Analyses,

f~+ \ ' * "t A

 f\ft*fx I *a ri/~\tn c oi^iri A nrrf^c V>UI * Cld-LlUIl^j d-llU. /\Ht;l3

r Pliocene and 

Ash Layers 

of

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1293

Chemical Analyses, 

Correlations, and Ages 

of Upper Pliocene and 

Pleistocene Ash Layers 

of East-Central and 

Southern California

By A. M. SARNA-WOJCICKI, H. R. BOWMAN, C. E. MEYER,

P. C. RUSSELL, M. J. WOODWARD, GAIL McCov, J. J. ROWE, JR.,

P. A. BAEDECKER, FRANK ASARO, and HELEN MICHAEL

GEOLOGICAL SURVEY P R O F E S S I O N A L P A P E R 1293

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1984
UNITED STATES DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary

GEOLOGICAL SURVEY

Dallas L. Peck, Director

Chemical analysis, correlations, and ages of upper Pliocene and Pleistocene ash 

layers of east-central and southern California.

(Geological Survey Professional Paper 1293)

Bibliography

1. Volcanic ash,tuff, etc. California. 2. Geology, Stratigraphic Pliocene. 3.

Geology, Stratigraphic Pleistocene. I. Sarna-Wojcicki, Andrei M. II.

Series. 

QE461.C4231983 552'.23'09794 83-600304

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

Washington, D.C. 20402
CONTENTS

Page

1

1

3

3

6

6

7

9

12

12

Bishop ash-bed group 19 

Friant Pumice Member (of the Turlock Lake FormaIntroduction 

Acknowledgments 

Criteria for correlation of tephra 

Methods 

Selection of elements for correlation 

Methods of evaluating chemical data for correlation 

Correlation of tephra units 

Discussion of specific correlations 

Lava Creek B ash bed (formerly the Pearlette type 0 ash

tion) 22

Bishop ash at the Insulating Aggregates quarry (Bishop 

ash, IAQ type) 22

Bishop ash at Owens River Gorge and at Red's Meadow 

(Bishop ash, ORG type) -- 23

Age and stratigraphic relations of the Bishop ash bed and the

Friant Pumice Member (of the Turlock Lake Formation) - 23 

Glass Mountain-D ash bed 26 

Glass Mountain-G ash bed 27 

Bailey ash 28

Thin white ash below the Bailey ash 30 

Lowermost gray ash, South Mountain area (Huckleberry 

Ridge? ash bed) 31

Age and stratigraphic relations of the Bishop ash bed and the 

Friant Pumice Member Continued

Ashes of the Manix basin, Mojave Desert 

Upper white ash 

Middle white ash 

Huckleberry Ridge ash bed (lowermost gray ash) 

Other tephra units of limited areal extent or recognition -

Ash in late Cenozoic lake beds of Searles Valley 

Tuffs of the Coso area 

Pumice overlying the Cahuilla beds, Salton trough 

Provincial relations of tephra of the Long Valley-Glass Mountain

Recognition of provincial characteristics of tephra

Appendix

Sampling methods 

Sample preparation 

Analytical methods

Neutron-activation analysis

Electron microprobe analysis

Energy-dispersive X-ray fluorescence analysis

Petrographic analysis

ILLUSTRATIONS

Page

31

32

32

32

33

33

33

Q/i ^q

34

OA O4

35

39

39

39

39

39

40

40

40

Page

FIGURE 1. Map showing generalized sample locations of tephra layers 2

2. Correlation chart of upper Pliocene and Pleistocene tephra layers 4

3. Chemical compositions of selected glass samples of tephra and differences between histogram pairs 8

4. Similarity coefficient matrix for glass samples based on neutron-activation analysis 10

5. Dendrogram showing relations between individual samples and sample groups based on neutron-activation analysis 12

6. Similarity coefficient matrix for glass samples, based on energy-dispersive X-ray fluorescence analysis 18

7. Generalized stratigraphic section of composite ash bed in the Borrego Formation of Tarbet and Holman (1944) east of the Salton

Qpo »wJC * _____________ - --- ______ ___ _________ _. ______________________________ _ _ _____ _______ ______________________ __ ^J£ 9A

8. Generalized stratigraphic section of the Bailey ash layer, Ventura area 29

9. Isotopic ages of the Bailey ash plotted against publication dates of analyses 30

10. Systematic depletion trends versus time in ash layers of the Long Valley-Glass Mountain tephra family 33

in
IV CONTENTS

TABLES

Page

TABLE 1. Neutron-activation analysis of volcanic glass from late Cenozoic tephra 13

2. Electron microprobe analysis of volcanic glass 16

3. Energy-dispersive X-ray fluorescence analysis of volcanic glass of selected ash layers 18 

4 Specific sflJifiDlc locjilitv infownsition ____ - __ -_ .__......__......__.....___......._........._«_«._....._........_. 20

5. Mineral abundances in tephra samples 27

6. Two-sample t-test testing the hypothesis that means of concentrations of selected elements in the glass of the Bishop ash bed

and the Glass Mountain-D ash bed are the same 28

7. Comparison of average compositions of seven samples of the Bailey ash bed from the South Mountain-Balcom Canyon area with

seven samples from the Ventura area 30

8. Analytical data on fission-track ages from an ash-flow tuff in the Coso area 34

9. Equations derived from linear regression analysis of split samples analyzed by two laboratories 39
CHEMICAL ANALYSES, CORRELATIONS, AND AGES OF UPPER 

PLIOCENE AND PLEISTOCENE ASH LAYERS OF 

EAST-CENTRAL AND SOUTHERN CALIFORNIA

By A. M. SARNA-WOJCICKI, H. R. BOWMAN, C. E. MEYER, P. C. RUSSELL,

M. J. WOODWARD, GAIL McCov, J. J. ROWE, JR., P. A. BAEDECKER,

FRANK AsARo 1 , AND HELEN MICHAEL l

ABSTRACT

Eight widespread Pleistocene ash layers of east-central and 

southern California are characterized and correlated on the basis of 

chemical composition of volcanic glass (determined by neutron activation, electron probe, and energy-dispersive X-ray fluorescence analysis), stratigraphic criteria, and petrographic characteristics. Irt order 

of increasing age, these are the Lava Creek B ash bed (formerly referred to as the Pearlette type 0 ash bed; about 0.6 m.y.), the Bishop ash 

bed (0.73 m.y.), the Glass Mountain-D ash bed (estimated to be about 

0.8-0.9 m.y.), the Glass Mountain-G ash bed (estimated to be about 

1.0-1.1 m.y.), the Bailey ash (1.2 m.y.), the middle white ash of the 

Manix basin (estimated to be about 1.9 m.y.), the Huckleberry Ridge 

ash bed (formerly referred to as the Pearlette type B ash bed; about 

1.9 m.y.), and the lowermost gray ash of the South Mountain area 

(Huckleberry Ridge? ash bed; estimated to be about 1.9 m.y.).

Three chemical types of the Bishop ash are recognized and assigned to an informal Bishop ash-bed group. The Friant Pumice Member (of the Turlock Lake Formation) of east-central San Joaquin Valley is one of the members of this group. The apparent 0.1-m.y. difference in K-Ar ages of the Friant Pumice Member (0.6 m.y.) and the 

Bishop Tuff (about 0.7 m.y.) may be due to factors other than differences in the true ages of these tephra units; alternatively, there may 

be two ash layers that have very similar glass chemistry and are here 

recognized as belonging to the Friant Pumice Member, but differ in 

age by as much as 0.1 m.y. The Huckleberry Ridge ash in the Manix 

basin is correlated with the same ash in Meade County, Kansas, over 

a distance of about 1,500 km.

Results of chemical analyses permit correlation of sedimentary 

strata deposited in diverse environments: marine, fluvial, and lacustrine. Chemical characteristics of ash layers also permit identification 

of source areas from which tephra was erupted; the main eruptive centers were the Long Valley-Glass Mountain area of east-central California, the Coso volcanic field of southeastern California, and the Yellowstone area of northwestern Wyoming and eastern Idaho. Systematic chemical depletion trends with time provide a possible independent 

method of estimating ages of ash layers of the Long Valley-Glass 

Mountain family.

INTRODUCTION

The Quaternary tephrochronology of east-central 

and southern California is summarized in this report. 

The purpose of the study is to help provide stratigraphic 

control for both site-specific and regional geologic

1Lawrence Berkeley Laboratory, University of California, Berkeley, Calif.

studies, such as regional tectonic syntheses, determinations of ages, rates, and directions of crustal movements, calibration and evaluation of provincial and regional faunal, paleomagnetic, isotopic, and chemical age 

dating methods, and correlation of continental and 

marine faunal and isotopic stages.

Tephra layers (volcanic ashes and tuffs) are very 

useful in correlation of stratified sediments and rocks. 

Tephra produced by an explosive eruption can be spread 

over a large area within a matter of days or even hours 

(Sarna-Wojcicki and others, 1981b). Thus, tephra layers 

from past eruptions represent virtually instantaneous 

time horizons that can be used for correlating sedimentary and volcanic deposits. Tephra layers that have been 

carefully dated by isotopic or other methods at specific 

sites can be correlated with new exposures of tephra 

layers, allowing absolute as well as relative age correlations among separate basins of deposition.

An important application of tephrochronology is 

evaluation of existing radiometric and other types of age 

determinations. Radiocarbon, potassium-argon, and fission-track age determinations are subject to analytical 

and contamination errors that may be large for a wide 

range of Quaternary deposits; tephrochronologic correlations make it possible to cross-check age determinations from different localities of the same tephra unit 

and identify those ages that are determined on the best 

available materials, have the least possibility of contamination, have the lowest analytical error, or are in best 

agreement with other available stratigraphic or 

geochronologic data.

On the basis of chemical, petrographic, and isotopicage analyses, we propose a number of new correlations 

and confirm or reject several previously suggested by 

others. The correlations presented here make it possible 

to assign relative and absolute ages to Quaternary deposits at a number of locations in the study area (fig. 1) 

and correlate deposits of diverse depositional environments fluvial, glacio-fluvial, lacustrine, and marine 

(fig. 2). Owing to the ongoing nature of our work, some
CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Samples from other states:

16 Grand County, Utah

39 Grand County, Utah

40 Marian County, Nebraska

42 Mead County, Kansas

17,19 .34

 2

 53

46,47

37,38^

51

 35 

/49

44,45

 28-33,41

50 100 150 200 KILOMETERS

i i___I i

\ 

50 100 MILES

20,21,24

11 6,7,12, 

 15,50

FIGURE 1. Map showing generalized locations of tephra layers sampled for analysis. For more detailed information on location, see table 4.
CRITERIA FOR CORRELATION OF TEPHRA

correlations proposed here are made on the basis of preliminary analyses, and subsequent work may require revision of our conclusions.

ACKNOWLEDGMENTS

Many workers have contributed tephra samples or 

information, advice, or constructive suggestions to this 

study. Among these are C. R. Bacon, R. A. Bailey, P. 

C. Bateman, J. L. Bischoff, R. L. Christiansen, G. B. 

Dalrymple, W. A. Duffield, A. J. Gude, 3d, E. W. Hildreth, N. K. Huber, R. J. Janda, D. E. Marchand, R. 

V. Sharp, R. A. Sheppard, G. I. Smith, and R. E. Wilcox of the U.S. Geological Survey; G. A. Borchardt and 

M. P. Kennedy of the California Division of Mines and 

Geology; Robert Drake and R. L. Hay of the University 

of California, Berkeley; Richard Merriam of the University of Southern California; M. 0. Woodburne of the 

University of California, Riverside; George Jefferson of 

the Los Angeles County Museum of Natural History; 

and R. S. Yeats of Oregon State University. Special 

thanks are given to G. A. Izett, C. W. Naeser, and R. 

E. Wilcox of the U.S. Geological Survey for providing 

samples and information on several key ash localities in 

the central region of the United States.

K. R. Lajoie and R. F. Yerkes of the U.S. Geological Survey contributed to our understanding of the 

structure and stratigraphy of the Ventura area and participated in field work related to this study. Lajoie and 

J. F. Wehmiller, University of Delaware, provided age 

calibration in the Ventura area through amino-acid 

racemization analysis of fossil mollusks. J. W. Hillhouse 

of the U.S. Geological Survey and J. C. Liddicoat, of the 

Lamont-Doherty Institute, N.Y., provided information 

on paleomagnetic stratigraphy of two key areas, the 

Lake Tecopa and Bishop areas, respectively. Both Hillhouse and Liddicoat provided preliminary information 

on paleomagnetic stratigraphy in the Ventura area.

Jose Rivera and Betsy Bradshaw separated and 

purified samples of volcanic glass for chemical analysis. 

The high quality of their work is reflected in the high 

precision of replicate analyses from individual tephra 

units.

CRITERIA FOR CORRELATION OF TEPHRA

For a successful correlation, tephra layers must 

possess characteristics by which they can be uniquely 

identified. The principal method of correlation used in 

this study is chemical "fingerprinting" of volcanic glass 

from tephra. Pure glass separates are analyzed by 

neutron activation, electron microprobe, and energydispersive X-ray fluorescence, and samples with similar 

trace-element compositions are matched to establish

correlations. These correlations are tested by 

petrographic analysis of tephra layers and, where available, by independent stratigraphic, biostratigraphic, 

and magnetostratigraphic control.

Previous studies (Jack and Carmichael, 1968; 

Sarna-Wojcicki, 1971, 1976; Sarna-Wojcicki and others, 

1979, 1981a; Izett, 1981) suggest that the chemical composition of glass is one of the more distinctive characteristics by which tephra of specific volcanic eruptions can 

be identified. This is possible because a number of 

major, minor, and trace elements in volcanic glass can 

be analyzed with a high degree of precision, because 

silicic volcanic glass tends to be relatively homogeneous 

within tephra derived from the initial, explosive phase 

of silica- and volatile-rich magmatic eruptions (SarnaWojcicki and others, 1981a), and because tephra units 

erupted at different times from the same or different 

source areas are usually different enough in chemical 

composition to make identification possible. Tephra 

units erupted from different volcanic source areas are 

especially different in chemical composition (Sarna-Wojcicki, 1976; Sarna-Wojcicki and others, 1979; this report), more so than those erupted from the same source 

area; this makes it possible to identify volcanic source 

areas of distal tephra layers deposited at great distances 

from their eruptive vents, as well as to make specific 

correlations among tephra layers.

In the present study we assume that the chemical 

composition of volcanic glass from successive eruptions 

is not exactly duplicated. This is an assumption that cannot be proved conclusively because probably not all 

tephra units of the study area have been analyzed and 

chemically identified. A sufficient number of cases have 

been studied (Sarna-Wojcicki, 1976; Sarna-Wojcicki and 

others, 1981a; this report), however, in which stratigraphic positions, and consequently relative ages of 

tephra units, are known; in such instances, the chemical 

compositions of volcanic glasses are not repeated, except for very closely spaced tephra layers that represent 

multiple eruptions from one center during a single brief 

eruptive episode (Sarna-Wojcicki and others, 1981a). 

From these studies, we conclude that tephra units 

erupted over periods as short as several tens to several 

hundreds of years apart can be distinguished on the 

basis of composition.

This assumption of the compositional uniqueness of 

volcanic glass of tephras derived from individual eruptions seems reasonable in view of the many factors that 

probably affect magma generation and differentiation, 

and the complex manner in which these factors interact. 

Rocks are compositionally heterogeneous assemblages, 

and it is unlikely that any two batches of magma formed 

from the fusion of rocks would ever be exactly the same. 

Furthermore, magmatic differentiation and crystalliza-
CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

SOUTHERN CALIFORNIA CENTRAL 

CALIFORNIA

SALTON TROUGH

 PENINSULAR RANGES »|« 

ANZA-BORREGO CHANEY HILL SOUTH MOUNTAIN

COASTAL SOUTHERN CALIFORNIA - 

VENTURA

AND BALCOM CANYON

SAN JOAQUIN 

VALLEY

c 

S *

is i ' '

/ it E',.' ,, £ 

A6 s =biL' 5' 11 |

r « i i \

\ 3 1 1 \ 

\ £ Bishop ash-bed group

iv

9

I IS

0 §T>

" ° g o

° -p . 0.2 m.y. -a

* i | /A.A.R. 1

t s s.

r 1 ;

"- i S i S o> TTc |

10

r !

«

: * rf .

: "O 1 -.3

I Tl k. IB ^

» 1:5 

i

I JLp ash-bed group (FP' 'AQI B' sh°<> «**" «"°u<> 

(ORG, FP, IAO.I "AQI

Thin white ash be ow Beiley ash 

Huckleberry Ridgel?) ash bed 

u 

fl

?0

 o

a

5 c

jl

11

S

a

I

;>

Ei

I

7

4

'[

1

? ?'

i

i £ S 

22, 23 f 1

/Bailey ash ^» 

/ j~v.

1.2 ± 0.2 m.y. F.T.

Hzett and others

1974)

1

 o

i 1

/43 £ §

2 s

M

I

I-G4 > *

r

M

N

p 

??

il

/(Lajoieand 5 E

others, 1979) "J |

Leva Creek « 3

/Brs'hop'as" 8~ «o Lava Creek Bash bed, 53 

/ bed group 5 °»° / 0.7 m.y. K-Ar Bishop Tuff, N

'/ IFP) ^ X' (Dalrymple and /a. 13. 14

/3, 4, N |S ,1 others. 19e5l \^r^/B|,hop ash-bed group N (OflG, IAQ)

18 Whit. ash. R =1 <7B"hOP "P;^ 9r°UD G

 r^ ^- -= : : 1U-J ^ -Z^s^17H Glass Mountain-D ash bed

\ S : - IN19, R 

20, 21 1 E -y - - 1 I

r 24, 25. 26 1 J | j 

Bailey ash, R c 'jj~

O 3

SH

8|

1

Huckleberry Ridgel?) ash bed^

EXPLANATION

- Megnetic polarity time scale

K-Ar Potessium-ergon age determinetion

FT. Fission track age determination

Q AA R -Amino-acid racemization ege estimete

/Lava Creek B ash bed Neme of tephra unit 

 Sample number for chemicel analys

ishop ash-bed group Ash leyers belonging to 

(FP, IAQ , ORG) Bishop esh group.

(FP)-Friant Pumice Member (of the

Turlock Leke Formetion) 

(lAOHnsulating Aggregates Quarry type 

(ORO-Owens River Gorge-Red's Meadow type

Solid connecting horizontal 

lines indicate correction on 

besis of chemical and other 

dete

 Interrupted horizontal lines indicate a specified tephre 

unit is absent or hes not 

| | been found at locelity 

I I

Correlation probeble but not 

certain

FIGURE 2. Correlation chart of upper Pliocene and Pleistocene tephra layers in east-central
CRITERIA FOR CORRELATION OF TEPHRA

EASTERN AND SOUTHEASTERN CALIFORNIA SELECTED KEY LOCALITIES IN THE CENTRAL U.S.

