(or locally, to walk), then they become a zone of halite-rich silt 

of varying shades of gray or brownish gray that has a tendency 

to form polygonal cracks and crusts that produce irregular 

surfaces (Smith, 1979, fig. 29), and finally they grade into the 

salt facies of unit D (pl. 1), which is smooth, slightly muddy, 

yellowish gray (5Y6-8/1) halite that is hard and coarsely crystalline. The contact between the salt facies and the surrounding 

halite-rich silt segment of the sand and silt facies, however, is 

gradational—almost hypothetical—because the properties of 

the surface layer change so gradually from one to the other; 

Haines (1959, fig. 6) plotted the approximate position of this 

transition as shown on plate 1.

Above the 1,760-ft contour, the gravel and sand facies of 

unit D (unit sdg; pls. 1, 3A, and 4) is a deposit generally less 

than a meter thick composed of angular to subangular pebbles 

or cobbles that weather to shades of dark orange-brown or 

black and are locally separated by a silt matrix. Below 1,760 

ft, the deposit consists in most places of a very thin gravel 

layer that is always either the uppermost or only bed of unit D. 

Fragments in it are similar but smaller, and they may form a 

widely scattered one-pebble-thick pavement (fig. 24). Where 

shown on plate 1 around the edge of Searles Lake, this facies 

mostly consists of a zone of lag gravel—concentrations of 

pebbles and small cobbles scattered upon the surface of the 

sand and silt facies. Near Argus (sec. F19-a,b), this facies 

consists of boulders as large as 0.5 m. Although the coarse 

fragments account for only a small fraction of the exposed 

material in these areas, they are mapped as part of this facies 

because they extend as much as a half kilometer further onto 

the dry-lake surface than any other coarse layer in this unit. 

These deposits appear to record a brief—quite possibly, a 

single—climatic event of uncommon intensity that transported 

angular alluvial gravels far into the lake, which then redistributed them laterally, parallel to its shore. This event probably 

occurred during the final stages of unit D deposition.

In secs. J29-q,r and J32-a (pl. 1), an area where schistose 

rocks from the Slate Range make up much of the alluvial and 

nearshore lacustrine sediment mapped as unit CD and the 

gravel and sand facies of unit D, many of the schistose pebbles 

and cobbles between about 1,700 and 1,800 ft elevation are 

partially split along their planes of schistosity. This splitting 

appears to be a product of the wedging action of subaerially 

crystallizing halite, where its dissolved components were 

repeatedly introduced by fluctuating lake levels or by splashing waves. This provides additional evidence of the high salinity of the lakes that deposited unit D.

In the area between the Spangler Hills and Searles Lake, 

deposits of unit D commonly rest on small terraces along the 

sides of the modern drainages. In numerous examples, the terrace level is about halfway between the present channel floor 

and the top of the nearly planar surface that sublacustrine erosion developed on exposures of unit B or C at the close of unit 

C deposition. It appears that the amounts of dissection prior 

to and following deposition of unit D were similar, and this 

implies that comparable climates and periods of time preceded 

and followed deposition of that unit.

In subsurface, the Overburden Mud (and thus unit D of 

this paper) averages about 7 m thick, but isopach contours of 

this subsurface unit (pl. 1) show a fairly systematically changing pattern of thicknesses. The criterion used here to determine 

the base of this unit in subsurface logs differs from that used 

earlier (Smith, 1979, p. 56, 66); here, only the core logs of 

Haines (1957, 1959) were used, as we know that the logging 

procedures were uniform. The contact between the Upper Salt 

and Overburden Mud is here placed at the top of the highest 

zone of mud-free salt that is several feet thick and clearly part 

of the Upper Salt. The resulting isopach contours on the Overburden Mud define a unit that ranges from less than 15 ft (4.6 

m) thick to more than 40 ft (12.2 m) thick.

Within the present limits of Searles (dry) Lake, the thickest zones of the Overburden Mud are composed almost solely 

of mud; they overlie the outer rim of the subsurface Upper 

Figure 22. Field sketch of exposures of Searles Lake Formation that document soft-sediment deformation of subunit sc4 and subaerially 

eroded channels cut on tops of both subunits sc3 and sc4. Deposits of unit CD subsequently filled those channels. Location: plate 1, sec. I18-a.

12

10

8

6

4

2

0 5 10 20 30

Approximate scale

(meters)

CD Thin lag gravel CD

Board

wall

EAST sc4 sc3 Level of alluvial wash sc4 sc3 sc3 sc4 WEST

? ?
Stratigraphy and Lithologies of Mapped Units 49

Salt, whose lateral limits (Smith, 1979, fig. 27) are generally 

within a kilometer of the 40-ft isopach contour of the Overburden Mud (pl. 1). The thinnest zones overlie the north-central 

part of the Upper Salt. A complete isopach map of unit D

(including the Overburden Mud) would show a circular zone 

just inside the edge of the present dry lake in which the unit 

has a thickness of more than 35 ft (11 m) and a thinning from 

all directions toward the center of the lake, where it is less than 

20 ft (6 m) thick. Outside the limits of Searles Lake, unit D

thins over a short distance to thicknesses less than 1 m.

Surface and subsurface evidence combine to show that 

unit D was deposited by an unusual lake: Its subsurface clastic 

deposits have a lower percentage of microcrystalline carbonate 

than any other perennial-lake unit (Smith, 1979, table 18); its 

saline layers are discontinuous and commonly composed of 

mixed aggregates of loose crystals (Smith and Haines, 1964, 

p. 34); and its basal contact beneath the present, nearly flat 

dry-lake surface has a concave-downward shape (pl. 1). These 

properties require development of a depositional model that 

differs substantially from those envisioned for earlier perennial lake stands. The most important element of this model 

is recognition of the evidence that expansion of the lake that 

deposited unit D followed the desiccation of the Upper Salt 

(Smith, 1979, p. 112). This means that fresh, rapidly moving 

water flowed directly onto the outer edges of the exposed salt, 

and those areas underwent the most intense solution. Presumably, less solution of salt occurred in the central area because 

by the time the inflowing water reached them, it was not flowing as rapidly and was partly or totally saturated with salts. 

This solution pattern meant that relative to the peripheral zone 

of deep solution, there was a shallower underwater plateau of 

undissolved salt, 20+ ft (6+ m) high, in the north-central part 

of the lake.

The inflowing water came mostly from China Lake overflow via Salt Wells Valley (fig. 1B), which is why the deepest 

and widest zone in which salt was removed by solution was 

along the southwest edge of the exposed salt body. Smaller 

volumes of water from Valley Wells, Randsburg, and Teagle 

Washes are probably responsible for the less intense solution 

along the southern and and northern edges, and still smaller 

volumes from the Argus and Slate Range canyons produced 

even shallower peripheral zones of solution. As the clastic 

loads brought by the inflowing waters entered the new lake, 

they tended to fill the deeper zones around the edges rapidly, 

and the floor of the lake once again approached its equilibrium 

shape—that of a shallow basin. This selective solution pattern 

is considered responsible, therefore, for the concave-downward geometry of the basal contact of the Overburden Mud—

the central facies of unit D of this report (pl. 1). Outside of the 

area of the Upper Salt, no solution occurred, and sediments 

deposited in this zone were only a meter or two thick.

Planimeter measurement of the areas of isopach contours 

(pl. 1) allows approximation of the volume of salt that was 

dissolved from the zone surrounding the underwater plateau 

(about 8x108

 m3). Converting this volume to weight of salts 

(17x1011 kg), and using the estimated volume of water in a 60-

m-deep lake (16x109 m3; Smith, 1979, fig. 32), suggests that 

the salinity was near 110 g/L. If some salt was dissolved from 

layers above the preserved level of the underwater plateau, the 

lake’s salinity was higher, but saturation was unlikely. Smith 

and others (1987, p. 814-817) describe processes observed in 

1969-70 at Owens Lake, California, when fresh water flowed 

onto the 2-m-thick salt body. They found that a year later only 

about 20 percent of the salt had dissolved at the study area, 

which was 12 km south of the inflow source, and the lake 

water, at 135 g/L, had only half the salinity required for saturation. It was later found that a thin layer of sediment had been 

deposited on the submerged surface of the partially dissolved 

salt, effectively armoring it. That layer apparently halted 

solution of the Owens Lake salts long before the lake water 

Figure 23. Vertical aerial view of two alluvial fans (left-center of 

photograph) at east end of Spangler Hills (pl. 4, secs. I19 and I30). 

North is toward top. Note lack of shorelines on the fans, composed chiefly of unit CD, even though they were later partially 

covered by lake that deposited unit D, whose silts and gravels 

overlie the coarse gravels of unit CD along the toe of the fans. 

Light-colored deposits northeast of fans are lacustrine sediments 

of units B, C, and D. (Segment of USGS photograph AXL-33K-117; 

because of the direction of the sun, this image is better seen in 

three dimensions when turned upside-down.)

0 1 MILE

0 1 KILOMETER

D

CD
50 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

became saturated. This process seems likely to be one that 

could accompany the solution of exposed salts in any lake.

Partially dissolved halite crystals in subsurface samples 

from this unit also show that the lake water that reworked 

them was unsaturated (Smith and Haines, 1964, p. 16), but 

the majority of crystals are now euhedral, requiring a postdepositional history of overgrowths. Therefore, the impure, 

poorly consolidated aggregates of salt crystals in the Overburden Mud (or unit D) are viewed as reworked mixtures of 

new clastic-silicate material and older salt crystals that were 

transported as sediments after being disaggregated during partial solution of the outer facies of the Upper Salt body. These 

impure aggregates of salt crystals and mud are concentrated 

in the central facies of the deposit. This may be because most 

salts have lower densities than silicates. The density of quartz is 

only about 23 percent more than halite, but after subtracting the 

buoyancy of these minerals in a brine having a density of 1.1, 

quartz is 46 percent heavier than halite. Salt crystals, therefore, 

may have responded to sorting processes like silicate fragments 

half their size, and thus they were transported and concentrated 

in the more central and deeper parts of the water body.

Tufa

Tufa deposits that take the form of encrustations, mounds, 

terraces, and pinnacles locally provide the most scenic and 

unusual aspect of the Searles Lake Formation. The tufa is 

composed of porous calcite or aragonite that is light to moderate brown (5-10YR4-6/2-4) on weathered surfaces and very 

pale orange to light brown (5-10YR6-8/2-4) where unweathered. Tufa assigned to this formation is found in mappable 

amounts at all elevations between the 1,680-ft contour and 

the top shoreline at 2,280 ft, but the most notable concentrations are found between the 1,800-ft and 2,000-ft contours and 

along the top shoreline. Concentrations of tufa large enough or 

thick enough to map are limited to the north, west, and south 

sides of Searles Valley (cover image and pl. 1). The reduced 

amount of tufa along the east side of Searles Valley is attributed to the probable continuous wave action along that shore, 

a result of the prevailing winds out of the west. This inference appears to conflict with some of the conclusions reached 

in a later section based on the directions in which lacustrine 

bars were built when the lake was nearly full, but those 

reconstructed wind directions reflect the most intense storms 

Figure 24. Scattered fragments that represent the characteristic appearance of the gravel and sand facies of unit D where 

it extends onto the flat surface of Searles Lake (pl. 1). The fragments are considered to be remnants of a more continuous 

layer that was introduced near the close of unit D time and spread laterally by lake-current action. Hammer is 33 cm long. 

View toward southwest; location: plate 1, sec. C34-f.
Stratigraphy and Lithologies of Mapped Units 51

rather than directions that prevailed during the long periods 

between storms.

In this paper, tufa deposited as part of the Searles Lake 

Formation is described as being one of two types, although 

none of the geologic maps (pls. 1-4) differentiate between 

them. The older form is termed lithoid tufa (Gr., lithoeides, 

like a stone), an allusion to its more dense and massive 

appearance; the term was proposed by Russell (1889, p. 

311) for application to tufas observed at Mono and Lahontan Lakes. The younger form is termed nodose tufa (L., 

nodosus, knot), alluding to its node-covered outer surface. 

The term was first used to describe tufa, I believe, by Scholl 

(1960, p. 419).

Scholl (1960, p. 416-418) divided the tufa lithologies 

found in the south half of Searles Valley into seven types: 

“massive lithoid” tufa constitutes the older tufa unit of this 

report and was discussed earlier. His “stony lithoid” and “cavernous lithoid” tufas are combined in this study into “lithoid” 

tufa. His “dendritic,” “nodose,” “tubular,” and “lobate” tufas 

are combined here into “nodose” tufa. Lithoid tufa is most 

commonly found in unit A of the Searles Lake Formation, 

but a few similar tufa beds are found in unit AB. Nodose tufa 

growth took place mostly during deposition of units B, BC(?), 

and C, although instances were noted where this tufa type is 

also interbedded in sediments of unit AB. Tufa is not associated with units CD and D.

Lithoid tufa is the most abundant type of tufa in Searles 

Valley, and the most unusual form of lithoid tufa is as tufa 

towers. The Pinnacles (secs. I32, I33, L4, and L5, pl. 4), 

near the center of an area designated as The Trona Pinnacles 

National Natural Landmark because of them, are tufa towers 

that are as tall as 25 m but more commonly are about half that 

high (figs. 25 and 26). Nodose tufa as thick as 1 m coats many 

of these towers, but the locations, shapes, and sizes of The 

Pinnacles were determined by the earlier episode of lithoid 

tufa growth. Similar but smaller towers composed mostly of 

lithoid tufa once characterized much of the southwest arm of 

Searles Valley, but mining of them in the 1950s and 1960s for 

ornamental rock has destroyed most. The lithoid tufa towers 

now project up through all younger deposits, but stratigraphic 

evidence indicates that many of the towers began to form 

early during deposition of unit A. Subunit sa3 commonly has 

tufa towers or tabular layers at its base; examples are found at 

elevations of 1,720 ft (sec. I32-r, pl. 4), 1,760 ft (sec. I32-m), 

1,920 ft (sec. K13-r, K24-p), and 1,960 ft (sec. L7-q). The 

bases of many of the large lithoid tufa towers and tabular 

masses, however, are concealed, and they could have commenced their growth on strata near the bases of subunits sa1

or sa2; examples where this relation is exposed are found in 

secs. L8-h and L18-c (pl. 4), where tufa is mapped resting on 

gravels of the Christmas Canyon Formation (fig. 9).

Massive tabular deposits of lithoid tufa also are found 

associated with the highest shoreline at 2,280 ft and between 

the 1,800-ft and 2,000-ft contours along the Argus Range 

and Spangler Hills. In sec. H11-l (pl. 1), lithoid tufa forms 

a bench 300 m long and 3 to 10 m wide along the highest shoreline, and its deposits extend 15 m down the slope. 

In sec. K22-e,f (pl. 1), at and below the highest shoreline, 

lithoid tufa forms a discontinuous sheet 0.3 to 2.0 m thick 

that covers an area of about 0.3 km2

 southeast of the shoreline. Smaller tabular masses of lithoid tufa are found at and 

below 2,280 ft elevation in almost every canyon in the Argus 

Range and Spangler Hills.

These tufa deposits are considered to be the combined 

product of inorganic and organic reactions. The organic 

processes inferred here depend on the consumption of CO2

by algae. Very similar structures growing on the floor of Lake 

Van, Turkey, that have similar mineralogies, zonations, and 

textures, are shown to be in large part the products of microbes 

(Kempe and others, 1991), but microscopic textures show 

algae that require sunlight to have been involved in the formation of the Searles Valley tufas. Inorganic chemical reactions 

that could have contributed to the deposition of tufa are as 

follows:

CO2 + H2O = H2CO3 (1)

H2CO3 = H+ + HCO3 ̄ (2)

HCO3 ̄ = H+ + CO3

= (3)

Ca++ + HCO3 ̄ + OH ̄ = CaCO3 + H2O (4)

Ca++ + 2 HCO3 ̄ = CaCO3 + H2O + CO2 (5)

Ca++ + CO3

= = CaCO3 (6)

Because H+ appears on the right sides of equations (2) and (3), 

and OH ̄ appears on the left side of equation (4), these reactions are affected by pH change. Mixing near-neutral spring 

waters that contain significant amounts of Ca++, H2CO3, and 

HCO3 ̄ with alkaline lake waters that contain abundant CO3

=

and a greater concentration of OH ̄ than of H+ drives all of the 

above equations to the right. This promotes increased concentrations of CO3

= and, to the extent that Ca++ becomes available, 

precipitation of CaCO3 (equations 4, 5, and 6). Similarly, loss 

of H2O by evaporation (equation 4), or loss of CO2 if its partial 

pressure exceeds that of the atmosphere (equation 5), promotes precipitation of CaCO3.

Two inorganic processes appear to have been active, most 

prominently in the deposition of the lithoid variety of tufa: 

(1) Springs on the floor of the lake injected relatively fresh, 

Ca-bearing ground water into the relatively saline, highpH, CO3  ̄ rich lake, causing precipitation of CaCO3 around 

the orifice; this process primarily followed equation 6, but 

processes following equations 4 and 5 probably also contributed. These precipitates grew into pinnacle-shaped masses that 

contained internal vertical conduits, still preserved in many 

of the tufa towers, which allowed spring-water injection to 

continue. Many of the pinnacle-shaped tufa masses are crudely 

aligned in en echelon patterns (figs. 25 and 26; pl. 4), as if the 

distribution of springs that produced them was controlled by a 

series of similarly oriented faults. A classic discussion of this 

process, based on evidence observed around Mono Lake, is 

provided by Russell (1889, p. 310-315). (2) In alkaline saline 
52 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

lakes, the partial pressure of CO2 in the lake water can be much 

greater than that of the CO2 in the atmosphere (Smith and others, 1987, p. 824). For this reason, the splashing of such waters 

along shorelines increases the water’s surface-exchange area 

and causes loss of CO2 to the atmosphere, producing CaCO3

(equation 5). Additional Ca++ can also come from surface drainage, increasing the volume of calcite and aragonite near the 

point where the drainage entered the lake (equation 6). This process is considered primarily responsible for the persistent tufa 

benches that parallel contour lines in many parts of the basin.

Algae may not have been required for deposition of the 

lithoid tufa that formed the pinnacle-shaped and shorelinebench masses, but remains of algae or organically pigmented 

zones are found in all samples of these materials. It appears 

that algae took advantage of the favorable environment 

provided by the growing tufa structures. The tufa deposits supplied a firm substrate, and the crystallization of tufa, following 

equation 5, created excess CO2 that was required by the algae 

during their photosynthesizing stage. Reactions in the wavezone environment depleted some of the lake-water CO2, but 

the shallow waters that characterized this zone also allowed 

ample sunlight, which was necessary for algal development. In 

this environment, loss of CO2, as a result of algal consumption 

or escape to the atmosphere, thus drove equation 5 to the right 

and caused deposition of CaCO3.

Nodose tufa deposits show more evidence of algal participation in their formation. They are darker brown (5YR3-5/2) 

than lithoid tufa because they contain more organic pigmentation, they tend to be thickest on the horizontal part of the 

substrate surface that faces the sun, and their nodular surfaces 

parallel the remains of algae growth patterns as seen in thin 

section (discussed below). Possibly the greater amount of 

organic pigmentation is a result of the younger age of these 

nodose deposits, relative to the age of the lithoid tufa, but the 

mineralogic and internal and external morphologic differences 

between the two types of tufa suggest that they are products of 

a different balance between depositional processes. Details of 

the role of modern algae in this depositional process, based on 

evidence observed in and around Mono Lake, California, are 

described by Scholl and Taft (1964).

Megascopic study of lithoid tufa samples reveals many 

different textures. The most common is a crude lattice strucPinnacles bar

Trona Railway

Figure 25. Oblique aerial view, looking north-northwest, of The Pinnacles and surrounding areas. Dirt road (light, irregular line 

leading toward base of photograph) indicates scale. Teagle Wash, trending diagonally toward upper right, divides pinnacle clusters. 

Tallest pinnacle (circled, right of center) is more than 30 m high. Straight feature in upper left is track embankment and cut of Trona 

Railway. Prominent gravel bar (dark ridge) between most distant pinnacles and railroad is The Pinnacles bar; gravel (subunit sa4) 

was derived from east end of Spangler Hills (upper left corner of picture).
Stratigraphy and Lithologies of Mapped Units 53

ture composed of short indistinct vertical and horizontal components about 10 to 20 cm in length (fig. 27A; see also Scholl, 

1960, fig. 3b), but outcrops were studied that displayed four or 

five different textures within a 1- to 2-m2 area. All, however, 

had large amounts of void space, and hand-lens study revealed 

botryoidal calcite linings on these surfaces in most samples. 

Scholl (1960, p. 418) reports the bulk density of lithoid tufa 

to average 1.3, meaning that approximately half the volume 

of an average sample is void space. X-ray diffraction analysis 

indicated all lithoid tufa samples to be calcite.

Thin sections of lithoid tufa reveal structures much 

like those illustrated by Scholl (1960, fig. 4). The material 

considered to be primary is cryptocrystalline calcite that in 

plane polarized light is tinted by its organic content to varying intensities of yellow brown (10YR5-6/2-4). All samples 

include areas characterized by banded structures created by 

differing concentrations of brown pigment considered to be 

algal remains. The crudely circular or elongated structures, 

typically 0.2 mm in the shortest dimension, tend to be massive 

in the middle and banded in their outer layers. In some lithoid 

tufa samples, though, 30 to 90 percent of the calcite is secondary in the form of discrete crystals 0.1 to 0.2 mm long. Some 

of these crystals are cross-cut by pigmented zones that parallel 

the outer boundary of the underlying more heavily pigmented, 

cryptocrystalline algal structure. As recrystallization processes 

normally reject material not required for the new crystals, it 

appears that the larger crystals were produced by inorganic 

crystallization of calcite. Later, though, algal mats temporar0 1 MILE

0 1 KILOMETER

Figure 26. Vertical air photograph of The Pinnacles and surrounding area; north is toward top. Note the 

tendency for groups of pinnacles to form north-trending rows (marked by long dashes), interpreted to be a 

result of the alignment of sublacustrine springs along fissures. The lacustrine bar and railroad, noted in figure 

25, are also visible in this view. (U.S. Navy photograph PTK-5-023.)
54 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Figure 27. Outcrop and thin-section 

photographs of tufa. A, Vertical face of a 

lithoid tufa outcrop. Irregular lattice-like 

texture is characteristic of this unit, but 

many other varieties also are noted. Scale 

is 15 cm long. B, Outcrop of nodose tufa. 

Nodular surface is caused by large numbers of hemispherical algal growth sites 

that collectively form a cauliflower-like 

outer surface. Pen cap is about 6 cm long. 

C, Thin section of nodose tufa in planepolarized light. Photograph by D.W. Scholl, 

who states (1960, fig. 5) that “[d]ark-colored 

lobate layers of banded tufa are probably algae secreted; banded calcite laths 

radiating from these layers may be largely 

of inorganic origin. Conceivably, the layers 

represent annual accruements. The oval 

pigmented bodies near the center of the 

photograph may be algal cells.” Image is 

about 4.7 mm wide.

BB ACC
Stratigraphy and Lithologies of Mapped Units 55

ily were re-established on the outer surface of the recrystallized material, and the new calcite deposits (containing algal 

remains) adopted the crystallographic orientation of the 

inorganic substrate. In more definite examples of secondary 

crystallization, radial wedges or anhedral crystals of colorless, optically continuous calcite cross-cut and replaced 

large sections of the cryptocrystalline material, sometimes 

systematically excluding the calcite in the center of the algal 

structures and sometimes including it. Angular silicate fragments are seen embedded in the cryptocrystalline calcite of 

many samples.

The other type of tufa in Searles Valley is nodose tufa. 

This is most commonly found as layers resting on lithoid tufa, 

bedrock, or lacustrine sediments. Deposits 2 to 5 cm thick 

are present over the same elevation range as lithoid tufa, and 

masses 50 to 100 cm thick are found in some areas between 

the 1,720-ft and 1,880-ft contours. Beds of nodose tufa, 2 to 

4 cm thick, also occur within units AB, B, BC, and C of the 

Searles Lake Formation.

Hand specimens of nodose tufa are mostly characterized 

by small-scale cauliflowerlike forms, with upward-flaring 

clusters of lobate masses that are 0.5 to 1 cm in diameter 

at their widest point (fig. 27B). The lobes are composed of 

adjoining hemispherical, tubular, or crenulated structures a 

few millimeters in diameter that are believed to be individual 

algal colonies (Scholl, 1960, figs. 4-6). Weathered surfaces 

are commonly pale brown (5YR5/2); fresh surfaces are 

lighter. Spaces between clusters generally range from 2 to 5 

mm at their bases to less that 1 mm at their tops; lacustrine 

silt or sand fills these spaces.

Thin-section study of nodose tufa samples confirms the 

cauliflowerlike description and shows the algal structures to 

be lobate bands that parallel the outer surfaces. The material 

is composed of cryptocrystalline aragonite that is tinted with 

varying intensities of brownish pigmentation. Individual algal 

structures are mostly 1 to 3 mm in diameter in a horizontal 

plane, but vertically oriented sections reveal lobate growth patterns having wavelengths of 10-20 mm (fig. 27C). Some zones 

of larger carbonate crystals appear to be secondary, but as in 

the lithoid tufa samples described earlier, a few pigmentation 

bands within these larger crystals suggest that there were temporary resumptions of organic tufa generation after the period 

of secondary calcite crystallization had started.

Both thin-section and hand-lens observations show 

secondary botryoidal calcite or aragonite linings in the cavities of many nodose tufa samples. Samples of tufa submitted 

for 14C dating early in this investigation yielded dates that 

were much too young according to stratigraphic evidence. 

More careful study of samples showed that contamination 

with more recent carbon in the form of secondary carbonate 

is common among the porous varieties of tufa. This inference 

was subsequently confirmed by Benson (1978, p. 303-312) 

in his study of tufa samples from Lake Lahontan, Nevada. He 

concluded that dates from dense tufa were the most reliable 

because they were nearly identical to dates from gastropods 

in the same sample.

Undifferentiated Gravels

In a number of places in Searles Valley, alluvial gravels 

that were thought to be equivalent in age to some part of the 

Searles Lake Formation could not be traced satisfactorily into 

any one unit. They have been assigned to the undifferentiated 

gravels unit (sg), which is considered the stratigraphic equivalent of the entire formation. Most of these gravels crop out at 

levels above 2,280 ft where lacustrine deposits are missing, or 

are gravels below that elevation that are isolated and cannot be 

traced laterally into lacustrine sections.

Gravel deposits assigned to this unit are considered to be 

of an age equivalent to the Searles Lake Formation because 

they are not graded to the levels of the middle and late Holocene alluvial units, nor are they similar to the lithologies of, 

or to the soils developed on, the Christmas Canyon Formation 

and equivalent or older alluvial units. Many of these gravel 

deposits are coated with desert varnish that creates a dark 

brownish-orange hue, similar to the outcrop colors of the alluvial layers in units A, AB, and BC of the Searles Lake Formation, but color alone was not considered a satisfactory basis for 

assigning the gravels to any one of those units.

Middle and Late Holocene Units

Five sedimentary units that are younger than the Searles 

Lake Formation have been separated on plates 1 through 4. 

The older alluvium unit appears to be a product of a depositional regime and climate that no longer exist. The windblown 

sand and colluvium and the windblown dune sand units are 

still accumulating or undergoing modification, but the major 

volumes of these units appear to have been deposited under 

aeolian regimes that are extinct. Sediments mapped as playa 

silt and active alluvium continue to accumulate.

Older Alluvium

Inactive alluvial deposits assigned here to the older 

alluvium unit (oal) account for more than three-fourths of 

the areas that would ordinarily be mapped as “alluvial” fans. 