EAST OWENS 

VALLEY

LAKE TECOPA GRAND COUNTY 

UTAH

MEAOE COUNTY 

KANSAS

YELLOWSTONE,

WYOMING, IDAHO

(CHRISTIANSEN AND

BLANK, 19721

I I 

I I 

I I 

1*1

/ 2.3 m.y. K-Ai 

' (Hay,1966)

I I

I I

I I

I I

;

K-Ar 

96)

i

\

See correlation 

x h.iinl

ii

y

TV

Lava Creek B ash bed, 51 

/(Light grey ash _ 

/ of Smith, 1964) -8

^

I

- 35

V Lava Creek B ash bad

y £-37. 38

= /9

JJT \Bishop ash-bed group (IAQ)

&R -"Gray" ash

5E

53 1

P

SH |

 . \ Huckleberry Ridgal?) ~ 

\ ash bed

._.

^

X

§

- 28, 29

- 30-33

1

J38

.-X^Lava Creek B ash bed (Naner and others, 1973)

SJr16 dietl and others, 1970)

i Bishop ash-bed group (ORG)

1

£

s B 

C

I

*

1

>

1 1

1 1

1 1

Huckleberry Ridga ash bed 42

^41 pn^^^lNaeser and others, 1973) 

Huckleberry Ridga ash bed 1 1 SH 44' 45

4

e

4

++

+

+

4

e

4

4

4

4

4

+

4+

4

S

4 

4

-0.6 m.y.

^- Lava Creek

Tuff

-1.2 m.y.

^ Masa Falls

Tuff

-2.0 m.y. 

^Huckleberry

Ridge Tuff

\ \ 

1 1

 ormation name, 

sediment type,

of deposition 

if known

 J.

i

^2.3 i 0.4 m.y., K-Ar Radiometric age and reference 

(Hay, 1966)

Magnetic polarity determinations N-normal; R-reversed

I I

I I

I I

I I

I I

- Arrows with queries indicate 

uncertainty of age range of 

tephra unit

 Tephra of Long Valley-Mono 

basin chemical affinity

- Tephra of Yellowstona chert 

cal affinity

- Tephra unit not analyzedtJanuary 1, 1979)

Dashed lines indicate 

uncertainty of age

California, southern California, and several key localities in the central United States.
CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

tion proceed at different temperatures, pressures, and 

rates, resulting in formation of different kinds and 

amounts of crystals in the melt. Crystals take up varying amounts of elements from the magma, leaving variable concentrations of elements in the residual liquids. 

Furthermore, wall rocks, the "crucible" in which magma 

is contained, are not inert; they probably continually interact with the melt, resulting in continuous compositional changes through time. Thus, it can be assumed 

that all such variables cannot be exactly repeated in an 

identical sequence and at identical rates.

Zoning within magma chambers may present problems in identification of tephra layers if the range of 

chemical compositions of tephras erupted during a single 

eruption overlaps with the range of compositions of 

tephra erupted at different times from the same caldera 

or source area. Zoning has been well documented for 

some calderas (Hildreth, 1979; Smith, 1979), and the 

spectrum of compositions erupted during a single eruption or eruptive sequence can be quite wide. The silicaand volatile-rich early phase of explosive (plinian) eruptions from major calderas, however, probably makes up 

a small fraction of the total volume of a magma chamber 

(Smith, 1979) and thus probably represents a rather 

narrow compositional range. Some tephras are compositionally heterogeneous owing to mixing of magmas, as in 

the eruption of Katmai in 1912 (Curtis, 1968), and zoning in magma chambers, as in the eruption of Hekla in 

1947 (Thorarinsson, 1949) and that of Mount Mazama 

about 7,000 yr B.P. (Williams, 1942; Smith, 1979). Mixing of compositionally different tephra layers can also 

occur as a result of surficial reworking after deposition 

(Cerling and others, 1978). Nevertheless, it is possible 

to test for effects of mixing or zoning, and as in the case 

of the 1947 eruption of Hekla (Thorarinsson, 1949), such 

effects may actually aid in the identification of ash 

layers, owing to their unique compositional or stratigraphic characteristics.

METHODS

We disaggregated and sieved tephra samples, 

separating the volcanic glass for chemical analysis and 

the mafic heavy minerals for petrographic analysis. 

Glass samples were analyzed by instrumental neutron 

activation for abundances of about 40 major, minor, and 

trace elements. About 16 to 20 elements were used in 

correlating tephra layers (see below). We also analyzed 

glass samples by electron microprobe for 12 elements: 

silicon, aluminum, iron, magnesium, manganese, calcium, barium, titanium, sodium, potassium, chlorine, 

and phosphorus. More recently, we have begun to 

analyze glass samples of tephra by energy-dispersive Xray fluorescence analysis (XES). In general, this

method is not as diagnostic as neutron activation, but 

more diagnostic than electron-probe analysis in chemical 

characterization of many tephra families. The advantage 

of the XES method is that it is rapid and relatively inexpensive compared to neutron-activation analysis but, 

unlike electron-probe analysis, requires careful separation of glass from other components of tephra. For a 

further description of sampling, sample preparation, 

and analyses, see the "Appendix."

SELECTION OF ELEMENTS FOR CORRELATION

For purposes of correlation, we selected elements 

on the basis of their natural variability within and 

among tephra layers of different age, as well as according to precisions attainable for each element in analysis. 

Analysis of samples from superposed tephra layers at 

several localities in the study area allows us to evaluate 

the internal and external variability of these layers and 

determine the resolution available for each element relative to independent age criteria. In other words, we can 

test whether the range of concentration of an element in 

glass of a single tephra layer overlaps with ranges determined for tephra layers at different stratigraphic 

levels, and we can determine the extent of overlap, if 

any exists.

On the basis of our experience in this and previous 

studies (Sarna-Wojcicki, 1976; Sarna-Wojcicki and 

others, 1979, 1981b), an element is useful in characterizing tephra if the mean of replicate analyses within a 

single tephra layer is different from that of another 

layer of demonstrably different age at a level of significance (alpha) equal to or less than about 0.05 (in other 

words, if we are 95 percent confident that the means are 

truly different). An element is useful in correlation if (1) 

it is relatively homogeneously distributed within the 

glass of a single tephra layer, (2) it usually differs in concentration in units of demonstrably different age, and 

(3) its full range of concentration can be accurately 

measured. In practice we use those elements for which 

analytical error is equal to or less than about 7 percent 

of their concentration in glass.

In neutron-activation analysis, from 16 to 20 major, 

minor, and trace elements are generally most useful for 

correlation of dacitic or rhyolitic tephra. These elements 

are, in order of increasing atomic number: scandium, 

manganese, iron, zinc, rubidium, cesium, barium, the 

rare-earth elements lanthanum, cerium, neodymium, 

samarium, europium, terbium, dysprosium, ytterbium, 

lutecium, and the heavy trace elements tantalum, hafnium, thorium, and uranium. In energy-dispersive Xray fluorescence analysis the most useful elements are 

calcium, titanium, manganese, iron, rubidium, strontium, and zirconium. Potassium is only marginally useful
METHODS

because it tends to be leached or enriched in volcanic 

glasses by postdepositional processes. Copper, zinc, yttrium, and niobium are also marginally useful because 

they occur in low concentrations in silicic glasses; consequently the analytical precision for these elements is 

relatively low. In electron microprobe analysis, we determined concentrations of sodium, aluminum, silicon, 

phosphorus, chlorine, potassium, calcium, titanium, 

manganese, iron, and barium. Of these, calcium and iron 

are the most useful. Sodium and potassium are strongly 

affected by postdepositional processes, aluminum and 

silicon tend to occur in about the same concentrations in 

silicic glasses of tephra layers derived from the same 

volcanic provinces, and the sensitivity for the remaining 

elements analyzed is often too low to adequately distinguish between tephra layers.

The utility of a certain element will vary from one 

volcanic source area to another and consequently among 

suites of tephra derived from different volcanic provinces. For instance, barium and europium are near minimum detection limits of neutron-activation analysis, and 

strontium is near the limit of X-ray fluorescence analysis, in tephra derived from highly differentiated silicic 

tephras of the Long Valley-Glass Mountain province of 

eastern California; the error in precision for these elements is as high or higher than compositional variations 

among tephra layers of different age erupted from this 

province. Thus, these elements cannot be used to discriminate among different tephra layers belonging to 

this tephra family. Strontium, barium, and europium 

can be used, however, to distinguish among tephra 

layers derived from other volcanic provinces (for instance, the Cascade Range) where the concentration in 

.silicic glass is higher.

The total error in replicate analyses of tephra samples from the same tephra layers, expressed as a percentage of concentration present in the glass, ranges 

from less than 1 to about 7 percent and averages about 

3 to 4 percent for the elements used for correlation in 

neutron-activation analysis of glass. This error is a combination of both analytical and sampling errors. The latter is a function of the natural homogeneity of the glass 

and the purity of glass separations.

METHODS OF EVALUATING CHEMICAL DATA 

FOR CORRELATION

For the purpose of visual representation of element 

concentrations in glass, we calculated ratios of concentrations of elements of selected samples to concentrations of the same elements in U.S. Geological Survey 

(USGS) rock standard G-l. Histograms of these ratios 

are shown in figure 3. Suggested or recommended 

values and magnitudes (Fleisher, 1969) are used except 

for cesium, terbium, and ytterbium, for which values of

6, 1, and 2.5 ppm, respectively, were arbitrarily assigned in order to minimize high ratios. This graphic 

method was chosen because one can plot elements that 

vary in concentration by several orders of magnitude on 

a single scale. Differences between pairs of histograms 

have also been calculated and are shown adjacent to 

sample histograms (fig. 3).

Similarity coefficients (Borchardt and others, 1972) 

have been calculated for every sample pair in the study 

group (fig. 4). The similarity coefficient is an average of 

ratios of element concentrations in two glass samples. 

Ratios of individual elements are calculated by dividing 

the concentration in one sample by the concentration in 

another. Unless concentrations in samples are identical, 

the lower concentration is divided by the higher, so that 

the ratio is always less than or equal to 1. The coefficients are averaged for all elements in the comparison. 

The ideal value of this coefficient is 1 for a chemically 

identical sample pair. This coefficient is given by:

d

where

(A,B)

= rf(B,A) = similarity coefficient for comparison between sample A and sample B

= element number,

= number of elements,

otherwise

= concentration of element i in sample

A, and 

= concentration of element i in sample B.

In practice, the values of the coefficient for replicate analyses of splits of the same sample, or of samples 

from a single emplacement unit, range from about 0.93 

to 0.99 owing to inhomogeneities in the glass, variations 

in purity of glass separations, presence of microlites, or 

analytical errors. The actual range of values for replicate analyses within single emplacement units also varies to some extent depending on the elements selected 

for comparison and the volcanic source area from which 

the tephra suite has been erupted.

Values of similarity coefficients for tephra layers of 

demonstrably different age (for instance, tephra layers 

in stratigraphic order within an exposed continuous section) range from about 0.35 to about 0.94; the exact 

range depends on the variables mentioned above. 

Tephra layers derived from the Long Valley-Glass 

Mountain volcanic province are very similar in chemical
CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Sample 22

ABC 

Bishop ash-bed group

b2-23l b2-2«l |22-2S| |22-26J \23-l4 |23-25J |23-26J {24-2s| [24-26J J26-

0 0.5

Sc

Mn

Fe

Zn

Rb

Cs

La

Ce

Nd

Sm

Eu

Tb

Oy

Yb

LU

Hf

Ta

Th

U

]

1 ]

]

1 1 I

i D o

Average 

differences III!

1

1

1

I 1 I 1 I

in ratios 0.04 0.03 0.03 0.05 0.04 0.05 0.02 0.02 0.05 0.0

Similarity

coefficient 0.95 0.97 0.98 0.95 0.95 0.95 0.97 0.98 0.95 0.9

G H 1

Fnant Pumice Member 

(of theTurlock Lake IAQ 

Formation)

Bishop ash

Mountain- Mountain- Bailev 

ash

Pearlene 

type O ash bed

Average

ratio to D

G-1 0.69

Age, m.y. 0.62 ?

I 0 i 0 D D n ED

Average differences in ratios 0.05 0.10 0.06 0.14 0.26 0.31 0.64 0.89

Average similarity coefficient 0.93 0.88 0.93 0.85 0.77 0.77 0.62 0.44
CORRELATION OF TEPHRA UNITS

composition and are harder to distinguish than tephra 

layers from other provinces. Similarity coefficients for 

different tephra layers of this family are sometimes as 

high as 0.95. Consequently, the range of similarity coefficients from 0.93 to 0.95 represents an interval of uncertainty for this tephra family, and correlations based 

solely on similarity coefficients within this interval must 

be regarded as uncertain. This degree of uncertainty 

can be quantified and expressed in probabilistic terms 

by using a modification of the similarity coefficient, 

whereby the average ratio is calculated for sample pairs 

by dividing element concentrations in one sample by 

those of another, the concentrations of the first being in 

the denominator, those of the second in the numerator 

regardless of which is the greater. Because deviations 

from the ideal value of 1 for different elements of a sample pair in this instance may average out to give a misleadingly high average ratio, this modification is riot as 

useful a guide to indicate correlation as the similarity 

coefficient; however, the standard deviation of the mean 

of these ratios for a population of variables (elements) is 

useful, because it measures the dispersion of values 

about 1, and the distribution of these values should be 

normal. Cluster analysis (Parks, 1970) of a data set similar to that presented here gives essentially the same 

groupings as those using the similarity coefficient 

(Sarna-Wojcicki, 1976).

Because ranges of similarity coefficients for replicate analyses of individual tephra layers generally do 

not overlap with those of tephra layers of different age, 

similarity coefficients can be used as quantitative guides 

to indicate correlation or its lack where stratigraphic or 

other types of age control are not available. The actual 

ranges of values for acceptance or rejection of correlation must be derived empirically for each suite of tephra 

erupted from a particular volcanic source area, calibratFIGURE 3. Chemical compositions of selected glass samples of 

tephra, shown as ratios to USGS rock standard G-l, and differences between histogram pairs. A, The left side of the figure 

shows glass compositions of five samples of the Bailey ash. The 

right side shows the absolute difference between samples. Thus, 

22-23 is a histogram showing the absolute difference between 

samples 22 and 23. Sample numbers are the same as in other tables and figures. Method of plotting ratios is adapted from 

O'Keefe (1978). B, The upper part of the figure shows glass compositions of tephra units of the Long Valley-Glass Mountain family (A-H) and the Lava Creek B ash bed (I), as ratios to G-l. Average values of analyzed samples are used for each tephra unit. 

The lower part of the figure shows absolute differences between 

ratios of the Friant Pumice Member and ratios of each successive 

tephra unit to the right. Thus, A-B shows the absolute difference 

between the Friant Pumice Member and the Bishop ash, IAQ (Insulating Aggregates Quarry) type; A-C shows the absolute difference between the Friant Pumice Member and the Bishop ash, 

ORG (Owens River Gorge and Red's Meadow) type, and so on.

ed and verified by replicate analyses of individual layers 

and multiple superposed layers at critical localities. For 

instance, the average analytical error on replicate 

analyses of glass samples by neutron activation of 

tephra layers derived from the Long Valley-Glass 

Mountain or Yellowstone tephra families averages about 

3 to 4 percent for those elements used in correlation. 

Consequently, we expect that similarity coefficients of 

samples from a single tephra unit belonging to one of 

these families would average between 0.96 and 0,97.

A similarity coefficient matrix is given in figure 4 

which compares all sample pairs in the group of 69 samples analyzed by neutron activation. Average values of 

the similarity coefficients and standard deviations of the 

averages for major groups have also been calculated and 

are given in figure 4. The matrix (fig. 4) is based on a 

comparison of 13 elements that were judged to be most 

reliable in distinguishing among the tephra samples: 

scandium, iron, rubidium, cesium, lanthanum, cerium, 

samarium, terbium, ytterbium, lutecium, hafnium, tantalum, and thorium. Elements excluded are manganese, 

dysprosium, and uranium, which were not determined 

for some samples, and zinc, neodymium, and europium, 

for which relative precision was low owing to low concentrations in glasses of some of the sample groups. A 

dendrogram (fig. 5) shows the relations among the 

samples and sample groups on the basis of the highest 

values of the similarity coefficient between individual 

sample pairs and the highest average values for the 

sample groups shown in the matrix (fig. 4).

CORRELATION OF TEPHRA UNITS

Figure 2 summarizes correlations presented in this 

study and available isotopic age, stratigraphic, and 

paleomagnetic data. Correlations are made primarily on 

the basis of glass chemistry (table 1) and stratigraphic 

sequence, supported by petrographic, isotopic age, and 

magnetostratigraphic data.