(Observations in other parts of the southeastern California deserts suggest that the ratios between areas covered by inactive 

alluvium of the type represented by this unit and truly active 

alluvium are similar to these ratios in Searles Valley.) Deposits 

of older alluvium typically have a slightly undulating, unchanneled surface, with small accumulations of windblown sand 

around the bases of plants, and a weak lag gravel in areas 

where the parent material contains pebbles (fig. 28). Surface 

relief is almost always only a few centimeters, and bar-andswale topography is absent. Colors range from near grayish 

orange (10YR7/4) in areas draining granitic terrane to light 

olive gray (5Y6/1) or near-gray hues in areas draining terranes of darker rock types. Beneath the surface, small pebbles 

constitute a few percent of the deposit, and sediment colors are 

a little darker and more intense. In most areas, the older allu-
56 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

vium unit is less than 1 m thick, and in areas where it has been 

dissected by channels transporting active alluvium, the channel depth is most commonly between 0.3 and 0.6 m. Obsidian 

flakes and other Native American artifacts are present on the 

surface of this unit, suggesting that these deposits have not 

been reworked during the past century.

It appears that these sediments were deposited by ordinary 

alluvial processes during a climatic regime that led to alluviation over much of the valley floor yet did not produce torrential 

flood events. Large fragments are rare in these sediments, unit 

thickness is fairly uniform, and channeling at the base of the 

unit generally created relief that is no greater than 10 to 30 

cm. Although channels must have originally characterized this 

surface, the presently smooth surfaces appear to be the result 

of enough time to allow reworking of the top layers by small 

animals, wind, and rain that induced microerosion. The rain 

apparently percolated down into the deposit without developing channels. The surfaces of older alluvium accumulations 

resemble those attributed to sheetwash depositional mechanisms, but this depositional mechanism is believed not to be 

involved. Sheetflood bedforms, like those described by Wells and 

Dohrenwend (1985, p. 512-514) from piedmonts in nearby desert 

areas, are not found on any of these surfaces.

Around the edges of Searles Lake, sediments assigned 

to the older alluvium unit overlie all facies of unit D of the 

Searles Lake Formation, although the base of the unit in some 

areas could have been contemporaneous with deposits of unit 

D. Because the 14C age of the middle of the Overburden Mud 

in subsurface, the equivalent of unit D, is about 3,500 years, 

the base of the older alluvium unit, if not partly contemporaneous with unit D, seems likely to have an age in the range 

of 500 to 2,000 years. Artifacts lying on its surfaces allow its 

younger age limit to be almost anything up to about A.D.1900, 

as a small population of Native Americans still lived in Searles 

Valley when it was first populated by miners and prospectors 

in the 1860s.

Figure 28. Characteristic lithology and unchanneled upper surface of older alluvium unit, exposed in modern stream channel. 

The sediment is fairly well bedded, but individual beds of granule- and pebble-size clasts rarely can be traced more than 1 m. 

Sorting is poor, but clasts larger than about 5 cm are rare. Note weak lag gravel and lack of channels on upper surface. Hammer 

handle is 33 cm long.
Geomorphology 57

This unit is probably equivalent to the Post-Palmdale I 

deposits of Ponti (1985, p. 84) in the southwestern Mojave 

Desert. His Upper Palmdale unit has a stratigraphic position (his 

fig. 3) that is compatible with the older alluvium of this study, 

and it forms similar surfaces (his fig. 2), but the thickness and 

soil development of his Upper Palmdale unit are much greater 

(Ponti, 1985, p. 83) than found in these older alluvium deposits.

Playa Silt and Clay

Several small playa lakes have been formed in Searles 

Valley and adjacent areas where closed depressions have 

been created by lacustrine bars (K24-j and L18-p, pl. 4) 

or structural deformation (A9-b, L26-m, and M33-b). The 

playa surfaces are smooth and composed of silt or clay (unit 

ps) that is in most places well compacted though pervaded 

by desiccation cracks. Typical colors are grayish orange 

(10YR7/2). After exceptionally severe rainstorms, water 

runs into the playa lakes and stands on the surface for a short 

period. Small amounts of new sediment are deposited at 

those times, meaning that the surfaces of these playas represent areas of continuing accumulation.

Windblown Sand and Colluvium

Large areas that are covered by a mixture of aeolian sand 

and gravel are mapped as windblown sand and colluvium 

(unit ws). The largest of these areas are north, east, and south 

of Searles Lake, the surface of which was the main source of 

sand. Some sand, however, was derived also from erosion of 

fault gouge in the Slate Range—after being water-transported 

westward into Searles Valley, some of this sand was blown back 

toward the base of the range and part way up its flanks (Smith 

and others, 1968, p. 15). West of the southern Argus Range, 

deposits included in this unit form a sheet that nearly buries a 

low pass in the range. Severe modern windstorms rework the 

sand on the surface of these deposits, but the major part of this 

unit, which is a meter or two thick in most areas, was probably deposited at an earlier time. The colluvial aspect of these 

sediments consists of a percent or less of scattered pebbles, a 

few centimeters in diameter, that are distributed throughout the 

deposit. They appear to have been reworked from underlying 

alluvial units by burrowing animals.

These sediments are composed mostly of sand in the 

same size range found in the windblown dune sand unit, but 

the windblown sand and colluvium unit is in the form of sheets 

with no residual dune forms. Sediment colors are similar 

to those of the older alluvium unit, but distinguishing this 

unit from the others is easy because some areas within it are 

typically so filled with animal burrows that walking across it 

becomes treacherous and driving is nearly impossible. The 

windblown sand and colluvium unit rests on deposits of older 

alluvium and yet appears to be prehistoric; it could have been 

deposited during a period that was as long as 2,000 years or as 

short as a few centuries.

Windblown Dune Sand

Sand dunes (unit wd) ranging in height from 1 m to 

about 3 m rest on older deposits in a large canyon on the west 

side of the Argus Range at the latitude of Trona, and in small 

areas north, east, and south of Searles Lake. Colors typically 

are very pale orange (10YR8/2). Dune shapes are not symmetrical. Most dunes lie within areas mapped as windblown 

sand and colluvium, and they probably should be considered a 

still-active part of those larger deposits. These dunes are most 

generally free of vegetation, and modern windstorms constantly modify their shapes and destroy vehicle tracks.

Active Alluvium

Alluvium in all modern, normally dry washes in Searles 

Valley and adjacent areas is reworked and transported downstream every few years. Storms in the area, which can occur 

in any season but tend to be most intense in autumn and 

winter, are sometimes so localized that the most voluminous 

streamflow events occur in only a small area—sometimes in 

a single canyon.

The composition of active alluvium depends on the 

lithology of the bedrock and older sediments upstream from a 

given site. Most alluvium (unit al) is fine to coarse sand, and 

the larger fragments generally constitute 5 to 25 percent of the 

sediment. Fragments 0.2 to 0.5 m across are common in many 

washes, and boulders measuring several meters in the long 

dimension are found in the alluvial floors of a few washes 

leading from the Slate and Argus Ranges. Colors of the sand 

matrix vary, but most center around grayish orange (10YR7/2).

Sediment firmness, an important factor when driving in 

active alluvial washes, varies greatly from year to year, apparently as a result of the character of the last significant streamflow event. Factors that may help determine these characteristics include (1) the volume and velocity of water flowing 

during an event, which determines the thickness of the alluvial 

bed that is remobilized, and (2) the rapidity with which alluvial transport processes ceased. The latter factor determines 

whether the alluvial sediment becomes close-packed and firm 

as a result of winnowing during a gradual decrease, or whether 

the transported fragments are released from suspension so 

rapidly that winnowing and sorting cannot occur, leaving the 

deposit uncompacted and soft.

Geomorphology

The very prominent shorelines around the edge of Searles 

Valley first alerted geologists to the former existence of a large 

lake in this basin. Shorelines are preserved at many levels, but 

the highest, at about 2,280 ft, is by far the most prominent. 

This resulted from the stabilizing effect of the spillway that 

maintained the water surface at this level, allowing erosional 

and nearshore depositional processes to persist for long peri-
58 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

ods. Whenever the lake surface fell below spillway level, seasonal and longer term climatic fluctuations would have caused 

the lake level to migrate up and down and rarely occupy any 

one level for comparably long periods.

Shorelines are nearly irrefutable evidence of a former 

lake in a basin. However, they provide little information on the 

number, history, or ages of the one or more lakes that formed 

them. In Searles Valley, where many details of lake history 

can be derived from the subsurface and exposed stratigraphy, 

it is evident how complex such a history can be, yet the most 

careful study of these shorelines could not have produced the 

detailed information that has been derived from this stratigraphic study.

Shorelines around Searles Valley (or any valley that once 

contained a large water body) are of two types, erosional and 

depositional, and the volumes of rock removed by erosion 

in some areas must be roughly balanced by the volumes of 

sand and gravel deposited in the nearshore zones of other 

areas, minus the volume of sediments brought in by streams. 

Erosional shorelines in Searles Valley are best developed 

along the east side of the valley on the flanks of the Slate 

Range and along parts of the south edge of the valley. The 

Slate Range has undergone extensive tectonic brecciation, and 

shoreline erosion easily removed large amounts of bedrock 

from exposed ridges that projected into the lake. Longshore 

currents transported the fragments to more protected areas 

within nearby canyons or to other parts of the valley. Along 

the flanks of the Slate Range, bedrock erosional benches as 

wide as 100 m are found at the level of the highest lake. Thick 

sections of strongly indurated older gravel were also eroded by 

waves, leaving shoreline scarps at the 2,280-ft level that are 3 m 

to more than 10 m high in places. If the original slope of the 

older gravels surface was 5°, a 10-m scarp implies more than 

100 m of horizontal retreat of the wave-cut cliff. The highest 

shoreline level was reoccupied more than once during deposition of the Searles Lake Formation, each episode presumably 

contributing to the erosional process. Searles Lake history as 

reconstructed later in this paper (figs. 39 and 40) shows that 

the lakes with maximum depths accounted for about 18,000 

years of the 150,000-yr period; 100 m of shoreline retreat during this length of time would translate into a horizontal erosion 

rate of 5.6 m/k.y.

Study of the areas characterized by swarms of erosional 

shorelines that were mapped as deposits of units A, B, or C of 

the Searles Lake Formation, as explained in the description of 

unit A, reveals that each shoreline is visible in part because of 

the changes in slope above and below the knickline (the base 

of the eroded slope), but more importantly because of variations in the lag gravel sizes that reflect horizontal zones where 

wave energy was greatest and least. The changes in slope are 

commonly very slight, and many might not be recognized 

while traversing the area. Recognition of shorelines from a 

distance or on aerial photographs, however, is easier because 

the concentrations of smaller fragments in the area below the 

knickline have led to concentrations of windblown fine sand 

and silt in their matrix. Plants favor these levels because they 

retain more moisture, and horizontal concentrations of plants 

on a gentle slope can make such shorelines highly visible.

Depositional shorelines, more commonly described as 

beaches or horizontal concentrations of shallow-water tufa, are 

also abundant around the edges of Searles Valley. Surfaces of 

these deposits have more varied slopes than do the erosional 

shorelines, and when viewed in low-angle sunlight, they 

provide highly convincing evidence of a former lake (fig. 29). 

As noted previously, the beaches tend to be composed of clasts 

that are characteristically smaller in successively younger 

deposits occupying the same general area. This statement can 

be best documented where the gravels of each unit can be 

traced downhill into their deeper water stratigraphic equivalents, which can be placed with confidence into stratigraphic 

context. In many regions, the sediment layer forming depositional shorelines is less than 1 m thick because it formed only 

a veneer along the edges of the successive lakes. Because of 

this, relatively minor erosion over large areas has removed 

one or more of the younger gravel layers, allowing underlying 

sediments that constituted older beaches and nearshore bars to 

be exposed and mapped.

Tufa deposits in the form of benches define shorelines 

in many areas. The most massive benches are the deposits 

along and immediately below the highest shoreline in the 

Argus Range and Spangler Hills. The most extensive tufa 

platforms along these shorelines were described in the section 

on tufa deposits of the Searles Lake Formation. Much smaller 

concentrations of tufa also occur as benches and horizontal 

rows at the same and many lower levels, including areas on the 

preserved remnants of the Searles Lake Formation west of the 

Slate Range (fig. 30), where they are too thin to map separately from the underlying deposits of unit B or C with which 

they are generally associated.

Offshore bars in lakes commonly lie some distance from 

the shore. Most of the lacustrine bars in Searles Valley would 

be classified as bayhead bars, baymouth bars, or spits. Transport directions are determined from clast composition. At least 

19 distinct offshore bars can be identified, and many of them 

have multiple subordinate crests at slightly different levels. 

When their crest lines are mapped, most are in the form of 

smooth curves (fig. 31) that reflect wave refraction and current 

patterns in the lake but not minor changes in the topography 

of the lake floor. Elevations of offshore bar crests, therefore, 

may vary over a kilometer or more by more than 10 m, and 

they clearly were not deposited along the shore or at uniform 

distances from shore.

In cross section, most lacustrine bars in Searles Valley are asymmetrical. Upslope faces can be as steep as 

25°; downslope faces are more commonly 1° to 5°. Where 

bars have been dissected, internal bedding near the surface 

normally has dips similar to the preserved surface slopes, 

although cross-bedding within individual beds generally dips 

at angles near 30°. Some dissected bars show that the crest 

migrated upslope as the bar accumulated; this is especially 

well displayed in exposures of the internal structure of the bar 

composed of unit A gravels immediately northwest of The 
Geomorphology 59

Figure 29. Depositional shorelines, mostly beach deposits in this example, provide unambiguous evidence of former 

lakes. Most of the deposits to left of crest (which formed a tombolo during its deposition) are composed of unit B, deposits to the right are mostly unit A. Distance between arrows is about 400 m.

Pinnacles. Other good exposures of the internal structures of 

bars are found in secs. C3-r and C15-q (pl. 2A), H21-r (pl. 3B), 

and M18-g,k (pl. 2B).

Sediments constituting offshore lacustrine bars range 

from cobbles as large as 15 cm in their longest dimensions to 

very coarse sand. Rounding also varies—some deposits are 

characterized by a high percentage of subangular fragments, 

whereas others are composed of notably well rounded fragments. Some gravel bars have a bimodal distribution of their 

clast sizes; sediment-size analyses of these materials (appendix 2) show that while most bar gravels contain little medium 

to coarse sand, 10 to 15 percent contain fine to very fine sand 

plus silt and clay. The gravel beds, nevertheless, appear clastsupported; that is, most large fragments are in contact with 

each other and otherwise separated by voids except where 

calcite cement or wind- or water-transported fine sediment has 

filled the voids.

The two shallow tufa-lined canyons whose origins are 

inferred to have been the cause of V-shaped channels cut in 

subunit sab6 (discussed earlier) are bounded by levees of 

coarse rubble as high as 2 m (fig. 20B). The rubble fragments 

are angular and 0.2 to 1 m across. Bedrock was not significantly eroded, but the desert varnish coating on bedrock was 

removed during sediment transport and has not been entirely 

restored. The slope angles of the bedrock segment of the 

channel range from 13° to 20°. The water required to mobilize and transport debris of the size and volume found in these 

levees must have been derived from an approximately 0.02-

km2

 precipitation-collection area above the highest elevation 

of the levees (about 2,240 ft). Possibly at that time, when 

subsurface mineralogic evidence for subsurface-equivalent 

unit S-7 of the Lower Salt suggests cooler climates than at 

any other period (Smith, 1979, p. 89-90), a large volume of 

snow accumulated as drifts on the east (presently, the lee) 

side of the Spangler Hills. An intense, warm rain could have 

later mobilized this snow mass very rapidly, creating a slurry 

of snow-water, older lake sediments, and talus that had the 

competency to carry rocks of the sizes found in the levees of 

these two channels.

At the other end of the erosion-intensity spectrum is the 

widespread evidence of exhumation of fairly large surfaces 

that were previously buried by younger lacustrine deposits. 

This process must have required a very uniform erosional 

removal of the overlying layers composed of soft deposits such 

➪

➪
60 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

tfs

LC Graben

al

B

AB

Figure 30. Oblique aerial view of the west side of the Slate Range and the east edge of Searles Valley. The range’s gently sloping upper 

surface (tfs) is an exhumed thrust-fault surface (Smith and others, 1968, p. 10-11, figs. 10 and 11) that slopes toward Layton Canyon (LC). 

In the lower half of the photograph, remnants of unit AB form an elevated surface that preserves smaller remnants of light-colored silts 

and tufa layers of unit B; older gravel is exposed in most gullys dissecting these areas. The AB and B deposits stand 1 to 2 m higher 

than alluvial gravels of unit CD (slightly elevated, channeled surfaces) and active alluvium (al) in adjoining areas. Tufa 5 to 20 cm thick 

forms a medium-gray coating on the surface of light-colored sediments of unit B in foreground. Graben, which parallels Slate Range 

front (see fig. 35), is visible at head of fan. View is toward the east; unit B exposure about 360 m wide; location: plate 1, sec. J10-l.
Geomorphology 61

Figure 31. Oblique aerial view of offshore lacustrine bars of the Searles Lake Formation in Valley Wells Wash area, about 10 km northnortheast of Trona. Note even curvature of bar crests, which vary in elevation by as much as 10 m. The bars were probably approximately parallel to, but not a uniform distance from, the lake shore. Crest of nearest bar in center of photograph composed of gravels of 

unit B, next prominent bar to its left composed of unit C, and dark bar in upper left corner is covered by unit B tufa, three samples of 

which yielded 14C dates ranging from 13,650±500 to 15,520±60 yr B.P. Width of Valley Wells Wash where it cuts nearest bar is about 150 

m. View toward southwest; present Searles (dry) Lake is to the south; photograph location: plate 1, sec. C15.
62 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

as marl and fine sand, eventually exposing a more resistant 

layer beneath them. Many of the areas mapped as outcrops of 

units AB, BC, and CD (pls. 1 to 4), which are generally composed of alluvium or coarse sand or gravel deposited in shallow water, were subsequently buried by many meters of finer 

sediment. Later, sublacustrine currents at intermediate depths 

(perhaps 2 to 10 m) apparently removed most of these soft 

sediments, inasmuch as evidence of subaerial erosion (channels, soils, or alluvium) is not found. Currents at all but the 

shallowest depths probably have limited ranges of erosional 

power that rarely exceed a certain competency. The upper 

limit of this competency would determine maximum sediment 

sizes that could be moved. In this way, the intermediate-depth 

currents would be capable of transporting the finer sediments 

to other areas, but incapable of moving the coarser fragments 

of the underlying layers. Although subaerial water-caused 

erosion processes exhibit a wide range of competencies, they 

tend to focus erosional energy into channels, which promotes 

dissection rather than exhumation. Examples of exhumation 

are the bar composed of subunit sa4 (sec. I32, pl. 4), the thin 

alluvial sheets of unit AB (secs. L1 and L12, pl. 1), the lacustrine delta composed of unit BC (secs. H13, H14, I18, and 

I19, pl. 3A), and the crests of bars composed of units B and C

(secs. C10 and C15, pl. 2A).

The much-deeper canyons that developed on the flanks 

of the Spangler Hills and the Argus and Slate Ranges clearly 

predate deposition of the Searles Lake Formation and probably all gravels equivalent in age to the older gravel unit and 

the Christmas Canyon Formation. Deposits assigned to the 

oldest unit in the Searles Lake Formation rest on the bedrock 

flanks of Poison Canyon (pls. 3A and 3B) and in numerous 

other canyons around Searles Valley (pl. 1). Deposits assigned 

to the Christmas Canyon Formation and partly correlative deposits assigned to the older gravel unit are inset into 

canyons along the Slate and Argus Ranges and the Spangler 

Hills. If the lacustrine gravels that are interbedded in the older 

gravels exposed in two canyons of the Slate Range (noted 

in the description of that unit) are equivalent in age to the 

lacustrine deposits of the Christmas Canyon Formation that 

are overlain by the 0.64 Ma Lava Creek ash, the base of the 

older gravels in those canyons could have an age approaching 

or exceeding 1 Ma.

On the basis of subsurface evidence, the period between 

2 Ma and 1 Ma is considered to have been characterized by 

intermediate to wet hydrologic regimes (fig. 32). Subsurface 

deposits indicating these environments are now 228 m to 425 

m below the present surface of the lake (Smith and others, 

1983, table 1). Possibly, streams in the canyons of the Slate 

and Argus Ranges and the Spangler Hills were initially graded 

to the base of this depth range. In that climatic setting, substantial downcutting of these canyons and deposition of large 

volumes of alluvial gravels on the flanks of these ranges probably took place. As the lacustrine basin filled, however, base 

level rose, causing younger alluvial deposits to begin filling 

the canyons eroded earlier, eventually building the fans to their 

presently observed gradients.

The earliest time that the presently extensive canyons 

along the flanks of these ranges could have been developed is 

limited only by the ages of the volcanic rocks in the northern parts of the Slate Range and the adjoining segment of 

the Argus Range (pl. 1). Those rocks were deposited prior to 

development of the Searles Valley Syncline, which subsurface 

data (Smith and others, 1983, p. 16) show occurred substantially before 3.2 Ma.

Neotectonics

Late Cenozoic faulting and tilting have affected virtually 

all of the deposits in Searles Valley. Layered deposits older 

than the Christmas Canyon Formation and the older gravel 

unit are moderately to strongly tilted and locally faulted (pl. 

1). The Christmas Canyon Formation itself is tilted a few 

degrees where broad folds can be identified that lie astride of, 

and subparallel to, the Garlock Fault (Smith, 1991a, p. 617-

620). Many segments of that fault have also placed deposits of 

the Christmas Canyon Formation adjacent to older or younger 

deposits, with scarps ranging from less than 1 m to more than 

75 m high.

Fault scarps associated with the Garlock Fault along the 

south edge of Searles Valley are notably prominent. Clark 

(1973, maps E and F) plots the varying types of recently active 

fault features in this zone, noting stream channels that are 

offset laterally 15 to 25 m, scarps as high as 2.5 m, and numerous shutterridges, aligned notches, and benches. Reversals in 

vertical displacement along this fault occur over distances of 

less than a kilometer. In Searles Valley, the most prominent 

topographic indications of this fault lie in sections N11 and 

N12. In and west-southwest of section N11, the fault has created low, aligned ridges composed of gravels assigned to the 

Christmas Canyon Formation or the Searles Lake Formation. 

Many of these ridges are only a few centimeters high and, 

although easily seen on aerial photographs, are detectable on 

the ground only because they produce slight concentrations 

of fragments that are larger and darker than those found in the 

Holocene-age older alluvium that nearly covers them.

Within the area shown on plate 1, the Garlock Fault does 

not offset either the older alluvium or active alluvium units, 

although older alluvium locally can be traced to the base of 

scarps formed in older units, making it appear on a map as if 

that unit were also displaced. A particularly clear example of 

undisturbed older alluvium was observed about 100 m west 

of where the U.S. Navy road crosses the fault at the mouth of 

Christmas Canyon. There, the Garlock Fault consists of a single trace. A vertical excavation, about 30 cm deep, along the 

side of a small wash showed that the fault separates siltstone 

and sandstone of Tertiary age, on the south, from deposits 

assigned to units C and CD of the Searles Lake Formation. 

The fault zone is about 15 cm wide and dips 60° south. The 

fault trace is overlain by undisturbed older alluvium. Vertical 

displacement since unit C was deposited has been up on the 
Neotectonics 63

south side. A left-lateral offset of the stream channel, which 

is cut into unit C, shows that about 8 m of slip has occurred. 

Displacement of 8 m in 10,000 years means an average lateral 

slip rate of 0.08 cm/yr, almost an order of magnitude lower 

than the 0.7-cm/yr horizontal slip rate suggested by Carter 

(1987, p. 135) for the Garlock Fault in an area 50 km to the 

west. Examples of stream-channel offsets in the area of plate 1 

that exceed 8 m (Clark, 1973, maps E and F) all lie in gravels 

of the Christmas Canyon Formation. A 50- to 60-m left-lateral 

displacement of a stream channel by the Garlock Fault at a site 

5 km west of the area of plate 1 (Clark, 1973, map E; Smith, 

1964, p. 46) is in gravels possibly equivalent in age to the 

Christmas Canyon Formation. This would imply a minimum 

displacement rate of 0.01 cm/yr (60 m in 600 k.y.).

Along the west edge of the Slate Range, the Sand Canyon 

Thrust Fault and a normal fault are well exposed (Smith and 

others, 1968, p. 21). The thrust fault separates pre-Cenozoic 

bedrock units of different ages. The normal fault (extending 

from sec. G-22 to J-3, pl. 1) curves so that its trace remains 

a few hundred meters west of the lowest elevation bedrock 

exposures. It displaces all of the shoreline-bearing surfaces 

and the gravels of unit CD that postdate them (fig. 33). The 

steepest scarp segments average 35°. Most scarps are 4 to 8 

m high, but near many washes they are a meter or less high. 

This was clearly documented in February 1984 by an exposure of this fault in a new channel cut in late 1983, where an 

unnamed wash had abandoned its former path and cut a new 

channel to its north (sec. G34-l). Vertical exposures that were 

still remarkably clean allowed detailed observations of the 

fault trace (fig. 34). Maximum offsets of identifiable beds 

in the lacustrine sediments of unit B or C are 0.4 m, yet the 

scarp formed in sediments of unit CD about 500 m north of 

these exposures exceeds 7 m in height, although that scarp 

may represent several offsets. A possible explanation is the 

following: Along the edges of mountain ranges, the sediment 

that underlies modern alluvial channels and rests on bedrock is 

thicker than alluvial sediment beneath areas adjacent to ridges, 

because the channels that are located at the mouths of bedrock 

canyons were also the sites of earlier channels and deeper 

incision. This fault scarp is presumed to be an expression of a 

normal fault of approximately uniform displacement in bedrock. The smaller offset of the present surface at the mouths 

of canyons could be because the bedrock displacement of the 

upthrown block was attenuated by upward splaying of the fault 

in thicker relatively unconsolidated late Cenozoic sediments. 

This would have distributed displacement over a wide zone 

normal to the fault, some of which may have consisted only of 

intergranular movements. Such attenuation would be approximately proportional to sediment thicknesses.

The larger clasts in the alluvial gravels of unit CD that 

have been up-faulted along the west edge of the Slate Range 

are characteristically pale brown and angular, with average 

sizes ranging from 10 to 25 cm; sediment colors on scarp 

faces are slightly lighter than on the flat unfaulted surfaces, 

but no soils were developed. The uplifted surfaces have relict, 

now-inactive channels that are as deep as 1 m and filled with 

Present 1 2 3

Wet

Intermediate

Dry

HYDROLOGIC REGIME (RELATIVE)

AGE, IN MILLIONS OF YEARS

Figure 32. Simplified plot showing periods characterized by wet, intermediate, and 

dry climates in the part of southeastern California including the drainage basin of 

the Owens River during the past 3.2 m.y. (after Smith, 1984, table 1). These different 

regimes were expressed in the succession of water bodies in the Owens River System, namely the lakes in Owens, China, Searles, Panamint, and Death Valleys. During 

dry regimes, which includes the present regime, the Owens River normally supplied 

enough water only to partially or totally fill Owens Lake, with rarely a small overflow 

into China Lake. During intermediate regimes, the Owens River flow typically filled 

Owens, China, and Searles Lakes, with rarely a little overflow into Panamint Lake. 

During wet regimes, the Owens River flow would have been great enough to fill all of 

Owens, China, Searles, and Panamint Lakes, and the overflow even formed a large 

lake in Death Valley (Lake Manly).
64 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

colluvium and wind-blown sand. Those channels are aligned 

with the counterpart relict channels on the downthrown blocks, 

indicating no lateral displacement.

Where active alluvial channels dissect these normal 

fault scarps, the modern alluvial surface and one or two older 

alluvial surfaces that are 2 m or less higher are not faulted; the 

higher (older) of these two has the unchanneled surface that is 

characteristic of the older alluvium unit, and its surface commonly lies 1 m to 1.5 m above the modern wash. These relations show that displacements along this fault occurred after 

deposition of unit CD and probably before deposition of the 

older alluvium, meaning that faulting probably ceased during 

or shortly after the Holocene deposition of unit D.