It was not possible to resolve differences in glass 

chemistry for a number of tephra units on the basis of 

electron-microprobe analysis alone (table 2). This was 

particularly true for ashes of the Long Valley-Glass 

Mountain family situated in close stratigraphic proximity. Likewise, it was not possible to distinguish definitively among ashes derived from the Yellowstone area 

(Pearlette-like ashes) by this method. However, it is 

possible to distinguish individual tephra units of several 

other tephra families derived from other volcanic source 

areas, such as Crater Lake, Mount St. Helens, and 

Glacier Peak, by this method (Smith and others, 1977; 

Davis, 1978; Sarna-Wojcicki and others, 1981a). Attempts to differentiate among ashes of the Long Valley-
10 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Similarity coefficients

Sample numbers 12 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 a b c 18 19 20 21 a b c d 22

Bishop 

ash-bed - 

group

Friant Pumice Member 

(of the Turlock Lake Formation)

Bishop ash, IAQ type

Bishop ash, ORG type

Glass Mountain-D ash bed

Glass Mountain-G ash bed

Bailey ash

Ash below Bailey ash

Upper white ash , Manix basin

Middle white ash, Manix basin

Ash in late Cen ozoic lake beds of Searles Valley

Unwelded, pumiceous ash-flow tuff in the Coso area

Lava Creek B ash bed

Mesa Falls ash bed

Huckleberry Rid

Huckleberry Ric

Air-fall pumice

ge ash bed

ge (?) ash bed

of the Coso area

Ash in Searles Valley

Pumice overlying Cahuilla beds, Salton trough

98 95 96 97 97 96 

91 96 97 98 95 

96 97 93 97 

97 96 96 

96 97 

96±1 91,

93±2

88±2

93±2

85±2

7712

77±2

88±2

62±1

92±1

62±1

44+1

4611

45±1

4511

56+2

7210

55+1

91 91 95 93 93 

90 90 93 92 92 

95 91 96 96 96 

92 92 96 91 91 

93 92 96 91 95 

89 89 93 91 91 

9D 911 97 96 96

97 95 97 96 

96 97 97 

9711 97 98 

98

9411

9311

8712

8112

8011

91ll

6511

9211

6211

4511

47+<l

4511

4511

5412

73±0

52 + 1

87 86 8? 86 

87 86 86 85 

92 90 91 90 

88 88 89 87 

89 88 89 88 

86 85 85 85 

90 90 90 89

96 91 95 91 

96 95 96 91 

92 91 92 91 

91 93 91 93 

93 93 93 92

97 97 96 

97H 98 97 

98

9111

9012

8412

83±1

9111

6811

9110

6011

46+1

48+1

4611

46+1

51 + 2

7011

5111

92 92 91 92 90 

91 92 91 91 90 

95 911 96 911 93 

93 93 95 93 91 

93 91 96 93 92 

91 91 93 91 89 

93 92 91 93 92

91 92 93 93 93 

93 92' 93 93 91 

93 93 95 93 92 

91 91 95 91 93 

91 93 95 91 92

92 90 91 92 92 

92 89 90 92 91 

92 89 91 92 91 

92 89 90 91 91

96 97 98 97 

97 97 96 

9711 97 96 

96

9012

8012

Sill

91±1

65+1

9411

6011

47+1

49+1

4711

47+1

5412

6911

5511

86 87 81 82 81 85 82 

86 87 81 82 81 85 82 

89 91 87 85 87 89 86 

86 88 85 82 81 86 83 

88 89 86 83 86 87 81 

81 86 83 80 82 81 81 

88 89 86 83 85 88 8H

91 92 88 86 88 91 87 

89 90 86 81 86 89 85 

87 88 85 83 85 88 81 

89 90 87 85 87 89 86 

89 90 86 81 86 89 85

92 92 89 86 89 91 88 

92 93 89 87 89 92 88 

91 92 88 86 88 90 87 

93 93 90 87 90 92 89

92 91 90 88 90 91 88 

90 93 88 88 88 89 86 

90 92 88 86 88 90 87 

92 91 90 88 89 91 88 

93 95 90 90 90 92 89

97 96 92 95 95 91 

911 92 911 911 92 

95 98 96 97 

9512 96 91 95 

97 97 

96

8713

86+1

88H

7112

8912

5711

4911

52+1

SOU

5011

5012

66+1

5111

77 

77 

81 

78 

79 

76 

79

83 

82 

81 

82 

82

81 

81 

83 

85

82

80 

81 

82 

83

88 

86 

91 

89 

91 

90 

93

'Average similarity coefficient excluding sample 23a

Averages of coefficients for selected widespread tephra

FIGURE 4. Similarity coefficient matrix comparing the chemical compositions of glass of tephra layers based on neutron-activation analysis.

of similarity coefficients for sample pairs; the lower-left half gives averages
CORRELATION OF TEPHRA UNITS 11

for sample pairs

a 23 a b c d 24 a b c 25 26 a 27 28 29 30 31 32 33 34 35 36 37 38 39 40 A 41 42 43 44 a 45 46 47 48 A

76 75 75 76 76 73 77 77 78 76 77 74 74 

75 74 74 75 75 72 76 76 77 75 77 73 73 

79 78 78 79 79 76 80 80 82 79 81 77 77 

77 76 75 77 78 75 78 78 79 77 78 75 75 

77 76 76 77 78 75 79 79 80 78 79 75 76 

75 74 73 75 75 72 77 76 77 75 77 73 73 

78 77 77 78 78 75 80 79 80 78 80 76 76

82 80 80 82 82 79 82 83 84 81 83 80 80 

81 81 78 83 83 80 81 82 82 80 81 80 80 

79 79 78 80 80 77 80 81 82 80 81 77 77 

80 80 79 81 81 78 82 82 83 81 82 78 79 

80 80 78 81 81 78 81 82 83 81 82 78 78

84 83 80 84 85 82 83 83 85 82 84 83 83 

83 84 80 86 86 83 83 84 85 83 84 83 83 

83 84 80 85 85 82 83 84 84 82 83 82 82 

84 85 81 86 86 83 84 85 86 84 85 83 84

80 80 79 81 81 79 82 82 83 81 82 79 79 

78 78 78 78 78 76 80 80 80 79 80 77 76 

79 78 78 80 80 77 81 81 82 80 81 77 77 

80 79 79 80 81 78 82 82 83 81 82 78 78 

81 79 79 79 80 78 82 81 82 80 83 79 79

85 84 84 85 85 82 87 87 88 85 88 84 83 

84 83 83 83 83 81 85 85 86 84 86 82 82 

88 87 87 87 88 85 90 89 91 88 91 87 86 

87 85 87 86 86 83 88 87 88 86 89 85 85 

88 87 87 87 87 85 90 89 90 88 91 87 86 

87 86 85 86 86 84 88 88 89 87 89 85 85 

90 88 88 89 89 86 91 91 92 90 92 88 88

97 95 93 94 95 93 97 97 96 96 98 95 94 

95 94 95 96 94 96 97 96 96 96 96 95 

94 96 96 96 95 96 94 96 95 97 96 

91 93 94 95 95 94 95 94 94 93 

98 94 94 96 95 94 94 95 95 

96 95 96 95 95 94 96 95 

93 94 93 96 93 96 97 

95±1 97 97 97 98 95 94 

98 98 97 95 95

(96+1)' 96 97 94 94 

( ' 97 96 95 

95 94 

97

76 

75 

79 

77 

77 

75 

78

81 

80 

79 

80 

79

83 

83 

83 

84

81 

80 

80 

81 

81

86 

83 

87 

85 

86 

85 

87

86 

86 

86 

88 

86 

86 

86 

88 

86 

86 

87 

87 

86 

86

86±1 /

81±1

79±2

80±1

57±1

52±1

55±1

52±1

52±1

48±2

64±1

46±1

86±1

79±1

48±1

52±1

47±<1

47±1

45±1

87 88 

87 87 

91 90 

88 89 

89 89 

86 87 

90 90

92 91 

91 92 

90 91 

92 91 

91 91

91 92 

91 91 

91 92 

90 91

91 91 

91 90 

91 89 

91 90 

91 90

91 90 

91 90 

88 87 

86 84 

88 87 

90 89 

86 85

82 81 

80 80 

80 81 

80 79 

80 81 

80 81 

79 79 

83 82 

82 82 

83 82 

81 81 

83 82 

79 79 

79 79

86 85

96

69±1

90±0

60±1

45±<1

47±1

46±1

46±1

51±1

70±1

54±1

62 61 61 61 61 

61 60 61 61 60 

64 63 63 63 64 

63 62 62 62 62 

63 62 63 63 62 

61 60 60 60 60 

64 63 63 63 63

67 65 66 66 67 

66 65 65 65 67 

65 63 64 64 65 

66 65 65 65 66 

66 64 65 65 66

68 67 67 67 68 

69 68 68 68 70 

69 68 68 68 69 

70 68 69 69 70

67 65 66 66 66 

65 64 64 65 64 

65 64 65 65 64 

66 65 66 66 65 

66 65 65 65 65

71 70 70 70 70 

69 68 68 68 68 

73 71 72 72 72 

7271 727271 

72 71 72 72 71 

71 70 70 70 70 

74 72 7 3' 73 73

77 75 76 76 77 

79 77 77 78 79 

80 78 79 79 81 

83 81 81 81 82 

78 77 77 78 79 

79 77 77 78 79 

82 81 81 81 82 

79 77 78 78 78 

79 77 77 77 79 

78 76 76 77 77 

80 78 79 79 80 

78 76 76 77 78 

81 79 79 79 81 

80 78 79 79 81

80 79 79 79 80

70 68 69 69 69 

69 68 69 69 69

97 97 98 96 

98 98 95 

97±1 ge 96 

96

92

91 

94 

93 

92 

91 

93

92 

92 

92 

93 

93

91 

91 

91 

91

95 

94 

95 

94 

94

91 

92 

89 

86 

88 

90 

87

81 

80 

79 

79 

80 

81 

78 

81 

82 

82 

80 

81 

78 

78

81

90 

90

66 

64 

65 

65 

65

65±1 /

65±1

53±1

56±<1

51±1

49±1

37±1

52±1

44±1

45±0

47±0

46±1

46±1

37±1

63 

62 

62 

62 63' 

63 

62

61 

62 

62

61 

62

60 

59 

60 

60

60 

60 

61 

59 

59

58 

58 

57 

55 

56 

57 

56

57 

56 

57 

55 

58 

57 

56 

57 

57 

57 

56 

56 

56 

57

56

59 

60

49 

48 

48 

49 

50

61

44 44 44 

44 44 44 

45 45 45 

45 45 45 

45 45 45 

44 44 44 

44 44 44

45 45 45 

45 45 44 

45 44 44 

46 45 45 

45 45 45

46 46 46 

46 46 46 

46 46 45 

46 46 46

46 46 46 

47 47 47 

46 46 46 

47 46 46 

47 47 47

49 48 49 

49 48 48 

50 49 50 

50 50 50 

50 50 50 

49 49 48 

50 50 50

52 51 52 

51 50 52 

52 51 52 

53 52 54 

51 50 51 

51 50 52 

52 51 53 

52 51 53 

51 50 52 

52 50 52 

52 51 53 

53 51 53 

52 51 53 

52 51 53

48 47 49

46 45 45 

45 45 45

54 51 53 

54 51 54 

54 51 53 

54 51 53 

53 50 53

45 45 45

34 32 34

^ 92 97 

33±1 93 

94±3

35±0 89±2

34±0 92±2

34±1 87±3

52±3 36±2

39±1

61±1

46 46 

46 46 

47 47 

47 47 

47 47 

46 46 

46 46

47 47 

47 46 

47 47 

47 47 

47 47

48 48 

48 47 

47 47 

48 48

48 48 

49 49 

48 48 

49 4g 

50 49

51 51 

51 50 

52 52 

52 52 

52 52 

51 51 

52 52

54 54 

55 55 

54 54 

56 56 

53 53 

54 54 

56 55 

55 55 

54 54 

54 53 

55 55 

55 55 

55 55 

55 55

52 51

48 47 

47 47

56 56 

57 57 

56 56 

56 56 

56 56

47 47

35 35

91 90 

86 87 

91 91

98

87±<1

84±1

35±2

43±0

58±0

45 44 

45 44 

45 44 

46 45 

46 45 

45 44 

45 44

46 45 

45 44 

45 44 

46 45 

45 44

47 46 

46 45 

46 45 

47 46

47 46 

47 46 

46 45 

47 46 

48 47

49 49 

49 48 

50 50 

51 50 

51 50 

49 48 

51 50

52 51 

51 51 

52 51 

53 52 

50 50 

51 50 

52 52 

52 52 

51 51 

51 51 

52 52 

52 52 

52 52 

52 52

47 47

46 45 

46 45

51 51 

51 51 

51 51 

50 50 

50 50

46 45

34 34

90 90 

95 94 

90 91

87 87 

87 87

97

93±1

35±2

39±1

61±1

44 45 45 44 

44 45 45 44 

45 46 46 45 

45 46 46 46 

45 46 46 46 

44 45 45 45 

44 45 45 45

46 47 47 46 

45 46 46 45 

45 46 46 45 

46 47 47 46 

45 46 46 46

46 47 47 46 

46 47 47 47 

46 47 47 46 

46 47 47 47

46 48 48 47 

47 48 48 47 

46 47 47 46 

47 48 48 47 

47 49 48 48

48 49 49 48 

48 49 49 48 

49 50 50 50 

51 52 52 51 

50 51 51 50 

49 50 50 50 

50 51 51 51

52 53 52 52 

51 52 52 51 

52 52 53 52 

53 54 54 53 

50 52 51 51 

51 52 52 51 

52 52 52 52 

52 53 53 52 

51 52 52 51 

51 52 52 51 

52 52 52 52 

52 53 53 52 

52 53 53 52 

52 52 53 52

47 47 48 47

46 47 47 46 

45 46 46 45

50 49 49 49 

50 50 50 49 

50 50 50 49 

49 49 49 49 

49 49 49 48

45 46 46 46

33 34 34 33

85 84 84 85 

92 90 91 91 

86 85 85 86

84 83 83 84 

85 83 84 84

94 92 92 94 

94 92 93 94

96 97 98 

97±1 9896

36±2

38±0

60±1

60 56 56 56 

60 56 56 56 

58 54 54 54 

58 55 55 54 

58 55 54 54 

60 56 56 56 

58 54 54 54

56 53 52 52 

56 53 52 52 

58 54 54 54 

56 53 53 53 

57 53 53 53

54 52 51 51 

54 51 50 50 

54 51 50 50 

54 51 50 50

56 53 53 52 

56 52 52 52 

56 53 53 53 

56 53 53 52 

56 53 53 52

53 50 50 49 

53 51 50 49 

52 50 49 48 

51 49 48 47 

52 50 49 48 

53 51 50 49 

52 49 49 48

50 48 48 47 

50 47 47 46 

48 46 45 45 

47 45 45 44 

49 46 45 45 

49 47 46 45 

47 45 44 44 

49 47 46 45 

49 47 47 46 

50 48 47 46 

49 47 46 45 

50 48 47 46 

48 46 45 45 

48 46 45 45

47 45 45 44

53 51 50 50 

54 51 51 50

39 37 37 37 

38 37 37 36 

39 37 37 36 

38 37 37 36 

40 38 38 37

57 53 53 53

51 48 50 50

39 36 35 34 

39 36 35 34 

39 37 36 35

38 35 34 34 

38 35 34 33

38 34 33 33 

38 35 34 33

39 35 35 34 

40 37 36 35 

40 36 36 35 

38 35 34 33

91 87 87 

91±4 93 92

61±2

39±2

49 50

72 

72 

72 

73 

72 

72 

72

72 

73 

73 

73 

73

72 

70 

70 

69

69 

69 

70 

69 

70

67 

67 

66 

64 

66 

67 

65

65 

65 

64 

62 

65 

65 

63 

64 

65 

65 

64 

65 

64 

64

61

70 

69

52 

51 

51 

51 

53

69

49

40 

38 

39

43 

43

39 

38

38 

38 

38 

38

63 

61 

59 

59

bb 

56 

54 

55 

54 

55 

53

52 

52 

53 

53 

52

51 

51 

51 

50

54 

55 

55 

55 

54

52

52 

50 

52 

51 

52 

50

46 

46 

46 

47 

46 

46 

45 

46 

47 

47 

46 

47 

45 

45

49

54 

53

44 

45 

45 

44 

43

52

38

61 

60 

61

58 

58

62 

60

59 

60 

60 

61

41 

39 

38 

37

45

1 

2 

3 

4 

5

76

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

17a 

17b 

17c 

18 

19 

20 

21 

21a 

21b 

21c 

21 d

22 .

22a 2

23 « 23a 0 

23 b E 

23c 3 

23d C 

24 

24a a 

24b c 

24c £ 

25 0) 

26 

26a 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

40A 

41 

42 

43 

44 

44a 

45 

46 

47 

48 

48A 

49 

50

units and for tephra groups, plus or minus one standard deviation

Values given are in percent. A value of 100 percent represents a perfect match. The upper-right half of the matrix gives individual values 

of sample groups, plus or minus one standard deviation of the average.
12 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

1.0

SIMILARITY COEFFICIENT 

0.9 0.8 0.7 0.6 0.5

48A ,

48 ' |

1 47 L-i

46 '

 i 

2 « o £" £ -C in =

Ashes and tuffs erupted « £ cj .«

in the Coso area

Ash in the Coso area/ 

49 Ash in Searles Valley/

16 -i 

15 H 

14 -H _ . 13 r^

10 n

'i^

9 =l

1 -i

2 -h 6 -1 

4 

5 

3 

7 '

17 -i 17c -L,

17a 

17b 

18 '

 1C o j

28 1__ 29 1 

21 -r-i

21b -H

21c ] 21d ' 

19 -T 

20 '

h

RG

-IAQ

-

Bishop

ash-bed

group

-Friant Pumice ^

_

lember (of the

r ,

Turlock Lake Formation)

J

1

>

E

CO

^

Ash of Glass Mountain 'm

J

Ach frr

C

3

O

m rnrp in lakp ^

beds of Searles Lake w(A

 ]- Upper white ash, Manix basin ^

21a '

22 -.

25 -h

24 -1

24b -| 

24a -4-1 24c -1

22a S

26 H

26a 

23d H

23 H

23b ^

23a 

27 

30 -, -i-i _J oo

32 -\

31 34 '

-.

1

m

'Gray ash beneath ash o> 

of Glass Mountain §

-1

n

£

"o

CO

Q.

-Bailey ash

|- Middle white

J ash, Manix

basin

Pumice overlying Cahuilla beds.

45 | -i Salton trough

J? IJ i h Huckleberry R dge(?)

44 J

41 | __ 42 J 

37 i

39 ' i

38 '

40 -i

J ash bed

-, i 

1

5 « 1

L }-Huckleberry Ridge _ "ii^-j^

"] ash bed 5 = ;

^ £ 

FT h  

Lava Creek B ash bed v £. «

i

40A J -T

<^ a-

\ "

 Mesa Falls ash bed * 

Glass Mountain provenance by electron-microprobe 

analyses alone can result in misidentification.

DISCUSSION OF SPECIFIC CORRELATIONS

In the following discussion of specific correlations, 

we will be referring to samples analyzed in this study by 

locality numbers shown in figure 1. The same numbers 

are used in figure 2, the summary correlation chart, tables 1-3, which present chemical analyses, and table 4, 

which gives specific location information.

LAVA CREEK B ASH BED (FORMERLY THE 

PEARLETTE TYPE O ASH BED)

The Lava Creek B ash bed is the youngest of several widespread tephra units that are important stratigraphic markers in the central and western United 

States. This ash was erupted from volcanic sources in 

the Yellowstone area and is equivalent to the Lava 

Creek Tuff, dated at 0.6 m.y. (Christiansen and Blank, 

1972). The age of the Lava Creek B ash bed has been 

dated independently at 0.6 m.y. by the fission-track 

method on zircons (Naeser and others, 1971, 1973; Izett 

and others, 1971). It was previously called the Pearlette 

type 0 ash bed but has since been informally renamed 

after the near-source formation, the Lava Creek Tuff, 

with which it is equivalent (Izett, 1981). Our chemical 

data confirm identification by Izett and others (1972) of 

the Lava Creek B ash bed in lake deposits of Pleistocene 

Lake Tecopa. Sample 37 (table 1), taken from the basal 

7 cm of a 2.1-m-thick water-deposited ash (referred to as 

ash A by Sheppard and Gude, 1968) at the north end of 

Lake Tecopa, matches well with sample 39 (table 1) of 

the Lava Creek B ash bed from the locality at Onion 

Creek, Grand County, Utah (Izett and others, 1972). 

The similarity coefficient for this sample pair is 0.97 (fig. 

4). Another sample of this ash at Lake Tecopa, taken at 

91-106 cm above the base (sample 38; table 1), is somewhat different from the lower sample (37) and suggests 

that this tephra bed may represent more than one eruption, or that it was deposited from an eruption of a compositionally zoned magma. Alternatively, the chemical 

differences may represent postdepositional reworking of 

somewhat different ash compositions within the Lake 

Tecopa basin after eruption. The similarity coefficients

FIGURE 5. Dendrogram showing relations between individual samples and sample groups, using similarity coefficients, based on 

neutron-activation analysis. Highest values of the similarity coefficient are used to link sample pairs, and highest average values 

of the coefficient are used to link sample groups. Values of the 

similarity coefficient at which linkages are made are shown by the 

horizontal scale at top.
DISCUSSION OF SPECIFIC CORRELATIONS 13

Table 1. Neutron-activation analysis of volcanic glass from late Cenozoic tephra

of east-central and southern California.

[ Concentrations in parts per million except for iron, which is in percent 1

Sample 1

number Sc Mn Fe Zn2 Rb Cs La Ce Nd2 Sm Eu2 Tb Dy2 Yb Lu Hf Ta Th U

ASHES HAVING CHEMICAL AFFINITY TO TEPHRA OF THE LONG VALLEY-GLASS MOUNTAIN AREA

13

2

3

4

5

6

7

X 4

s5

a.a.e.

8

9

10

11

12

X

s

a.a.e.

2.83

2.89

2.87

2.75

2.80

2.68

2.96

2.83

.09

.02

3.06

2.99

2.85

2.95

2.92

2.95

.08

.02

252

252

254

258

258

245

252

253

4

2

265

254

262

266

266

263

5

3

0.52

.54

.53

.50

.52

.52

.52

.52

.01

.01

0.54

.50

.50

.51

.49

.51

.02

.01

32

28

36

34

21

31

25

30

5

2

30

20

32

32

33

29

5

2

Friant

171

169

182

179

186

170

178

176

7

6

Bishop

187

185

181

188

186

185

3

7

Pumice Member (of the Turlock Lake Formation) and correlative

5.4 24.1 50.8 20 3.57 0.04 0.53 3.42 2.39

5.3 25.0 52.2 17 3.56 .06 .52 3.53 2.40

5.7 22.6 48.7 19 3.64 .04 .58 3.57 2.48

5.1 23.6 50.9 19 3-59 .04 .55 3.61 2.49

5.3 22.6 51.9 20 3.64 .05 .55 ND 2.40

5.3 25.2 51.9 20 3.53 .06 .52 3.28 2.29

5.6 21.6 48.6 18 3.61 .04 .55 3.70 2.54

5.4 23.5 50.7 19 3.59 .05 .54 3.52 2.43

.2 1.3 1.5 1 .04 .01 .02 .15 .08

.1 .5 .6 2 .01 < .005 .03 .09 .03

ashes

0.30

.31

.37

.35

.32

.33

.31

.33

.03

.02

3.64

3.56

3.57

3.46

3.64

3.48

3.53

3.55

.07

.06

1.91

1.91

2.00

1.96

1.96

1.87

2.04

1.95

.06

.01

19.4

19.0

19.5

19.2

19.5

18.5

20.1

19.3

.5

.2

6.08

6.08

6.38

6.18

6.09

5.80

6.50

6.16

.23

.05

ash at the Insulating Aggregates quarry (8) and correlative ashes

6.0 19.4 47.1 20 3.74 0.04 0.56 4.10 2.70

5.9 18.7 42.9 17 3.59 .04 .58 3.99 2.66

5.4 20.3 46.6 18 3.60 .03 .57 3-74 2.55

5.4 20.0 46.8 20 3.65 .04 .57 4.02 2.64

5.6 20.2 46.2 17 3.62 .04 .58 3.91 2.64

5.7 19.7 45.9 18 3.64 .04 .57 3.95 2.64

.3 .7 1.7 2 .06 < .005 .01 .14 .06

.1 .5 .7 1 .02 .01 .03 .10 .04

0.37

.36

.34

.37

.35

.36

.01

.02

3.74

3.79

3.67

3.60

3.67

3.69

.07

.07

2.15

2.10

2.04

2.10

2.08

2.09

.04

.01

21.0

21.0

19.8

20.8

20.2

20.6

.5

.1

6.69

7.44

6.53

6.70

6.68

6.81

.36

.06

Bishop ash at Owens River Gorge (13) and at Red's Meadow (14) and correlative ashes

13

14

15

16

X

s

a.a.e.

3.17

3.22

3.20

3.16

3.19

.03

.03

281

274

272

279

277

4

3

0.55

.50

.50

.51

.52

.02

.01

66

33

29

27

39

18

3

200

185

195

202

196

8

8

6.1 18.5 42.2 20 3.89 0.04 0.60 4.21 2.84

6.1 18.3 42.1 18 3.77 .03 .63 3.98 2.87

6.1 17.7 42.6 19 3.74 .03 .61 4.27 2.77

6.2 18.1 43.4 17 3.79 .03 .65 4.26 2.80

6.1 18.0 42.6 19 3.78 0.03 0.62 4.18 2.82

.1 .4 .6 1 .08 .01 .02 .14 .04

.2 .5 .7 1 .01 .01 .03 .08 .04

0.37

.41

.39

.42

.40

.02

.02

3.92

3.99

3.84

3-74

3.87

.11

.07

2.18

2.25

2.25

2.27

2.24

.04

.01

21.4

21.9

21.9

22.0

21.8

.3

.2

7.13

7.19

7.22

7.20

7.14

.08

.06

Glass Mountain-D ash bed (17, 17a-c) and correlative ash, Ventura area (18)

17

17a'

17b

17c

18

X

s

a.a.e.

2.91

2.91

2.90

2.95

3.01

2.94

.05

.03

276

ND

ND

ND

301

289

 

2

0.50

.52

.51

.51

.58

.52

.03

.01

29

34

26

31

39

32

5

1

189

186

184

186

186

186

2

5

5.7 24.0 53.2 22 4.15 0.02 0.63 3.98 2.74

5.3 24 58 26 4.6 .07 .59 ND 2.8

5.3 23 53 22 4.0 .02 .58 ND 2.8

5.6 24 55 23 4.1 .12 .59 ND 2.9

5.4 22.7 54.9 22 4.34 .02 .64 4.22 2.77

5.5 23.5 54.8 23 4.2 .05 .61 4.10 2.80

.2 .6 2.0 2 .2 .04 .03 .06

.2 .3 .7 2 .04 .005 .02 .09 .05

Glass Mountain-G ash bed (19) and correlative ash, Ventura area (20, 21

19

20

21

21a

21b

21c

21d

X

s

a.a.e.

3.09

3.00

2.87

2.98

2.87

2.94

2.96

2.96

.08

.03

313

316

348

ND

ND

ND

ND

326

__

4

0.54

.53

.54

.57

.55

.56

.56

0.55

.01

.01

36

(111)

27

37

29

31

31

31

4

2

211

204

210

188

201

191

203

200

9

5

6.0 22.2 52.6 21 4.48 0.03 0.71 4.51 3.00

6.0 22.8 57.9 24 4.33 .02 .69 ND 2.90

6.6 22.3 52.3 23 4.50 .03 .75 4.68 3.21

6.9 23 60 28 5.0 .05 .73 ND 3.3

6.5 22 53 22 4.5 .04 .73 ND 3.3

6.5 22 50 21 4.3 .04 .64 ND 3.3

7.1 22 52 22 4.4 .04 .75 ND 3.3

6.5 22.3 54.0 23 4.5 .04 0.71 4.60 3.19

.4 .4 3.6 2 .2 .01 .04 .17

.2 .3 .7 2 .04 .01 .03 .13 .06

0.38

.36

.38

.39

.38

.38

.01

.01

, 21a-d)

0.42

.40

.45

.49

.46

.46

.47

0.45

.03

.02

3.76

3.6

3.6

3.8

3.76

3.7

.1

.1

4.04

4.00

3.98

4.2

4.0

4.0

3.9

4.02

.09

.06

2.09

2.11

1.98

2.10

2.19

2.09

.08

.03

2.31

2.26

2.52

2.52

2.56

2.41

2.76

2.47

.17

.04

19.7

19.0

19.2

19.6

19.5

19.4

.3

.2

22.0

21.7

22.7

23.5

23.1

22.6

23.8

22.8

.8

.2

6.55

ND

6.1

6.3

6.65

6.4

.2

.1

7.27

6.60

7.48

ND

8.2

6.7

9.0

7.5

.9

.12
14 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Table 1. Nuetron-aetivation analysis of volcanic glass from late Cenozoic tephra

Sample

number

22

22a

23

23a

23b

23c

23d

24

24a

24 b

24o

25

26

26a

5?

s

a.a.e.

So

2.68

2.73

2.68

2.82

2.67

2.74

2.78

2.68

2.70

2.70

2.67

2.66

2.72

2.79

2.72

.05

.03

Mn

426

ND

438

ND

ND

ND

ND

426

ND

ND

ND

428

444

ND

432

8

3

Fe

0.57

.58

.50

.53

.48

.50

.50

.52

.51

.53

.51

.55

.55

.57

0.53

.03

.01

Zn2

Bailey

30

36

27

30

29

34

34

31

30

29

32

37

27

31

31

3

2

Rb

of east-central and southern California. Continued

Cs La Ce Nd2 Sm Eu2 Tb Dy2 Yb Lu

ash, South Mountain (22, 22a, 23, 23a-d) and Ventura (24, 24a-o, 25, 26, and

227

256

229

244

233

240

249

233

231

222

241

223

237

233

236

10

6

8.1 20.2 45.8 19 4.36 0.04 0.77 5.14 3.71 0.

8.1 19 45 20 4,2 .08 .76 ND 3.8

8.4 17.2 42.6 19 4.36 .03 .73 5.14 3.95

8.5 20 49 17 (5.5) (.21) .81 ND 4.0

7.7 17 41 19 4.0 .05 .75 ND 3.9

8.0 18 41 21 4.0 .06 .75 ND 3.9

8.8 18 42 18 4.3 .06 .79 ND 4.1

8.0 20.1 48.4 21 4.44 .04 .81 5.03 3.78

8.3 20 46 19 4.2 .05 .76 ND 3.8

8.0 20 47 21 4.1 .06 .79 ND 3.8

8.4 20 47 18 4.3 .06 .79 ND 3.8

7.7 20.0 47.1 20 4.35 .03 .78 5.27 3.81

8.4 17.4 42.4 19 4.35 .04 .85 5.23 3.90

8.8 17 42 19 4.1 .05 .80 ND 3.8

8.2 18.9 44.7 19 4.24 .05 .78 5.16 3.86

.3 1.3 2.8 1 .15 .01 .03 .09 .10

.2 .3 .7 2 .03 .01 .03 .10 .06

26a)

50

55

54

56

55

55

58

51

54

53

55

51

55

57

54

02

01

Hf

areas

4.01

4.1

4.28

4.3

4.1

4.0

4.2

4.14

4.2

4.2

4.1

4.17

4.16

4.2

4.15

.09

.08

Ta

3.02

3.04

3.14

3.05

2.87

2.97

3.27

3.08

2.95

2.79

3.25

3.08

3.19

3.19

3.06

.14

.05

Th

26.7

26.7

27.6

27.8

26.1

26.9

28.4

26.7

26.4

26.0

27.3

26.7

27.5

27.9

27.1

.7

.3

U

8.95

8.8

9.42

ND

8.2

8.2

10.4

8.86

8.7

8.5

10.2

9.13

9.56

9.6

9.1

.7

.14

Thin white ash below the Bailey ash, South Mountain area

27

a.e. 8

4.47

.03

472

3

0.52

.01

54

3

245

9

7.5 17.2 48.7 22 5.28 0.04 0.78 5.14 3.26 0.

.2 .4 .6 1 .01 .01 .03 .07 .04

43

02

4.55

.08

3.21

.01

18.7

.1

9.20

.05

Upper white ash, Manix basin, Mojave Desert

28

29

X

a.a.e.

3.76

3.67

3.72

.02

346

354

350

3

Middle white

30

31

32

33

34

5!

s

a.a.e.

4.89

4.95

4.86

4.92

4.66

4.86

.11

.03

688

696

698

701

701

697

5

5

0.52

.50

0.51

.01

ash,

0.45

.44

.46

.45

.46

.45

.01

.01

42

36

39

3

192

197

192

4

Manix basin,

48

51

52

50

61

52

5

3

317

315

327

321

323

318

9

10

5.8 19.5 49.9 20 4.59 0.01 0.57 3.83 2.60 0.

5.8 18.4 48.8 22 4.47 .01 .61 4.03 2.50

5.8 19.0 49.4 21 4.53 .01 .59 3.93 2.56 0.

.2 .6 .6 1 .02 < .005 .03 .11 .03

Mojave Desert (30-33), and ash in the lacustrine Waucoba Beds of Hopper

10.3 17.1 51.0 25 6.30 < 0.005 1.08 7.0 4.34 0.

10.8 17-3 51.5 21 6.44 < 0.005 1.00 6.7 4.46

11.1 17.5 52.3 27 6.33 .02 1.04 7.1 4.52

10.6 16.9 52.3 27 6.37 .03 1.04 7.2 4.38

10.7 16.0 45.3 24 6.00 .06 1.06 6.9 4.38

10.7 17.0 50.5 25 6.29 .02 1.04 7.0 4.42

.3 .6 2.9 2 .17 .02 .03 .2 .07

.2 .5 .7 1 .02 .01 .04 .1 .05

39

34

37

02

4.17

4.12

4.15

.07

(1947), E.

56

64

60

58

58

59

,03

,03

5.73

5.85

5.81

5.91

5.53

5.77

.15

.09

2.39

2.36

2.38

.01

Owens

4.57

4.67

4.71

4.74

4.61

4.66

.07

.02

17.9

18.1

18.0

.2

Valley

29.5

30.2

29.7

29.7

30.5

29.9

.4

.2

7.38

7.22

7.30

.06

(34)

13.51

13.78

13.49

13.37

13.24

13.48

.20

.10

Ash in late Cenozoic lake beds of Searles Valley

35

a.e. 8

2.86

.02

607

8

0.51

.01

36

2

174

6

5.8 23.3 50.7 19 3.92 0.12 0.66 ND 2.86 0.

.1 .5 .7 1 .01 .01 .03 .04

,36

,02

3-51

.06

2.23

.01

17.0

.1

4.84

.04

Unwelded, pumioeous ash-flow tuff in the Coso area

36

a.e.

2.48

.02

484

4

0.36

.01

23

2

228

10

10.7 6.2 15.8 7 0.99 0.09 0.16 1.34 1.67 0.,26

.2 .3 .5 1 .01 .01 .02 .11 .03 .01

3.60

.06

1.59

.01

16.5

.1

7.75

.05

ASHES HAVING CHEMICAL AFFINITY TO TEPHRA OF THE YELLOWSTONE AREA, WYOMING

Uppermost

37

38

39

*

a.a.e.

1.33

1.33

1.29

1.32

0.01

259

290

270

273

5

1.05

1.15

1.05

1.08

.01

ash (ash

94

94

90

93

7

A), Teoopa area (37, 38) and Lava Creek B ash bed (Pearlette-type 0 ash bed)

222

199

235

219

8

, Grand Co.

4.2 81 160 66 12.47 0.37 2.08 14.27 8.35 1.11

3.7 92 182 73 13.39 .59 2.10 13.89 7.91 1.00

4.0 83 161 63 12.60 .41 2.05 14.20 7.95 1.11

4.0 84 168 67 12.63 0.46 2.08 14.25 8.07 1.06

.11 22 .09 .01 .09 .15 .08 .03

8.50

9.26

8.59

8.78

.10

, Utah

4.29

3.84

4.03

4.05

.03

(39)

30.0

29.2

29.0

29.4

.2

6.62

5.77

6.29

6.13

.06
DISCUSSION OF SPECIFIC CORRELATIONS 15

Table 1. Nuetron-activation analysis of volcanic glass from late Cenozoio tephra

Sample 1 

number

40 

40A 10

x

a.a.e.

41 

42

x

a.a.e.

So

1.70 

1.74

1.72

.02

Lower

1.77 

1.68

1.73

.02

Mn

240 

244

242

3

gray ash.

287 

281

284

3

Fe

0.99 

1.03

1.01

.02

, Man ix

1.21 

1.20

1.21

.02

Zn 2

69 

69

69

3

basin

106 

103

105

3

Lowermost gray ash,

43 

44 

44a 

45

X

3

a.a.e.

46

a.e.

47

a.e.

48 

48A

X

a.a.e.

1.74 

1.75 

1.71 

1.80

1.75 

.04 

.02

1.41

.02

1.05

.02

.91 

.87

.89 

.02

301 

305 

ND 

310

305 

5 

2

251

3

284

3

281 

283

282

3

1.24 

1.25 

1.24 

1.28

1.25 

.02 

.02

1.02

.02

.95

.02

.90 

.86

.88 

.02

122 

120 

104 

125

118 

9 

3

48

3

42

3

41 

36

39 

3

Rb

Mesa

264 

268

266

13

(41), and

201 

211

206

8

of east-central and southern California. Continued

Cs La Ce Nd 2 Sm Eu2 Tb Dy2 Yb Lu Hf Ta Th U

Falls ash bed (Pearlette-type S ash bed), Harlan County, Nebraska'

4.6 81 161 58 11.41 0.40 1.92 13-00 7.53 

4.6 83 161 60 11.50 .'12 1.88 13.20 7.68

4.6 79 161 59 11.01 0.41 1.90 13.20 7.61

.11 22 .02 .01 .06 .17 0.08

Huckleberry Ridge ash bed (Pearlette-type B ash bed), Borchers

3.7 92 181 73 13.78 0.69 2.20 13.9 7.93 

3.5 96 187 74 13.95 .72 2.13 14.5 7.89

3.6 92 184 74 13.54 0.71 2.17 14.38 7.91

.11 22 .03 .01 .08 .17 .08

1.09 

1.04

1.03

.04

locality,

1.08 

1.15

1.09

.04

South Mountain area (43), and gray ash (ash C) 11 , Teoopa area (Huckleberry Ridge?