South of this normal fault, a narrow graben and several 

normal faults displace deposits of the Searles Lake Formation (sec. J2 to J28, pl. 1; fig. 35A). The graben, described 

elsewhere (Smith, 1966a, p. 65-75, fig. 8; Smith and others, 

1968, p. 23-24), is a little more than 3 km long, and photogrammetrically determined profiles show that it has an average 

width of about 30 m and depth of 5 m. South of the graben, a 

zone of less systematic normal faulting continues for another 

3.5 km. The overall trend of the graben is nearly north and 

straight, but in detail the boundary faults are sinuous and 

composed of nearly aligned, left-stepping and overlapping en 

echelon fractures (fig. 35B). Faults outside and south of the 

main boundary faults of the graben have characteristics that 

are similar to the boundary faults. The faults constituting the 

graben are apparently of Holocene age. They displace deposits of the Searles Lake Formation as young as unit B, and the 

normal faults that extend south of the graben displace gravels 

of unit CD. The lack of deposits belonging to unit C within 

the boundaries of the graben, which would have acted as a trap 

for sediments when the lake that deposited unit C stood above 

the graben’s elevation, further supports the conclusion that the 

graben and associated faults are Holocene in age and possibly 

middle Holocene. As with the normal fault exposed north of 

the graben, sediments mapped as older alluvium (unit oal) and 

active alluvium (unit al) are not displaced by this fault.

Smith and others (1968, p. 21, 24) tentatively attributed 

the graben and associated faults to normal displacements on 

the low-angle Sand Canyon Thrust Fault (pl. 1) or to compaction of the valley fill. While displacements along the thrust 

fault might explain the graben, which overlies the buried trace 

of that thrust, this mechanism cannot explain the normal fault 

to the north, which offsets sediments that clearly rest on the 

upper plate of that thrust. The compaction mechanism is also 

unattractive as an explanation because it would be expected 

to result in the greatest displacements being at the mouths of 

canyons where the fill is thickest, rather than the opposite. 

Possibly, normal displacements along a concealed low-angle 

Figure 33. Oblique aerial view of the west edge of the Slate Range, showing scarp of normal fault. The west-dipping fault 

displaces sediments ranging in age from unit B to unit CD. Scarp is as much as 8 m high, but tends to be lower where it 

crosses mouths of canyons. View is toward northeast; the lighter-colored Panamint Range forms most of the skyline. Where 

scarp cuts alluvial fan in lower center of photograph (labeled f), location is plate 1, sec. G27-m.

f
Neotectonics 65

C

C

3 m

W

E

4 cm ?

Fault dip 89° W

View 1

wash

floor

C

C

1.5 m

W

E

40 cm Fault dip 78° W

View 3

wash

floor

C

C

2.5 m

W

E

20 cm 10 cm

Fault dip 87° W

View 2

wash 

floor

B

C

C

C

(new channel)

(old channel)

CD

CD

CD

CD

C

C

al

al

oal

oal

oal

view 1

view 2

view 3 oal

0 10 METERS

(Approximate scale)

A

N

talus

oal

oal

oal

Figure 34. Field sketches of normal fault (medium line) exposed 

on sides of channel recently eroded through sediments of unit 

CD and older alluvium (oal) and floored by active alluvium (al). 

Location: plate 1, sec. G34-l. A, Map view, showing locations of 

the three views (vertical profiles) of channel walls. B, Sketches 

of channel walls showing fault traces and sense of movement. 

Displaced sediments are mapped as unit C, but they could be unit 

B; overlying older alluvium is not displaced (although some cracks 

have propagated to the surface). Vertical displacements of identifiable horizons are indicated; they range from 4 cm to 40 cm. Note 

that one strand of the fault in view 2 shows reverse displacement.

fault, parallel to but west of the Sand Canyon Thrust Fault, 

caused extension along both the normal fault and the graben, 

but direct evidence of such a fault was not seen.

The short fault that is subparallel to the Garlock Fault 

and extends from section L32-m to section N2-r in southern 

Searles Valley is probably a left-lateral strike-slip fault (like 

the Garlock Fault), although good evidence was not found. 

This fault is straight, and vertical displacements along its trace 

vary—two common characteristics of strike-slip faults. Sediments assigned to older gravels and unit B of the Searles Lake 

Formation are displaced, and playa silts along its southeast 

side document the creation of a sag pond.

The sinuous fault along the southeast side of the Spangler Hills (K31 to K23) is a normal fault. The fault trace is 

expressed topographically and by linear zones of caliche, and 

in a few places the fault surface is exposed, revealing highangle slickensides. Dips on these exposed surfaces range 

from 50° to 80° southeast, with the southeast block being 

consistently depressed. The fault’s age is Quaternary, but late 

Quaternary activity is not provable. Only deposits correlated 

with the Christmas Canyon Formation and bedrock are clearly 

faulted (tufa and sediments of unit A of the Searles Lake Formation also may be faulted, but the exposures are inadequate 

to be certain).

Folding of late Cenozoic sediments is evident in several 

parts of the valley. Along the Garlock Fault, an east-northeasttrending anticline and two parallel flanking synclines can 

be identified from the elevations of the basal contacts of the 

Christmas Canyon Formation (Smith, 1991a, p. 617-619). 

Deformation during the 20th century along known geologic 

structures is also detectable where benchmark lines have been 

resurveyed (Smith and Church, 1980, table 4). Crustal movements appear also to be causing continuing elevation of the 

crest of the Slate Range anticline and depression of the troughs 

of the Searles Valley and Pilot Knob Valley Synclines at longterm (10-100 years) average rates of about 0.015 cm/km/yr. 

Folding or tilting may also be indicated by differences in the 

elevation of the top shoreline. In most places, however, the rate 

of tilting cannot be determined because this shoreline is the 

product of erosion during each of the periods when overflow 

occurred, and it is difficult to establish accurately either the 

level or age of the lake primarily responsible for this feature.
66 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

A

Figure 35. Photograph and map of graben along west edge of the Slate Range. A, 

Oblique aerial photograph looking south along west edge of the Slate Range. The prominent graben paralleling the range has an average width about 30 m, depth about 5 m. 

Bounding faults displace chiefly older gravel and unit AB, but normal faults that represent 

its southern continuation displace gravels of unit CD; older alluvium and active alluvium 

are not displaced. White mine dump (“Deans Mill”) to right is in plate 1, sec. J10-h. B, 

Photogeologic map, with uncontrolled base, showing pattern of faults (heavy lines) along 

graben shown in A. Stippled area represents younger sediments not displaced, area 

without pattern is sediments and rocks older than the faulting. Major faults are hachured 

on downthrown side, minor faults show ball on downthrown side (if known).

0 100 200 300

South METERS

Layton Canyon

New York Canyon

B
Paleolimnology 67

In most areas, the elevations of the uppermost outcrops 

of lacustrine sediments, determined from 40-ft contours, are 

not considered more accurate than about +20 ft (6 m). In areas 

characterized by tufa benches, where water level at the highest 

shoreline can be more precisely reconstructed, a barometric 

survey of shorelines that are near benchmarks only indicated 

small and questionable elevation differences. Uplift may be 

indicated in one area that lies just north of the Garlock Fault 

and near Christmas Canyon (sec. O4-e), where lacustrine 

gravels assigned to unit A of the Searles Lake Formation are 

mapped to an elevation that is 10 m above the probable top 

shoreline elevation elsewhere in the valley. Rates of uplift indicated by this observation would range from 0.007 to 0.03 cm/

yr, depending on whether the age of the gravels is taken to be 

near the beginning or end of that unit’s depositional period.

Paleolimnology

Many aspects of the physical limnology of Searles 

Lake during deposition of the Searles Lake Formation can 

be reconstructed from the evidence described in this report, 

especially when supplemented by evidence obtained from 

the subsurface record (Smith, 1979). During relatively dilute 

stages, the lake’s salinity level can be inferred from fossils, 

and its ionic composition can be reconstructed from the composition of any salts deposited later. Lakes that were density 

stratified as a result of differing concentrations of salts in 

the upper and lower layers are implied by laminated sediments, and horizontal salinity gradients are revealed by the 

zonation of fossils. The character of the clastic and chemical sediments—their physical, textural, and mineralogical 

properties—indicate the nature of both the low- and highenergy environments that existed in the deep and shallow 

parts of the water body, respectively. Storm-wind directions 

can be inferred from the location and orientation of a sand 

and gravel bar wherever the source of its components can be 

identified. Each of these paleolimnological attributes helps to 

infer the lake characteristics and climates that existed during 

successive periods, and these are discussed in a later section. 

Additional criteria useful in reconstructing the paleolimnological record offered by the lacustrine deposits are reviewed 

by Currey (1990).

Lake-Water Chemistry and Density Stratification

As indicated by subsurface saline deposits, the water in 

the lake occupying Searles Valley during deposition of the 

Searles Lake Formation (as well as all of the periods extending 

back to 300 ka) was dominated by sodium, chloride, carbonate plus bicarbonate, and sulfate. The ostracode populations 

lead to a similar conclusion. The lake was also alkaline, as 

all of the subsurface salt layers that formed at times of lake 

shrinkage or desiccation contain high percentages of sodium 

carbonate-bearing salts, and many layers contain sodium 

borates (Smith, 1979), all being salts composed of components 

that dissociate in water into strong bases and weak acids. As a 

1-percent Na2CO3 solution has a pH near 11.6 (Handbook of 

Chemistry and Physics, 1966, p. D80), it is probable that Searles Lake was alkaline even at more dilute stages. Also, Owens 

and Mono Lakes, the modern termini of the drainages that 

provided most of the water and dissolved solids to Pleistocene 

Searles Lake, are carbonate rich and alkaline. The major-anion 

mole percentages of the Upper Salt and Lower Salt (salts plus 

brines), and the waters of Mono Lake and (predesiccation) 

Owens Lake, are:

CO3+HCO3 SO4 Cl

Upper Salt (Smith, 1979, p. 64) 16 11 73

Lower Salt (Smith, 1979, p. 47) 36 7 57

Mono Lake (Mason, 1967, table 9) 37 11 52

Owens Lake

(Gale, 1914, p. 258, column 9)

31 9 60

Mono Lake waters have a pH near 9.5 (unpub. data, 

samples collected August 1956), and Owens Lake brines (in 

1969-1971, after solution of the top 0.2 m of salts) had pH values ranging from 9.6 to 11.0 (Friedman and others, 1976, table 

1). Interstitial brines from Searles Lake have pH values mostly 

between 9.2 and 9.5 (Smith, 1979, tables 9 and 16).

Stratified lakes in which the stratification is caused by 

salinity differences can be very stable, lasting years or even 

centuries. Many temperate-region lakes become stratified each 

year because of temperature-caused changes in density whose 

numerical expressions involve numbers in the third decimal 

place; salinity stratification can be a result of density differences that involve numbers in the second or even first decimal 

place. For example, Big Soda Lake, Nevada, is chemically 

stratified with density contrasts of about 0.04 g/cm3, and calculations suggest that it could require as much as a century for 

wind energy to mix the upper and lower layers (Hutchinson, 

1937, p. 78, 125; Hutchinson, 1957, p. 512). Nevertheless, in 

order for Searles Lake to have retained a stratified structure 

for many hundreds or several thousands of years, a periodic 

renewal of its density stratification was probably required. 

Annual flooding of the lake surface by fresh water during 

the early-summer melting of Sierra Nevada snow might have 

prolonged the stratified condition, with the ensuing evaporation removing most of the fresh water before it was mixed 

extensively down into the saline zone. But even this process, 

with some dilution of the underlying saline water body each 

year, would have eventually converted the lower saline layer 

to one that would more easily mix with the less dense annual 

influx. However, the most extreme dry period of each century 

or two might have evaporated all of that year’s annual inflow 

layer plus part of the underlying saline layer, restoring that 

deeper layer to its former density and allowing stratification to 

continue for an additional period.

After periods of persistent rain, outcropping fine-grained 

sediments assigned to units B and C of the Searles Lake 

Formation sometimes develop a zone of efflorescent salts on, 
68 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

or a few centimeters beneath, their outer surfaces. The efflorescent salts are apparently crystallized from rain waters that 

first penetrated the outer layers of the outcrop sediments and 

then migrated back toward the surface as a result of capillary 

processes, bringing trace amounts of any soluble salts in the 

sediments. Sediments of unit A rarely develop efflorescences, 

probably because any salts they contained were leached out 

long ago. This eliminates an alternative explanation—that 

efflorescent salts are recycled by wind-blown dust. Determining the mineralogy of these salts by X-ray diffraction is 

believed, therefore, to indicate the composition of salts that 

were in the waters trapped in the interstitial spaces of the sediment at the time of their deposition. These mineral compositions thus serve as a crude indicator of the composition of the 

lake waters at the time of deposition (Smith, 1966b). Halite 

(NaCl), thermonatrite (Na2CO3•H2O), thenardite (Na2SO4), 

and ulexite (NaCaB5O9•8H2O) are the most common efflorescences. Gypsum (CaSO4•2H2O) is locally common in some 

units, but rather than forming efflorescences it forms eudedral 

crystals a centimeter or more long; they may have been produced by a different process, possibly involving the oxidation 

of sulfides in the sediments (pyrite has been noted in subsurface sediments).

Some stratigraphic units, even from widely separated 

parts of the valley, consistently produce efflorescences having 

similar mineralogies, and this is taken to be good evidence of 

the chemical composition of the lake water in which they were 

deposited. Halite that is clearly secondary is nearly ubiquitous 

in fine-grained sediments below the level reached by the lake 

responsible for unit D. That middle Holocene lake was quite 

saline, and salt from it impregnated and cemented the upper 

few centimeters of all sediments on its floor, especially those 

of units B and C, making them highly resilient.

Low-Energy Environments

Fine-grained lacustrine sediments exposed as outcrops in 

Searles Valley represent low-energy, nearly current-free sites of 

deposition. Because current energy was low, clastic sedimentation rates were also low, and chemical sediments composed 

chiefly of carbonates contributed significantly to the lithologic character of the deposit. Every sample of fine-grained 

lacustrine sediment tested with acid for its carbonate content 

effervesced vigorously. However, the amount of carbonate in 

those sediments, judging from their color, response to acid, and 

chalky feel, varies both stratigraphically and areally.

Stratigraphic variations in the carbonate content of deepwater sediments in Searles Valley appear to reflect variations 

in the volume of the lake’s inflow, which is inferred to have 

been the major source of variation in the amounts of available dissolved Ca. The concentration of Ca in those inflowing 

waters would have tended to be constant because it was controlled by the solubility of calcite, with which it was saturated, 

a fact known to be true because calcite is also abundantly represented in the subsurface sediments of both upstream lakes, 

China Lake (Smith and Pratt, 1957, p. 14-25) and Owens lake 

(Bischoff and others, 1997, figs. 2, 3). Quantitative estimates 

of the amounts of carbonate deposited in Searles Valley have 

not been made, but the persistently calcareous character of the 

perennial-lake sediments and the nearshore tabular tufa deposits indicate its constant replenishment by inflowing streams.

Areal variations in the carbonate content of low-energy 

deposits, like those of unit A, appear to be a consequence 

of the lack of stratification and the development of “chemical deltas” near the inlet regions. As discussed in the earlier 

section on the Searles Lake Formation, chemical deltas 

developed in the basin where inflowing, relatively fresh, 

Ca-bearing water partially or completely mixed with water of 

the alkaline lake near its inlet, resulting in the rapid precipitation of CaCO3 minerals near the mixing sites. During these 

periods, carbonate available for deposition in other parts of 

the basin was reduced.

In contrast, the common presence of aragonite laminae 

in the low-energy deposits observed in both subsurface (Smith 

and Haines, 1964, p. 52, fig. 14) and exposed sediments, like 

those of units B and C (fig. 10), is interpreted to mean that 

the lake was alkaline, frequently stratified, and periodically 

receiving large amounts of fresh, Ca-bearing waters. This 

combination of characteristics allowed the Ca in inflowing 

waters to be first spread throughout most of the basin, because 

it was dissolved in the relatively fresh, less dense upper layer, 

and then precipitated as aragonite when the underlying denser 

and alkaline waters mixed with the fresher inflowing waters 

along the chemocline.

Although the local abundance of very fine grained 

dolomite in both subsurface and exposed sediments could also 

be produced by the mixing of dissimilar waters, the largest 

concentrations of dolomite in subsurface mud layers are near 

the contacts with saline layers, in layers formed when lake 

salinity was either approaching or retreating from salt-saturation levels (Smith, 1979, p. 81). In this study, when outcrop 

evidence indicates a period of lake contraction, dolomite-rich 

zones in outcropping sediments are considered supporting 

evidence of a shrinking lake whose waters had a high pH and 

increased salinity, yet which had to receive periodic influxes of 

fresh Mg- and Ca-bearing waters for dolomite crystallization 

to continue. Some of the processes that control the crystallization of lacustrine dolomite, however, are not well understood.

These inferences are based on relations such as those 

found between the lithologic, chemical, and mineralogic data 

from core GS-16 (Haines, 1959, p. 245-268; Smith, 1979, 

table 13; and unpub. data). Figure 36 shows the character and 

distribution of laminated and unlaminated sections of the Parting Mud in that core. In most cores of the Parting Mud, segments of finely laminated mud are found primarily in its upper 

third. Dissolved Ca has a very low solubility once mixed with 

alkaline waters, and aragonitic laminae require the periodic 

replenishment of the lake’s Ca after most of the previously 

introduced content has precipitated. Finely spaced laminae, 

therefore, require a frequent resupply of enough fresh water to 

re-create stratified conditions and replace the previously precipitated Ca. Counts of white laminae in thin sections from the 
Paleolimnology 69

upper third of the Parting Mud, however, show that laminae 

represent only about a third of the years that 14C ages suggest are represented within an interval, meaning that only one 

out of three years produced enough inflowing Ca for distinct 

laminae to be deposited in the basin’s center. Periods of high, 

yet still-increasing inflow thus introduce increasing amounts 

of dissolved Ca, which then precipitates as calcite, dolomite, 

or aragonite. In core GS-16, two intervals of upwardly increasing CaO are separated by an interval of decreasing CaO, and 

the two thickest sections of finely laminated sediments are 

those characterized by the next upward increases in CaO. 

This inferred history of a lacustrine fluctuation agrees with 

the evidence derived from outcrop data, as will be shown 

later, as well as with fossil pollen evidence of climate changes 

(Roosma, 1958).

The acid-insoluble component of low-energy deposits 

(fig. 36) also shows trends that are significant and independently confirm the fluctuations in the lake levels inferred 

from outcrops of units A, B, BC, and C. The acid-insoluble 

component primarily represents the clastic fraction in the 

layers of low-energy deposits that was mostly derived from 

the materials surrounding Searles Valley (Smith, 1979, p. 53, 

67, 81-82). At a fixed, midbasin site (such as represented by 

core GS-16, fig. 36), the percentage of acid-insoluble material 

reflects chiefly the proximity of that site to the surrounding 

sources of clastic materials—shallow water sandy zones and 

the enclosing beaches and bedrock. Therefore, increasing clastic percentages should accompany decreasing CaO percentages, as both indicate decreasing inflow and lake size. In core 

GS-16, this inverse relation is well illustrated.

The estimated abundances of aragonite and dolomite also 

reflect the same fluctuation in lake size and salinity (fig. 36). 

Samples containing major to intermediate amounts of aragonite (or its postdiagenesis products, gaylussite and pirssonite) 

came from horizons that were characterized by fine or coarse 

laminae, sediments that now contain 10 to 18 percent CaO; 

only one sample falls below this range. The dolomite content, 

a measure of increasing salinity, remains at intermediate levels 

throughout much of the interval, but it is most abundant in the 

sample (from 73 to 74 ft) that also contains the lowest CaO 

and highest acid insoluble percentages. These criteria indicate 

the interval between 73 and 74 ft in core GS-16 to be representative of a shrinking lake that was not stratified (no aragonite) and receiving less inflow (decreasing CaO percentage), 

causing the shallow-water source of clastics to move closer to 

the sample site (increasing acid insolubles) and increasing its 

salinity (increasing dolomite).

High-Energy Environments

The characteristics of sediments deposited in the shallow 

waters of Pleistocene Searles Lake were controlled primarily 

by the current strengths and the local supply of clastic material. Reconstruction of the limnologic nature of former lakes, 

by studies of the sediments in their high-energy environments, 

chiefly produces information concerning changes in the relative intensities and directions of wind-driven currents during 

various periods and in various parts of the basin.

Changes with time in the maximum sizes of fragments 

in gravel beaches and bars and along wave-eroded shorelines 

were noted earlier. Many of the deposits of gravel in bars and 

along shorelines, as well as lag gravels that were depleted of 

their smaller fragments by waves, cannot be confidently related 

to the stratigraphy that is based largely on finer sediments. 

However, some gravel deposits can be traced laterally or downhill into finer facies, especially in the Valley Wells Wash area 

(pl. 2A), along the north and east edges of the Spangler Hills 

(pls. 3A and 4), and in many of the longer canyons of the Argus 

and Slate Ranges (pl. 1). In stratigraphic sequences that can be 

traced with confidence, one finds that gravel-fragment sizes 

decrease with decreasing age. For this reason, one can hypothesize that even where stratigraphic control is equivocal or 

absent, gravel deposits of unit B, for example, will probably be 

less coarse-grained than nearby coarse-grained gravels of unit 

A, and the successively younger gravels of units C and D will 

be less coarse-grained than those of unit A and unit B. If this 

working hypothesis is valid, it means that storm-wind velocities 

during deposition of the Searles Lake Formation were statistically at their maximum during deposition of unit A, and they 

diminished during successively later periods.

Within unit A, however, fragment sizes in the only wellexposed gravel bar deposited during unit A time (pl. 4, sec. I32-

q) are coarsest and most angular in the youngest subunit (sa4), 

suggesting that storm-wind intensities increased as deposition 

of that unit progressed, then later decreased during deposition 

of units B, C, and D. In his study of Pleistocene Lake Lahontan, Nevada, Morrison (1964, p. 29, 99) notes that gravels 

in the Eetza Formation (Eetza Alloformation of Morrison, 

1991), near the middle of the several formations assigned to 

the mostly lacustrine Lahontan Valley Group (Lake Lahontan 

Allogroup of Morrison, 1991), are coarser than any lacustrine 

gravels of younger deposits, but he finds the coarsest gravels 

to be at the base of that formation. If the Eetza Formation and 

younger units of the Lahontan Valley Group are time-correlatives of the Searles Lake Formation, the late Pleistocene history 

of windiness indicated in the two regions is broadly similar but 

different in this detail.

Although the high-energy environment was dominated by 

coarse-fragment sedimentation, large amounts of CaCO3were 

also deposited in the matrix of the coarse deposits. Some of the 

carbonate is still preserved as marl that fills interstitial spaces 

or forms thin beds between gravel layers; both lithologies indicate that (short?) periods of carbonate deposition interrupted 

the (longer?) episodes of coarse-fragment deposition. Some 

carbonate, however, may be younger because it is now found 

as a translucent calcite lining that fills much of the empty space 

between clastic fragments and cements them together. In some 

instances, this calcite constitutes an estimated 5 (volume) percent of the gravel. The volume of water required to introduce 

that much CaCO3 is enormous. For example, 1 m3

 of gravel 

containing 5 (volume) percent calcite (13.6x104 g) would have 
70 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

CaO

5 10 15 20 10 15 20 25

Acid Insoluble

(salt bed)

(core lost)

Age Depth Lamination Sample Weight Mineral

(ka) (feet) Character Intervals Percentages Abundances

Dolomite Aragonite

Parting Mud

10

15

20

25

70

72

74

76

78

80

82

84

Lower Salt

Upper Salt

u

f

c

f

c

f

c

u

c

u

c

u

P

G

G

Figure 36. Diagrams showing lithologic, chemical, and mineralogic characteristics of subsurface Parting Mud in core GS-16 at Searles 

Lake (location: plate 1, corner of secs. 26, 27, 34, 35; see Haines, 1959, p. 245-268). Ages are interpolated from the ages of the basal and 

top contacts of the Parting Mud (24 ka and 10.5 ka). Bedding characteristics of mud shown as u (unlaminated), c (coarsely laminated), or 

f (finely laminated) as described in text. Weight percentages of CaO and acid-insoluble material in samples of GS-16 (sampled intervals 

as shown) from unpublished data (H. Almond, analyst, written commun., October 1956). Mineral abundances from Smith (1979, table 

13) and unpublished data; dashed lines on aragonite-abundance diagram labeled P and G represent abundances of diagenetic pirssonite (CaCO3•Na2CO3•2H2O) and gaylussite (CaCO3•Na2CO3•5H2O), respectively. Those two minerals probably consumed part or all of the 

primary aragonite, explaining its diminished abundance in those sections of the core.
Paleolimnology 71

required about 9,700 m3 of saturated fresh water to transport 

that amount of CaCO3 to the site of deposition. Transport by 

alkaline lake water would require an even greater volume of 

saturated water. If the lake water was 5° cooler than today, and 

the evaporation rate was 1.2 m per year (Smith and Street-Perrott, 1983, table 10-20), each m2

 of lake surface would evaporate 9,700 m3

 of water in about 8,100 years.

In a few areas where coarse sand was being deposited at 

the edge of the enlarged Searles Lake, defluidization structures 

formed (fig. 37). In Searles Valley, these structures mostly take 

the form of vertical columns of calcite-cemented sand, 10 to 

50 cm high and 3 to 10 cm in diameter. Similar structures now 

form around the edges of carbonate-rich Mono Lake (salinity 

5 to 10 percent) where fresh, calcium-bearing ground water 

impinges on the more dense lake water that impregnates the 

sand around the edges of the lake (Cloud and Lajoie, 1980). 

These columns form as follows: (1) Because of the density 

contrast between the saline-lake water and ground water, 

encroaching fresh ground water is forced upward through the 

overlying sandy sediments, forming vertical conduits. (2) Mixing of ground and lake waters occurs in the sediment forming 

the edges of the conduits. (3) This process supersaturates the 

water mixture with calcite, which precipitates in the interstices along the conduit’s edge and cements the vertical sides. 

Much evidence leads to the conclusion that Searles Lake had, 

at times, a composition and salinity similar to that of modern 

Mono Lake and that the same processes were at work. In Searles Valley, excellent examples of defluidization structures occur 

in sec. C3-r (2,070 ft) and sec. L9-q (1,860 ft). The significance 

of these structures is that they indicate sediments deposited in 

a lake-edge environment, that the lake at that level was alkaline 

and had a moderately high salinity, and that the ground-water 

table at that time and place was virtually at the surface.

Bar-Gravel Transport Directions

The wide variety of rocks exposed in the mountains 

surrounding Searles Valley (fig. 1B) provides a means of 

reconstructing the sources of the gravel in its lacustrine bars. 

The Slate Range is lithologically the most diverse. Paleozoic 

limestone and dolomite that are partially covered by Cenozoic basalt and gravel crop out in the northern part of the 

range, Mesozoic plutonic rock dominates its central area, and 

Mesozoic metavolcanic rock and Precambrian(?) metaplutonic 

and schistose rock crop out in its southern part (Smith and 

others, 1968, pl. 1). The Lava Mountains are mostly composed 

of Cenozoic arkosic sandstone and volcanic rocks (Smith, 

1964, pl. 1); the unnamed hills to their northeast expose large 

areas of the gravel and sand facies of the Christmas Canyon 

Formation (pl. 1), most easily identified from its vesicular 

basalt cobbles and boulders. The Spangler Hills are composed mostly of Mesozoic plutonic rock, plus a small area of 

stretched conglomerate; they are intruded by mostly mafic 

hypabyssal dike rock (Smith, 1962, p. 90-100). The part of the 

Argus Range draining into Searles Valley is also composed 

mostly of Mesozoic plutonic rock, but mafic hypabyssal dike 

rock crops out in the range’s south end and Cenozoic basalt 

partially covers the plutonic rock of its north end.

The locations of the most prominent lacustrine bars in 

Searles Valley are plotted in figure 38A, and their elevations and 

locations are listed in table 8. All but three of the listed bars are 

close to the north or south ends of the valley. Because the rock 

assemblages from the surrounding mountains are so different, 

the fragment assemblages found in each bar indicate clearly the 

source area and allow a generalized reconstruction of Pleistocene 

storm-wind directions. Many bars derived material from two 

sides of the valley, but the directions of transport listed in table 8 

are believed to have been dominant because the distinctive components were those determined near the middle of the bar.