196 

189 

189 

192

192 

3 

8

111

6

105

5

101 

103

102 

5

3.0 104 203 78 14.45 0.82 1.98 13.91 7.62 

2.8 102 189 78 14.29 .81 1.98 13.37 7.05 

2.9 102 188 78 13.99 .81 1.98 ND 7.22 

3.2 102 202 80 14.28 .89 2.03 13.60 7.62

3.0 103 196 79 14.25 0.83 1.99 13.63 7.38 

.21 81 .19 .04 .03 .27 .29 

.11 22 .05 .01 .05 .12 .07

TEPHRA HAVING CHEMICAL AFFINITIES TO OTHER VOLCANIC PROVINCES

Air-fall pumice of the Coso area

2.9 25.1 44.4 16 2.31 0.49 0.20 1.60 1.03

.1 0.6 .8 1 .01 .01 .02 .10 .03

2.6 24.1 44.1 14 1.97 .44 .20 1.48 .91

.1 .6 .7 1 .01 .01 .02 .11 .03

2.8 24.4 45.9 13 1.87 .41 .15 1.25 .85 

2.7 25.3 43.6 14 1.82 .41 .15 1.17 .86

2.8 24.9 44.8 14 1.85 .41 .15 1.21 .86 

.1 .6 .7 1 .01 .01 .02 .10 .03

1.03 

1.00 

.98 

1.05

1.02 

.03 

.03

0.17

.02

.12

.01

.13 

.14

.14 

.01

7.11 

7.20

7.16

.10

3.79 

3.81

3.80

.02

Meade County

9.51 

9.10

9.31

.12

ash

9.39 

8.97 

9.25 

9.60

9.30 

.26 

.11

3.74

.07

3.91

.08

3.81 

3.60

3.71 

.07

3.53 

3.56

3.55

.02

bed) (44,

3.30 

3.01 

3.13 

3.25

3.17 

.13 

.02

0.66

.01

.71

.01

.74 

.72

.73 

.01

33.9 

34.1

34.0

.2

, Kansas

29.9 

29.8

29.9

.1

45)

28.6 

27.8 

27.5 

28.1

28.0 

.5 

.2

7.95

.06

7.67

.06

8.19 

8.16

8.18 

.06

7.25 

7.37

7.03

.05

(42)

6.24 

6.17

6.21

.06

5.70 

5.57 

5.25 

5.63

5.54 

.20 

.07

2.49

.04

2.34

.04

2.48 

2.44

2.46 

.04

Ash in Searles Valley

49

a.e.

2.46

.02

479

4

0.79

.02

43

2

88

4

4.5 19.8 39.3 17 3.14 0.57 0.44 3.14 2.51

0.1 .4 .6 1 .01 .01 .02 .12 .31

0.36

.02

4.30

.70

0.50

< .005

8.74

.06

3.90

.04

Pumice overlying the Cahuilla beds, Salton trough

50

a.e.

3.88

.03

403

3

1.90

.03

68

5

137

8

4.0 45.9 107 51 12.18 1.76 0.40 16.7 12.1

.1 .6 1 2 .02 .02 .05 .1 .1

1.72

.05

12.8

.2

1.75

.01

19.1

.2

5.40

.04

Sample numbers are the same as in fig. 1.

These elements were not used in calculation of the similarity coefficient and other statistical sample comparisons. 

^Samples with a number designation only were analyzed at Lawrence Berkeley Laboratory, by H. W. Bowman, Frank Asaro, and Helen Michael.

Average of sample group. 

^Standard deviation of group.

Average analytical error based on counting statistics. Generally taken as plus or minus one sigma of the mean.

'Samples with a number followed by a small letter designation are splits of single samples designated by number only, and were analyzed 

at the U.S. Geological Survey, Radiochemistry Laboratory, Reston, Va. , by J. J. Rowe and P. A. Baedecker. Concentrations

for these samples are predicted (y) values from regression analysis of 22 sample pairs analyzed jointly by Lawrence Berkeley Laboratory (x) 

and the U.S. Geological Survey Radiochemistry Laboratory, Reston, Va. (y). 

^Analytical error for a single analysis. 

9 Izett and others (1972).

Samples with a number followed by a capital letter designation are splits of a single sample analyzed by Lawrence Berkeley Laboratory. 

''Sheppard and Gude (1968).
16 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Table 2. Electron microprobe analysis of volcanic glass from late Cenozoio

[Concentral 

Oxide

Sample Si02 A12 03 Fe 2 03 1

tephra of east-central and southern California.

;ions in oxide weight percent except for Cl and P, which are in atomic weight percent, 

concentrations are recalculated to totals of 100 percent. C. E. Meyer, analyst.]

MgO MnO CaO BaO Ti02 Na20 K20 Cl P Total2 Total 3

ASHES HAVING CHEMICAL AFFINITY TO TEPHRA OF THE LONG VALLEY-GLASS MOUNTAIN AREA 

Friant Pumice Member (of the Turlock Lake Formation) (1, 1A , 1B), and correlative ashes

1 

1A 

1B 

2 

3 

4 

5 

6

x 6 

3 1

77.34 

77.90 

77.58 

77.18 

77.81 

77.28 

78.00 

77.49

77.57 

0.30

12.68 

12.45 

12.87 

12.89 

12.22 

12.88 

11.71 

12.97

12.58 

0.44

0.76 

.75 

.77 

.79 

.79 

.79 

.78 

.79

.78 

.02

0.04 0.05 0.45 0.00 0.08 3. 60 4.99 ND5 0. 

.03 .05 .45 .00 .06 3.53 4.77 ND 

.03 .02 .46 .00 .07 3.72 4.43 0.05 

.06 .05 .48 .00 .06 3.92 4.51 .06 

.04 .04 .47 .02 .05 3.72 4.80 ND 

.04 .03 .49 .00 .07 3.84 4.53 .06 

.03 .03 .47 .01 .07 3.47 5.39 .05 

.04 .05 .46 .00 .07 4.48 3.60 .07

.04 .04 .47 .00 .07 3.79 4.63 .06 

.01 .01 .01 .01 .01 0.32 0.52 .01

00 

01 

ND 

ND 

04 

ND 

ND 

ND

93.34 

96.44 

94.58 

93.44 

94.29 

93.75 

92.08 

93.07

93.87 

1.29

99.99 

100.00 

100.00 

100.00 

100.00 

100.01 

100.01 

100.02

Bishop ash at Insulating Aggregates quarry (8) and correlative ashes

8 

10 

11 

12

X

s

77.37 

77.35 

78.15 

77.31

77.55 

0.40

12.72 

12.84 

11.87 

12.81

12.56 

0.46

0.75 

.78 

.69 

.79

.75 

.06

0.04 0.04 0.45 0.00 0.06 3.34 5.22 ND 0. 

.02 .03 .46 .00 .05 4.10 4.31 0.06 

.02 .02 .44 .00 .07 4.11 4.58 .04 

.04 .05 .47 .00 '.05 4.58 3.84 .07

.03 .04 .46 .00 .06 4.03 4.49 .06 

.01 .01 .01 .00 .01 0.51 0.58

00 

ND 

ND 

ND

94.17 

92.93 

89.02 

92.66

92.20 

2.22

99.99 

100.01 

99.99 

100.01

Bishop ash at Red's Meadow (14) and ash at Onion Cr., Grand Co., Utah (16)

14 

16

77.33 

77.50

12.86 

12.73

0.77 

.77

0.04 0.02 0.4? 0.00 0.05 4.10 4.28 0.04 

.03 .05 .45 .01 .07 3-88 4.44 .07

ND 

ND

95.64 

93.10

100.00 

100.00

Glass Mountaln-D ash bed (17) and correlative ash, Ventura area (18)

17 

18

77.91 

77.19

12.24 

12.86

0.74 

.80

0.03 0.05 0.41 0.00 0.06 3.53 5.00 ND 0. 

.04 .05 .42 .01 .07 3.89 4.60 0.06

01 

ND

95.64 

93.11

99.99 

99.99

Glass Mountain-G ash bed (19) and correlative ash, Ventura area (21)

19 

21

77.24 

77.12

12.90 

12.66

0.83 

.86

0.03 0.03 0.43 0.00 0.05 3.85 4.57 0.05 

.04 .10 .43 .00 .07 3.55 5.16 ND 0.

ND 

02

94.56 

93.56

100.00 

100.01

Bailey ash, South Mountain (22, 23) and Ventura (24, 25) areas

22

23 

24 

25

X

s

77.32 

77.06 

77.23 

76.98

77.15 

0.16

12.32 

12.91 

12.92 

12.99

12.79 

0.31

0.83 

.81 

.80 

.82

.82

.01

0.03 0.05 0.51 0.00 0.06 3.83 5.03 ND 0. 

.04 .05 .49 .02 .05 3.89 4.63 0.06 

.03 .04 .48 .01 .06 3.83 4.55 .06 

.03 .04 .47 .00 .05 3.88 4.67 .06

.03 .05 .49 .01 .06 3.86 4.72 .06 

.01 .01 .02 .01 .01 0.03 0.21

01 

ND 

ND 

ND

92.05 

93.42 

93.20 

93.43

93.03 

0.66

99.99 

100.01 

100.01 

99.99

Thin white ash below the Bailey ash, South Mountain area

27 76.77 12.87 0.79 0.03 0.05 0.31 0.00 0.05 3.94 5.14 0.06 ND 94.03 100.01
DISCUSSION OF SPECIFIC CORRELATIONS 17

Table 2. Electron microprobe analysis of volcanic glass from late Cenozoic

Sample Si02 A1 203 Fe 20o 1 

number

tephra of east-central and southern California. Continued

MgO MnO CaO BaO Ti02 Na20 K20 Cl P Total2 Total 3

Middle white ash, Manix basin, Mojave Desert (33), 

and ash in the lacustrine Waucoba Beds of Hopper (1947), E. Owens Valley (34)

33 78.33 11.99 0.71 

34 77.48 12.34 .68

0.02 0.09 0.34 0.01 0.07 4.68 3.72 0.03 ND 91.30 

.03 .09 .32 .01 .05 3.61 5.35 .04 ND 93.25

99.99 

100.00

Ash in late Cenozoic lake beds of Searles Valley

35 78.57 12.98 0.82 0.03 0.05 0.50 0.01 0.06 5.27 1.69 ND 0.01 90.71 99.99

Unwelded, pumiceous ash-flow tuff in Coso area

36 77.04 12.66 0.56 0.02 0.07 0.74 0.00 0.04 3.07 5.79 0.00 ND 91.00 99.99

ASHES HAVING CHEMICAL AFFINITY TO TEPHRA OF THE YELLOWSTONE AREA, WYOMING

Lava Creek B ash bed (Pearlette-type 0 ash bed), Grand Co., Utah 8 (39), 

and ash in Christmas Canyon Fm. , Searles Valley (51)

39 76.85 12.21 1.57 

51 77.00 11.76 1.75

0.02 0.03 0.54 0.00 0.10 3.57 4.98 0.12 ND 94.02 

.02 .03 .56 .02 .12 3.45 5.18 .11 ND 92.95

99.99 

100.00

o

Mesa Falls ash bed (Pearlette type S ash bed), Harlan County, Nebraska

40 76.79 12.24 1.49

Lowermost

41 75.97 12.95 1.69 

42 76.51 12.25 1.78

Lowermost gray ash

43 76.52 12.11 1.90 

44 76.40 11.90 2.01 

45 75.94 12.47 1.94

x 76.28 12.16 1.95

0.04 0.03 0.58 0.00 0.11 3.21 5.41 0.11 ND 94.14

gray ash, Manix basin (41) and Huckleberry Ridge ash bed (Pearlette type B ash bed), 

Borchers locality, Meade Co., Kansas (42)

0.03 0.03 0.61 0.02 0.13 4.06 4.36 0.15 ND 94.84 

.02 .05 .58 .03 .12 3.34 5.21 .12 ND 93.98

, South Mountain area, Huckleberry Ridge? ash bed (43), and ash (ash C)9 t Tecopa area (44,

0.02 0.05 0.60 0.05 0.10 3.63 5.01 ND 0.01 94.19 

.03 .03 .64 .04 .14 2.85 5.94 ND 0.02 93.58 

.02 .03 .64 .04 .12 3-45 5.23 0.12 ND 93.99

.02 .04 .63 .04 .12 3.31 5.39 93.92

100.00

100.00 

100.01

45)

100.00 

99.98 

100.00

TEPHRA HAVING CHEMICAL AFFINITIES TO OTHER VOLCANIC PROVINCES 

-Air-fall pumice of the Coso area

46 75.65 13.17 1.43 

48 75.68 13.35 1.32

0.23 0.06 1.23 0.14 0.14 3.42 4.49 0.05 ND 90.85 

.19 .02 1.19 .12 .14 3.53 4.44 .03 ND 91.84

100.01 

100.01

Ash in Searles Valley

49 75.65 13.87 1.17 0.22 0.07 0.83 0.10 0.20 3.42 4.32 0.15 ND 95.42 100.00

1 Total iron as Fe 20o 

Original totals. These are low due to presence of water as well as other volatiles, such as C0 2 , in the glass. 

3 Totals recalculated to 100 percent. 

Samples 1A and 1B are replicate analyses of sample 1. 

j? ND not determined. 

Group average. 

' Standard deviation of group.

° T^ot-f =nH ^l-Viar-o , 1 Q7 3 . 

9 Sheppard and Gude (1968).
18 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

[Values given are normalized, integrated peak intensity counts, divided by total counts 

in each of two spectral regions: 2.96 to 9.01 kev for elements Ca through Zn, and 12.

for elements Rb through Nb. Resultant ratios are multiplied by 10,000

Sample

38h

38g

38f

38e

38d

38c

38b

38a

39

51

52

53

9a

Ca

33

35

33

33

33

.,

34

33

34

33

37

30

50

Ti

92

91

92

91

92

92

91

83

83

92

87

86

88

Mn Fe

118 948

117 947

121 943

120 9H8

117 948

171 791

117 951

117 917

114 940

120 9H2

121 932

113 937

181 789

Cu

41

42

H2

43

43

121

44

44

44

142

146

41

67

Zn

192

192

187

197

190

181

193

196

197

189

190

178

158

Rb

1586

1675

1610

1618

1638

2225

1604

1729

1582

1760

1661

1608

2361

Sr

211

203

223

217

2114

338

212

198

201

212

216

220

301

Y

1109

1203

1157

1141

1151

980

1175

1216

1227

1148

1212

1174

995

Zr

2927

2772

2881

2912

2911

1837

2872

2963

2657

2937

2773

2725

1717

(peak plus background) 

32 through 17.00 kev

to give whole integers.]

Nb

1073

1063

1043

1032

1041

832

1104

1098

1118

1040

1095

1075

851

Sampled interval 

(era above base)

185-196

119-132

99-107

81-91

56-66

47-52

33-43

5-15

 

 

 

 

Color

light gray

Do.

Do.

Do.

Do.

White

light gray

Do.

Do.

Do.

Do.

Do.

White

38a through 38h - Samples of ash layers collected vertically in compound ash bed (ash A of Sheppard and Gude, 1968), in

lake beds of Pleistocene Lake Tecopa. 

39 - Lava Creek B ash bed, Grand Co., Utah

51 - Ash in pluvial lake beds of Searles Valley.

52 - Ash in marine San Pedro Formation, Ventura.

53 - Ash in lake beds of E-Clay zone, Wasco site (Davis and others, 1977), south San Joaquin Valley.

9a - Bishop ash bed (ash B of Sheppard and Gude, 1968), in pluvial lake deposits of Pleistocene Lake Tecopa.

between samples 37-38 and 38-39 are 0.92 and 0.93 (fig. 

4), respectively, considerably lower than similarity coefficients for replicate analyses from a single emplacement 

unit of this type of tephra. Eight additional samples 

were collected subsequently from this tephra bed and 

analyzed by energy-dispersive X-ray fluorescence spectrometry to test whether multiple emplacement units 

are present. Examination of spectral data for these samples (fig. 6; table 3) suggests that at least two and 

perhaps three compositional types are present in this 

ash bed. Seven of these samples are very similar to each 

other (38a, b, and d through h) and to the Lava Creek 

B ash bed. The eighth sample (38c) was collected from 

a 5-cm-thick layer of white ash within this ash bed, 47 to 

52 cm above the base. This layer contrasts with the light 

gray of the other layers in the bed. The chemical composition of glass of the white layer is quite different from 

that of the rest of the bed and is most similar to ashes 

of the Long Valley-Glass Mountain volcanic province, 

such as the Bishop ash-bed group. The presence of this 

ash in a bed correlated with the Lava Creek B ash bed 

suggests either that an eruption from Long Valley caldera occurred about 0.6 m.y. ago, at about the same 

time as the eruption of the Lava Creek B ash from the 

Yellowstone area, or that the Bishop ash has been reworked locally within the drainage basin tributary to 

Pleistocene Lake Tecopa. A thick bed of Bishop ash is 

present within the Tecopa lake beds of Sharp (1972),

Sample h g f

97 98 98 99 76 98 95

96 97 97 76 98 97

99 99 77 98 95

99 76 98 95

76 98 95

34 32 32 33 33 75 75

3 34 96

6 32

FIGURE 6. Similarity coefficient matrix comparing chemical spectra 

of glass determined by energy-dispersive X-ray fluorescence of 

ash layers (samples 38a-h) collected from the compound ash bed in 

lake beds of Pleistocene Lake Tecopa (samples 38a-h) (ash A of 

Sheppard and Gude, 1968). Upper right-half of matrix shows similarity coefficients for sample pairs, in percent (100 represents a 

match of an identical sample pair). Lower-left half of matrix 

shows standard deviation of means of ratios for each sample pair. 

See text for discussion.
DISCUSSION OF SPECIFIC CORRELATIONS 19

stratigraphically several meters beneath the Lava 

Creek B ash bed (see below). Consequently, Bishop ash 

from topographically higher parts of the drainage basin 

tributary to Lake Tecopa may have been periodically 

eroded and transported into the lake basin for some 

period of time after the eruption of the Bishop ash. The 

latter explanation is somewhat less probable than the 

former, because it requires that reworking take place 

during or shortly after deposition of the Lava Creek B 

ash bed, but not during deposition of texturally similar 

lake beds that overlie and underlie the Lava Creek B 

ash bed. The presence of this thin white ash layer within 

the compound Lava Creek B ash bed at the Tecopa locality adds a further degree of complexity to the problem of the age and correlation of the Friant Pumice 

Member of the Turlock Lake Formation and the Bishop 

ash-bed group (see below).

A sample of the ash (sample 38a) from the lower 

part of the Lava Creek B ash bed of the Tecopa area differs slightly from the other overlying samples (38b, and 

38d through 38h). Similarity coefficients comparing the 

sample from the lower part of the ash bed with the six 

other overlying samples average 0.955, but coefficients 

comparing the upper six samples to each other range 

from 0.97 to 0.98 (fig. 6). One explanation is that the two 

lower samples (38a and 38b) represent two separate 

eruptions of Lava Creek B ash. The upper ashes (samples 38d through 38h) overlying the exotic layer of Long 

Valley-Glass Mountain provenance (sample 38c) may 

represent locally reworked material, mostly composed 

of ash similar in composition to sample 38b, with 

perhaps some small amounts of glass from layers represented by samples 38a and 38c.

In addition to the massive exposures in the Lake 

Tecopa beds, the Lava Creek B ash bed has also been 

identified from the following localities (fig. 1):

(1) In Searles Valley of southeastern California, 

about 100 km west-southwest of Lake Tecopa (G. A. 

Izett, written commun., 1979; this report, sample 51).

(2) In Pleistocene marine beds near the base of the 

San Pedro Formation, east of the town of Ventura, 

Calif, (sample 52). This is the first instance in which this 

ash has been found in marine deposits and also represents the westernmost locality reported for the Lava 

Creek B ash bed. Near Ventura, the ash is 850 m below 

the top of the San Pedro Formation, estimated to be 

about 0.2 m.y. old on the basis of amino-acid-racemization age estimates (Lajoie and others, 1979; Wehmiller 

and others, 1978), and 670 m above the Bishop ash bed 

(0.73 m.y. old; see below), in the upper part of the underlying marine Santa Barbara Formation. Identification of the Lava Creek B, Bishop, Bailey, and several 

other isotopically dated ashes in the Ventura basin (see 

below) has enabled calibration of existing marine faunal

stages and estimation of sedimentation rates within the 

basin.

(3) In subsurface alluvium near Wasco, Calif, (sample 53; fig. 1). The ash sample was obtained from a core 

taken about 84 m below the surface of the southern San 

Joaquin Valley, in the "E-clay" unit correlated with the 

Corcoran Clay Member of the Tulare Formation (Davis 

and others, 1977). This ash has been previously identified as the "Bishop Tuff' (Davis and others, 1977), but 

we identify it as the Lava Creek B ash bed on the basis 

of energy-dispersive X-ray fluorescence of the glass 

(table 3), glass shard morphology, and color. Shards are 

dominantly solid-glass, bubble-wall and bubble-wall 

junction types typical of the Yellowstone tephra family, 

with very few pumiceous shards that are so typical of 

the Bishop ash-bed group. The color of this ash is light 

gray, like the Lava Creek B ash bed, and unlike the 

chalky white of the Bishop ash-bed group. All the mineral grains in ash at the Wasco locality lack glass selvages and are probably detrital. The rapid-scan X-ray 

fluorescence method used by Davis and others (1977) is 

not diagnostic for identification of many tephra families.

BISHOP ASH-BED GROUP

The Bishop ash-bed group is another important and 

widespread stratigraphic marker in the western and 

central United States (Izett and others, 1970). This ash 

was erupted from the Long Valley caldera east of the 

central Sierra Nevada in California (Gilbert, 1938; Bateman, 1965; Sheridan, 1965; Bailey and others, 1976; Hildreth, 1979). Near the source north of the town of 

Bishop, and at several localities in the vicinity of Long 

Valley, there are good exposures of a thick basal air-fall 

ash (sample localities 8, 13; fig. 1) that underlie the later 

ash flows of the Bishop Tuff. At locality 8, the air-fall 

ash has a minimum thickness of 4.5 m. Three chemical 

types of the Bishop ash, here collectively and informally 

termed the Bishop ash-bed group, are recognized on the 

basis of the chemical composition of the associated glass. 

These three types are referred to as (1) the Friant 

Pumice Member, (2) the Bishop ash at the Insulating 

Aggregates quarry (or Bishop ash, IAQ type), and (3) 

Bishop ash at Owens River Gorge and at Red's Meadow 

(or Bishop ash, ORG type). The three types are chemically very similar to each other. The small compositional 

differences among the three types may be due to zoning 

in the pre-emption magma chamber, or tephra of somewhat variable composition may have been generated 

during one eruption or during several eruptions. At 

present we do not have a sufficient number of analyses 

to determine whether compositional variations among 

these three chemical types are continuous or discontinuous.
20 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Table 4. Specific locality information.

Sample State County Quadrangle Quarter and Town Range Lat (n) Long (w) Collector(s) Field Lab 

number Section ship Number Number

Friant Pumice Member (of the Turlock Lake Formation) (1), and correlative ashes

1 Calif. Madera Millerton Lake 15' NE1/4 NE1/4, 1 10S 20E N37°00'40" W119°44'10" R. J. Janda 63cj-26 N-ASW- 2

2 do. Tulare Alpaugh 7.5' NW1/4NE1/4, 16 23S 24E N35°52'30" W119°23'15" Bureau of Reclamation 23-24-16B do. 4

3 do. Ventura Ventura 7.5' L.G. 1 N34°17'56" W119°16'58" A. M. Sarna-Wojcicki Pico-15 do. 58

4 do. do. do. do. N34°17'57" W119°15'48" do. Pico-24 do. 69

5 do. San Diego Clark Lake 15' NW1/4 NE1/4, 24 9S 5E N33°22'50" W116°24'35" R. V. Sharp ST-RT-3 do. 125

6 do. Imperial Durmid SE 7.5' NW1/4 SW1/4, 19 do. 12E N33°22'29" W115°46'07" A. M. Sarna-Wojcicki Salton-2 do. 63

7 do. do. do. do. do. do. do. do. do Salton-2A do. 117

Bishop ash at Insulating Aggregates quarry (8), and correlative ashes

8 Calif. Inyo Bishop 15' NW1/4 NW1/4, 4 6S 33E N37°27'40" W118°21'55" A. M. Sarna-Wojcicki, BT-8 N-ASW-115

J. W. Hillhouse

9 do. do. Shoshone 15' SW1/4 NE1/4, 32 22N 7E N35°58'02" W116°14'52" do. Teco-5 do. 183

10 do. Riverside Murrietta 7-5' SW1/4 NW1/4, 7 7S 3W N33°34'52" W117°14'25" M. P. Kennedy, ELSI-1 do. 75

G. A. Borchardt

11 do. do. Id'ylwild 15' SE1/4SW1/4, 32 6S 3E N33°36'00" W116°41'44" R.V. Sharp ST-RT-2 do. 124

12 do. Imperial Durmid SE 7-5' NW1/4 SW1/4, 19 9S 12E N33°22'29" W115°46'07" A. M. Sarna-Wojcicki Salton-5 do. 71

Bishop ash at Owens River Gorge (13), Bishop Tuff at Red's Meadow (14), and correlative ashes

13 Calif. Mono Casa Diablo 15' W1/2 NE1/4, 5 5S 31E N37°32'47" W118°35'26" E. W. Hildreth B-93 922K

14 do. Madera Devil's Postpile 15 N.F. 2 N37°37'35" W119°03'20" R. J. Janda J-328 N-ASW- 3

15 do. Imperial Durmid SE 7.5' NW1/4 SW1/4, 19 9S 12E N33°22'29" W115°46'07" A. M. Sarna-Wojcicki Salton-1 do. 116

16 Utah Grand Polar Mesa 15' SE1/4 NE1/4, 26 24S 24E N38°41'25" W109°14'11" R. E. Wilcox 66W5 do. 149

Glass Mountain-D ash bed (17, 17a-c) and correlative ash, Ventura area (18)

17 Calif. Inyo Bishop 15' NE1/4 NE1/4, 23 6S 32E N37°27'24" W1l8°40'25" A. M. Sarna-Wojcicki BT-2 N-ASW- 55

18 do. Ventura Ventura 7.5' L.G. N34°19'05" W119°20'43" do. Pico-23 do. 68

Glass Mountain-G ash bed (19) and correlative ashes, Ventura area (20, 21)

19 Calif. Inyo Bishop 15' NE1/4 NE1/4, 23 6S 32E N37°27'24" W118°40'25" A. M. Sarna-Wojcicki BT-1 N-ASW-101

20 do. Ventura Ventura 7.5' L.G. N34°18'10" W119°16'14" do. Pico-27 do. 129

21 do. do. do. do. N34°18'05" W119°18'14" do. Pico-14 do. 64

Bailey ash, South Mountain (22, 23), and Ventura (24, 25,

22 

23 

24 

25 

26

Calif, 

do. 

do. 

do. 

do.

Ventura 

do. 

do. 

do. 

do.

Moorpark 7.5' 

do. 

Ventura 7.5' 

do. 

Pitas Point 7.5'

NW1/4 SW1/4, 21 

NE1/4 SW1/4, 20 

L.G. 

do. 

NW1/4 SE1/4, 16

Thin white

3N 

do.

3N

20W 

do.

24W

ash below

N34°19'41" 

N34°19'34" 

N34°18'10" 

N34°18'13" 

N34°20'20"

the Bailey ash,

W118°58'37" 

W119°00'00" 

W119°18'15" 

W119°20'48" 

W119°23'33"

South Mountain

26)

A. M. Sarna-Wojcicki 

do. 

do. 

do. 

do.

Pico-4 

Pico-3 

Pico-5 

Pico-21 

Pico-18

N-ASWdo. 

do. 

do. 

do.

56 

54 

57 

67 

65

27 Calif. Ventura San.ta Paula 7.5' NE1/4 NW1/4, 27 3N 21W H3lt°19'00" W119°04'24" A. M. Sarna-Wojcicki Pico-7 N-ASW- 66

Upper white ash, Manix basin, Mojave Desert

28 Calif. San Newberry15' NW1/4 SW1/4, 11 10N 4E N34°58'23 11 W116°32'12" Richard Merriara, Manix-1 N-ASW- 41 

Bernardino J. L. Bischoff

29 do. do. do. do. do. do. do. do. A. M. Sarna-Wojcicki Manix-5 do. 113

& others

Middle white ash, Manix basin, Mojave Desert (30-33), and ash in Pleistocene lake beds (Waucoba Beds of Hopper, 1947), E. Owens Valley (34)

30 Calif. San Newberry 15' SW1/4 NW1/4, 11 ION 4E N34°58'26" W116°32'08" A. M. Sarna-Wojcicki Manix-4 N-ASW-112 

Bernardino & others

31 do. do. do. do. do. do. do. do. Richard Merriara, Manix-2 do. 42

J. L. Bischoff

32 do. do. do. NW1/4 NW1/4, 11 do. do. N34°58'44" W116°32'06" A. M. Sarna-Wojcicki Manix-7 do. 120

4 others

33 do. do. do. SW1/4 3W1/4, 2 do. do. N34°58'50" W116°32'07" do. Manix-8 do. 121

34 do. Inyo Waucoba Mt. 15' Section 18(?) 9S 34E N37°10' W118°12' D. E. Marchand W3A do. 76
DISCUSSION OF SPECIFIC CORRELATIONS 21

Table 4. Specific locality information Continued

Sample 

number State County

Quarter and TownQuadrangle Section ship Range Lat

Ash from core in lake beds

(n) Long(w) Collector(s)

5 of Searles Valley

Field Lab. 

Number Number

35 Calif. San Searles Lake 7.5' Corner of 22, 25S 43E N35°44'15" W117°19'30" G. I. Smith KM3A N-ASW-126 

Bernardino 23, 26, & 27

Unwelded, pumiceous ash flow tuff in the Coso area

36 Calif. Inyo Haiwee Reservoir 15' NE1/4 NW1/4, 13 19S 37E N36°11'55" W117°55'17" W. A. Duffield, 9-85~2A

C. R. Bacon

Uppermost ash (ash A), Tecopa area (37, 38), and Lava Creek B ash bed (Pearlette-type 0 ash bed), Grand Co., Utah (39)

37 Calif. Inyo Shoshone 15' NW1/4 NW1/4, 31 21N 6E N35°58'16" W116°16'28" A. M. Sarna-Wojcicki, Teco-3 N-ASW-181

J. W. Hillhouse

38 do. do. do. do. do. do. do. do. do. do. Teco-4 do. 182

39 Utah Grand Polar Mesa 15' SE1/4 NE1/4, 26 24S 24E N38°4l'25" W109°14'11" R- E. Wilcox 67W104 do. 150

Mesa Falls ash bed (Pearjette-type S ash bed), Harlan County, Nebraska

HO Nebr. Harlan Stamford 7.5' SW1/4 NW1/4, 12 2N 2W N40°09'19" W99°32'30" R. E. Wilcox 66W4 N-ASW-147 

do. do. do. do. do. do. do. do. do. do. do. 148

Lower gray ash, Manix basin (41) and Huckleberry Ridge ash bed (Pearlette type B ash bed), Borchers locality, Meade County, Kansas, (12)

41 Calif. San Newberry 15' NW1/4 NW1/4, 11 10N 4E N34°58'44" W116°32'06" A. M. Sarna-Wojcicki Manix-6 N-ASW-114

Bernardino & others

42 Kansas Meade Irish Flats NE 7.5' NW1/4 NE1/4, 21 33S 28W N37°10'08" W100°22'08" R. E. Wilcox 68W98 do. 151

Huckleberry Ridge(?) ash bed; lowermost ash, South Mountain area (43), and ash (ash C), Tecopa area (44, 45)

43 Calif. Ventura Santa Paula 7.5' N1/2, 28 3N 21W N34°18'50" W119°05'13" A. M. Sarna-Wojcicki ASW-3-23 N-ASW- 70

-75-1

44 do. Inyo Tecopa 15' SE1/4 SE1/4, 23 21N 7E N35°54' W116°11' M. 0. Woodburne 1; Teco-1 do. 73

45 do. do. do. NE1/4 SE1/4, 23 do. do. do. do. do. 2; Teco-2 do. 74

Air-fall pumice of the Coso area

46 Calif. Inyo Haiwee Reservoir 15' SE1/4 NE1/4, 35 21S 38E N36°03'57" W117°50'22" W. A. Duffield, 13-42-5 N-ASW-118

C. R. Bacon

47 do. do. do. do. do. do. do. do. do. 13-U2-4 do. 119

48 do. do. do. NE1/4 NE1/4, 23 21S 38E N36°05'58" W117°50'04" do. 9-8-11; do. 122

Cos o-1 

do. do. do. do. do. do. do. do. do. do - do. 123

Ash in Searles Valley

49 Calif. San Searles Lake 15' N.R. 3 N35°33'19" W117°17'41« G. I. Smith AXL-30K- N-ASW-176 

Bernardino 160-5

Pumice overlying Cahuilla beds, Salton trough

50 Calif. Imperial Durmid 7.5' SE1/4 NE1/4, 24 9S 11E N33°22'50" W115°46'05" A. M. Sarna-Wojcicki Salton-7 N-ASW- 72

Samples of Lava Creek B ash bed analyzed by energy-dispersive X-ray fluorescence only

51 Calif. San Searles Lake 15' N.R. 3 28s 43E N35°31'12" W117°22'56" G. I. Smith 2V-198-4 

Bernardino

52 do. Ventura Saticoy 7.5' L.G. 3N 22W N34°17'54" W119°13'44" A. M. Sarna-Wojcicki P-133

53 do. Kern Pond 7.5' ND4 25S 25W N35°40' W119°20' Paul Davis, P5-23

James Smith

Land grant, 

National Forest, and

3Naval Reserve: no township and range coordinates on available maps. 

Not determined.
22 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

FRIANT PUMICE MEMBER (OF THE 

TURLOCK LAKE FORMATION)

Ash and pumice are exposed in quarries near the 

town of Friant in east-central San Joaquin Valley, about 

110 km west-southwest of the Long Valley caldera. According to Janda (1965, p. 110),

the pumiceous alluvium in the quarries of the California Industrial 

Minerals Company*** lies near the base of the alluvium deposited 

during the youngest aggradational cycle of the Turlock Lake Formation. In these quarries, 60 feet [18 m] of rhyolitic ash and pumice rest 

on a weathered surface that has 25 feet [8 m] of relief developed on 

sand and silt of an older part of this alluvial unit. The lower 10 to 30 

feet [3 to 9 m] of the rhyolitic material consists of flat-lying, remarkably even beds of fine ash 1 to 30 mm thick. The rhyolitic alluvium is 

progressively coarser, more impure, and thicker-bedded upward in 

the section. Large scale fluviatile cross-bedding is present. The upper 

30 feet [9 m] of the deposit commonly contains light-gray to grayishpink pumice pebbles 25 to 50 mm in diameter.

Sample 1 (figs. 1, 2; table 1) is from pumice pebbles 

picked from the coarser, upper part of the gravelly alluvium (R. J. Janda, oral commun., 1972). Sample 2, a 

fine ash, is from a Bureau of Reclamation borehole some 

120 km to the south, near the town of Alpaugh. At this 

locality, the ash is interbedded with lacustrine clays of 

the Corcoran Clay Member. Although the Turlock Lake 

Formation overlies the Corcoran Clay Member in the 

Friant area, the Turlock Lake Formation probably 

grades laterally into the Corcoran Clay Member to the 

south, in the vicinity of Alpaugh, because the tephra at 

these two localities is essentially identical. The similarity coefficient comparing samples 1 and 2 is 0.98 (fig. 4).

The age of the Friant Pumice Member is about 

0.62 ±0.02 m.y.2, as determined by K-Ar analysis of 

sanidine separated from pumice cobbles at the quarry 

locality (Janda, 1965). As discussed below, pumice and 

associated ash of the Friant Pumice Member is chemically and petrographically very similar to the Bishop 

Tuff, dated at about 0.73 m.y. (Dalrymple and others, 

1965). An Irvingtonian vertebrate fauna is found 

stratigraphically below the Friant Pumice Member 

(Janda, 1965; J. Firby-Durham, oral commun., 1974).

Other sites where ash chemically similar to that of 

the Friant Pumice Member has been found are:

(1) In the Salton trough, where it is interbedded in 

a 2-m-thick composite ash bed in the highly deformed 

lacustrine Borrego Formation of Tarbet and Holman 

(1944) east of the Salton Sea, adjacent to the San Andreas fault (samples 6 and 7; figs. 1, 2; table 1).

2Janda (1965) cites a K-Ar age of 0.60 ±0.02 m.y. for this pumice unit based on written 

communication with Dalrymple in 1963. We have multiplied this age by 1.0268 to correct for 

the new I.U.G.S. decay constants (Mankinen and Dalrymple, 1979), and all subsequent K-Ar 

ages cited in this report are corrected. Dalrymple (1980) cites two K-Ar ages (corrected) for 

the Friant Pumice Member: O.618±0.031 and 0.612±0.031 m.y., both from sanidine separates.

(2) In the Anza-Borrego area of the southern Peninsular Range, west of the Salton trough, where it is interbedded with fluvial sand, gravel, and lacustrine silt 

and clay of the Bautista Beds of Frick (1921) (sample 5; 

figs. 1, 2; table 1; R. V. Sharp, written commun., 1978).

(3) Near the town of Ventura in the western Transverse Ranges, in deformed, well-bedded marine silts 

and clays of the Santa Barbara Formation (samples 3, 4; 

figs. 1, 2; table 1). According to Natland (1952), the 

stratigraphic interval within which this ash bed is 

situated is close to the boundary between the Hallian 

and Wheelerian foraminiferal stages.

Similarity coefficients for the seven samples belonging to this chemical type (samples 1-7) range from 0.93 

to 0.98, and average 0.96 ±0.01 (fig. 4). Sample 7 appears to be transitional between the Friant Pumice 

Member (samples 1-6) and the Bishop ash, IAQ type 

(samples 8-12; see below). The average similarity coefficient (fig. 4) between sample 7 and the average of samples of the Friant Pumice Member is only slightly higher 

(0.96 ±0.01) than between this sample and the Bishop 

ash, IAQ type (0.95 ±0.01).