Reconstructions of storm-wind directions are based on the 

following assumptions and conceptions: (1) In Searles Valley today, winds are usually strongest downwind from the low 

points in the surrounding mountains. Therefore, Pleistocene 

winds from the west are assumed to have been strongest east 

of the inlet from China Lake, which is the lowest part of the 

mountains bounding the west side of the valley (fig. 1B). Winds 

from the east seem likely to have been strongest west of Layton 

Pass, the lowest part of the Slate Range (which is due east of 

the inlet from China Lake). Winds from either of these directions would probably have promoted oppositely rotating gyres 

in the north and south halves of Searles Lake. Storm winds from 

the north or south do not seem to be represented by many, if 

any, bars in the basin (fig. 38A). (2) The most effective erosion 

and bar deposition probably occurred where winds entered the 

basin from a direction that provided a large fetch. (3) Wave 

erosion and the longshore drift that transported the eroded material long distances required wind-caused currents that arrived 

from a direction oblique to the shore being eroded. (4) Studies 

show that in lakes, wind-driven currents usually maintain their 

strength and orientation only down to depths of 5 m or less 

(Hutchinson, 1957, p. 286-289), which probably approximates 

the depth range in which these lacustrine bars in Searles Valley 

were constructed. While staying within this depth range, the 

longshore currents constructed bars with curving trends that 

roughly parallel the shore but in most instances only approximate the detailed shoreline configurations (fig. 31).

At elevations near 2,200 ft and 2,100 ft (fig. 38B), bars 

assigned to units AB and C in the north end of the valley 

(secs. A28 and C3, table 8) were built mostly from clastic 

fragments transported northeastward from the Argus Range; 

bars in the southern part of the valley assigned to these units 

are constructed from clastics transported westward from the 

Lava Mountains (sec. N8-d, table 8) and Slate Range (sec. 

L15-q). However, when the lake fell to levels between 2,000 ft 

and 1,800 ft, debris forming bars mapped as units B and C in 

the north end of the valley was eroded from the northern Slate 

Range and transported northwest and west, and bars mapped 

as unit C in the south part of the valley derived their components from the southern Slate Range and transported them 

southwest by longshore currents.

Exceptions to these generalizations must be made for the 

bar gravels mapped as belonging to unit A. The bar near 2,200 
72 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

ft mapped as part of unit A (secs. L22 and L27) is composed 

of fragments eroded from the Christmas Canyon Formation and transported eastward, but this bar may have been 

assigned to the wrong stratigraphic unit because it lies in an 

area without other lacustrine sediments for reference. The bar 

mapped as unit A near 2,000 ft elevation (H21-q,r) was built 

by wind-driven currents that carried the fragments northwest, 

and the one near 1,800 ft (I32-m,l,q) transported debris from 

the Spangler Hills toward the southeast.

Although the meteorologically significant topography did 

not change during deposition of the Searles Lake Formation, 

the shape of the lake did as it expanded and contracted. These 

changes must have altered the circulation patterns in the lake, 

and this could be responsible for some of the apparently conflicting evidence of storm-wind directions. However, because 

bars account for a very small percentage of the lacustrine 

deposits in the valley, construction of them probably occurred 

only when the strength of wind-generated currents greatly 

exceeded that of current resulting from normal circulation. 

From this, one can conclude that bar-forming currents occurred 

only during the strongest windstorms and did not necessarily 

reflect the prevailing winds, which probably came from the 

west as inferred from the distribution of tufa in the valley.

Figure 37. Defluidization structures (see text) preserved in outcrops of unit AB (location: pl. 2A, sec. C3-r). Tube-shaped 

vertical defluidization structures are mostly 20 to 30 cm high and 3 to 6 cm wide.

The lacustrine bars formed during deposition of units AB

and C, when the lake level was near 2,200 ft and 2,100 ft (fig. 

38B), suggest that the storm winds came from northeast, east, 

or southeast, causing erosion along the western shores. Near 

the north end of the lake, where a clockwise gyre presumably 

formed, eroded debris was transported by currents moving 

northeast and then east and southeast as the shoreline configuration required. Correlative-aged debris eroded from the southern part of the lake was transported southwest. The two bars at 

lower levels mapped as part of unit A—near the 2,000-ft level 

and the 1,800-ft level—also imply storm winds arriving from 

the east or northeast. This suggests that the strongest storm 

winds during the highstands accompanying deposition of units 

AB and C, and the lowstands during deposition of unit A, were 

created by counter-clockwise-moving low-pressure centers 

that migrated along paths south of Searles Valley, probably 

reflecting the positions of the jet stream during those periods. 

However, the placement of these two unit A bars in the basin, 

and the orientations of their crests, may also reflect a time 

when the synoptic weather patterns were unlike those that 

prevailed during deposition of any of the younger units.

The lake-water circulation patterns characterizing the 

period when Searles Lake was relatively low and depositing 
Paleolimnology 73

N

T25S

T26S

R43E R44E

A

Lake 

 level

2,100 ft.

unit 

AB

unit AB

Lake 

 level

 1,900 ft.

unit C

units B

and C

Lake 

 level

 2,000 ft.

unit C

unit 

unit A C

unit c

unit C

Lake 

 level

2,200 ft.

unit C

unit A

Lake 

 level

 1,800 ft.

unit A

unit C

B

0 5 10 15 20 KILOMETERS

SCALE (FOR ALL)

Figure 38. Outlines of Searles Lake and patterns of bar-forming currents at various lake levels. A, Extent of Searles Lake when its surface stood at its approximate maximum elevation of 2,280 ft or 696 m (stippled areas were above lake level) and the positions and shapes 

of major lacustrine bars (short curving lines) within the basin. Arrows show sites of inflow from China Lake and overflow into Panamint 

Valley. Reference cross in central part of lake shows intersection of boundaries separating T. 25 S. from T. 26 S., and R. 43 E. from R. 44 

E. B, Outlines of Searles Lake at various lower levels, showing inferred current directions that constructed nearshore bars near each 

level; current directions determined from the lithologies of rock fragments and their bedrock sources. Note that a particular level (and 

its associated current pattern) may have been present at several different times; units of the Searles Lake Formation represented by 

lacustrine bars formed in each current pattern are indicated.
74 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

units B and C near the 2,000-ft, 1,900-ft, and 1,800-ft levels 

indicate that storm winds came from a westerly direction, 

eroding material from the Slate Range fans and transporting it 

north to northwest, and eroding material from the Lava Mountains and moving it southwest. Storm winds from the west 

suggest low-pressure zones that characteristically passed north 

of this area—which is the norm today.

Reconstructed History of Searles Lake 

A major goal of this study is to reconstruct the history of 

Searles Lake over as many years as are recorded by lacustrinesediment outcrops. Periods of expanded lakes are inferred from 

lacustrine sediments or tufas that can be traced laterally to high 

elevations on the valley sides, with the highest elevation, reliably correlated outcrop being used as the criterion of maximum 

lake depth during that period. Periods of lake contraction are 

inferred from alluvial sediments that can be traced to low levels 

in the valley. Where such layers can be reasonably correlated 

with subsurface saline layers, the shallower depths of those 

lakes can be approximated from the salinities implied by the 

mineralogy of their saline layers (Smith, 1979, p. 108-112).

Study of the accompanying geologic maps (pls. 1- 4) 

provides a first basis for reconstructing the changes in the depth 

of water during the time the Searles Lake Formation was being 

deposited. The highest elevation exposures of lacustrine deposits of each unit or subunit are listed in table 9, as are examples 

of the lowest elevation outcrops of interbedded alluvial units or 

subunits. The uppermost or lowermost elevations of outcrops 

of the same unit or correlative subunit were determined on each 

map that included exposures of them; the common similarities 

in the uppermost or lowermost elevations derived from two or 

more plates show that the tabulated elevations are unlikely to be 

the result of miscorrelation or misplotting. However, 20- to 30-ft 

(6 to 9 m) differences between elevations are not considered significant because (1) every outcrop has undergone some erosion, 

(2) interpolation between 40-ft contours can introduce this much 

error, and (3) the geologic contacts in areas of closely grouped 

contours can be misplotted by that much.

These outcrop elevations, when combined with data indicating the subsurface distribution of saline layers (Smith, 1979, 

fig. 41, pl. 2B) lead to a first approximation of the history of 

Searles Lake during deposition of the Searles Lake Formation 

(figs. 39A and 40A). Units and subunits of outcropping deposits 

assigned to the Searles Lake Formation are indicated in those 

figures, as are the named subsurface saline and mud layers. 

For units A, AB, BC, and C, supplemental data were derived 

from subsurface information on the chemistry and mineralogy 

of correlative units, and these are plotted in figures 39B and 

40B. Combining these data leads to my interpretation of Searles 

Lake’s history during the period between 35 ka and the present 

(fig. 39C) and the period between 170 ka and 30 ka (fig. 40C). 

The reasoning behind each of these interpretations is outlined 

below; more specific documentation of the rationale followed is 

presented in appendix 3. The diagram representing the younger 

of these two periods is discussed first because more information 

is available on these deposits, which allows us to test the rationale used to add detail to the history of the older deposits.

Units AB to D

Highstands of Searles Lake during deposition of units 

AB through D are plotted in figure 39A, solely on the basis 

of the highest elevations at which lacustrine sediments of 

each unit or subunit have been mapped (table 9). The lowstand lake level represented by unit BC is determined from 

the lowest elevation of alluvial deposits of that unit (table 9); 

the other lowstands are based on the presence and mineralogy of correlative subsurface saline layers. Monomineralic 

salt beds are assumed to have precipitated from lakes having 

about 13 percent salinity, implying an estimated lake depth 

of 130 ft (40 m) above the present deepest levels of those 

saline horizons (Smith, 1979, fig. 32). Multimineralic (but 

predesiccation) assemblages are assumed to be products of 

about 25 percent salinity, implying a depth of 65 ft (20 m). 

Desiccation assemblages indicate 35 percent salinity, implying depths of 0 to 40 ft (0 to 12 m). Salinity and lake-depth 

data, and depths to saline layers, are from Smith (1979, p. 1, 

figs. 7, 22, 26, and 32).

Subunits of units B and C that are dominated by finegrained, deep-water lithologies were conservatively assumed 

during construction of figure 39A to represent lake-surface 

levels that were only about 50 ft (15 m) above the highest 

outcrop levels, but always with the understanding that the lake 

water could have been deeper. Units and subunits composed 

mostly of lacustrine gravel or sand were assumed to represent 

lake surfaces that were 10 ft (3 m) or less above the highest 

outcrop elevations.

Every deep-water segment of the lake-level curve plotted 

for unit B (fig. 39A) is alternatively plotted (dashed lines) up 

to the level of the spillway because of the abundance of lacustrine gravels assigned to unit B that can be traced up to that 

level. These gravels, plus abundant coatings of nodose tufa 

above 2,200 ft, show that at least one, and possibly several, 

of those proposed highstands is correct. The subunit assignment of the highstands plotted at 2,280 ft elevation for unit B, 

however, cannot be documented on the basis of outcrop stratigraphy. The two highest stands plotted for unit C (fig. 39A) 

are based on the mapped extent of that unit in the Valley Wells 

Wash area (pl. 2A). There, nearly continuous exposures of unit 

C and several other lacustrine units allow their upper elevation 

limits to be determined more accurately than in any other part 

of the basin.

Modifications of the history represented by unit B, and 

confirmation of the history proposed for units BC and C, 

can be made on the basis of correlative subsurface data—

the absence or presence (and character) of laminae, their 

mineralogy, the acid-insoluble and acid-soluble CaO content 

of the Parting Mud in the GS-16 core, and on the thin saline 

layer near the base of the Parting Mud in that core (fig. 36). 
Reconstructed History of Searles Lake 75

The values for CaO were the prime basis for modifying the 

lake history represented by unit B (fig. 39C), although the 

character and mineralogy of the laminae provide supportive 

secondary criteria. (Although the acid-insoluble data from 

the GS-16 core are not used in refining the history of unit 

B, they are plotted in figure 39B, with the scale reversed so 

that the inverse relation between the CaO and acid-insoluble 

percentages produce similar curves. In the Bottom Mud, discussed below, data points based on the CaO content are few, 

but points based on the acid-insoluble content are numerous, 

and thus they become an important criterion in refining the 

history of unit A.)

In plotting the part of the curve representing unit B

(fig. 39C), the following assumptions were made: (1) The 

percentage of CaO was directly proportional to inflowing 

water volume, (2) the lowest CaO percentage (at about 14 ka) 

reflected the inflow needed to sustain a lake at the 1,690-ft 

level (see description of unit BC), (3) the highest percentage 

of CaO reflected the inflow volume needed to reach the lake’s 

overflow level, and (4) evaporation rates remained constant so 

that all of the difference in lake volume between its lowstand 

(7x109

 m3) and its highstand (87x109 m3) was created by 

changes in inflow volume that led to proportionate changes in 

the percentage of Ca-bearing carbonate minerals deposited at 

the core site. Conversion of water volume to lake level is based 

on Smith (1979, fig. 32). Inasmuch as these analyses represent 

average conditions during approximately 1-k.y. intervals, brief 

fluctuations during deposition of unit B are not recorded by 

these data. Units BC and C remain plotted primarily on the 

basis of the elevation data in table 9, although those data are 

compatible with the lithologic and chemical information (figs. 

36 and 39B).

Using the interpolated age scale, these analytical data and 

the information presented in figure 36 suggest the following: 

(1) Between 24 ka and 22 ka, the lake responsible for unit B

remained small and briefly almost dry at one point (GS-16 is 

one of only two of the 41 GS-series cores that contained halite 

or trona at this horizon in the Parting Mud; Haines, 1957). 

(2) During the period from about 22 ka until about 15.5 ka, 

the lake received fluctuating but ever-increasing inflows of 

Ca-bearing water. Between 22 and 19 ka, when inflow could 

only sustain intermediate-size lakes, the amounts of CaO were 

inadequate and introduced too infrequently to produce many 

aragonite layers, so only unlaminated to coarsely laminated 

sediments were deposited throughout the basin. From 19 ka to 

15.5 ka, as inflow continued to increase, it introduced CaO at 

a greater rate and on a more consistent basis, so laminae were 

deposited more frequently. (3) Between about 15.5 ka and 13.5 

ka, lake inflow was markedly lower, reducing the amounts of 

Ca-bearing minerals being precipitated, and only coarsely laminated beds were deposited. (4) Starting at about 13.5 ka, concentrations of Ca-bearing minerals increased, showing that the 

volumes of inflowing water again increased; inflow reached 

a peak at about 12 ka, and a high inflow rate was maintained 

until almost 11 ka. During this period, finely laminated mud 

was frequently deposited in a stratified environment, as new 

influxes of water spread over the surface of the saline water 

body created during the previous shrinking stage. (5) By about 

10.5 ka, the lake had shrunk to a level where the saline minerals borax and trona, which constitute the basal layer of the 

Upper Salt, were deposited.

Data obtained by F.M. Phillips and reported by Benson and others (1990, p. 270) may conflict with the history 

inferred here for the period between about 18.2 ka and 10.5 

ka. Those data, based on the 18O fluctuations in primary 

dolomite in the subsurface Parting Mud, are interpreted by 

Benson as follows: a shallow but slowly rising lake existed 

between 18.3 ka and 16.0 ka; it then rose to a highstand 

between 16.0 ka and 13.5 ka; a decline to moderately deep 

levels followed until 11.0 ka; and the lake rose briefly 

between 11.0 ka and 10.5 ka. Besides the uncertainties in 

the exact ages of these events, the source of the 18O in the 

primary carbonate minerals must be carefully evaluated. 

Benson’s interpretation assumes that isotopically light 18O 

values indicate periods of expanding or relatively deep lakes 

(because fresh, isotopically light inflowing water was diluting the isotopically heavy brines of the earlier, shallower 

lake) and that isotopically heavy values indicate periods of 

shrinking or relatively shallow lakes (because inflow was 

too low to offset the evaporation that enriches water in the 

heavy isotope). In a saline, CO3-rich lake, however, much 

of the inflow during periods of lake expansion entered a 

density-stratified lake; the CO3-rich brine that resulted from 

the preexisting low stand constituted the lower layer, and the 

inflowing fresh water formed the upper layer. The CO3 in the 

primary carbonate minerals precipitated during those periods 

may have largely—if not entirely—been the product of mixing along the chemocline, and their 18O values may reflect 

the isotopic composition of the CO3 in the older, underlying 

body of water rather than the average isotopic composition—

and depth—of a homogeneous lake. Thus, while such isotopic data may accurately reflect periods of shrinking lakes, 

when there was little or no stratification, they are likely to 

incorrectly reflect periods—or depths—of expanding lakes, 

which is what characterized Searles Lake during much of the 

time the Parting Mud was being deposited (fig. 36).

The two expansions of Searles Lake between 13.5 ka 

and 10.5 ka, plotted in figure 39C, also conflict with data 

derived from cosmogenic 3

He in olivine crystals from basalt 

that constitutes the floor of the abandoned channel formerly 

connecting Owens Lake and China Lake, both upstream from 

Searles Valley (Cerling, 1990, p. 155). Those data indicate 

the age of the last streamflow capable of exposing fresh 

rock along the channel surface to be 15.5 ka (or 16.7 ka, 

depending on the calculation method used). This agrees well 

with the age of the highstand inferred by this study to have 

ended at 15.5 ka (fig. 39C), but not with the later expansions 

proposed here. Possibly, the subsequent episodes of Searles Lake expansion, between 13.5 ka and 10.5 ka, were too 

short or insufficiently intense to rescour the previously well 

polished and—even now—unweathered channel in the area 

studied by Cerling (1990).
76 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

20

15

10

5

10

15

20

25

A

B

C

D CD C BC B AB A

sc1

sc2

sc3

I

II

III

sc4

Salinity I

Salinity II

Salinity III 

s-2s-3 s-1

s-6s-7 s-4s-5

sb6 sb5 sb4 sb3 sb2 sb1

sab7

sab6

sab5

sab4

sab3 sab1

sab2

Floor of lake

Overflow

Overburden

Mud

Upper Salt Parting Mud Lower Salt Bottom

Mud

CaO

Acid Insoluble

I

II III

Overflow

Salinity I

Salinity II

Salinity III

AGE, IN THOUSANDS OF YEARS

ELEVATION, IN FEET Ca0 (WEIGHT PERCENT) ELEVATION, IN FEET

ACID INSOLUBLE

(WEIGHT PERCENT)

Figure 39. Inferred lake-level history of Searles Lake from 35 ka to the present. A, History of lake fluctuations (heavy lines) based on 

outcrop geology and subsurface salt beds. Age spans of outcrop units of Searles Lake Formation shown at top of diagram; selected 

subunits indicated immediately above solid lake-level line. Age spans of correlative, informally named subsurface units (table 3; Smith, 

1979) shown near base of diagram; selected thinner subsurface units (salt beds) shown immediately below lake-level line. Plotted ages 

are linear interpolations between ages of subsurface-unit boundaries supplemented by dated samples from outcrops. Elevations of

high-level stages based on data of table 9 (solid heavy line) and other data (dashed heavy lines, see text); elevations of low-level stages 

based on mineralogy of subsurface salines (Smith, 1979, p. 86-91, table 4; this report, fig. 36) and on lowest elevations of alluvial units 

(table 9). Short-dashed line shows elevation of overflow channel into Panamint Valley. Long-dashed, subhorizontal lines represent 

lake-surface elevations at three salinity levels: salinity I (near 13 weight percent) would permit winter crystallization of monominerallic 

suites, salinity II (25 percent) would permit multimineralic (but pre-desiccation) suites, and salinity III (35 percent) represents saturation 

or desiccation (see text). Elevation of floor of lake shown by hachured line. Slopes of bottom and salinity lines assume constant deposition rate (except during deposition of Upper Salt and Overburden Mud). B, Weight percentages of CaO and acid-insoluble material from 

figure 36; note that acid-insoluble scale is inverted. C, Levels of Searles Lake inferred from combining data in A, B, and selected other 

sources (see appendix 3).
Reconstructed History of Searles Lake 77

Deposits of unit CD can be traced to the edge of 

now-dry Searles Lake, and although there is no subsurface 

evidence of subaerial deposition on the floor of the lake after 

crystallization of the Upper Salt, it is unlikely that clastic 

or salt sedimentation at that level ceased entirely. The depth 

and age of the lake responsible for the unit overlying the 

Upper Salt, unit D (fig. 39C), are based on data in table 9 

and the 14C date of 3.5 ka on wood that was recovered 2.4 m 

below the surface of Searles (dry) Lake, about a third of the 

distance between the surface and the base of the Overburden 

Mud. The ages of the beginning and end of that cycle are 

plotted at about 6 ka and 2 ka. The age of the beginning of 

this readvance (6 ka) is a very inexact estimate based on the 

thickness of sediment underlying the dated wood sample 

in the Overburden Mud (unit D) (Stuiver and Smith, 1979, 

p. 73); the estimated age of redesiccation (2 ka) is based 

on an assumed correlation with the age of the close of the 

Dechambeau Ranch highstand in Mono Lake (Stine, 1990, 

fig. 3), and data from Owens Lake cited by Smith (1976, p. 

99, footnote 2). These ages, however, conflict with evidence 

from Owens Lake and Little Lake (50 km south of Owens 

Lake), which indicate the time of the last overflow from 

Owens Lake was prior to 5 ka (Smith and others, 1997, p. 

148; Mehringer and Sheppard, 1978).

The suggested boundaries between the correlative outcrop units are not plotted in figure 39C because the mechanics 

of lacustrine deposition during transgressive and regressive 

stages result in the actual ages of the contacts between outcropping units differing slightly from one elevation to the next.

Unit A

Age control within the outcropping section of sediments 

mapped as unit A is not as good as for younger units (fig. 40). 

With two exceptions, the 14C ages on outcrop material from 

unit A (table 5) appear to be too young, which may be a result 

of contamination by the waters of subsequent lakes, exposure 

to the atmosphere, or unknown complications. Three of the six 

U-series ages determined on samples from that unit appear much 

too young and three are possibly correct, but two samples from 

the same bed differ by 23 k.y. (Garcia and others, 1993). Three 

other samples were submitted for U-series dating at an earlier 

date. Two were samples of nodose(?) tufa that gave similar and 

reasonable-appearing dates (average, 21.6 ka) by U-series and 

Pr-series methods; one was a sample of marl from unit A that 

gave a date inconsistent with its stratigraphic position.

In this study, the age range represented by outcrops of 

unit A is based on the estimated ages of upper and lower contacts of the subsurface Bottom Mud (Smith, 1979, p. 16-17, 

49, 79, 108-112, figs. 6, 31, 32, 41, and pl. 2; Stuiver and 

Smith, 1979, p. 73-75; Peng and others; 1978, Bischoff and 

others, 1985). Age control on the top of this subsurface correlative is good; both 14C and U-series ages indicate its age to 

be near 32 ka. However, a 20-k.y. difference in the age of the 

basal contact of the Bottom Mud arises from two approaches 

to the question. Depositional-rate extrapolation suggests a 

130-ka age (Smith, 1979, p. 75), and the U-series age of the 

one subsurface sample of a saline mineral layer closest to that 

horizon also indicates its age to be near 130 ka (Bischoff and 

others, 1985, table 1, sample 7). However, by disregarding that 

single radiometric-age point and using the remarkably linear 

age-depth trend set by seven other U-series dates above and 

below this contact (Bischoff and others, 1985, fig. 2, samples 2 

through 6, 8, and 9), the age of the contact appears to be nearer 

150 ka. This age of lake-level change, which is used in this 

paper, also conforms with that estimated from the chloridebudget studies of Searles Lake by Jannik (1989).

There are also significant discrepancies between some of 

the U-series and 14C ages from within the Bottom Mud (fig. 

40A). About 3 m below the upper contact, a 14C age of 46.3 ka on 

organic carbon differs from a U-series age of 58.4 ka from gaylussite crystals at about the same horizon, and two U-series ages 

from the uppermost part of the Mixed Layer differ by 26 k.y. 

Furthermore, many of the U-series ages differ from the linearly 

interpolated ages plotted below the base of figure 40A, suggesting that the assumption of uniform depositional rates may misrepresent the ages of various events during this part of the lake’s 

history by 10 to 30 k.y. Therefore, a second time scale is plotted 

just above the base of figure 40A that indicates the approximate 

ages of various horizons according to the U-series dates. (It is 

constructed by using the seven linear-plotting U-series dates as 

follows: the two closely spaced dated samples that bracket the 

60-ka age were used to establish that point, and linear interpolation between 32 ka and 60 ka and between 60 ka and 150 

ka was used to establish the remaining points.) This U-series 

scale, however, requires the sedimentation rate of marl during 

the period between 60 ka and 32 ka to have been about half the 

rate of earlier deposition as well as of the rate determined, using 

14C dates, for the younger Parting Mud (Smith, 1979, p. 76-77). 

These inconsistencies illustrate why reservations must always 

accompany ages determined on the basis of a sedimentation rate 

calculated using another part of a core. For simplicity in discussing the lake-level variations reconstructed by this study, however, 

the time scale based on the assumption of uniform depositional 

rate—what could be considered a nominal age—is used in 

subsequent discussions because the inconsistencies between 

the existing radiometric dates make it difficult to devise a more 

assuredly accurate method of plotting the data.

Some of the largest masses of lithoid tufa near The Pinnacles are stratigraphically at the base of subunit sa1, implying 

that a favorable period for the growth of lithoid tufa existed 

near the beginning of deposition of unit A. Plotting the level 

of the lake responsible for the middle part of that subunit at 

the overflow level is also justified by the massive lithoid tufa 

deposits found at and just below the high shoreline, as well 

as the massive deposits of lacustrine gravel assigned to unit A

that were deposited just below that shoreline. This inference 

of an overflowing lake in Searles Valley during deposition 

of subunit sa1 is also supported by evidence of chloride loss 

from Searles Valley to Panamint Valley at this time (described 

below). The highest elevation deposits mapped as subunit sa3

lie at 1,920 ft (table 9), but overflow levels are also postulated 
78 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Elevation

ranges of

lithoid tufa

concentrations

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

32.8

32.7

35.3

46.35

58.4 65.5 69.8 89.3 122.3

160.5

134.4

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

32 40 50 60 70 80 90 100 110 120 130 140 150 160

sa4

sa3 sa3 sa3

sa2

sa1

Floor of lake

Salinity I 

Salinity II 

Salinity III 

Overflow Level A

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

20

10

0

0

10

20

30

40

50

x

x

x x Acid-insoluble

Salts

CaO

K. feldspar

K. feldspar

Analcime

Searlesite

Analcime

B

LINEARLY INTERPOLATED AGE SCALE

ACID INSOLUBLE (WEIGHT PERCENT)

ELEVATION, IN FEET

U-SERIES AGE SCALE

ELEVATION, IN FEET

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

Floor of lake

Lake overflowing

Lake possibly

overflowing

AGE, IN THOUSANDS OF YEARS

C

Ca0 (WEIGHT PERCENT)

Figure 40. Inferred lake-level history of Searles Lake from 170 ka to 30 ka. A, History of lake fluctuations (heavy lines) based on outcrop 

geology and subsurface salt beds. Subunits of outcropping unit A of the Searles Lake Formation, which extends from 150 ka to 32 ka, 

are labeled above lake-level line; lake history before 150 ka based on lithologies of the subsurface Mixed Layer. Elevations of high-level 

stages based on data of table 9 (solid heavy line) and other data (dashed heavy lines). Radiometric ages plotted near base of diagram 

(bars show experimental uncertainty); 14C ages (dots) are from Stuiver and Smith (1979, fig. 30), and U-series ages (circles) are from Bischoff and others (1985, table 1). Age scale plotted below bottom line of diagram A is interpolated linearly from the ages of the base (150 

ka) and top (32 ka) of the Bottom Mud (this scale also used in parts B and C ); age scale plotted above bottom line of diagram A based 

on U-series dates (see text). Overflow level is elevation of spillover channel into Panamint Valley. Dashed, subhorizontal lines represent 

lake-surface elevations at three salinity levels: salinity I (near 13 weight percent) would permit winter crystallization of monominerallic 

suites, salinity II (25 percent) would permit multimineralic (but pre-desiccation) suites, and salinity III (35 percent) represents saturation 

or desiccation (see text). Elevation of floor of lake shown by hachured line. B, Compositional data for Bottom Mud. Age ranges of diagenetic minerals that suggest higher lake salinities (K-feldspar, analcime, and searlesite), acid-insoluble content (moving 5-point averages 

shown: small dots, accurate data; x’s, less accurate data), and ages of monomineralic salt beds (stippled vertical bars) are from cores 

254 and L-30 (Smith, 1979, figs. 6 and 41, plate 2B); CaO analyses (circles) are from core KM-3 (Smith and others, 1983, pl. 2). Note that 

scale for acid insoluble is inverted. C, Lake history as inferred from data in parts A and B and selected other sources (see appendix 3).
Reconstructed Paleohydrology of Lakes in the Owens River System 79

(fig. 40A) for the lakes responsible for subunit sa3. These are 

thought permissible because field notes record observations of 

lacustrine gravels at levels between 2,000 ft and 2,280 ft elevation, mapped as part of unit A, that rested on alluvial gravels 

having fossil soils similar to those developed at lower elevations on subunit sa2, but not similar to those on gravels of 

the Christmas Canyon Formation and older gravels unit. The 

upper level plotted for the lake responsible for subunit sa4 is 

based on the elevation of the gravels that can be traced to the 

surface of the prominent bar northwest of The Pinnacles that is 

composed of that unit (pl. 4).