BISHOP ASH AT THE INSULATING

AGGREGATES QUARRY (BISHOP

ASH, IAQ TYPE)

Sample 8 (figs. 1, 2; table 1) is taken from a 4.6-m 

section of air-fall pumice lapilli ash that underlies the 

Bishop Tuff at the southeast margin of the volcanic 

tableland formed by the tuff, about 11 km north of the 

town of Bishop. The ash sample was taken about 1 m 

below the contact with the overlying unwelded phase of 

the ash-flow tuff. Dalrymple and others (1965) dated 

samples obtained from this locality, using sanidine separated from pumice lapilli. Ages of 0.76 ±0.07 and 

0.77 ±0.08 m.y. were obtained by the K-Ar method on 

samples from this locality, with an average of 0.73 m.y. 

for all dated samples of the Bishop Tuff (Dalrymple and 

others, 1965). Tephra of this chemical type is also found 

at the following localities:

(1) In lake beds of Pleistocene Lake Tecopa in 

southeastern California (sample 9; figs. 1, 2; table 1; this 

ash is equivalent to ash B of Sheppard and Gude, 1968; 

also see Izett and others, 1970; Hildreth, 1979). At this 

locality, the ash (sample 9) is situated between 4 and 8 

m below the Lava Creek B ash bed (samples 37, 38; figs. 

1, 2; table 1).

(2) In deformed Pleistocene alluvium exposed at 

Chaney Hill, along the Elsinore fault zone in the Peninsular Range of southern California (sample 10; figs. 1, 2; 

table 1; M. P. Kennedy, written commun., 1976).

(3) In alluvium of the Bautista Beds of Frick (1921) 

(R. V. Sharp, written commun., 1979) of the Anza-Borrego area of the southeastern Peninsular Range, west of
AGE AND STRATIGRAPHIC RELATIONS OF BISHOP ASH BED AND FRIANT PUMICE MEMBER 23

the Salton trough (sample 11; figs. 1, 2; table 1).

(4) In the previously mentioned 2-m-thick bed in deformed lacustrine beds of the Borrego Formation in the 

Salton trough east of the Salton Sea, immediately west 

of the San Andreas fault (sample 12; figs. 1, 2; table 1). 

This ash underlies ash matched chemically with the 

Friant Pumice Member, samples 6 and 7, by, 1.32 and 

1.17 m, respectively.

Similarity coefficients for Bishop ash of this chemical type (samples 8-12) range from 0.95 to 0.98 and average 0.97 ±0.01 (fig. 4).

BISHOP ASH AT OWENS RIVER GORGE AND AT RED'S 

MEADOW (BISHOP ASH, ORG TYPE)

Fine- to medium-grained air-fall ash is exposed beneath unwelded ash-flow tuff of the Bishop Tuff in the 

west wall of the Owens River Gorge north of the town 

of Bishop in the Casa Diablo quadrangle (sample 13; 

figs. 1, 2; table 1; Hildreth, 1979) and at Red's Meadow, 

in the Devil's Postpile quadrangle, within the 

headwaters of the San Joaquin River drainage basin in 

east-central Sierra Nevada (sample 14; figs. 1, 2; table 1; 

R. J. Janda, oral commun., 1972). Air-fall pumice from 

this locality has been dated at 0.68 ±0.02 m.y. by the KAr method (Huber and Rinehart, 1967).

This chemical type is present at two additional 

localities:

(1) At the previously mentioned locality in the Borrego Formation east of the Salton Sea (sample 15; fig. 1; 

table 1), where it overlies ash of the Friant Pumice 

Member, samples 6 and 7, by about 1 and 23 cm, respectively (figs. 2, 7).

(2) At Onion Creek, Grand County, Utah (sample 

16; figs. 1, 2; table 1), where this ash again underlies the 

Lava Creek B ash bed (formerly called the Pearlette 

type 0 ash bed; sample 39; figs. 1, 2; table 1; Izett and 

others, 1972; G. A. Izett, written commun., 1978).

Similarity coefficients for Bishop ash of this chemical type range from 0.96 to 0.98 and average 0.97 ±0.01 

(fig. 4). Individual similarity coefficients among the 

three chemical types of the Bishop ash-bed group range 

from 0.85 to 0.97. Average coefficients among the three 

types are 0.88 ±0.02 between the Friant Pumice Member and Bishop ash (ORG type), 0.93 ±0.02 between the 

Friant Pumice Member and Bishop ash (IAQ type), and 

0.94 ±0.01 between the two latter Bishop ash types (fig. 

4).

AGE AND STRATIGRAPHIC RELATIONS 

OF THE BISHOP ASH BED AND THE

FRIANT PUMICE MEMBER (OF 

THE TURLOCK LAKE FORMATION)

The three chemical types composing the informally

named Bishop ash-bed group are chemically very similar 

and were considered to be members of a single eruptive 

episode of short duration (Sarna-Wojcicki and others, 

1980). The evidence for this assignment, however, is not 

entirely convincing, particularly in light of new stratigraphic and chemical data, as well as previous isotopic 

ages. Sarna-Wojcicki and others (1980) correlated the 

Friant Pumice Member at its type locality near Friant 

(Janda, 1965; sample 1), as well as at several other distal 

localities in southern California, with the Bishop ash bed 

for the following reasons: (1) Ash chemically matching 

the Friant Pumice Member at its type locality (sample 

1, obtained from R. J. Janda, 1972) was found in a composite 2-m-thick ash bed in the Borrego Formation east 

of the Salton Sea (sample 6), interbedded with ash 

chemically matching the Bishop ash. The ash layer from 

which sample 6 was obtained overlies ash correlated 

with the Bishop ash (IAQ type; sample 12) by about 140 

cm and underlies ash correlated with the Bishop ash 

(ORG type; sample 15) by about 5 cm (fig. 7). Thus, ash 

at the locality east of the Salton Sea, chemically correlated with the Friant Pumice Member, is sandwiched in 

between two ash layers correlated with Bishop ash on 

the basis of glass chemistry. Although the composite ash 

bed exposed east of the Salton Sea contains thin interbeds of tuffaceous silt and clay between some of the ash 

layers, the total time required for its deposition was 

probably not as long as the 0.1 m.y. represented by the 

difference in isotopic ages of the Friant Pumice Member 

and the Bishop Tuff. Although there is a possibility that 

the stratigraphic order of these ashes was reversed 

owing to local reworking within the depositional basin of 

the Salton trough, such reworking would probably take 

place within a short time after deposition. (2) Ash chemically matching the Friant Pumice Member (sample 1) at 

its type locality is found in the marine Santa Barbara 

Formation of the Ventura area (samples 3, 4), 530 m 

stratigraphically below ash identified as the Lava Creek 

B ash bed (see above). Because the age of the Lava 

Creek B ash bed is about 0.6 m.y. B.P. (Christiansen 

and Blank, 1972; Naeser and others, 1973), it seems improbable that an ash 530 m lower in the section would be 

about the same age as well. Estimates of sedimentation 

rates in the Ventura basin based on all available age 

control range from about 2.5 to 5.0 m/1,000 yr over the 

period from about 2.0 to 0.2 m.y. B.P. If the difference 

in ages between the Lava Creek B and Friant ashes in 

the Ventura area is indeed only about 0.02 m.y. (0.62 

m.y., the K-Ar age of the Friant Pumice Member minus 

0.60 m.y., the isotopic age of the Lava Creek B ash 

bed), then the sedimentation rate for the interval between these two ashes would have been an uncharacteristic 27 m/1,000 yr. The nature of the beds within this 

interval well-bedded silt, clay, and mudstone, with
24 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

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Descriptive lithology

 Light-yellowish-brown silt

 Oxidized brown to orange zone, cemented

 Coarse to medium sand-sized vitric and crystal ash; beige to white, with reddish 

oxidized zone near base; loose

 Massive, silt-sized to fine sand-sized pure white vitric ash, fairly loose

 Light-gray, silty(?) vitric ash, silt-sized to fine sand-sized, loose

 Massive, silt-to sand-sized pure white vitric ash

 Laminated zone of pure white vitric ash, silt- to clay(?)-sized

 Light-grayish-tan to white tuffaceous silt and clay, shaley

 Pure white silt-to clay(?)-sized vitric ash

 Massive, white, fairly well indurated ash (tuff), or tuffaceous or diatomaceous 

fractured mudstone. Sharp upper contact, gradational downward

 Tuffaceous silt and clay, grading upwards to massive ash (tuff); fairly loose

 Gray to tan, medium-sized sand; tuffaceous

 Thin zone of brown silt, possibly infiltrated down along fracture parallel to bedding plane. Contains partings of gypsum

 Gray to tan, medium-sized sand; tuffaceous

 Thin zone of brown silt, possibly infiltrated down along fracture parallel to bedding plane

 Massive, fractured, fairly well indurated white to creamy-white, vitric ash (tuff); 

some detrital material

 Thin zone of brown silt and sand, probably infiltrated down along fracture parallel 

to bedding plane. Ash bed above and below zone may be single emplacement 

unit

 Massive, white to creamy vitric ash, medium- to well-indurated, sand-to si It-sized; 

fractured

 Thin zone of brown silt and sand, probably infiltrated down along fracture parallel

to bedding plane

 White to creamy, fractured, fairly well indurated vitric-biotite ash (tuff)

 Zone of interbedded thin brown and gray silt, with discontinuous veins of ortstein 

(limonite?)

 Dark-brown silt

1 Sample not analyzed, January 1, 1979

FIGURE 7. Generalized stratigraphic section of composite ash bed in the Borrego Formation of Tarbet and Holman

(1944) east of the Salton Sea.
AGE AND STRATIGRAPHIC RELATIONS OF BISHOP ASH BED AND FRIANT PUMICE MEMBER 25

only minor sand and gravel near the top does not 

suggest that any such radical acceleration of sedimentation rates occurred.

We have not observed, nor seen any reference to, a 

widespread ash of Long Valley-Glass Mountain provenance that overlies the Bishop ash or Bishop Tuff with 

obvious stratigraphic separation that would represent 

an age difference of about 0.1 m.y., with the exception 

of the thin white ash layer found within the compound 

Lava Creek B ash bed in the lake beds of Pleistocene 

Lake Tecopa (see above). Bailey and others (1976) report no widespread, major post-caldera tephra eruption 

from the Long Valley caldera after the eruption of the 

Bishop Tuff. According to their isotopic age data, there 

is a period of inactivity between the early post-caldera 

rhyolites (about 0.73 to 0.65 m.y.) and the early moat 

rhyolites (about 0.52 to 0.48 m.y.). Moreover, it does 

not seem reasonable that one of the greatest climactic 

eruptions of Quaternary time, that of the Bishop Tuff, 

would not leave any trace of its products in the lower 

parts of a closely adjacent drainage basin (the ancestral 

upper San Joaquin River), while an eruption 100,000 

years later (presumably that of the Friant Pumice Member) would deposit large volumes of pumice and ash 

within this basin, but not anywhere else nearby particularly not within its probable source area. It would 

make much more sense if the Friant Pumice Member 

and the Bishop Tuff were part of the same eruptive sequence and about the same age. Lastly, if the ash and 

pumice at Friant represent only local reworking of an 

0.6-m.y. tephra layer down the ancestral San Joaquin 

River, then we cannot explain the presence of chemically identical tephra at other locations in southern 

California (samples 3-7; figs. 1 and 2) in close association 

with the Bishop ash, unless there have been two or 

more separate eruptions of tephra of essentially identical composition, separated by over 100,000 years.

To compound the problem, if the age of the Friant 

Pumice Member is in fact about 0.6 m.y., it is difficult 

to understand why ash of a chemical composition identical to that of the Friant Pumice Member has not been 

found near the source area overlying the Bishop Tuff, at 

the Owens River Gorge locality, the Insulating Aggregates quarry, or at Red's Meadow. Alternatively, if the 

Friant Pumice Member is approximately coeval with the 

Bishop Tuff, why have we not found a chemically matching type in the proximal exposures of the Bishop Tuff? 

Perhaps this absence can be attributed to inadequate 

sampling at proximal localities not all of the major 

lobes of the Bishop Tuff have been adequately sampled. 

Only at the distal Salton trough locality (samples 6, 7, 

12, and 15) do we appear to have a complete compositional spectrum of the Bishop ash-bed group that includes the Friant Pumice Member.

With respect to the differences in isotopic ages of 

the Friant Pumice Member and the Bishop Tuff, two 

nearly identical K-Ar analyses of 0.61 and 0.62 m.y. 

(Dalrymple, 1980) were determined on sanidine separated from pumice pebbles of the Friant Pumice Member. K-Ar ages of the Bishop Tuff, by contrast, range 

from 0.66 to 0.77 m.y., with an associated error of about 

0.07 to 0.083 for individual analyses (0.66 ±0.07, 

0.71±0.06, 0.74±0.07, 0.75±0.07, 0.76±0.07, and 

0.77±0.08 m.y.) (Dalrymple and others, 1965). In addition, an age of 0.68 ±0.04 m.y. was obtained on ash-fall 

pumice underlying ash-flow tuff at Red's Meadow 

(Huber and Rinehart, 1967; Dalrymple, 1980). Within 

the error of K-Ar analyses, the age of the Friant Pumice 

Member is not significantly different from the age of the 

ash at Red's Meadow and the younger individual ages of 

the Bishop Tuff but is different from the average calculated age of the Bishop Tuff, 0.73 m.y., and its associated error of ±0.04, one standard deviation away 

from the mean of the six individual determinations. The 

average ages of the Friant Pumice Member and the 

Bishop Tuff are not significantly different at two standard deviations from the mean (see Dalrymple, 1980, for 

a further discussion of the isotopic ages of the Friant 

Pumice Member and the Bishop Tuff).

The disparity in K-Ar ages of about 0.1 m.y. between the Friant Pumice Member and the Bishop Tuff 

may be due wholly or in part to reasons other than differences in the true ages of these units. Dalrymple and 

others (1965) have shown that certain early K-Ar 

analyses of samples containing xenolithic contamination 

have resulted in spuriously old ages for the Bishop Tuff, 

probably due to incomplete degassing of these accidental 

inclusions. Recent mineralogical work (P. C. Russell, A. 

M. Sarna-Wojcicki, unpub. data, 1983) on cleaned 

pumice lapilli separated from the Bishop ash collected at 

the south end of the volcanic tableland north of the town 

of Bishop indicates the presence of xenocrystic minerals 

within the lapilli. Heavy mineral separates from 

crushed, ultrasonically cleaned lapilli indicate the presence of epidote, sphene, clear mica (muscovite?), blue, 

light-green, and clear (metamorphic?) amphibole, and 

brown to green (plutonic?) hornblende minerals that 

could not have crystallized from the parent magma of 

the Bishop ash (table 5; Hildreth, 1979). These minerals 

do not have glass coatings or jackets, with the rare exception of an occasional green hornblende. Fitch and 

others (1978) have reported older zircon crystals within 

cores of pumice clasts obtained from the KBS tuff in 

east Africa. These crystals must have been incorporated 

into the pumice before "consolidation of the lava froth," 

because no connecting vesicles were present in the

3Estimate of the precision of the analysis at the 95-percent confidence level.
26 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

clasts. The absence of glass jackets on most of the suspected xenocrysts in the Bishop ash is puzzling and argues for detrital rather than xenocrystic contamination. 

Alternatively, perhaps glass adheres only to those crystals that are thermally equilibrated with the magma and 

spalls from xenocrysts that are colder. These observations, considered together, suggest that the Bishop Tuff 

may be even younger than the weighted mean age of 

0.73 m.y. Apparently, it cannot be much younger in 

view of the age of the post-Bishop Tuff early rhyolites 

(Bailey and others, 1976), if the K-Ar analyses on these 

flows reflect their true ages. Significantly, even among 

these flows there may be some contamination, because 

the oldest age obtained on these rhyolites is 0.75 m.y., 

and they clearly postdate the Bishop Tuff on the basis of 

field criteria (Bailey and others, 1976).

In summary, the uncertainty regarding the true 

ages and correlation of the Friant Pumice Member and 

the Bishop ash bed remains unresolved. This uncertainty may be resolved by further sampling and 

analyses in particular, the mineralogy and chemistry 

of the pumice relative to the fine ash underlying it at 

Friant needs to be further investigated. We are hampered to some extent by an incompatible data base; 

many of the recent glass analyses are by rapid, but not 

entirely diagnostic, energy-dispersive X-ray fluorescence. Much of the earlier data base, as well as some of 

the continuing analytical work, is by the slower and 

more expensive but more definitive neutron-activation 

analysis. For the present, the preponderance of evidence, chemical as well as stratigraphic, suggests that 

what we have identified as distal ash layers of the 

Friant Pumice Member (samples 3, 4, 6, 7) should be essentially coeval with the Bishop Tuff. The possibility 

exists that tephra of the Friant Pumice Member at its 

type locality was erupted later than the Bishop Tuff, 

from some as yet undiscovered vent, perhaps in the 

upper reaches of the San Joaquin River basin (R. A. 

Bailey and N. K. Huber, written commun., 1979). If this 

is the case, and the true ages of these units (as 

suggested by Dalrymple, 1980) are indeed significantly 

different, then the correlation between the Friant 

Pumice Member and the distal ash layers (samples 2-7) 

proposed here would have to be considered spurious and 

coincidental; such a conclusion would also imply that 

tephras from two eruptions, separated in time by as 

much as about 0.1 m.y., have essentially the same chemical composition. Thus, for the present, correlation of 

distal ash layers (other than those of samples 3, 4, 6, 7) 

with the Friant Pumice Member by the chemical 

methods employed here entails an age uncertainty of 

about 0.1 m.y.

Correlations of the Bishop ash-bed group presented 

here confirm several correlations made by Merriam and

Bischoff (1975) of the Bishop Tuff. Their ash sampling 

localities 1, 3, 4, and 6 are at or close to corresponding 

sample localities 6, 5, 11, and 10 of this study (figs. 1, 2; 

table 1), all of which have been correlated here with the 

Bishop ash-bed group (Friant Pumice Member and the 

Bishop ash, IAQ type). However, their samples 8, 9A, 

9B, 10A, and 10B, collected from the Manix basin, and 

corresponding to our samples 28 through 34 (fig. 1; table 

1), are not part of the Bishop ash-bed group, as can be 

seen from the large differences in a number of trace and 

minor elements (figs. 3, 4, 5). Ashes of the Manix basin 

are considerably older than the Bishop ash (see below). 

The wavelength-dispersive X-ray fluorescence rapid 

scan technique for rubidium, strontium, and zirconium 

used by Merriam and Bischoff (1975) is not sufficiently 

precise to resolve the small compositional differences 

that can be determined in tephra of the Long ValleyGlass Mountain family by neutron-activation or more 

precise energy- or wavelength-dispersive X-ray fluorescence analyses. We suggest that the rapid-scan technique should be used only for local correlation problems 

where contrasts in chemical composition of tephra layers 

are high, or for initial feasibility studies.