The lacustrine retreat and alluvial readvance during 

deposition of subunit sa2 is plotted within the interval 112 to 

102 ka (fig. 40A), because that is the interpolated age of the 

thickest of five zones of monomineralic salts in the Bottom 

Mud as represented by core 254 (Smith, 1979, pl. 2; shown 

here in fig. 40B). The placement of alluvial subunit sa2 is also 

supported by its position in the lower third of good exposures 

of unit A (secs. I32-r and K24-p,q, pl. 4). The other four lowlevel stands in unit A (fig. 40A), representing the other four 

zones of monomineralic salts in cores 254 and L-30, are plotted at the intervals extending from 81 to 77 ka, 70 to 68 ka, 46 

to 45 ka, and 36 to 35 ka; these layers also may have alluvial 

counterparts in the exposed record, but none were recognized. 

Sediments deposited in lakes having higher salinities and 

lower levels are placed within zones in the subsurface deposits 

containing diagenetic analcime, searlesite, and K-feldspar, 

which imply higher salinities (fig. 40B). Evidence described 

by Sheppard and Gude (1968, p. 33-36) suggests that diagenetic K-feldspar and searlesite are products of reactions with 

interstitial brines having higher salinities than those involved 

in the formation of diagenetic analcime and that all three minerals are indicative of elevated salinities. It is clear, however, 

that the ages inferred for these shallow- to intermediate-level 

stands of Searles Lake during deposition of unit A (fig. 40C) 

must be used cautiously, because they have large uncertainties.

The lack of short-period variations in the lake history 

plotted for subunit sa1 contrasts with that plotted for younger 

units. This resulted in part from differences in the preservation 

and exposure of the older and younger records. However, if 

Searles Lake did stand at overflow levels during most of the 

period subunit sa1 was being deposited, relatively few fluctuations would appear in even the most accurate curve depicting 

that part of its history. This is because when the overflow from 

Searles Lake was voluminous, smaller magnitude climatic 

fluctuations like those revealed by the lacustrine sediments 

assigned to younger units in the Searles Lake Formation would 

have been expressed downstream, by the lakes in Panamint 

and Death Valleys, rather than in Searles Valley (fig. 41; note 

history plotted between 1.6 Ma and 1.2 Ma).

A large lake in Panamint Valley requires inflow from 

Searles Valley, because Panamint Valley’s drainage area 

is inadequate to collect the necessary amounts of water 

(R. Smith, 1978). Table 10 lists the approximate areas and 

volumes of water contained by the five interconnected lakes 

in the Owens River system during their Pleistocene maxima. 

The volume of water required to fill Panamint Valley alone, 

similar to the volume required to fill Owens, China, and 

Searles Lakes together, indicates that runoff intensities during times when Panamint Valley contained a large lake were 

much greater and more persistent than at any subsequent 

time. Data compiled by Jannik (1989, fig. 38) on the chloride 

budgets in Searles and Panamint Valleys, supplemented by 

36Cl and other radiometric data from both valleys, indicate 

a period of major chloride transport into Panamint Valley 

between 150 ka and 120 ka. Smith and Street-Perrott (1983, 

table 10-2) estimate the Owens River runoff volume needed 

to fill Panamint Valley was about 6.5 times that of present 

runoff, assuming that a temperature decrease of 5°C accompanied the precipitation increase.

A temperature decrease of about 5°C during wetter periods of the late Pleistocene is indicated by many types of data, 

but the evidence of Winograd and others (1988, table 2, fig. 

4) from the Death Valley area indicates that a relative warming period started about 150 ka. This requires the overflow 

period of Searles Lake, plotted between 140 ka and 118 ka 

(fig. 40C), to have coincided with the interglacial period as 

proposed by those authors. If the atmospheric temperatures 

during that overflow period were about the same as today’s 

temperatures, rather than 5°C cooler, regional runoff volumes nearly nine times those of the present would have been 

required to fill and maintain a lake in Panamint Valley and all 

of the lakes upstream from it (Smith and Street-Perrott, 1983, 

table 10-2). Possible support for a modern-temperature evaporation rate comes from the results of computer modeling 

of Lake Lahontan’s (Nevada) response to changes in inflow 

(Benson and Paillet, 1989, fig. 8); computer-simulated filling 

of that lake to its highest late Pleistocene level required a 

ninefold increase in inflow.

Reconstructed Paleohydrology of 

Lakes in the Owens River System

Much of the justification for mapping lacustrine and 

other late Cenozoic sediments in Searles Valley is based on 

the need to know more details of the regional hydrologic and 

climatic changes. Studies of Pleistocene lakes in other western United States basins, largely oriented toward the same 

goals, have been carried out over more than a century. Milestone studies prior to 1980 are noted by Smith and Street-Perrott (1983, p. 190), and subsequent studies are summarized 

by Benson and Thompson (1987b, p. 244-251) and Benson 

and others (1990). Most of the studies made over the past 

few decades have had the advantage of radiometric and other 

quantitative methods of determining the ages of lacustrine 

deposits. However, precision in dating many deposits has 

proved elusive for a variety of reasons that are summarized 

earlier in this paper. Nonetheless, though some of the dates on 

outcrop material presented in this report are also considered 

unreliable (table 5, dates enclosed by parentheses), the overall 
80 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

consistency of dates from outcrop units less than 30 ka in age, 

the variety of materials dated, and the stratigraphic correlation 

with better dated subsurface sediments combine to support 

the approximate ages assigned here.

In addition to the dating problems noted above, reconstruction of a succession of hydrologic environments from 

a lacustrine history requires that the response of rivers and 

lakes to changes in each of several aspects of climate be 

quantified. Many studies of these aspects have been made; the 

earliest was probably Halley (1715), but more modern studies include those of Langbein (1961), Snyder and Langbein 

(1962), Schumm (1965), Benson (1981, 1986), Smith and 

Street-Perrott (1983), Benson and Paillet (1989), Benson and 

others (1990), and Smith (1991b). Most of them acknowledge 

the ambiguities among several elements of climate that could 

have affected runoff volumes and lake levels. These include 

changes in (1) the total amount and seasonal distribution of 

precipitation, (2) air and lake-surface-water temperatures, 

(3) relative humidity, (4) cloudiness, (5) windiness, and (6) 

vegetation cover. Almost none of these are accurately recorded 

in the geologic record, but they all influence the percentage of 

precipitation that became runoff and the inflow-evaporation 

ratios of lakes. Probable changes in evaporation rates are small 

when compared with the possible changes in inflow volumes 

(Smith, 1991b, p. 36). For some geologic purposes, records of 

the ages and magnitudes of variations in runoff volumes are of 

more value than reconstructions of the climatic balances that 

controlled them, because runoff-volume data can be applied 

directly to studies of geologically important processes such as 

stream sizes and velocities, flood frequencies, and sedimentation and erosion rates.

Interrelations between adjoining subbasins that first 

contribute to (or receive water from) an adjacent basin are 

necessary concepts when correlating lake histories (Benson 

and Thompson, 1987b, p. 244-247, figs. 4-7; Benson and 

others, 1990, p. 39). Both Lake Bonneville and Lake Lahontan, the two largest Pleistocene lakes in the Great Basin, are 

each composed of a series of adjoining subbasins. Many 

smaller Pleistocene lakes in the Great Basin also are thought 

to have overflowed into adjacent basins (Snyder and others, 

1964). Searles Lake represents a variation of those relations 

in that it was third in a series of as many as five sequential 

basins fed primarily by the Owens River, only two of which 

(Searles and China) ever merged to form a single lake. The 

0 0.5 1.0 1.5 2.0 2.5 3.0

Wet

Intermediate

Dry

INCREASING PRECIPITATION

AGE, IN MILLION YEARS

Panamint and Death Valleys

(Panamint Lake and Lake Manly)

Searles Valley ( Searles Lake)

Owens and Indian Wells Valley

(Owens and China Lakes)

CLIMATIC REGIME

LOCATIONS OF MOST DETAILED RECORDS 

OF SHORTER CLIMATIC FLUCTUATIONS

Figure 41. Diagrammatic representation of climatic regimes in the region of the Owens River system from 3.2 Ma to the present (modified from Smith, 1984, fig. 4). The position of Searles Lake in the middle of a chain of lake basins means that the degree of detail in its 

record of climatic variations is itself very variable. During long periods of dominantly wet climates, Searles Lake would generally remain 

full and overflowing, spilling its excess to downstream lakes (Panamint and perhaps Manly). During long periods of dominantly dry climates (like the present), Searles Lake would generally receive no input from overflowing upstream lakes (Owens and China) and remain 

dry or highly saline. Only during periods of dominantly intermediate climates, when it generally received input from upstream but rarely 

reached overflow level itself, would Searles Lake produce a detailed record of the many shorter, less extreme climatic fluctuations. The 

major fluctuations are plotted as 400,000 years long, the approximate frequency of the astronomical cycle suggested by Smith (1984) as 

the most important control of the climates that determined Searles Lake’s history. The minor cyclic fluctuations are plotted as 100,000 

years long, the longest of three periodicities well represented in the marine record of high-latitude glaciation. Theoretically, the 400,000-yr 

and 100,000-yr (and shorter) periodicities are astronomically induced by cyclic variations in the Earth’s tilt and orbit relative to the Sun.
Reconstructed Paleohydrology of Lakes in the Owens River System 81

Owens River chain also received water from the Mono Lake 

basin at times.

During periods that were on average dry, Searles Lake 

had the lowest potential of any of the five basins for significant runoff from its own drainage area (table 11), which 

includes no mountains higher than 6,562 ft (2,000 m). At 

such times, the impact of brief periods of climate change 

on the basin containing Searles Lake would have differed 

from the impact on lakes in basins bordered by high mountain ranges. Owens Lake, and China Lake at times, probably 

began enlarging very shortly after the first increase in regional 

precipitation produced additional inflow from the adjoining 

high-elevation slopes of the Sierra Nevada. Downstream Panamint Lake, with mountains ranging up to 11,048 ft (3,368 

m) on the east and 8,839 ft (2,694 m) on the west, might have 

received some increase in local inflow during transitions to 

a wetter climate, but calculations show that lakes as large 

as those recorded by its highest shorelines and sediments 

required inflow from Searles Lake and its upstream drainages (R. Smith, 1978). Searles Lake’s levels responded most 

sensitively to climate change during climatic regimes that on 

average were intermediate in intensity, compared with the 

present dry regime (when Searles Lake is almost permanently 

dry) or the most extreme wet regimes (when either Panamint 

or Death Valley contained the terminal lake). The schematic 

diagram of the history of lakes in Searles Valley since 3.2 Ma 

(fig. 41) illustrates the effect of this hydrologic setting on its 

record of past climates.

What this setting means is that when the Owens River 

supplied the water volume it carries today, no water from 

that system could have reached Searles Valley until a fairly 

substantial increase in regional runoff occurred. Smith and 

Street-Perrott (1983, table 10-2) calculate, for example, that 

assuming no change in temperature and no contribution from 

other streams, Owens River flow would have had to more than 

double relative to its modern (1872) flow for Owens Lake to 

fill and begin to overflow. Historically, even an abnormally 

wet year (1968-69) produced flow in the Owens River that 

did not equal the amount required to meet this average-flowvolume requirement. For China and Searles Lakes to also fill, 

river flow would have had to increase sixfold. Lake-surface 

temperature decreases of 5°C would have decreased evaporation and reduced these increased-flow requirements by about 

25 percent, but no reasonable temperature reduction could 

have eliminated the need for increased inflow for Owens River 

water to reach Searles Lake. In other words, for Owens River 

flow to have caused a perennial lake to develop in Searles 

Valley, regional runoff would have had to increase several-fold 

over present runoff, meaning that any record of perennial-lake 

sedimentation in Searles Valley documents a climatic scenario 

that most workers would consider to have already reached a 

pluvial-like level.

The lacustrine history recorded by the deposits of the 

Searles Lake Formation (figs. 39C and 40C) shows, therefore, that most of the past 150 k.y. have been characterized 

by a much wetter hydrologic environment and climate than 

now prevails. Unit A represents the wettest of these periods. 

During the 17-k.y. period between 140 ka and 118 ka (subunit 

sa1), a large and vigorously overflowing lake is interpreted 

to have occupied this valley. During subsequent periods, centered at the nominal ages of about 108, 79, 70, 45, and 35 ka, 

perennial lake sizes shrank to depths that allowed monomineralic salines to precipitate during cold periods (Smith, 1979, 

p. 16-18, pl. 2). Between these low stands, the lake stood at 

intermediate levels for periods as long as 25 k.y. Using the 

climatic labels of figure 41, the lake-level history represented 

by unit A indicates a climatic regime that varied from wet to 

intermediate but not to dry.

Lake fluctuations indicated by the stratigraphy of units 

AB through D of the Searles Lake Formation, however, 

imply more frequent climatic variations than during the 

deposition of unit A. Within a period of about 32 k.y. (fig. 

39C), 15 lake expansions are separated by 15 contractions 

but only 3 desiccations. These represent complete cycles, 

on average, about every 2 k.y. More than 84 percent of this 

period represented intermediate hydrologic regimes in this 

drainage area; the only “dry” episodes centered on periods 

near 28 ka (which was probably very brief), 8 ka (which 

perhaps accounted for about 4.5 k.y.), and 1 ka. These are 

documented by subunit S-5 of the subsurface Lower Salt, 

the subsurface Upper Salt, and the presently dry surface of 

Searles Lake, respectively.

Figure 42 plots Searles Lake fluctuations over the past 150 

k.y. in terms of required inflow volumes from the Owens River 

plus the small amounts from other streams that flowed directly 

into Owens, China, and Searles Lakes. This figure resembles 

the diagrams of Searles Lake levels (figs. 39C and 40C) but is 

Historic Pleistocene 

maximum

Lake name Area

(km2

) 

Volume

(109 m3)

Area

(km2) 

Volume

(109 m3)

Mono 2001 3.77 440 63.6

Owens 2852 2.95 695 14.3

China 

Searles

03

03

0

0 } 9954 79.44

Panamint 03 0 710 105.2

1

Scholl and others (1967, p. 584, fig. 4); value for 1964.

2

Gale (1914); data are for level of 1872, before irrigation and construction of Los Angeles Aqueduct.

3

Normally dry most of year. Approximate areas of playas (km2): China, 

20; Searles, 100; north Panamint, 18; south Panamint, 46.

4

Searles and China Lakes coalesced into one water body at highest 

stands.

Table 10. Approximate areas and volumes of historic 

and Pleistocene-maxima lakes of the Owens River system.
82 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

more subdued. The reason for this is that, during periods when 

Searles Lake fluctuated, the evaporation losses from upstream 

Owens and China Lakes, estimated to be 0.89 and 1.02 m/

yr, respectively (Smith and Street-Perrott, 1983, table 10-2), 

remained nearly constant because those lakes remained full. 

Thus, if Searles Lake was full but not overflowing, a reduction 

of about 56 percent in Owens River flow could cause Searles to 

desiccate—a 100 percent change in lake level that was caused 

by little more than 50 percent change in runoff.

Figure 42 also shows (1) that about 81 percent of the 

150-k.y. period was characterized by runoff volumes between 

about 2.0 and 4.5 times present Owens River runoff (and thus 

intermediate in the terminology used in fig. 41), (2) that about 

14 percent of the time those volumes exceeded 4.5 times 

present runoff (thus wet), and (3) that 4 percent of the time—

which includes the present—flow fell below twice present volumes (thus dry). A case could be made that the four wet pulses 

at about 125, 85, 50, and 15 ka, which are about 40 k.y. apart, 

were possibly expressions of the Earth’s 41-k.y. obliquity 

cycle, but the large uncertainties in the ages of deposits too 

old for 14C dating makes this suggestion tenuous. What is not 

tenuous, however, is the evidence (fig. 42) that, except for the 

past 10 k.y., most of the preceding 150 k.y.—including the last 

interglacial period, which is usually considered to have been a 

relatively dry time—was characterized by flow volumes in the 

Owens River that were more than twice historic flow volumes. 

This conclusion is supported and broadened by the study of a 

core from Owens Lake by Smith and others (1997, p. 149), in 

an area much less arid than Searles Valley, which shows that in 

this watershed, and probably in a much larger area, the period 

since 5 ka has been more arid than any other period since 

sometime before 800 ka!

Considering again the entire 3.2-m.y. lacustrine record 

from Searles Lake (Smith and others, 1983, table 1), we 

see that during Pleistocene and late Pliocene time, only two 

periods represent times of nearly continuous desiccation and a 

lack of significant inflow. The first lasted from approximately 

2.56 to 2.04 Ma (a period of about 0.52 m.y.) and the second 

from 0.57 to 0.31 Ma (0.26 m.y.), together accounting for 

about a quarter of that total 3.2-m.y. period. Since 0.31 Ma, 

however, the desiccations of Searles Lake that occurred at 

about 28 ka, and during the early and late Holocene, account 

for less than 3 percent of that period.

In this area, paleohydrologic trends during the past 

3.2 m.y. were also caused by continuing uplift of the Sierra 

Nevada, which affected climates in the drainage areas of the 

Owens River and downstream lakes. The part of the Sierra 

Nevada just west of the Owens River’s headwaters has 

been uplifted by nearly 1,000 m in the past 3 m.y. (Huber, 

1981). At the outset of this period, air masses had capacities 

to transport almost 50 percent more moisture to areas east 

of the Sierra Nevada than they do now (Smith and others, 

1983, p. 23), so that continuing uplift steadily intensified 

the rain shadow east of the range. Other lines of evidence 

support this trend; increasing percentages of chemical sediments in the lake deposits in Searles Valley are attributed to 

Table 11. Distribution of drainage-area elevations for five lake 

basins in Pleistocene Owens River system.

Drainage areas

(km2

)

Elevation

range

(103

ft)

Mono

Lake

Owens

Lake

China

Lake

Searles

Lake

Panamint

Lake

14+ 8

13 to 14 512

12 to 13 34 217

11 to 12 93 247 l

10 to 11 217 388 2

9 to 10 264 394 16

8 to 9 435 476 3 26

7 to 8 1,320 862 256 145

6 to 7 956 896 131 3 396

5 to 6 1,300 373 21 632

4 to 5 1,698 399 158 717

3 to 4 1,424 1,432 352 823

2 to 3 417 637 1,004

1 to 2 461 810

Total 3,319 8,422 3,011 1,632 4,571

this encroaching aridity (Smith and others, 1983, p. 19), and 

isotopic studies of fluid inclusions in calcite veins in Death 

Valley reflect this uplift and increased blockage of precipitation (Winograd and others, 1985). It is significant, however, 

that the longest dry episode and the longest wet episode in 

the 3.2-m.y. record from Searles Lake were both in the earliest third of that period. Clearly, climatic variabilities have 

greatly exceeded any effects caused by geological changes 

in this area.

Comparison of the Owens River System 

with the Reconstructed Paleohydrologies of Other Areas in the Western 

United States

Correlation and comparison of the paleohydrologic 

history represented by the Searles Lake Formation with the 

histories of other areas shows several meaningful similarities and some differences. Some of the apparent differences 

may be caused simply by a lack of accurate age control, but 

many others appear to be real. Problems with age control for 

the period preceding 35 ka, the approximate older limit of the
Comparison of the Owens River System with the Reconstructed Paleohydrologies of Other Areas 83

7

6

5

4

3

2

1

AGE, IN THOUSANDS OF YEARS

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

RATIO OF ESTIMATED PAST OWENS RIVER FLOW VOLUMES TO MODERN (1872) FLOW VOLUME

Variations in past flow volumes greater than this amount expressed by variations in the sizes of lakes downstream from Searles Lake

Variations in past flow volumes less than this amount expressed by variations in the sizes of lakes upstream from Searles Lake

Present average flow of Owens River

?

?

Figure 42. Estimated past flow volumes from the Owens River and tributaries to Owens, China, and Searles Lakes, relative to the modern 

(1872) flow volume of the Owens River. Calculated past flow volumes are the amounts that would offset evaporation from the surfaces of 

lakes existing at the time. The evaporation volumes were calculated by assuming that if a lake of any size was in Searles Valley, Owens and 

China Lake were at their maximum areas, and that the area of Searles lake was proportionate to the levels plotted in figs. 39C and 40C. The 

evaporation rates (Owens, 0.89 m/yr; China, 1.02 m/yr, and Searles 1.19 m/yr) assume a 5°C lowering of temperature; the areas of Owens 

Lake (694 km2

) and China Lake (155 km2) and the discharge of the modern Owens River (0.41 x 109 m3/yr) are from Smith and Street-Perrott 

(1983, table 10-2). Area of Searles Lake at different levels derived from Smith (1979, fig. 32); areas of lakes whose levels were beneath the 

present lake surface are presumed to have been in basins that had the same depth-area characteristics as the present basin.

14C dating method, result from both smaller percentages of 

preserved deposits as outcrops and the difficulties in finding 

reliable dating materials and methods for these older deposits.

Even though some subbasin lakes may have coalesced 

as they approached their maximum sizes, problems arise 

when correlating the earlier histories of the individual basins, 

because they were inherently different if their individual 

hydrological settings were not similar. A study of the 

responses by Owens and Searles Lakes to major climate 

changes since 800 ka documents large differences in the 

timing of when those changes registered in each lake’s sediments. The explanation for these timing differences is that 

Searles Lake lies in a much more arid region than Owens 

Lake, as measured by the amounts of precipitation that fall 

within their respective drainages. For example, when the climate changed from a relatively wet one, which allowed Owens 

Lake to contribute water to China and Searles Lakes, to one 

that was more arid, the overflow from Owens Lake would have 

decreased and eventually stopped. With a probable evaporation rate of >1 m/yr at Searles Lake (Smith and Street-Perrott, 

1983, table 10-2), a few centuries with no inflow would have 

caused it to desiccate. At the same time, however, Owens Lake 

would probably still be full or almost so, depositing sediments 

indicative of a wet environment. Conversely, when the climate 

changed back from arid to wet, Owens Lake would have been 

the first to receive inflow from the Sierra Nevada and the first 

to expand, almost immediately depositing sediments indicative 

of a deeper lake and a wetter climate. During the time required 

for Owens Lake to fill and overflow into China Lake, and for 

that lake to also fill and overflow, Searles Lake would have 

remained a salt flat. Only when the flow into Searles Lake 

became voluminous enough to offset annual evaporation and 

end saline deposition did the sediments deposited in Searles 

Lake belatedly register a change of climate.

In this way, sediments deposited in the basin most remote 

from the main source of runoff were the first to record a 

period of decreasing runoff, and sediments deposited in the 

basin closest to the main source of runoff were the first to 

record a period of increasing runoff. The sedimentary records 

from Searles and Owens Lakes show that they followed this 

anticipated sequence, and that they required long delays before 

the same climatic change was recorded in the basin slower 

to respond. Considering that these staggered sedimentary 

responses reflected the same climate changes as recorded in 

successively connected basins fed by the same river, the very 

long delays seem to document some climate changes that were 

very gradual. The apparent delays in the Owens and Searles 

Lake records covering the past 800 k.y. ranged from 5 k.y. to 

100 k.y., but only the delay that lasted from 10 ka to 5 ka lies 

within the period discussed by this study.
84 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Paleohydrologic Records for the Period 

Between 150 and 35 ka 

The largest late Pleistocene lake in the Great Basin 

was Lake Bonneville in northwestern Utah, first studied and 

named by Gilbert (1890); its modern remnant is the Great 

Salt Lake. Studies of Lake Bonneville and its chronology 

up until about 1980 are summarized elsewhere (Smith and 

Street-Perrott, 1983). Morrison (1991, p. 305-307) concluded 

that a succession of two or three deep-lake phases existed 

in Lake Bonneville between 290 and 130 ka. He assigned 

these ages by correlating their sediments with marine-isotope 

stages 8 through 6, having concluded that all 14C dates and 

most U-series dates from Lake Bonneville sediments are 

too young. Morrison termed the sediments deposited during these lake stages the Alpine Alloformation. Scott and 

others (1983, p. 280-281, fig. 2), after studying lake sediments at Little Valley in the Bonneville basin, concluded that 

they represented a brief expansion of Lake Bonneville that 

occurred after 150 ka and ended about 130 ka. Their age control was based on 14C ages (wood and charcoal), on amino 

acid ratios in shells, and on the 232Th/230Th dates of Broecker 

and Kaufman (1965, table 7) and Kaufman and Broecker 

(1965, table 9). Similarly, Varnes and Van Horn (1984, 1991) 

reported U-Th dates from the lower part of the Alpine Alloformation ranging from ~108 to ~140 ka.

The evidence indicating a large and overflowing lake 

in Searles Valley during the period between about 140 ka 

and 118 ka (fig. 40C) is more compatible with the younger 

ages assigned to the depositional period responsible for 

the Alpine Alloformation. The Lake Bonneville evidence, 

however, does not reflect as intense a pluvial period during this time as does the Searles Lake record. Morrison 

(1991, p. 307) considered the period between 130 and 30 

ka, which he assigned to the overlying Promontory Geosol, 

to be correlative with isotope stages 5 through 3 and to 

have primarily been one of subaerial deposition. Oviatt and 

others (1987, fig. 4), however, presented evidence of Lake 

Bonneville expansions at 65 ka and 40 ka which, although 

subordinate to the preceding expansion at 140 ka, might 

be equivalent to the single expansions proposed here for 

Searles Lake centered at about 50 ka.

Lake Lahontan, a late Pleistocene lake in northwestern 

Nevada, was first studied and named by Russell (1885). Lake 

deposits in the several basins making up the Lake Lahontan 

group have yielded few dates in the range 150 ka to 35 ka. 

The Eetza Alloformation (Morrison, 1964, 1991) was the 

first deep-lake phase of the late Pleistocene Lake Lahontan 

group. Morrison divided its history into three major pulses 

plus several smaller ones and assigned the formation to the 

period between about 350 and 130 ka. This age assignment 

was in large part because of the occurrence of the Wadsworth 

tephra (~200 to ~150 ka) in the upper part of the alloformation and the Rockland tephra (400 ka) in the upper part of 

the underlying alloformation (Morrison, 1991, p. 297), and 

he tentatively correlated it with isotope stages 10 through 6. 

In the upper part of this alloformation, outcrops of lacustrine 

sand about halfway between the present low point of the 

basin and the highest shoreline contained gastropods that 

gave a 230Th/234U date of 120±20 ka (Broecker and Kaufman, 

1965, p. 565, table 7; Kaufman and Broecker, 1965, table 9). 

Similarly, a 230Th/234U date of approximately 50 ka on highlevel tufa suggests that the level of Lake Lahontan at that 

time was about 90 percent of its maximum depth (Benson 

and Thompson, 1987a, fig. 5, table 4). If the radiometric 

dates are about correct, these periods of expansion could be 

equivalent to the major expansions of Searles Lake postulated for these times (fig. 40C).

The wide differences between the ages assigned to the 

same formations deposited in Lakes Bonneville and Lahontan make it difficult to compare those lakes with the history 

of Searles Lake between 150 ka and 30 ka. The ages of most 

lacustrine stages in both Bonneville and Lahontan assigned by 

Morrison (1991, fig. 5) are 150 ka or older and thus lie outside 

of the age range being considered here. The younger ages 

proposed by other workers, based on radiometric and other 

techniques, correlate approximately with the deep-lake events 

proposed here for Searles Lake (fig. 40C).

Atwater and others (1986, p. 103-104, fig. 6) describe 

several zones of lacustrine silts beneath the present surface 

of Tulare Lake, west of the southern Sierra Nevada. Lakes 

developed in this area during periods of high runoff derived 

from glaciation in the Sierra Nevada. The lowest of these 

silt zones, which they term the “West Lake Silt,” represents 

lacustrine expansion that they estimate to have lasted about 

30 k.y. within a period bounded by 130 ka and 70 ka. Two 

or three smaller lacustrine expansions followed during the 

internal between 70 ka and 26 ka. Considering the differences 

in the hydrologic settings of Searles Lake and Tulare Lake, 

which received its water directly from the Sierra Nevada, their 

records present no conflict as paleoclimatic histories.

Sediments deposited in Pleistocene Lake Chewaucan 

crop out north of Summer Lake, south-central Oregon. That 

area is less arid than most of the Pleistocene-lake sites in 

the Great Basin segments of California, Nevada, and Utah. 

More than 50 tephra beds provide excellent age control 

and allow correlations with lacustrine deposits elsewhere. 

The interbedded sediment lithologies document lacustrine 

deposition during the entire period between 70 ka and 16 

ka, and extrapolation of the indicated sedimentation rates 

suggests that lacustrine deposition was virtually continuous since some time prior to 335 ka (Davis, 1985, p. 50-51). 

This suggestion is similar to one based on the Searles Lake 

record that indicates pluvial to semipluvial conditions existed 

almost continuously from about 300 ka to 10 ka (Smith, 

1986). Davis also notes a possible lake recession, but no 

evidence of desiccation, that might indicate an interpluvial 

correlative with interglacial isotope-stage 5e. This recession 

may also correlate with the succession of intermediate to low 

stands in the Searles Lake record between about 110 ka and 

60 ka (fig. 40C).
Comparison of the Owens River System with the Reconstructed Paleohydrologies of Other Areas 85

All four of these lake-basin chronologies, however, 

show what may be real and important similarities to the 

reconstructed sequence for Searles Lake during this period. 

Three of the four basin chronologies find evidence of a highstand that could include the period between 140 and 120 ka, 

as in Searles Lake, and two find highstands at about 50 ka, as 

is proposed for Searles. This consistency lends credibility to 

the accuracy of other details of the several lacustrine histories, despite the variety of hydrologic settings and differing 

choices of criteria used to compile those histories.

Paleohydrologic Records for the Period 

Between 35 ka and the Present 

A comparison of the paleohydrologic histories indicated 

by lacustrine deposits in the Great Basin that have been dated 

in the range 35 ka to the present, based on published and 

unpublished records from Searles Lake, Lake Lahontan, Lake 

Bonneville, and Lake Russell (now Mono Lake, in east-central 

California), is presented by Benson and others (1990). Each 

lake-level curve differs from the others in certain respects, but 

detailed comparisons between these areas are inherently difficult, in part because of variations in their basin geometries. 

Lakes Bonneville and Lahontan were composed of several 

basins whose lakes coalesced into one water body when nearly 

full, Lake Russell was in a single basin at the base of the 

Sierra Nevada, and Searles Lake was two basins downstream 

from the highest part of the Sierra Nevada, the main source of 

inflow for the Owens River system.

In Lake Bonneville, the Bonneville Alloformation represents its last major expansion. Morrison (1991, p. 307-308, 

fig. 13) proposes a history covering this period that shows 

a gradual rise of the lake starting at ~30 ka and reaching its 

maximum level at ~16 ka, followed by a rapid decline (caused 

by a partial breaching of its basin at Red Rock Pass) and then 

a fall to near desiccation at ~12 ka. This was followed by a 

short reexpansion, indicated by sediments assigned to the 

Draper Alloformation, that lasted from 10 to 8 ka. This phase 

has proven controversial: mapping by Van Horn (1979) shows 

this unit, but studies by Scott and others (1983), Currey and 

Oviatt (1985), and Currey (1990), although reconstructing 

histories for the period 30 to 12 ka similar to that of Morrison (1991), do not recognize the Draper phase. Between 3.7 

ka and 1.7 ka, a shallow lake reoccupied the low parts of the 

basin (Van Horn, 1979).

In Lake Lahontan, northwestern Nevada, the Sehoo Alloformation records the period between 35 ka and 8 ka. Morrison (1991, p. 298-299) divided the Sehoo into three periods 

that were characterized by deep lakes, separated by relatively 

low stands. The deep-lake intervals extended from ~35 ka 

to ~18.5 ka, ~17.5 ka to ~11.5 ka, and ~9 ka to ~8 ka. His 

ages are largely based on the stratigraphic positions of dated 

volcanic ash layers. Benson and others (1990, p. 246-249) propose a chronology for the same period that places highstands 

during periods between ~35 ka and 16 ka, ~15 ka and ~13.5 

ka, and a small expansion between ~11.5 ka and ~10 ka; these 

ages are based primarily on 14C and U-series determinations. 

The first of these highstands was briefly interrupted by a low 

stand at ~26 ka, based on a single 14C date.

Neither of the chronologies for Lakes Bonneville and 

Lahontan closely resembles the Searles Lake chronology for 

the period between 35 ka and the present. As explained earlier, 

Searles Lake probably should not have a history that is similar 

to those lakes because their histories are largely based on work 

carried out in basins that received runoff directly from the 

adjoining high mountains. Searles Lake, in contrast, was the 

third lake in the Owens River system and was surrounded by 

relatively low mountains.

Additional variations in their reconstructed histories are 

to be expected in view of possibly real differences in the exact 

timing of climate change in each drainage area and significant differences in the criteria and methods used to date and 

reconstruct lake-level curves. In an attempt to minimize the 

differences between lake histories, Benson and others (1990) 

offer alternative interpretations for three lakes, including the 

Searles Lake history as presented by Smith and Street-Perrott 

(1983, fig. 10-5). His alternative lake-level history for Searles 

Lake resembles somewhat the history proposed in this paper 

(fig. 39C), but it suggests lower lake levels during the period 

between 24 ka and 16 ka in unit B time and during all of unit 

C time, and he questions the existence of the Holocene lake 

represented by unit D. Those suggestions clearly conflict with 

the stratigraphic data presented in this paper.

Tulare Lake, west of the southern Sierra Nevada in the 

San Joaquin Valley, expanded twice since 35 ka, in response 

to variations in Sierran runoff (Atwater and others, 1986, p. 

101-103, fig. 6). The earlier expansion resulted in continuous 

lacustrine deposition of the Chatom Silt over a period that 

lasted from about 26 ka to sometime before 13 ka; deposition 

of the overlying lacustrine Blakeley Canal silt, at about 11 ka, 

documented a renewed episode of deep-water deposition. The 

Chatom silt is a reasonable correlative of unit B in Searles 

Valley, and the Blakely Canal silt appears correlative with unit 

C. Tulare Lake expansions are interpreted as likely indicators 

of glaciation pulses in the Sierra Nevada (Atwater and others, 

1986, p. 107-109), as are Searles Lake expansions.

South of the Great Basin, in central New Mexico, Lake 

Estancia had a late Pleistocene history that was mostly similar 

to those of lakes in the Great Basin (Bachhuber, 1989; the ages 

cited below were derived by my interpolating and extrapolating between the three 14C dates considered by him to be reliable: 24,300, 20,040, and 12,460 yr B.P.). In a reconstructed 

record starting before 35 ka, an “initial freshwater phase” 

began about 24.5 ka. Although the maximum inferred water 

depth was reached about 19.7 ka, the mostly freshwater lake 

persisted until about 16.0 ka. Playa deposits represent the 

interval between 16.0 ka and 13.5 ka. A second period characterized by freshwater deposits followed, and the lake reached 

its maximum freshness around 12.5 ka. Soils started forming 

on the older deposits around 10.7 ka. This sequence of stages 
86 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

and their ages are similar to those from both the Tulare Lake 

and Searles Lake records.

Another type of paleohydrologic record, studied in three 

areas northwest of Las Vegas, Nevada, consists of alternating 

alluvial and paludal (marsh) environments, with each change in 

depositional environment separated by a period of soil development. The initial studies of Haynes (1967) in the Tule Springs 

area and subsequent studies by Quade (1986, fig. 2) in the 

Corn Creek Springs area show that the marshes in their areas 

appear to have had the following histories: (1) They were dry 

or possibly dry from sometime before 35 ka or 32 ka. (2) Then, 

after development of a strong noncalcic soil, wet conditions 

prevailed until 16 ka. (3) After development of a moderate to 

strong calcic soil, wet to moist conditions, indicated by spring 

and marsh deposits, mollusks, and plants (separated by a short 

period represented locally by a weak soil), prevailed until about 

8 ka. (4) Finally, dry conditions existed until the present. A 

third study in the nearby Cactus Spring area (Quade and Pratt, 

1989, fig. 4) involved similar deposits but found no evidence of 

a depositional hiatus at the 16-ka horizon. The noncalcic soils 

developed in both of these areas at about 30 ka are possibly 

correlative with the (normally) noncalcic soil that formed at 

about 24 ka on unit AB in Searles Valley, marking the end of 

an intermittently dry period and the start of a wet one (unit B). 

The 14-ka calcic soil in the Corn Springs area may be equivalent to the soil on unit BC in Searles Valley that separates a 

long period of wet conditions, which ended at about 15.5 ka 

(unit B), from a short period characterized by fluctuating wet 

conditions that started at about 13.5 ka (unit C).

The two or three reexpansions of Searles Lake during the 

short interval between 13.5 ka and 10.5 ka, documented by 

deposits of unit C, have small counterparts in the Lake Bonneville record, which indicates a lake-level rise of about 25 m 

between 11 ka and 10 ka, and in the Lake Lahontan record, 

which includes a rise of about 10 m above the highest historic 

level of Pyramid Lake at about 11 ka, but no support is found 

in the record from Lake Russell (Benson and others, 1990, p. 

249, 258, figs. 4, 7, 14). The Searles Lake history, however, 

may reflect its sensitivity to short climatic variations because 

of the lake’s small size and position in the chain of lakes. At 

its maximum size, Searles Lake, including China Lake with 

which it coalesced, had an area that was 5 percent and 2 percent, respectively, of the areas of Lakes Lahontan and Bonneville. Therefore, a few centuries of very intense inflow into 

Searles Valley could have filled the basin, whereas the same 

volumetric increase in inflow to the larger basins would not 

have caused a major increase in lake level. Furthermore, the 

low-level, but perennial, character of the lake responsible for 

unit BC suggests that Owens and China Lakes contained water 

during this period and intermittently contributed overflow to 

Searles Valley. Under this condition, almost 100 percent of any 

increase in runoff from the Owens Lake watershed, caused by 

an increase in regional precipitation, would have immediately 

reached and started raising the level of Searles Lake.

Several other records from areas nearer the latitude of 

Searles Lake, however, indicate a wet period at about 12 ka. 

The paludal records from northwestern Las Vegas Valley 

(Quade, 1986, fig. 2) show two separate periods that represent 

moist conditions during the interval between about 13 ka and 

8 ka, and these may be more complete records of the same 

climatic events as recorded in truncated form by the sediments 

of unit C in Searles Valley.

In Death Valley, dates on the organic 14C in three core 

segments composed of black to green lacustrine silt and clay 

fall near 21.5 ka, 13 ka, and 12 ka (Hooke, 1972, fig. 3, table 

3). These came from the 10-km-wide segment of the valley 

floor that includes its lowest elevations, implying the existence of perennial lakes of that width until sometime after 12 

ka. Thirty-seven 14C dates and numerous artifacts from Silver 

Lake, 90 km southeast of the lowest part of Death Valley and 

now the occasional sump of the Mojave River, date pluvial 

events in that area. An earlier study showed that the lake 

receded from its highest stand (10 m) about 14.5 ka, but readvances occurred during the periods 13.75 ka to 12 ka, 11 ka to 

9 ka, and 8.5 ka to 7.5 ka (Ore and Warren, 1971, fig. 7). The 

expansion starting at 11 ka eroded the lake’s outlet 2 m deeper, 

suggesting that this episode was characterized by a relatively 

larger-than-normal volume of overflow. A later study, based 

on outcrops, trenches, and cores, revealed a more complex history, but one that indicated a major drying event at 15.5 ka, a 

refilling event at 13.7 ka, a termination of that nearly continuous high stand at 11.5 ka, and the end of an intermittent-level 

lake at 8.7 ka (Wells and others, 1989, figs. 24 and 25).

Nelson Lake, a small (2 km2

), hard-surface playa lying 55 

km southeast of Searles Lake, is rimmed on its southeast side 

by well preserved beach and bar deposits indicating a 2-m-deep 

lake; cultural materials along the crest of the bar, whose ages 

are considered to be 11 to 10 ka (Bachhuber, 1984, p. 595; 

Warren and Schneider, 1989, p. 18, fig. 1), show that the bar is 

at least that old. Inasmuch as Nelson Lake, at an elevation of 

930 m, receives drainage from an area of only about 225 km2

that includes no mountains more than 600 m above the lake 

surface, this water body seems to document at least one intense 

wet episode in very late Quaternary time. McLean Lake, 6 km 

north of Nelson Lake, appears on aerial photographs to have a 

similarly developed bar along its southeast edge.

The segment of the Searles Lake paleohydrologic record 

from 10 ka to 6 ka (fig. 39C) documents dry conditions, as 

does some part of almost every other lacustrine record from 

the Great Basin (Smith and Street-Perrott, 1983, fig. 10-6). 

The record of a 60-m-deep lake in Searles Valley, whose age is 

constrained by one 14C age on wood (3.5 ka), leaves the ages of 

its rise and fall unconstrained. Its rise could have been contemporaneous with an 85-m rise in the level of Walker Lake, a 

remnant of Lake Lahontan, that postdates 4.7 ka (Benson and 

Thompson, 1987a, fig. 5), or with the 15-m to 20-m fluctuations in Great Salt Lake, the remnant of Lake Bonneville, at 

about 3.5 ka and 2.3 ka (Spencer and others, 1984, p. 332). 

Lake Russell (now Mono Lake) also indicates a rise of about 30 

m, starting possibly as early as 7.0 ka and reaching maximum 

level by 3.5 ka (Stine, 1990, p. 365; Benson and others, 1990, 

fig. 14). A shallow water body in Silver (dry) Lake, 125 km 
Comparison with History of High-Latitude Glaciation 87

southeast of Searles Lake, developed over a short period that 

centered near 3.6 ka (Enzel and others, 1989, p. 44, fig. 1b).

Comparison with History of 

High-Latitude Glaciation

The basal age of the Bottom Mud at Searles Lake 

(described earlier) is apparently correlative with the onset of 

termination 2, the end of the next-to-last major glacial period 

(Martinson and others,1987, fig. 18, table 2; Johnson, 1991). 

However, if the Searles Lake fluctuations described herein 

at 150 ka and the high-latitude glacial fluctuations termed 

termination 2 at 127 ka as described by Martinson and others 

(1987) are correlated, they lie 23 k.y. apart. If we use 130 

ka as the age of the base of the Bottom Mud, this contact 

would almost coincide temporally with the termination of the 

Oxygen Isotope Stage (OIS) 6 glaciation according to marine 

records, but strong evidence assembled by others indicates an 

earlier date for termination 2. Johnson (1991) suggests that 

sea-level rise and concurrent ice-sheet melting actually started 

at about 140 ka, 13 k.y. before 127 ka, and Stein and others 

(1993) conclude that sea-level rise began nearer to 134 ka and 

ended near 118 ka. In addition, the well documented evidence 

for pronounced climatic warming at about 140 ka is recorded 

in vein calcite at Devils Hole, Nevada, an area about 100 km 

northeast of Searles Lake (Winograd and others, 1992, p. 257). 

Thus, the Searles Lake record and the marine and nonmarine 

records published in the 1990s indicate closer ages for what 

seem like reasonably correlated events. A problem, however, is 

that the rise in Searles Lake at that time coincides temporally 

with both the deep-sea and Devils Hole records of a warming 

trend, whereas much of the evidence, and most of the initial 

modeling of global climates, relates pluvial periods to glacial 

periods; this is discussed in more detail below.

The Searles Lake fluctuations since 35 ka (fig. 39C), for 

which age control is better than for older deposits, again have 

an uneven record of correspondence with high-latitude glacial 

events. The contact between the Bottom Mud and Lower Salt 

at 32 ka does not correspond with any significant change in 

the marine isotopic record of high-latitude glaciation (Bischoff 

and others, 1985, fig. 2; Martinson and others, 1987, fig. 18, 

table 2). The brief lacustrine desiccation at 28 ka in Searles 

Lake corresponds only with minor fluctuations in the marine 

isotopic record, but that event and several adjoining periods of 

less extreme lake fluctuations have been tentatively related to 

stadial-interstadial fluctuations recorded by an ice core from 

Greenland (Phillips and others, 1994). Also, the period represented by the Lower Salt subunits S6 and S7 (28 ka to 24 ka), 

considered on the basis of salt mineralogy to have been deposited at times ambient temperatures were about 5°C cooler than 

those characterizing earlier salt deposition (Smith, 1979, p. 

89-90), corresponds approximately with the ages of deposits 

representing the cold Farmdalian interglacial period in the icesheet history of the northeastern United States (Follmer, 1983, 

p. 141, fig. 7-2; Baker and others, 1989, p. 1375).

Searles Lake overflow at 16 ka could correspond with 

either the 18 ka glacial maximum or the subsequent trend 

toward deglaciation. The major—but very brief—lake fluctuations between 13.5 ka and 10.5 ka have no counterpart in the 

ice-sheet history as derived from the marine record. They do, 

however, approximately correspond in time with oscillations 

of the ice-sheet margin in the northern Great Lakes region 

of the United States (Mickelson and others, 1983, p. 25-26) 

and with water-temperature changes in the North Atlantic 

Ocean that produced very rapid temperature changes, termed 

the Allerod-Dryas oscillations, in the adjoining continental 

areas (Ruddiman and McIntyre, 1981, p. 178-182, 185-191; 

Broecker and others, 1985, p. 23-25). If the Allerod-Dryas 

climatic oscillations, which have been considered events that 

occurred only in the North Atlantic’s climatic sphere of influence (Broecker and others, 1985, p. 24; Broecker and Denton, 

1989, p. 2481), were in fact expressed also in this part of the 

western United States, it may reflect a history of changes in 

the western United States (Haynes, 1991, p. 447, fig. 6) and 

the Northeast Pacific Ocean (Mathewes and others, 1993, p. 

104) that resembled those reconstructed for the North Atlantic by Ruddiman and McIntyre (1981). DeDecker and others 

(1991) report evidence from an area just north of Australia that 

indicates a dry event that had the same age and duration as the 

Dryas cold event, implying that this short climatic event was 

expressed in some manner worldwide.

Overall, changes in Searles Lake levels show an inconsistent relation to high-latitude glacial fluctuations, and establishing the ages and directions of middle-latitude climatic changes 

on the basis of deep-sea isotopic chronologies appears to be 

a risky practice. The best example of this is provided by a 

review of Searles Lake’s fluctuations that accompanied the last 

two apparently rapid terminations of high-latitude glaciations 

indicated by isotopic data from deep-sea cores. As noted earlier, ice-sheet melting during the period that deep-sea records 

indicate was between 135 ka and 125 ka (OIS 5/6 boundary) 

approximately coincided with the sustained expansion of 

Searles Lake and probable overflowing into Panamint Valley 

(regardless which age is used for the base of the Bottom Mud), 

as well as with warming in the Devils Hole record near Death 

Valley (Winograd and others, 1992, fig. 4). In contrast, the 

rapid destruction of the next generation of high-latitude ice 

sheets, between 14 ka and 8 ka (OIS 1/2 boundary), coincided approximately with the near desiccation of Searles Lake 

between about 15 ka and 13.5 ka, then the brief expansions of 

the lake between about 13.5 ka and 10.5 ka, and finally again 

the desiccation of Searles Lake at about 10.5 ka. All of this 

occurred during the global deglaciation period. Earlier major 

changes in ice-sheet sizes, as documented by the boundaries between marine OIS 6, 7, 8, and 9, influenced climates 

in the Searles Lake drainage area so little that they produced 

no stratigraphic evidence of significant changes in lake size 

(Smith, 1984, p. 13; Bischoff and others, 1985).
88 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Furthermore, the durations of the most extreme changes 

in regional precipitation and runoff for this area may have been 

affected importantly by the Earth’s orbital perturbations that have 

a cycle length of about 413 k.y., a cycle that is well recorded by 

changes in low-latitude sea-surface temperatures and tropical 

sea-floor sedimentary carbonate percentages but appears to be 

unrecorded in ice-sheet chronologies (Smith, 1984, p. 13-14). 

Shorter astronomical cycles, which have durations of about 100 

k.y., 40 k.y., and 20 k.y., appear to have been more important in 

determining the timing of high-latitude glacial events (Hays and 

others, 1976). The 100-k.y. cycles are recorded in the Owens 

Lake record (Smith and others, 1997), but many of them were 

not of sufficient magnitude to be transmitted downstream to 

Searles Lake with an intensity that registered in its sedimentary 

record. The shorter cycles appear responsible for some cyclic 

changes in the Searles Lake record when the prevailing hydrologic regime was at intermediate levels (fig. 41), but the longer 

period orbital perturbations seem likely to have been responsible 

for the major changes in regional hydrology and in the numbers 

and sizes of lakes in the Owens River chain. 

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Smith, G.I., 1990, Searles Lake, California; a multi-billion 

dollar “salt” deposit: Reno, Nevada, Geological Society 

of Nevada and U.S. Geological Survey, Symposium of the 

Geology and Ore Deposits of the Great Basin, Program with 

abstracts, p. 124.

Smith, G.I., 1991a, Anomalous folds associated with the 

east-central part of the Garlock fault, southeast California: 

Geological Society of America Bulletin, v. 103, p. 615-624.

Smith, G.I., 1991b, Continental paleoclimatic records and 

their significance, in Smiley, T.L., and others, Quaternary 

paleoclimates, chap. 2 of Morrison, R.B., ed., Quaternary 

nonglacial geology, conterminous U.S.: Boulder, Colorado, 

Geological Society of America, The Geology of North 

America, v. K-2, p. 35-41.

Smith, G.I., and Church, J.P., 1980, Twentieth-century crustal 

deformation in the Garlock fault-Slate Range area, southeastern California: Geological Society of America Bulletin, 

part 1, v. 91, p. 524-534.

Smith, G.I., and Haines, D.V., 1964, Character and distribution 

of nonclastic minerals in the Searles Lake evaporite deposit, 

California: U.S. Geological Survey Bulletin 1181-P, 55 p.

Smith, G.I., and Pratt, W.P., 1957, Core logs from Owens, 

China, Searles, and Panamint basins, California: U.S. Geological Survey Bulletin 1045-A, 62 p.

Smith, G.I., and Street-Perrot, F.A., 1983, Pluvial lakes of the 

western United States, chap. 10 of Wright, H.E., Jr., ed., 

Late-Quaternary environments of the United States: Minneapolis, University of Minnesota Press, p. 190-212.

Smith, G.I., Troxel, B.W., Gray, C.H., Jr., and von Huene, 

Roland, 1968, Geologic reconnaissance of the Slate Range, 

San Bernardino and Inyo Counties, California: California 

Division of Mines and Geology Special Report 96, 33 p.

Smith, G.I., Barczak, V.J., Moulton, G.F., and Liddicoat, 

J.C., 1983, Core KM-3, a surface-to-bedrock record of late 

Cenozoic sedimentation in Searles Valley, California: U.S. 

Geological Survey Professional Paper 1256, 24 p.

Smith, G.I., Friedman, Irving, and McLaughlin, R.J., 1987, 

Studies of Quaternary lakes—III. Mineral, chemical, and 

isotopic evidence of salt solution and crystallization processes in Owens Lake, California, 1969-1971: Geochimica 

et Cosmochimica Acta, v. 51, p. 811-827.

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year paleoclimatic record from core OL-92, Owens Lake, 

southeast California: Geological Society of America Special 

Paper 317, p. 143-160.

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America Abstracts with Programs, v. 10, no. 3, p. 148.

Snyder, C.T., and Langbein, W.B., 1962, The Pleistocene lake 
References 93

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1:1,000,000.

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94 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California
Introduction 95

Appendixes 1–3
96 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Appendix 1. Measured Sections

Stratigraphic sections were measured in various parts of 

Searles Valley to provide specific examples of the sediments 

that are present. Most measurements were made on single 

steep to vertical exposures, but some sections (identified as 

“composite”) combine measurements made on exposures 

scattered over a small area (such as 0.5 km2). Most sections 

primarily describe sediments assigned to the Searles Lake 

Formation. For each described interval of sediments from this 

formation, the unit or subunit assignment for it is listed in the 

left column. Where sediments belonging to the older gravel 

unit or the Christmas Canyon Formation were included in the 

measured section, they are so identified in the unit column. 

Where samples were collected from a bed in a section for 14C 

dating, the uncorrected results and the material that was dated 

are given. Sediment terminology follows Wentworth (1922); 

colors modified by parenthetical expressions follow Goddard 

(1951); parenthetical data in the headings (for example, S125-

3) are the author’s field-note numbers.

The sections are arranged according to the alphanumeric 

order of the locality designation (explained in the section on 

field and laboratory methods); for example, Section G5-k is 

followed by G10-m, and then by H14-r. Descriptive locations 

and the approximate elevation at the top of the section (in feet 

and meters) are also given.

Most of the geographic features cited in the headings to 

help locate the sampled sites are shown on the base maps of 

plates 1-4 or in figure 1B. However, three informal geographic 

terms are also used: (1) The Pinnacles bar refers to the 2-kmlong lacustrine bar that trends southeast from the east end of 

the Spangler Hills into The Pinnacles area (fig. 1B); (2) the 

Poison Canyon amphitheater refers to the 0.5-km-wide streamcut area of low relief at the mouth of Poison Canyon where 

it enters Searles Valley from the west; and (3) State Highway 

178 enters the study area from the west and runs eastward 

adjacent to Salt Wells Valley Wash—technically, this highway 

ends at the dirt road leading southeast to The Pinnacles, but in 

fact it continues as a paved road east and north through Trona 

to northern Searles Valley, then continues north and east to 

Panamint and Death Valleys.

Section C36-h. Sediments exposed on northwest side of unnamed canyon in Slate Range (S125-3); approximate elevation at top of 

section: 2,040 ft (620 m).

Unit Thickness Description

(m)

A 1.0 Gravel, gray, pebble to cobble sizes, well rounded, equivalent to layer that veneers bench on southeast side 

of canyon, lacustrine.

4.6 Sand, medium to fine, orange yellow.

1.5 Sand and silt, yellow but more orange in upper half.

0.3 Gravel, well rounded, gray.

1.6 Sand, pebbly, tan.

1.5 Sand, medium, grayish orange.

0.3 Silt, efflorescences.

1.5 Gravel, alluvial(?), pebbles and cobbles well rounded, sorting fair to poor, grayish orange.

1.2 Sand, medium grading down to very fine, yellow orange, lower part distinctly lacustrine.

0.6 Gravel, pebble size, well rounded, lacustrine.

1.5 Silt, light tan.

1.2 Sand, very coarse to medium, calcareous soil at top.

3.0 Sandy gravel, pebbles well rounded, some deltaic bedding, upper third possibly alluvial.

6.0± Alternating pebbly sand and sandy gravel, grayish orange, poorly exposed, lacustrine(?).

Older 

gravel

(unit og )

15± Gravel, angular pebbles to cobbles, some boulders, grayish orange, alluvial; resting on fractured, orangestained plutonic rock.

Total thickness: 40.8+ m (134+ ft)
Section E25. Composite description of sediments exposed along north wall of canyon in Argus Range, west of Borosolvay site (S79-

1, 2, 3); approximate elevation at top of section: 2,040 ft (620 m).

Unit Thickness Description

(m)

B 10 Pebble gravel, light gray, well rounded, numerous fragments of rounded nodose tufa, lacustrine.

Tufa

(unit st)

7.5 Lithoid tufa, in form of towers and shoreline benches.

A 3.0 Silt and sand, grading up to gray gravel, subangular to subrounded, lacustrine.

6.1 Gravel, fragments 2-30 cm (average 15 cm), angular, sandy matrix, gray to slightly orange, alluvial.

1.2 Sand and gravel, gray, lenticular, lacustrine.

Older gravel

(unit og)

10+ Gravel, fragments to 2 m, medium to dark gray, alluvial.

 Total thickness: 37.8+ m (124+ ft)

Section G5-k. Description of sediments exposed along north side of Copper Queen Canyon, Slate Range (S92-1); approximate elevation at top of section: 2,160 ft (660 m).

Unit or Thickness Description

Subunit (m)

AB 0.6 Boulder gravel, fragments to 0.6 m across, subangular, dark orange brown, alluvial.

sa3 1.5 Gravel, fragments to 10 cm, gray, uncemented, lacustrine. 

1.5 Sand, medium, tan, uncemented, lacustrine.

0.3 Gravel, fragments to 20 cm, either alluvial or a lacustrine lag gravel.

0.9 Gravel, pebbles to granules, well sorted, gray, well cemented, lacustrine.

1.2 Sand, medium to coarse, soft, tan, lacustrine.

0.3 Gravel, pebble size.

1.0 Gravel, pebbles to granules, well sorted, gray, cemented, lacustrine

sa2 1.3 Gravel and sand, tan, poorly sorted, alluvial (or colluvial).

0.6 Gravel, fragments 3 to 6 cm, angular, alluvial.

sa1 1.5 Sand, fine to coarse, soft, tan, lacustrine.

Sand, medium to coarse, gray, lacustrine.

Gravel and sand, dark brown to gray, very well cemented, locally flaggy, lacustrine.

1.8

0.3

Older

gravel

1.5

3.1

Colluvial gravel, fragments mostly pebble sizes, tan.

Sand and gravel, fragments to 30 cm in size form 3% of unit, tan, well bedded, alluvial.

(unit og) 1.5+ Sand and gravel, fragments to 60 cm form 10% of unit, upper 1 m has concentrations of calcite on 

boulders (soil?).

Total thickness: 18.9+ m (62+ ft)

Appendix 1. Measured Sections 97
98 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Section G10-n. Composite description of sediments exposed on both sides of canyon leading to Standard Mine, Slate Range (S94-7); 

approximate elevation at top of section: 2,280 ft (695 m).

Unit Thickness Description

 (m)

Older

gravel

10 Gravel, poorly sorted mixture of sand and pebble to cobble gravel, some boulders, tan to slightly 

orange, poorly bedded, alluvial.

(unit og) 1 Gravel, pebble to cobble, little finer matrix, gray, well rounded and sorted, lacustrine.

3 Gravel, alluvial, like above.

1 Gravel, lacustrine, like above.

12 Sand and gravel, 60% to 80% of unit is sand or silt, balance is pebbles and cobbles, scattered boulders to 2 m across, gray to tan, alluvial.

1 Gravel, mostly pebble size, gray, lacustrine but not as well rounded as gravels above.

2+ Sand and gravel, like 12-m-thick alluvial gravel above.

Total thickness: 30+ m (98+ ft)

Section H14-r. Sediments exposed on north side of Poison Canyon amphitheater area; see fig. 7; approximate elevation at top 

of section: 1,850 ft (564 m).

Unit or

Subunit

Thickness

 (m)

Description

BC 2+ Sand, medium to very coarse, fairly well sorted, moderate yellowish brown (10YR5-6/4-6), very 

faint bedding, pebble lag gravel on surface, pebbles 0.5 to 3 cm long, numerous fragments of pale 

brown (5YR5/2) nodose tufa on surface.

sb4 2.7 Silt, slightly calcareous to very calcareous, silt contains high percentage of greenish-gold mica 

flakes, 0.2- to 0.3-m-thick lenticular marl layers in lower third, unit is moderate yellow (5Y6/2) on 

weathered surfaces, light olive brown (5Y5/2) on fresh surfaces, lower half mostly massive, faint 

bedding in upper half; in fig. 7, this unit exposed only on north wall of wash that is concealed 

behind nearest low ridge.

sb3 3.1 Marl, yellowish gray (5Y8/1) on weathered surface, grayish orange (10YR7/4) on fresh surface, very 

faint thin bedding on weathered surface, nearly massive on fresh surface; near middle of unit and 

0.5 m apart are two hard, nearly white 2-cm-thick silty limestone layers and a 1-cm-thick nodose 

tufa layer.

sb2 0.7 Sand, fine to very coarse, some granules, interbeds of greenish-gold-colored mica-rich silt, yellowish 

brown (5YR6/4), faint bedding, scattered mollusks.

0.5 Silt, calcareous, yellowish gray (5Y7/2), lower third well bedded, upper part faintly bedded.

1.1 Sand, like 0.7-m-thick bed above, faint bedding, dips on beds variable

sb1 3.6 Marl and silt, layer is mostly calcareous silt, yellowish gray (5Y7/2) to very pale orange 

(10YR8/2) on weathered surfaces, grayish orange (10YR7/2) on fresh surfaces; locally includes 

a hard, 0.3-m-thick, basal marl that is yellowish gray (5Y7/2) and has beds 1 to 2 mm thick; 

1-cm-thick nodose tufa bed present 1 m below top of bed, basal contact sharp in most areas; in 

fig. 7, this unit is basal bed of nearest exposure. (Exposed on east face of small ravine)

1.8 Pebble sand, sand is coarse to very coarse, pebbles to 3 cm long and granules make up a few percent, 

grayish orange (10YR7/2) on weathered surface, yellowish brown (10YR6/4) on fresh surface, 

locally cross bedded, indurated.

0.2 Marl, yellowish gray (5Y7/2), high percentage of greenish-gold mica flakes.

1.6+ Pebble sand, like 1.8-m-thick unit above.

Total thickness: 17.3+ m (57+ ft)
Section H23-a. Sediments mapped as Unit B exposed on north side of Poison Canyon amphitheater (HQI32E-59); approximate elevation at top of section: 1,840 ft (560 m).

Subunit Thickness

 (m)

Description

sb6 0.6 Silt, very thinly bedded, moderately well indurated, light brownish gray (5Y6/1); contact with unit C at top of bed.

4.9 Silt, thinly bedded, slightly indurated, light brownish gray (5Y6/1).

4.9 Cross-bedded medium sand in lower third, flat-bedded sandy gravel in middle; flat-bedded pebble sand in coarser 

layers could be fluvial.

sb5 0.9 Silt, micaceous, calcareous, well sorted, greenish yellow (7Y7/6).

4.6 Silt, faint bedding 20-50 cm thick, weathers with puffy surface, calcareous, yellowish gray (5Y6-8/1).

0.6 Silt, micaceous, calcareous, well sorted, greenish yellow (7Y7/6).

0.9 Marl, thinly bedded, slightly indurated, yellowish gray (5Y8/1).

sb1 1.2 Fine to pebbly sand, poorly sorted, moderate yellowish brown (10YR5/4), local concentrations of mollusks; 

contact with unit sab3 at base of bed.

Total thickness: 18.6 m (61 ft)

Section H23-f. Sediments exposed on west side of Poison Canyon amphitheater, north of State Highway 178 (HQ131-21); approximate 

elevation at top of section: 1,900 ft (580 m). 

Unit or

Subunit

 Thickness

 (m)

Description

sc3 6.8 Silt to very fine sand, calcareous (calcite, aragonite) beds laminated to 2 cm, yellowish gray (5Y7/2) to pale olive 

(10Y6/2), weathers puffy but well cemented on fresh surfaces.

sc2 0.7 Sand, coarse to very coarse, locally well bedded.

sc1 2.3 Silt to very fine sand, calcareous (dolomite, calcite, aragonite), beds laminated, weathers yellowish gray (5Y7/2) 

and pale olive (10Y6/2), well cemented on fresh surface.

BC 1.5 Sand, very fine to medium, calcareous (calcite), well bedded, dark beds to 2 cm thick alternate with light beds, 

contorted in lower part, soft, thickness varies, more tan than underlying sand.

sb6 2.5 Sand, medium to very coarse, arkosic, poorly sorted and rounded, some pebbles to 2 cm, poor bedding, conspicuous amounts of pink feldspar, very pale.

sb5 2.5 Sand, very fine, well sorted, yellowish gray (5Y7/2) calcareous (calcite), well bedded, 0.3 m bed of orange sand 1 

m up from base, a few snails and clams, lower half weathers puffy, light tan to white.

0.7 Silt to very coarse sand, calcareous (aragonite, calcite), laminated at base, light gray (5Y7/1-2) to white, contact 

with underlying sand is sharp, some sand incorporated in basal 30 cm.

---------------------------------------------------------disconformity------------------------------------------------------

sab3 1.0 Sand, coarse to very coarse, a few pebbles, conspicuous amounts of pink feldspar, fragments subangular to subround; bedding distinct, 2-30 cm thick, light olive gray (5Y6/2), snails and clams in lower 0.5 m.

2.0 Sand, fine to very fine, bedded, well sorted, micaceous, soft, calcareous (calcite), light olive gray (5Y6/2); 

weathers slightly puffy; snails and clams noted throughout, common in middle part.

2.5 Sand, medium to very coarse, pebbly, massive to poorly bedded, brownish yellow (10YR6/6) to light gray 

(5Y7/2), fragments subangular to subrounded, poorly sorted, weathers to smooth surface; a few snails and 

clams in upper 0.5 m.

Appendix 1. Measured Sections 99
100 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

sab3 1.3 Sand, fine to coarse, bedded and cross-bedded, ripple marks, olive yellow (5Y6-7/2), weathers slightly puffy, 

some thin layers of very coarse sand.

sab2 1.8 Silt to very fine sand, a few layers of very coarse sand, thinly bedded to laminar, calcareous (calcite), 

weathers puffy, snails, light olive gray (5Y6-7/2).

sab1 1.0 Sand, coarse to very coarse, massive, pale yellow (5Y7/4), may be fluvial, local lag gravel at top.

1.8 Sand, medium to very coarse, well bedded, beds 1-4 mm defined by dark or calcareous layers, very few pebbles, 

pale yellow (5Y7/4), snails throughout.

0.9 Sand, very fine, beds thin to massive, calcareous (calcite), pale yellow (5Y7/2).

0.6 Sand, medium to coarse, well rounded, calcareous pods, pale yellow (5Y7/2), snails, some pebbles, cobbles, and 

clay balls, some orange streaks and pods.

1.5 Sand to silt, very fine, calcareous (calcite, dolomite), weathers puffy, locally laminated, pale yellow (5Y7/2).

0.7 Sand, fine to very coarse, bedded, well indurated, calcareous pods in upper part; pale yellow (5Y7/4) with streaks 

of light yellowish brown (10YR6/4).

0.2 Sand to silt, very fine, massive, weathers puffy, soft, pale yellow (5Y7/2).

Section H23-f. Sediments exposed on west side of Poison Canyon amphitheater, north of State Highway 178 (HQ131-21); approximate 

elevation at top of section: 1,900 ft (580 m). —Continued

Unit or

Subunit

Thickness

 (m)

Description

A 2+ Silt, calcareous (calcite), greenish, massive to faint bedding, 1-mm pods of (secondary?) halite, weathers pale yellow (5Y8/3).

Total 

thickness: 34.3+ m (113+ ft)

Section H23-g. Sediments exposed along highway, south side, east of Poison Canyon (HQ132E-53B); approximate elevation at top of 

section: 1,800 ft (550 m).

Subunit Thickness

 (m)

Description

sb6 1.2 Sand, medium to very coarse, pebbly, slightly orange near top, numerous small mollusk shells.

sb5 2.0 Silt to very fine sand, tan, faint thin bedding, locally laminated, uniform texture; contact with underlying unit 

gradational here but distinct channels exposed west of section.

2.5 Silt to fine sand, orange-gray, mostly massive, some cross-beds.

1.0 Marl, weakly laminated, oolitic; 14C date: 18,560±10 yr (marl).

sb4 0.5 Sand, fine, well sorted, faintly bedded, dark orange, contains mollusk shells, pods of ulexite, gypsum near base; 14C date: 18,600±130 yr (shells).

sb3 2.0+ Marl, bedding thin to laminar, locally contorted, thin lenses of fine sand, gypsum crystals.

Total 

thickness: 9.2+ m (30+ ft)
Sections H23-h and H24-e. Generalized description of sediments exposed south of State Highway 178, southwest side of Poison Canyon amphitheater (HQ 131-44); approximate elevation at top of section: 1,850 ft (565 m).

Unit or

Subunit

Thickness

(m)

Description

CD 2 Sand, tan to orange.

C 2 Silt, white to light green, laminated.

 1 Sand, very coarse, cross-bedded, tan to pink; 14C date: 14,210±120 yr (shells).

 3 Silt, white to light green, laminated, layer of tufa near base, tuff bed 1-2 m up from base; 14C date: 10,430±120 yr (tufa).

B 1 Gravel, lenticular, grades laterally and downward into medium to very fine sand, orange to greenish gray, 

cross-bedded, large quantities of tan tufa at or near top.

 3 Silt, greenish to white, lenticular, massive to thin bedded, some interbeds of sand.

sab7 1 Orange sand and gravel, prominent lag gravel at top.

 1 Silt, greenish, lenticular.

 1 Sand, orange, not as coarse as overlying sand bed; contact with unit below gradational in many areas.

sab6 5 Alternating fine sand and silt, greenish gray to tan, resistant sand lenses commonly less than 10 cm thick; 

prominent 0.5-2 m silt at base; 14C date: 32,100±1,200 yr (organic matter).

sab5 1 Sand, very coarse, cross-bedded, persistent, tan to pinkish gray in some areas, orange in others; local prominent gravel layer at top which in places contains concentration of snails, clams, and ulexite.

sab4 3 Silt, white in lower part, grades to greenish in upper part, thin orange tuff(?) bed overlain by thin nodose 

tufa bed in many areas; 14C date: 27,800±1,200 yr (organic matter), 28,800±400 yr (tufa carbonate).

sab3 1 Sand, locally very fine but generally medium to fine, well to poorly sorted, some deltaic beds, interbedded 

with tan to orange silt, in places has up to 1-m thick interbeds of silt; 14C date: 35,000±1,600 yr (shells).

sab2 2 Silt, greenish, generally massive.

sab1 1 Sand, tan to orange, lag gravel at base, very sharp top contact.

A? 1 Silt, white to tan, very fine.

Total thickness: 29 m (95 ft)

Section H28-f. Composite description of sediments exposed north of State Highway 178, east of “The Y” (HQ131E-14, 17, & 22); 

approximate elevation at top of section: 2,000 ft (610 m). 

Unit or

Subunit

Thickness

(m)

Description

sc3c 3.6 Sand, very coarse, well sorted, pebble lag on surface, light olive gray (5Y6/1) with lighter silt at base, abundant nodose tufa fragments.

sc3b 1.8 Sand, medium to very coarse, some pebbles and clay, beds 1-5 cm thick, calcareous (aragonite, calcite), 

grayish orange (10YR6/4), deltaic bedding dips east.

sc3a 7.0 Silt, sandy near top, calcareous (aragonite, calcite, traces of dolomite), yellowish gray (5Y7-8/1-2), mostly 

massive, some beds 0.3-0.5 m thick, weathers with “popcorn” surface.

sc2 2.2 Sand, medium to coarse, well sorted, 1-m-thick light colored silt layer in middle, moderate yellowish brown 

(10YR5/4), some mollusks.

Appendix 1. Measured Sections 101
102 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Section H28-f. Composite description of sediments exposed north of State Highway 178, east of “The Y” (HQ131E-14, 17, & 22); 

approximate elevation at top of section: 2,000 ft (610 m). —Continued

Unit or

Subunit

Thickness

 (m)

Description

sc1 5.1 Clay separated by thin beds of very fine sand, calcareous (calcite, some aragonite and dolomite), basal 1 m is well 

exposed, beds 3 to 10 mm thick, yellowish gray (5Y7/2), similar to underlying unit except not contorted, small 

patches of nodose tufa at base, upper 4 m weathers with “popcorn” surface, gypsum crystals in top 1 m, oolitic 

sand and fragmentary tufa 1 m up from base.

----------------------------------------------------------unconformity------------------------------------------------------

B 1.8 Silt and clay, calcareous (calcite), contains black organic(?) fragments, light olive gray (5Y6/2), darker on fresh surface, white salt efflorescence on expose surfaces, pronounced bedding 1-10 mm thick, locally contorted, sticky and 

plastic when moist.

AB 0.3+ Boulder gravel, well cemented, alluvial; exposed in floor of wash.

Total 

thickness: 16.8+ m (55+ ft)

Section H30-g,h. Generalized description of sediments exposed in Salt Wells Valley (HQ131-58, 63); approximate elevation at top of 

section: 1,960 ft (595 m).

Unit Thickness

(m)

Description

Tufa

(unit st)

 1.0 Lithoid tufa, massive, 5 cm of pale brown (5YR5/2) nodose tufa on upper surface.

A 2.0 Silt and grayish orange (5YR6/2) tufa fragments, jumbled; basal contact flat and smooth.

 1.0 Silt or fine sand, massive, yellowish gray (5Y8/1), much of

“sand” appears to be composed of indurated clay fragments.

 0.3 Clay-fragment breccia, yellowish gray (5Y8/1), grades into underlying unit.

 3.3+ Silt, light green (10Y6-7/1-2), laminae 1-3 mm thick, 5-10

mm apart; lower 3/4 of section poorly exposed.

Total 

thickness: 7.6+ m (25+ ft)
Section I8-l,m,n. Composite description of sediments exposed near wash on both sides of railroad tracks (S-58-7,9,10 and S-59-7); 

approximate elevation at top of section: 1,660 ft (505 m).

Unit or

Subunit

 Thickness 

 (m)

Description

D 0.03 Gravel, thinly scattered fragments of dark rocks to 3 cm long; matrix is silt of underlying unit.

0.1 Silt, soft, saline efflorescences, moderate brown (5YR4/4).

CD 1.5 Gravel, alluvial, poorly bedded and sorted, pebbles to 6 cm, pale yellowish brown (10YR6/2), weak soil in top 

20 cm, calcareous pods 1 to 2 cm across.

0.2 Sand, many pebbles, massive, color and sorting as above.

sc4 1.0 Clay and silt, calcareous (calcite, aragonite), massive to very faintly bedded, undeformed, grayish yellow green 

(5GY5-7/1-2), plastic when moist.

0.6+ Clay and silt, like above but with contorted bedding.

Total 

thickness: 3.43+ m (11+ ft)

Section I18-a. Section exposed on south side of Poison Canyon Wash; approximate elevation at top of section: 1,700 ft. (520 m). 

Illustrated by figure 22.

Unit or

Subunit

Thickness 

 (m)

Description

CD 4 to 11 Mostly sand and pebble gravel, alluvial, some thin lacustrine-silt layers; alluvial material is tan, poorly sorted, 

local rippled foreset beds, subrounded to subangular fragments of rock, nodose tufa, laminated silt, and 

reworked mollusk shells (14C date: 16,200 + 300 yr); silts are generally massive, but locally well bedded; 

beds dip to 50°; partially developed lag gravel on top surface; unit rests on a deformed and subaerially eroded 

surface of underlying unit.

sc4 1 to 6 Sand and silt, lacustrine; sand is fine to very fine, tan to olive, well bedded to massive, well sorted; some silt 

layers contain much clay, which is massive, light green, calcareous, very plastic when wet, strongly contorted 

as a result of soft-sediment deformation; rests on subaerially eroded surface cut on underlying unit.

sc3 1 to 2 Silt and clay, lacustrine; calcareous, characterized by numerous thin white laminae.

Total 

thickness: about 12 m (39 ft) but variable (see fig. 22)

Appendix 1. Measured Sections 103
104 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Sections I19-p,q,r and I30-a. Composite description of sediments exposed west of railroad, east of Spangler Hills (HQ132E-31); 

approximate elevation at top of section: 1,700 ft (820 m).

Unit or

Subunit

Thickness 

 (m)

Description

sc3 0.5 Silt, white, very prominently laminated.

sc2 0.2 Sand, very coarse, tan, ripple marks.

sc1 0.2 Silt, white, prominently laminated.

BC 0.2 Sand, medium to very fine, tan to gray, well bedded, weakly developed ripple marks.

sb6 0.6 Silt, greenish gray, thinly bedded but not laminated, some snails and clams.

sb5 0.3 Sand, medium to very coarse, tan, some tan-orange zones.

 0.5 Silt to very fine sand, very light greenish gray, weakly laminated in upper half, prominently laminated in 

lower half.

sb4 0.3 Sand, very fine to medium, tan with streaks of orange, well bedded. 

 0.8 Silt, white, prominent laminae.

sb3 0.2 Sand, fine, gray-orange, ripple marks in upper part.

sb2 0.5 Silt and very fine sand, massive, greenish gray; 14C date: 19,150±150 yr (marl).

sb1 0.5 Sand, medium, orange, some ulexite, snails and clams.

 0.3+ Silt, greenish, massive.

Total 

thickness: 5.1+ m (17+ ft)

Section I30-b,c,g. Composite section of sediments exposed east of alluvial fan on east end of Spangler Hills (5-21-89); approximate 

elevation at top of section: 1,720 ft (525 m).

Unit or

Subunit

Thickness 

 (m)

Description

D 0.1-1 Gravel with silt matrix, very angular (fragments possibly fractured by salt wedging) to slightly rounded 

fragments near toe of fan, average 10 cm in size, range from 2 to 30 cm (100 to 200 m east of fan, average 

5 cm in size, range from 2 to 20 cm), fragments are grayish black (N2) to dark brown (5YR3-4/2-4); probably alluvial gravel reworked by near-shore lacustrine processes.

 1-2 Silt and sand, some granules and pebbles, grayish orange (10YR6-7/2-4), massive, saline efflorescence, 

weathers with puffy surface, pods of ulexite 10 to 20 cm below surface found locally (some years); deposited on uneven surface.

CD 1+ Gravel, alluvial, fragments average about 20 cm in length, range from 5 to 30 cm; fragments, which have 

lighter colors than those in unit D, are moderate brown (5YR3-5/4-6); poorly sorted sand matrix is grayish 

orange (10YR7/4), poorly bedded.

sc1 2+ Marl, laminated, on fresh surfaces, 1- to 2-mm-thick laminae are white (N9), intervening thicker layers 

are grayish yellow green (5GY6-7/2) to pale olive (10Y6-7/2).

Total 

thickness: 6+ m (20+ ft)
Section I32-j. Description of sediments exposed near north end of wash that dissects southeast end of The Pinnacles bar (HQ132-10); 

approximate elevation at top of section: 1,740 ft (530 m).

Unit or

Subunit

Thickness 

 (m)

Description

Tufa 0.5 Nodose tufa, dark brown.

BC 0.6 Sand, very coarse, numerous pebbles, grayish tan, cross-bedded, well cemented.

B 1.1 Silt and very fine sand, grayish tan, coarse sand layer in middle, weathers with “puffy” surface.

sa4 0.3 Sand, fine to very coarse, grayish tan, cross-bedded, well cemented lens of lithoid tufa at base.

sa3 0.8 Silt to very fine sand, scattered pebbles, greenish gray, massive, weathers puffy, lithoid tufa lens at base.

sa2 0.3 Coarse sand and pebbles, poorly sorted, subangular fragments, orange, alluvial.

sa1 0.8 Sand, medium to very fine, extensively cross-bedded; pods of lithoid tufa, defluidization structures.

 0.6 Silt and very fine sand, greenish, laminar bedding.

 1.0+ Sand, coarse to very fine, arkosic, lenses of pebble conglomerate, tan-gray, streaks of orange stain, 

numerous defluidization structures.

Total 

thickness: 6.0+ m (20+ ft)

Section I32-r. Composite description of sediments exposed along wash cutting crest of The Pinnacles bar (PTK5023B-16 and -37); 

approximate elevation at top of section: 1,760 ft (535 m); see figure 9.

Unit or

Subunit

 Thickness 

 (m)

Description

Tufa 1.2± Tufa, lithoid and nodose, lenticular; base of tufa 14C-dated: 13,700±350 yr.

sa4 0.5 Gravel, angular to subangular cobbles; forms crest of large lacustrine bar.

sa3 1.0 Pebble to cobble sand and gravel, calcareous, poorly sorted, lacustrine; nearby marl lens, 1 m below top of 

bed, 14C-dated: 21,910±100 yr.

 4.0 Silt, sand, and gravel, interbedded, lacustrine, poorly sorted, massive to well bedded, medium to light 

gray, well indurated, calcareous.

 0.3 Tufa, lithoid type, bedded, medium gray.

sa2 0.5 Gravel, alluvial, poorly sorted, small angular fragments, grayish orange, lenticular, moderate to strong 

calcareous soil developed locally on unit (sediments exposed only in small area on west side of wash; 

horizon expressed as a 30-cm-thick calcareous soil elsewhere in wash).

sa1 0.5 Sand, calcareous, indurated, gray, lacustrine.

 0.5 Silt, calcareous, white; basal contact flat, no channels exposed, lacustrine.

 0.4 Gravel and coarse sand, lacustrine, very calcareous.

Christmas

Canyon

Formation

(ccg)

 1.8+ Gravel, alluvial, very poorly sorted, volcanic-rock cobbles.and boulders to 30 cm long constitute 20-30 

percent of unit, matrix is poorly sorted very coarse sand, strong calcareous soil developed in upper 1.3 

m (upper 0.2 m nearly solid calcareous sand), composed of horizontal and vertical stringers of sandy 

calcite, 2-5 cm across, and a zone rich in pedogenic clay which is yellowish gray (5Y7/2) to light olive 

(5Y5/2) (olive hues, strongest in finest beds, fade out downward).

Total 

thickness: 10.7+ m (35+ ft)

Appendix 1. Measured Sections 105
106 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Section K24-p,q. Composite description of sediments exposed along Teagle Wash (V175-4); approximate elevation at top of section: 

1,960 ft (595 m).

Unit or

Subunit

Thickness 

 (m)

Description

B 0.1 Pebble pavement, composed of older tufa (unit ot) fragments.

AB(?) 0.6 Conglomerate, light gray fragments of older tufa, faint orange stain on top fragments.

sa3 0.3 Tufa, uncommon variety of lithoid type. Sand, tan, well bedded, calcareous, vertical 

defluidization structures. 0.3

sa2 1.8 Gravel, alluvial, greenish to tan, top of soil zone is orange or reddish, vertical columnar 

(desiccation?) structures 0.6 m long.

sa1 1.2 Tufa, lithoid, massive.

Silt, white, very calcareous, massive to well bedded

Sand, very coarse, calcareous, dark tan.

 0.3

 0.3

Christmas

Canyon

Formation

 (ccg)

 3.0+ Gravel, alluvial, arkosic, tan; soil developed on equivalent surface 250 m to west.

Total thickness: 7.3+ m (24+ ft)

Section L8-k. Sediments exposed along southeast sideof Teagle Wash, 2 km southwest of The Pinnacles (PTK5023B-7, 31); approximate 

elevation at top of section: 1,850 ft (565 m); see figure 16. 

Unit or

Subunit

Thickness 

 (m)

Description

sc3 1.2 Silt, greenish, thinly laminated.

sc2 0.3 Sand, tan, very fine to medium, ripple marks.

sc1 0.3 Silt, greenish, thinly laminated, gypsum crystals.

BC 0.4 Pebble gravel, tan to slightly orange, abundant nodose tufa fragments, well rounded.

B 1.0 Silt, some very fine sand, well bedded, not laminated like overlying subunits. 

 0.4 Gravel, pebbles, some cobbles, and well-rounded nodose tufa, intermixed clay and silt; some 

fragments stained orange, 65 percent of cobbles from Spangler Hills, balance from south.

 0.9 Silt, some sand, well bedded not laminated, 14C age in upper part: 16,970±400 yr (marl).

sab7 0.3 Gravel, pebbles and very coarse sand, pebble lag gravel at top contact, cross bedded, stained 

dark orange, some fragments still have vestige of desert varnish; rests with sublacustrine 

unconformity on underlying sediments.

sab6(?) 1.5 Silt and sand, gray, discontinuous lenses of orange to gray pebble gravel or sand, some probably alluvial, some cross-bedded lacustrine layers.

sab5(?) 0.4 Sand, medium to very coarse, grayish orange, cross-bedded, possibly alluvial in part.

sab3(?) 0.3 Sand and silt, silt is laminated, unit lenses out to south.

 0.2 Sand, some pebbles near base, orange, lens of silt at base, lower contact broadly undulating.

 1.2 Gravel, alluvial, a few rock fragments to 20 cm, rounded green-clay fragments (containing 

ostracodes) to 70 cm. Basal contact flat and sharp

Christmas

Caynon

Formation

(ccg)

 1.2+ Gravel, matrix is arkosic, pale red (10R5-6/2-4), rounded pebbles and cobbles composed of 

dacite, andesite, and vesicular basalt.

Total thickness: 9.6+ m (31+ ft)
Section M18-k. Sediments exposed on east side of Randsburg Wash (PTK4-141-4); approximate elevation at top of section: 1,860 ft (565 m).

Unit Thickness 

 (m)

Description

C 1.0 Gravel, fragments well rounded, to 10 cm diameter, lacustrine, possible faint soil at top.

 0.5 Sand, very coarse, some pebbles, probably lacustrine, could be alluvial.

 0.5 Silt, yellowish green, tufa at base.

 1.2 Gravel, sand with streaks of pebbles, alluvial(?), yellowish gray, slightly cross-bedded.

 1.2 Gravel, cobbles and boulders, poorly sorted, faintly bedded, light olive gray, alluvial.

 0.5 Silt, yellow green, nodose tufa at base, 14C age: 12,000±400 yr (tufa).

B 3.8 Gravel, pebbles and cobbles to 15 cm across, well rounded, some layers of lacustrine sand.

 0.3 Silt and sand, greenish.

 0.5 Sand, some pebbles, tan, well bedded.

AB 2.5+ Gravel, cobbles and boulders, mostly angular, poorly sorted sand matrix, tan, moderately indurated, poorly 

exposed.

Total 

thickness: 12.0+ m (39+ ft)

Appendix 1. Measured Sections 107
108 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Appendix 2. Sediment Studies

During the early mapping stages of this project, a study 

of the lacustrine and alluvial sediments exposed in Searles Valley was initiated by Robert J. McLaughlin and the author. Its 

goal was to establish field criteria—objective and numerical if 

possible—for distinguishing lacustrine and alluvial sediments. 

Because silt and marl beds rarely require special criteria to 

eliminate an alluvial origin, our studies concentrated on sand 

and gravel units. Most of the criteria that we developed are 

summarized in table 1; additional criteria were those summarized by Clifton (1973), who also conferred with us in the field.

Field criteria involving visual estimates of grain-size 

distributions have to be verified by laboratory measurements. 

For our study, we concentrated on the sediments exposed at 27 

sites in Searles Valley. The field observations, measurements, 

and sampling were carried out by McLaughlin and the author, 

and all of the laboratory analyses and the ensuing plotting of 

data and statistical calculations were by McLaughlin. A selection representing about half of the clastic-size data that we 

collected are presented in tabular form in table 12.

Field measurements at each site were made as follows: 

We (1) selected an exposure that included a well-exposed bed 

or series of beds, (2) measured, marked, and photographed the 

most suitable 5-m-wide study area, (3) visually identified and 

separated one or more beds for detailed study, (4) where possible, outlined two or more rectangular clast-count zones that contained 100 or more clasts greater than 10 mm in length, and (5) 

designated two or more vertical zones along which we would 

make visual grain-size estimates and take channel samples for 

laboratory grain-size analysis at a later time. Several beds were 

sampled at many sites, but the clast-count (“field measurements”) and channel-sample (“laboratory measurements”) data 

listed for each site in table 12 represent the same beds.

Lacustrine deposits were classified as representative of one 

of three depositional environments commonly represented by 

coarse clastic deposits in Searles Valley, namely beach, deltaic, 

and bar. These classifications were based largely on bed morphology, inferred wave-energy requirements, bedding character, 

vertical position in the stratigraphic sequence, and horizontal 

position in the basin. Alluvial deposits were not subdivided.

Within the clast-count zones, clasts greater than 10 mm 

long in the longest exposed dimension were measured with a 

millimeter scale. Measurements continued until the lengths 

of about 100 clasts had been recorded. These data were then 

sorted to permit calculation of the percentage of clasts whose 

exposed sizes fall between each integer in the phi scale (ø), 

giving a measure of the distribution of clast populations. In the 

phi scale, ø = -log x (grain diameter), where the log is to base 

2 and the grain diameter is in millimeters (Krumbein, 1934). 

Records were kept of the largest clast in the sampled bed and 

the largest one in the 5-m-wide outcrop of the same unit or 

subunit (“Maximum clast sizes” in table 12). Visual estimates 

were also made of the volume percentage of clasts larger than 

10 mm in the bed being sampled; these estimates were made 

independently by two or more people, when possible, and 

averaged (“Clast % in bed” in table 12).

The channel-sample material was brought to the laboratory, treated with HCl to disaggregate the fragments (Searles 

Valley does not have large areas that contribute limestone or 

dolomite clasts), and sieved using a stack of 8-inch sedimentsizing screens graduated in intervals of 1 ø unit. After mechanical shaking of each sample for about 10 minutes, the fraction 

retained by each screen was weighed to the nearest 0.01 gram. 

The results of these analyses, in weight percent, are also listed 

in table 12.

Results of the laboratory-determined size analyses were 

then plotted against the ø scale on logarithmic probability 

graph paper (if sediment grains have a perfectly log-normal 

distribution, they plot as a straight line on this type of graph 

paper). This enables one to estimate the value of ø for any 

percentile of the sample. To determine the desired statistical 

parameters, the ø values for 1, 5, 16, 50, 84, and 95 percentiles 

were determined from the plots (table 13, left columns). From 

these values, the mean size, standard deviation, skewness, and 

kurtosis represented by each sample were calculated (table 13, 

right columns). Average values for each of the four sediment 

categories give some measure of the processes active during 

deposition in each environment.

In table 12, the coarse-clast and fine-clast statistical data 

each separately add to 100 percent. Plotting the coarse-clast 

data on the logarithmic probability graph paper generally 

showed a curve similar to that from the fine-clast data, but 

offset. Attempts to extend the laboratory-determined size-distribution curve into the coarse-clast section by combining the 

clast-count data and the clast-percentage estimate did not work 

well. Although the field estimates may contain substantial 

errors, most of the difficulty is attributed to the difference in 

the nature of the data from the field and laboratory measurements. Sieve measurements sort on the basis of the intermediate dimension of each fragment, and directly measure the 

weight and weight-percent of the entire population of those 

fragments. In contrast, our field measurements determined 

the longest exposed dimension of fragments, but we found no 

satisfactory way to estimate the probable relation between that 

dimension and those fragments’ intermediate dimension, or to 
estimate the relative weight percentage of those large, usually 

irregularly shaped fragments.

These data (tables 12 and 13) also show how statistical 

measures based on size-distribution studies of sediments can 

be misleading when the sediment contains clasts too large to 

include in the laboratory sample. For example, the averaged 

values for the mean size and standard deviation of alluvial-fan 

environments (table 13) suggest that such deposits contain 

smaller and better sorted materials than the lacustrine-bar 

gravel deposits, but the pebble counts and large/largest clast 

data show that most alluvial materials have a notably wider 

total range in fragment size and are clearly less well sorted 

than the bar gravel deposits. Similarly, the skewness values, in 

which positive values indicate a predominance of fine material and negative values indicate the opposite, suggest that the 

bar gravels contain a higher percentage of fine material than 

the fan materials, whereas inclusion of the coarsest alluvial 

fragments in the statistical calculations would almost certainly 

reverse this relation. The kurtosis, which indicates the peakedness or flatness of size-distribution curves, suggests that the 

beach and deltaic environments produce near-normal distributions, whereas the alluvial gravels—without the very large 

clasts included—appear to have a better-than-normal sorting 

and the bar gravels a much poorer-than-normal sorting.

Appendix 2. Sediment Studies 109
110 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Table 12. Distribution of clast sizes in sediments from Searles Valley.

1

 Follows usage of Wentworth (1922).

2

 Clasts greater than 10 mm long; 100 or more fragments in most counts.

3

 Maximum dimension of pebbles greater than 10 mm in count area/maximum in exposed bed; in millimeters.

4

 Clasts greater than 10 mm in size; average of two- or three-person estimate.

5

 “Pebbles” and “cobbles” are carbonate-rimmed mud balls.

6

 Determined by comparing sample weight before and after treatment with cold, dilute HCL.

7

 Map unit or subunit label used on plate specified.

8

 See text and plate 1 for explanation of location system.

9

 Lacustrine layer interbedded in older gravel unit.

Size terms1

 and 

dimensions (mm) 

of fragments and 

screen openings; 

other data

 Phi

 Scale 

Lacustrine “beach” 

environments 

 Site Number

Lacustrine “deltaic” environments

1 2 3 4 5 6 7 8 9 10

I. Field measurements (population-percent of clasts in successive phi-scale categories2

)

Maximum clast sizes3 29/35 -/- -/- -/12 40/185 -/- -/12

Boulders 0 0 0 0 -- 0 0 0 0 0

— 256 — -8

0 0 0 0 -- 0 0 0 0 0

128 -7

0 0 0 0 -- 0 0 0 0 0

— 64 — -6

0.9 0 0 0 -- 0 0 0 0 0

32 -5

22.2 0 0 0 -- 0 0 0 0 0

16 -4

76.9 0 0 0 -- 0 0 0 0 0

8 -3

Clast % in bed (est.)4 10 0 0 0 35 0 0 0 0 0

II. Laboratory measurements (weight-percent of sediments caught between screens of indicated sizes)

— 64 — -6

0 0 0 0 0 0 0 0 0 0

32 -5

0 0 0 0 0 0 0 0 0 0

16 -4

0 0.2 0 0 0 0.2 0 0 0 0

8 -3

0.8 1.4 0.4 0.7 0.1 0.1 2.1 1.2 0 1.7

— 4 — -2

Granules 1.8 17.9 6.2 3.4 0.8 2.6 2.8 2.2 0.7 9.9

— 2 — -1

Very coarse sand 7.4 41.4 37.2 7.5 4.1 4.2 5.7 5.2 1.1 19.4

— 1 — 0

Coarse sand 57.7 36.4 53.0 14.1 9.1 8.5 15.0 13.5 5.5 21.1

— 0.5 — 1

Medium sand 24.9 1.3 1.9 26.6 33.1 31.4 30.4 36.1 56.9 32.0

— 0.25 — 2

Fine sand 2.2 0.5 0.6 31.2 40.7 42.5 38.2 36.7 32.2 12.5

— 0.125 — 3

Very fine sand 0.8 0.2 0.2 10.9 7.1 6.8 4.4 3.1 1.8 1.2

— 0.0625 — 4

Silt and clay 4.4 0.7 0.5 5.6 5.1 3.7 1.4 2.0 1.8 2.2

III. Other data

Percent CaCO3(

6

) 4.4 21.6 23.3 22.3 13.2 3.8 17.8 15.3 8.6 9.7

Map unit or Subunit7 Ts sab6 sab6 sa sab5 sb sbc sbc sbc sbc

Plate no. 2B 2A 2A 3A 3A 3A 3A 3A 3A 3A

Location8 M19-1 C3-r C3-r H13-c H24-f I7-g I19-f I19-f I17-m I17-m Cobbles Pebbles Pebbles
Table 12. Distribution of clast sizes in sediments from Searles Valley. —Continued

Appendix 2. Sediment Studies 111

Size terms1

 and 

dimensions (mm) 

of fragments and 

screen openings; 

other data

 Phi

 Scale

Lacustrine “bar” gravel environments

 

 Site Number 

11 12 13 14 15 16 17 18

I. Field measurements (population-percent of clasts in successive phi-scale categories2

)

Maximum clast sizes3 81/152 53/60 100/190 50/125 100/100 95/200 70/150 35/80

Boulders 0 0 0 0 0 0 0 0

— 256 — -8

0 0 0 0 0 0 0 0

128 -7

2.0 0 1.0 0 4.6 5.0 0.7 0

— 64 — -6

15.0 4.0 16.0 6.4 5.4 19.0 14.5 1.0

32 -5

24.0 34.0 46.0 41.6 44.5 37.0 35.5 27.6

16 -4

59.0 62.0 37.0 52.0 45.5 39.0 43.9 71.4

8 -3

Clast % in bed (est.)4 50 14 35 58 62 40 75 4

II. Laboratory measurements (weight-percent of sediments caught between screens of indicated sizes)

— 64 — -6

0 0 16.1 0 17.3 51.4 22.8 0

32 -5

0 0 27.5 26.6 28.8 18.4 19.3 0

16 -4

3.0 8.8 19.5 31.1 21.8 10.4 24.7 0.7

8 -3

12.8 9.5 7.0 15.5 10.8 2.9 16.2 20.6

— 4 — -2

Granules 50.3 19.9 4.4 5.0 2.6 1.2 5.3 45.8

— 2 — -1

Very coarse sand 16.6 25.7 5.5 3.5 0.9 1.1 2.0 21.4

— 1 — 0

Coarse sand 2.2 21.3 3.8 1.4 1.8 1.3 1.2 4.6

— 0.5 — 1

Medium sand 1.2 5.0 1.7 0.8 9.3 2.3 2.3 1.1

0.25 2

 Fine sand 3.6 1.4 0.7 2.4 6.0 3.1 4.4 3.6

— 0.125 — 3

Very fine sand 3.8 1.0 0.6 3.4 0.5 1.5 1.3 1.5

— 0.0625 — 4

Silt and clay 6.5 7.4 13.2 10.3 0.2 6.4 0.5 0.7

III. Other data

Percent CaCO3(6

) 17.9 7.3 1.4 4.2 1.8 n.d. 5.2 n.d.

Map unit or Subunit7 og9 sal sal sal sab6 sb sc sclc

Plate no. 1 3A 4 4 2A 1 1 2A

Location8 G15-m I23-r I32-r I32-m C15-k I7-a C14-1 C34-a Cobbles Pebbles Pebbles
112 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Table 12. Distribution of clast sizes in sediments from Searles Valley.—Continued 

Size terms1

 and 

dimensions (mm) of 

fragments and screen 

openings; other data

Phi

Scale

Alluvial “fan” environments

 Site Number

19 20 21 22 23 24 25 26 27

I. Field measurements (population-percent of clasts in successive phi-scale categories2

)

Maximum clast sizes3 370/455 50/50 80/410 165/165 90/190 52/400 60/400 50/130 115/265

Boulders 1.0 0 0 0 0 0 0 0 0

— 256 — -8

4.1 0 0 0 0 0 0 0 0

128 -7

15.3 0 1.4 1.1 3.3 0 0 0 1.8

— 64 — -6

24.5 1.2 18.2 3.4 14.0 4.0 17.0 2.0 7.3

32 -5

46.9 23.4 41.9 26.1 34.7 3.0 47.0 26.0 22.9

16 -4

8.2 75.4 38.5 69.4 48.0 65.0 36.0 72.0 68.0

8 -3

Clast % in bed (est.)4 70 29 60 6 32 58 62 8 25

II. Laboratory measurements (weight-percent of sediments caught between screens of indicated sizes)

— 64 — -6

7.4 0 6.5 0 0 0 0 0 0

32 -5

29.6 0 19.8 0 0 1.3 0 1.1 0

16 -4

15.4 6.2 17.9 3.9 8.9 6.9 3.7 2.2 3.6

8 -3

15.2 11.4 12.9 19.2 8.5 7.0 7.3 3.1 9.5

— 4 — -2

Granules 10.4 21.4 11.6 19.9 14.5 11.9 17.5 9.3 23.2

— 2 — -1

Very coarse sand 7.7 22.7 13.0 14.1 20.1 17.9 22.7 24.2 23.3

— 1 — 0

Coarse sand 5.3 15.3 8.7 10.5 20.1 16.8 20.0 27.2 17.0

— 0.5 — 1

Medium sand 3.5 9.2 3.8 8.7 14.9 18.3 12.7 18.1 10.4

— 0.25 — 2

 Fine sand 3.0 5.9 2.0 8.6 8.8 13.4 9.2 7.7 6.2

— 0.125 — 3

Very fine sand 1.9 2.5 1.1 5.9 2.6 5.8 3.6 1.6 2.5

— 0.0625 — 4

Silt and clay 0.6 5.4 2.7 9.2 1.6 0.7 3.1 5.5 4.3

III. Other data

Percent CaCO3(

6

) n.d. n.d. n.d. n.d. n.d. 4.3 4.3 5.2 n.d.

Map unit or subunit7 og ccg saa sab sab5 sab5 sab5 scd5 al

Plate no. 1 4 1 1 2A 2A 2A 3A 1

Location8 G15-m L8-k B25-h C8-m C3-h C15-k C15-k I8-f F31-m Cobbles Pebbles Pebbles

l, 

 

es 

d 
Formulas and sources for parameters:

Mean size = (phi 16) (phi 50) (phi 84) (Folk and Ward, 1957)

Standard deviation = (phi 84)- (phi 16) (phi 95)+ (phi 5) (Folk and Ward, 1957)

Skewness = (phi 84)+ (phi 16) - 2 (phi 50) + (phi 95) + (phi 5) - 2 (phi 50)

Kurtosis = [(phi 95)- (phi 5)] - [(phi 84)- (phi 16)]

3

4 6.6

2 [(phi 84) - (phi 16)] 2[(phi 95) - (phi 5)]

[(phi 84) - (phi 16)] (Inman, 1952)

 (Mason and Folk, 1958)

+

+ + 

Table 13. Statistical parameters for 27 sediment samples, based on sieve analyses listed in table 12.

[Values in phi units; formulas and references below. x ̄ = mean of values for given group of sites. For locations of sample sites, see table 12.]

Appendix 2. Sediment Studies 113

Sample 

site

Phi values at successive percentiles Mean

size 

(phi)

Standard

deviation

(phi)

Skewness Kurtosis

Phi 1 Phi 5 Phi 16 Phi 50 Phi 84 Phi 95

Lacustrine “beach” environments

 1 -1.8 -0.5 +0.2 +0.8 +1.6 +3.0 +0.87 0.88 +0.200 1.50

 2 -2.3 -1.6 -1.1 -0.2 +0.4 +0.8 -0.30 0.74 -0.185 0.60

 3 -1.7 -1.1 -0.6 -0.1 +0.6 +0.9 +0.03 0.60 -0.283 0.66

x ̄ (1-3) -1.9 -1.1 -0.5 +0.2 +0.9 +1.6 -0.20 0.74 -0.089 0.92

Lacustrine “deltaic” environments

 4 -1.8 -0.8 +0.4 +1.9 +3.1 +4.1 +1.80 1.42 -0.107 0.81

 5 -1.0 0.0 +1.1 +2.1 +2.9 +4.0 +2.03 1.06 -0.081 1.22

 6 -1.5 -0.4 +1.0 +2.1 +2.8 +3.8 +1.97 1.09 -0.206 1.33

 7 -2.7 -1.0 +0.4 +1.8 +2.7 +3.3 +1.63 1.23 -0.260 0.87

 8 -2.0 -0.6 +0.6 +1.8 +2.6 +3.1 +1.67 1.06 -0.249 0.85

 9 -0.7 +0.7 +1.3 +1.8 +2.4 +2.9 +1.88 0.61 +0.045 1.00

10 -2.2 -1.5 -0.7 +1.0 +2.0 +2.7 +0.77 1.32 -0.225 0.55

x ̄ (4-10) -1.7 -0.5 +0.6 +1.8 +2.6 +3.4 +1.67 1.11 -0.155 0.95

Lacustrine “bar” gravel environments

11 -6.6 -2.7 -2.0 -1.3 +0.6 +4.5 -0.90 1.74 +0.537 1.77

12 -3.9 -3.6 -2.2 -0.5 +0.9 +6.5 -0.60 2.31 +0.144 2.26

13 -5.5 -5.8 -5.0 -3.7 +1.0 +10.0 -2.57 2.14 +1.567 1.63

14 -5.7 -5.2 -4.3 -3.3 +2.0 +6.2 -1.87 3.31 +0.674 0.81

15 -4.4 -5.2 -4.7 -3.8 +1.0 +2.2 -2.50 2.55 +0.653 0.30

16 -6.3 -6.7 -5.9 -4.6 -1.0 +4.5 -3.83 2.99 +0.554 1.37

17 -2.9 -5.5 - 4.9 -3.7 -1.9 +2.2 -3.50 1.92 +0.366 1.57

18 -3.5 -2.5 -2.1 -1.4 -0.3 +2.2 -1.27 1.16 +0.377 1.61

x ̄ (11-18) -4.8 -4.6 -3.9 -2.8 +0.3 +4.8 -2.13 2.26 +0.609 1.42

Alluvial “fan” environments

19 -5.8 -5.2 -4.6 -3.2 -0.3 +2.1 -2.70 2.19 +0.400 0.70

20 -4.3 -3.2 -2.1 -0.5 +1.7 +4.1 -0.30 2.06 +0.209 0.92

21 -5.1 -4.7 -4.2 -2.5 +0.3 +2.4 -2.13 2.20 +0.312 0.58

22 -3.6 -2.9 -2.2 -0.5 +2.9 +5.0 -0.07 2.48 +0.363 0.54

23 -5.0 -3.5 -2.1 -0.1 +1.8 +2.9 -0.13 1.95 -0.044 0.64

24 -4.2 -3.3 -1.9 +0.3 +2.2 +3.2 +0.20 1.01 -0.017 0.58

25 -3.9 -2.7 -1.6 -0.1 +2.0 +3.3 +0.10 1.81 +0.150 0.67

26 -4.1 -2.4 -1.0 +0.4 +2.0 +4.2 +0.47 1.75 +0.109 1.20

27 -3.8 -2.8 -1.8 -0.7 +1.7 +3.8 -0.27 1.88 +0.368 0.89

x ̄ (19-27) -4.4 -3.4 -2.4 -0.8 +1.6 +3.4 -0.54 1.93 +0.206 0.75
114 Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California

Appendix 3. Evidence and Reasons Used for Determining Slopes, Elevation 

Ranges, and Ages of Segments of Lake-History Diagrams (Figures 39C and 40C)

[Unless otherwise noted, required data are plotted in figures 39A, 39B, 40A, and 40B. “Section” refers to 

measured sections in appendix 1.]

Age ranges of 

segments (ka) Evidence and rationale

170–150 Mud layers interbedded with thin monomineralic saline layers characterize upper part of Mixed Layer (Smith 

and others, 1983, p. 12-13, fig. 5., pl. 1); plotted lake fluctuations are diagrammatic; depths near 110 ft. (34 m) 

deposited saline layers, depths near 170 ft. (52 m) deposited mud.

150–149 Lack of subunit sa1 exposures below 1,720 ft suggests rapid rise of lake.

149–145 Deposition of lithoid tufa, as both tabular and pinnacle-shaped masses, present at base of subunit sa1 between 1,720 

and 1,960 ft near and southwest of The Pinnacles (section I32-r); process required shallow water and significant time.

145–140 Overflow into Panamint Valley had to start early enough for Panamint Lake to fill well before Searles Lake began 

to recede at 120 ka; insoluble components show most rapid decrease during early part of this interval.

140–118 Overflow period; end of overflow based on compilation by Jannik (1989) of chloride budget and periods of its loss 

caused by overflow from Searles Lake.

118–117 Diagenetic mineral zone, commencing at about 117 ka, indicates increasing salinity of lake water caused by 

shrinking lake.

117–111 Deposition of lithoid tufa on top of subunit sa1, at and below 1,960 ft (sections H30-g and K24-p), required shallow water near this level for an appreciable time.

111–102 Presence of monomineralic salt beds, increasing percentages of acid-insoluble minerals, diagenetic minerals abundant; 

considered equivalent to subunit sa2.

102–86 Deposition of tabular (and pinnacle-shaped ?) lithoid tufa masses at base of subunit sa3, between 1,740 and 1,960 

ft (section I32-j), near and southwest of The Pinnacles, required significant interval; diagenetic analcime deposition ended at 91 ka; increased CaO content of core KM-3 centered at 86 ka, inferred to be correlative with highest level of this lake rise, which is plotted approximately proportional to CaO content.

86–81 Increase in acid-insoluble percentage, period precedes salt deposition.

81–77 Monomineralic salt beds present in subsurface deposits.

77–71 Perennial lake beds found in cores; moderate decrease in acid-insoluble content implies lake expansion; overlying 

salt layers require this expansion to be followed by contraction.

71–69 Monomineralic salt bed present in subsurface deposits.

69–58 Increasing(?) CaO content, little change in acid-insoluble content, authigenic mineral zone ends at 58 ka.

58–50 CaO content increases to highest level in core at 50 ka, rapid decrease in acid-soluble content; age of maximum 

lake-level elevation based on position of highest CaO value; possible overflow into Panamint Valley.

50–46 Overlying monomineralic salt bed requires shrinking of lake.

46–45 Presence of monomineralic salt bed, very low CaO content.

45–41 Return to high levels of CaO and continued intermediate-level acid-insoluble content.

41–39 Decrease in lake level required to allow deposition of bar gravels of subunit sa4 near The Pinnacles (section I32-r).

39–36 Deposition of subunit sa4.

36–35 Thin salt bed found in about a quarter of the GS-series of cores about 3 ft below top of Bottom Mud (Haines, 1959; 

Smith, 1979, p. 16).

35–32 Perennial-lake deposits constitute upper 3 ft of Bottom Mud.
32–24 High stands based on table 9, low stands based on mineralogy of salt beds in Lower Salt (Smith, 1979, p. 88-89); 

stillstand prior to 24 ka reflects time needed to develop desert varnish and AB soil now found on subunit sab7

and alluvial deposits of this unit (see text).

24–22.5 Perennial-lake deposits, unlaminated and coarsely laminated, separate salt bed in Parting Mud (fig. 36) from 

Lower Salt.

22.5–15.5 High stands proportional to CaO content of GS-16 core, lowstands from table 9; high stands plotted as still-stands 

at estimated level because marl layers are thicker than sand layers in subunits sb1 to sb6 in area east of Spangler 

Hills (pls. 3A, 4).

15.5–15.0 Lake-level decrease required prior to following lowstand.

15.0–13.5 Lowstand elevation from table 9, duration of lowstand from CaO and acid-insoluble data and from distribution of 

coarsely laminated bedding in core GS-16 (fig. 36); substantial duration of lowstand also indicated by soil developed on surface of unit BC alluvial beds.

13.5–12.5 Lake rise and stillstand based on prominent bars deposited at base of unit C, north and south ends of basin, 1,900 to 

1,940 ft elevation.

12.5–10.5 Highstands and lowstands from table 9.

10.5–9.5 Estimated duration of Upper Salt deposition, which appears to have been uninterrupted (Smith, 1979, p. 112).

9.5–6.0 Period of minimal deposition on exposed surface of Upper Salt.

6.0–2.0 General age control based on one 14C age (3.5 ka) from wood in Overburden Mud (Stuiver and Smith, 1979, p. 73); 

lake level from table 9; duration of lake stand is only an estimate (see text).

2.0–0 Lack of evidence of younger lakes suggests period of minimal deposition on surface of Overburden Mud.

Appendix 3. Evidence and Reasons Used for Determining Slopes, Elevation Ranges, and Ages 115
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Introduction 117

Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, June 22, 2006

Text edited by Peter Stauffer and Julia Thomas

Plates edited by Jan Zigler and Carolyn Donlin 

Layout and design by Judy Weathers
Smith—Late Cenozoic Geology and Lacustrine History of Searles Valley, Inyo and San Bernardino Counties, California—Professional Paper 1727