GLASS MOUNTAIN-D ASH BED

Several lenticular beds, 5 to 15 cm thick, of fine- to 

medium-grained water-deposited white vitric ash occur 

within a 2- to 2.5-m-thick zone of tuffaceous lacustrine 

sediment at the south end of the volcanic tableland, 

about 6.5 km north of the town of Bishop (samples 17, 

17a-17c; figs. 1, 2; table 1). The ash underlies unwelded 

ash-flow tuff of the Bishop Tuff by about 17 m. The actual position of the Bishop ash in this section has not 

been located; it is either absent or covered by thick talus 

at the base of the Bishop Tuff, exposed in the upper half 

of the slope. The informally named Glass Mountain-D 

ash bed is situated 14 m below a magnetic reversal believed to be the Brunhes-Matuyama boundary (J. C. 

Liddicoat, written commun., 1978). This compound depositional or eruptive unit is referred to informally as the 

Glass Mountain-D ash bed because it contains small, angular accidental fragments of black obsidian believed 

to be derived from the obsidian of Glass Mountain, 

about 28 km to the north of the sampling locality. G. A. 

Izett (oral commun., 1978) has dated these obsidian 

fragments by the fission-track method, obtaining an age 

of 0.9 m.y. This age agrees with the 0.9-m.y. age of obsidian at Glass Mountain, dated by the K-Ar method by 

Gilbert and others (1968). Izett (1981), however, correlates this ash with the tuff of Taylor Canyon (Krauskopf 

and Bateman, 1977) on the basis of glass chemistry and 

field characteristics; he has dated the latter at 1.0 m.y.
AGE AND STRATIGRAPHIC RELATIONS OF BISHOP ASH BED AND FRIANT PUMICE MEMBER 27

Table 5. Mineral abundances in tephra samples

[Figures given represent line count of heavy mineral separates ( 2.85 specific gravity, unless otherwise noted) from 

the magnetic fraction (+ 0.6 amps). Size fraction used was 100-200 mesh (0.1U-0.08 mm). P - present but not counted.]

Sample 

number

,

!a 2

2

3

6

a4

QvD OD

12

19

21

22

23

2H

27

35

36

U1

t3

H8

Biotite

250

272

6

23

301

3

1U5

11

552

131

243

210

290

2H

603

512

153

27U 3

97

Gr.-Br. 

Hblde

9

82

30

72

I.Q

HO

83

117

mo

u

15

35

7

228

2

56

__

P

396 3

69

Br. 

Hblde

T

"I

2

 

2

2

2

1

5

 

1

7

Clino- Hyperpyroxene sthene

1? 2

1 12

27 3

8

P

5

11 2

1 1

3

1 

il 1

3 

3 1

80 I 3

2 __

P

1 5 

31 28

Allan! te

6

1?

 

P

1 *>£. 12b

17

Q£ OD

1

"3 "83

P3

P

1?

Zircon Ilmenit<

6

1 

12

35 50

11 U

21

1

2

1 

3

3

1 2

P

57 3 1353

p,o 2 ,

P3? ^ P 1

2 H

3 Sphene

3

29

H?

_

1

18

2

15

15

13

 

6

Epidote Treraolitegroup actinolitf

8

22 7

163 3

2?

oQ38 

19 3

__ __

9 4

28 1

5

5 3

9

28

2

38

30 3

P

3 6

- Bl.-Gr. Clear 

s Hblde mica

__

5

5

18

26

15

3

3

 

 

 1

U8 31

P

10

Oxy- Apatite 

hblde

H

1

3 1

_ _

_ _

 

1 

2

2 2

2 5

1 

P

2

Opaque 

(unident.

178

12

118

191

12

57

6

8

7

29

8

33

1

538

9

1

50

Other

"I

5

2

3

16

2

16

8

6

3

12

5

 

1

^Minerals separated from pumice pebbles only, with specific gravity <2.85.

Minerals separated from fine ash underlying unit which contains pumice pebbles; specific gravity <2.85. 

^Mineral grains with adhering glass.

Minerals separated from pumice lapilli only, with specific gravity <2.85. 

^Minerals separated from pumice lapilli only, with specific gravity <2.65.

Minerals separated from total sample, including matrix and pumice lapilli, with specific gravity <2.85.

by the K-Ar method. Because the obsidian fragments in 

this ash appear to be accidental rather than cogenetic, 

we believe they define a maximum age for this ash. This 

observation is supported in part by the reversely magnetized direction of the ash (J. C. Liddicoat, written 

commun., 1978). If the ash were 0.90 to 0.97 m.y. in 

age, it would be normally magnetized, because it would 

have been deposited during the Jaramillo normal polarity event (Mankinen and Dalrymple, 1979).

Chemical analyses of this ash (samples 17, 17a-17c; 

table 1) compare well with those of an ash in deepwater marine silt and clay of the Santa Barbara Formation exposed in the Ventura Avenue anticline west of 

the Ventura River (sample 18; figs. 1, 5; table 1). The 

ash in the Santa Barbara Formation is 9.5 mm thick, but 

only the lower 6.5 mm is pure and massive, water-laid, 

fine air-fall(?) vitric ash. The upper 3 mm is finely laminated tuffaceous clay. The stratigraphic position of this 

ash below the Bishop ash (correlative with the Friant 

Pumice Member) at Ventura is inferred from its stratigraphic position above the Glass Mountain-G ash bed and 

the Bailey ash (see below), and lateral projection into 

sections where the Bishop ash is locally exposed. Its relative position below the Bishop ash is also deduced from 

its correlation with the Glass Mountain-D ash bed at 

Bishop, which underlies the Bishop Tuff. In the Ventura 

area, the stratigraphic position of the Glass Mountain-D

ash bed places it in the Wheelerian microfaunal stage of 

Natland (1952). Similarity coefficients for the five 

analyses of this ash from both localities range from 0.96 

to 0.98 and average 0.97 ± 0.01 (fig. 4).

The Glass Mountain-D ash bed is similar in composition to the Bishop ash-bed group. Individual similarity 

coefficients among this ash and the three chemical types 

of the Bishop ash-bed group range from 0.89 to 0.96, 

with among-group averages equal to 0.93 ±0.02, 

0.93 ±0.01, and 0.91 ±0.01 (fig. 4). Student's two-sample t-tests show that despite several high individual 

similarity coefficients between the Bishop ash, IAQ 

type, and the Glass Mountain-D ash bed, these two sample groups are significantly different with respect to 

lanthanum, cerium, neodymium, samarium, ytterbium, 

and thorium (table 6).

GLASS MOUNTAIN-G ASH BED

A gray ash (sample 19) about 0.8 m thick underlies 

the Glass Mountain-D ash bed (sample 17) by about 6 m 

at the south end of the volcanic tableland (Chalk Bluffs), 

6.5 km north of the town of Bishop (figs. 1, 2; table 1). 

This ash is also a compound depositional (or eruptive?) 

unit. It is correlated on the basis of its glass chemistry 

with a gray ash that crops out in the Ventura Avenue
28 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

concentrations of selected elements

ash bed, IAQ type (1), and the

in the glass of the Bishop

"Glass Mountain-D ash" (2), are

the same, versus the alternative hypothesis that the means are

not the same. The null

significance

Ash

1

2

1

2

1

2

1

2

1

2

1

2

Element n

La 5

5

Ce 5

5

Nd 5

5

Sm 5

5

Yb 5

5

Th 5

5

(first) hypothesis is rejected at

levels (oC) shown below

Mean

19.

23.

45.

54.

18.

23.

3.

4.

2.

2.

20.

19.

72

54

92

82

40

00

64

24

64

80

56

40

St.

0.

0.

1.

2.

1.

1.

0.

0.

0.

0.

0.

0.

dev.

67

64

72

01

52

73

06

24

06

06

54

29

t oc

-9.24 <;0.0001

-7.53 < 0.0001

-4.47 0.0029

-5.47 0.0055

-4.50 <0.0001

4.23 0.0054

anticline near the town of Ventura (samples 20, 21, 21a21d; figs. 1, 2; table 1). Similarity coefficients for this 

ash range from 0.92 to 0.97, with an average of 

0.95 ±0.02 (fig. 4). The lower average value of the similarity coefficient and the somewhat greater spread of 

these values indicate that, like the Bishop ash-bed 

group, the informally named Glass Mountain-G ash bed 

may also be a compound unit and represent several 

closely spaced eruptions, although there is not a sufficient number of analyses to determine whether this is 

the case.

The Glass Mountain-G ash bed in the Ventura area 

is about 2.5 cm thick, fine, vitric, and generally uniform 

in thickness. Stratigraphic separation between this ash 

and the underlying Bailey ash on the south limb of the 

doubly plunging Ventura Avenue anticline north of the 

town of Ventura is about 120 m (samples 20, 21). The 

Glass Mountain-G ash bed is situated within the Wheelerian microfaunal stage of Natland (1952). The age of the 

ash is unknown, but its paleomagnetic orientation is reversed (J. C. Liddicoat, written commun., 1978). Because this ash underlies the Glass Mountain-D ash bed 

by only 6 m near Bishop, its age probably lies somewhere between 0.97 m.y., the end of the Jaramillo normal magnetic event, and 1.2 m.y., the age of the Bailey 

ash. An alternative interpretation is that the age of both 

the Glass Mountain-D and -G ash beds lies within the reversed polarity period between 0.73 and 0.91 m.y. This 

seems less likely, because within the Ventura Avenue 

anticline, the Glass Mountain-G ash bed is situated 

stratigraphically much closer to the Bailey ash, dated at 

1.2 m.y. (see below), than it is to the Bishop ash. Thus,

it is more likely that the Glass Mountain-G ash bed was 

deposited before, while the Glass Mountain-D ash bed 

was deposited after, the Jaramillo normal polarity 

event. According to J. C. Liddicoat (written commun., 

1979), however, the entire section exposed at Chalk 

Bluffs near Bishop is reversely magnetized below the 

Brunhes-Matuyama boundary, including the Glass 

Mountain-D ash bed and Glass Mountain-G ash bed 

below it. The Jaramillo event has not been found there, 

although it may be situated within a sandy interval 

within this section, or normally magnetized sediments of 

this age may have been eroded away. Pending further 

paleomagnetic work and direct age determination by the 

fission-track method, we tentatively consider the Glass 

Mountain-G ash bed to be about 1 m.y. old (±0.1 m.y.). 

Current work by G. A. Izett and A. M. Sarna-Wojcicki 

on the tuff of Taylor Canyon (Krauskopf and Bateman, 

1977), a thick, compound unit that in its upper part is 

probably about the same age as Glass Mountain-D and 

-G ash beds, may shed more light on the ages and 

correlations of these units.

BAILEY ASH

The informally named Bailey ash (Yeats and others, 

1967; Izett and others, 1974) has been recognized to date 

only within the South Mountain-Balcom Canyon and 

Ventura areas of coastal southern California (samples 

22-26a). Its glass chemistry strongly indicates that it belongs to the Long Valley-Glass Mountain family of ashes 

erupted from sources east of the central Sierra Nevada 

(figs. 1, 2, 3; table 1). The Bailey ash may be covered at 

its inferred source area by younger volcanic rocks, such 

as the Bishop Tuff or younger alluvium. The Bailey ash 

is the thickest of nine ashes presently recognized in the 

Balcom Canyon-South Mountain-Ventura area and consequently represents a sizable eruption. In some exposures, such as the one west of the Ventura River, the 

ash is about 20 cm thick, but only the lowermost 3 cm is 

air-fall ash. The lower part consists of creamy to chalky 

white fine vitric ash (fig. 8). The upper part consists of 

fine layers and laminae of silty to clayey ash, alternating 

with partings of silt and clay.

We have mapped the Bailey ash in the Balcom Canyon-South Mountain area, where it is situated wholly 

within the Pico Formation (as mapped by Weber and 

others, 1973). To the west, in the foothills north of the 

town of Ventura, the ash is situated near the contact between the Santa Barbara and the underlying Pico Formations, and we have mapped it both above and below 

this contact. We have also mapped this ash over a distance of about 23 km, on both the south and north flanks 

of the Ventura Avenue anticline, and it is a useful stratigraphic marker. No exposures exist between the Ven-
AGE AND STRATIGRAPHIC RELATIONS OF BISHOP ASH BED AND FRIANT PUMICE MEMBER 29

0)

o .0

(0 ^

II«- -= 

5 Q) ^ <s UU ^ ^~

200

175-

150

125-

100

75

50-

ex a 

E E

<0 (0

</) </) X

25-

Descriptive lithology

 Section grades upward into silt, clay, and sand

- Light-gray, tuffaceous clayey silt; finely bedded

- Olive-gray, silty clay

- Gray tuffaceous silt, laminated to finely bedded

- Finely laminated, very thin (<1 mm to several mm) tuffaceous silt, clay, and fine 

sand and clayey and silty ash. Very evenly and regularly bedded: varve-like

- Pure white vitric ash, chalky; upper part slightly coarser than lower part

- Laminated tuffaceous silt, with partings of pure ash

Fine, pure white vitric ash; silt-sized

Coarser, creamy white vitric ash; fine sand-sized

Fine, pure white vitric ash, chalky

Slightly coarser, creamy-white vitric ash; silt- to fine sand-sized 

Fine, pure white ash. Silt-sized. In places forms a doublet with thin, orange partings in the middle 

Coarser, creamy-white ash, fine sand-sized. In places discolored orange

Layer of ortstein (limonite?) 

Clay, silt, and fine sand

FIGURE 8. Generalized stratigraphic section of the Bailey ash in the uppermost part of the Pico Formation, Ventura area.
30 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Table 7. Comparison of average compositions of seven samples of the Bailey ash from the South Mountain-Balcom Canyon area

with seven samples from the Ventura area

[Similarity coefficient comparing the averages of the two groups is 0.98. Concentrations in parts per million except for iron, 

which is in percent. Manganese and dysprosium were analyzed from only a few samples in each group.)

South MountainBalcom Canyon

area (Avg. 7)

s 1

Ventura area

(Avg. 7)

s

2.73 (432)

±0.06

2.70 (436)

±0.04

0.52

±0.04

0.53

±0.02

31

±3

31

±3

240

±11

231

±7

8.2

±0.4

8.3

±0.4

18.5

±1.3

19.2

±1.4

43.8 19

±3.0 ±1

45.7 20

±2.5 ±1

4.2

±0.2

4.3

±0.1

0.05

±0.02

0.05

±0.01

0.77

±0.03

0.80

±0.03

(5.14) 3.91

±0.13

(5.18) 3.81

±0.04

0.55

±0.02

0.54

±0.02

4.14

±0.12

4.16

±0.04

3.05 27.2

±0.13 ±0.8

3.08 26.9

±0.16 ±0.7

9.00

±0.83

9.22

±0.60

Sample standard deviation.

tura and Balcom Canyon-South Mountain areas, because 

the section between these two areas is down-dropped 

between two antithetical, high-angle reverse faults, the 

Oak Ridge and the Ventura-Pitas Point faults. The presence of this ash in the intervening area is inferred from 

subsurface magnetostratigraphic and biostratigraphic 

data by Blackie and Yeats (1976).

Seven chemical analyses of the Bailey ash from the 

Balcom Canyon-South Mountain area correlate well 

with seven analyses of the ash from the Ventura area 

(table 7). The similarity coefficient comparing averages 

of the two groups is 0.98 (fig. 4), demonstrating quite 

convincingly that this ash can be correlated across the 

intervening structures.

Similarity coefficients for all 14 analyses of this ash 

range from 0.91 to 0.98 and average 0.95 ±0.01. If 

analyses of sample 23a are not included (this analysis, a 

replicate of sample 23, is suspect; it deviates sharply 

from the average of the four other replicates, samples 

23, 23b, c, and d; fig. 4), the similarity coefficients range 

from 0.93 to 0.98 and average 0.96 ±0.01.

The Bailey ash has been dated by both the K-Ar 

and fission-track methods (fig. 9), but only the latter 

method appears reliable in view of the fine-grained and 

water-deposited nature of the ash. Early K-Ar ages (fig. 

9) are too old to be consistent with stratigraphie evidence and correlated ages of other ashes, such as the 

overlying Glass Mountain-G and -D ash beds and the underlying lowermost gray ash (Huckleberry Ridge? ash 

bed) (see below). The older ages would also be inconsistent with the Wheelerian microfaunal stage assigned to 

the stratigraphie interval within which this ash is 

situated (Natland, 1952; Van Eysinga, 1975). According 

to Izett and others (1974), some of the earlier age 

analyses are probably too old owing to detrital contamination. The age of 1.2 ±0.2 m.y. on a sample of this ash 

collected from the Balcom Canyon locality (our sample 

locality 22; figs. 1, 2; Izett and others, 1974) and an age 

of about 1.2 ±0.3 m.y. obtained by the fission-track 

method on glass (Boellstorff and Steineck, 1975) are

most compatible with other available ages, and stratigraphic and biostratigraphic information.

THIN WHITE ASH BELOW THE BAILEY ASH

A thin fine-grained white vitric ash about 6 mm 

thick (sample 27; figs. 1, 2; table 1) crops out in silty tuffaceous beds of the Pico Formation where this formation 

butts against strongly deformed beds of the Modelo Formation, west of South Mountain (the "sea knoll" of 

Yeats, 1965), about 4.5 km south of the town of Santa 

Paula. This ash is about 245 m stratigraphically below

14

oc

o

8-

6-

4-

2-

Yeats and others 

(1967); K-Ar, feldspar

Ingle (1967); 

K-Ar, feldspar

Izett and others 

(1974); F.T., zircon

Yeats (1965);

K-Ar, glass

I

Boellstorff and Steineck 

/(1975); F.T., glass

I Boellstorff and Steineck Yeats and others V^n-,^ ,- T , i(1967);K-Ar,glasslNl974)' F-T-' g ' aSS

1965 1970 1975 1980

DATE OF PUBLICATION OF ANALYSIS 

1 "Less than" ages

FIGURE 9. Isotopic ages of the Bailey ash plotted against publication 

dates of analyses. Analytical methods and material analysed are 

shown adjacent to each reference. K-Ar, potassium-argon dates; 

F.T., fission-track dates.
AGE AND STRATIGRAPHIC RELATIONS OF BISHOP ASH BED AND FRIANT PUMICE MEMBER 31

the Bailey ash. It is chemically similar to the Long Valley-Glass Mountain family of ashes and probably represents a minor eruption from that source, although the 

ash has been found only in the South Mountain area. No 

direct isotopic age has been determined for this ash, but 

it must be older than the 1.2-m.y. age of the Bailey ash 

higher in the section and probably younger than about 2 

m.y., an age estimated for the lowermost gray ash 

(Huckleberry Ridge? ash bed) lower in the section. We 

can estimate the age of this ash by calculating the average sedimentation rate between the Bishop ash bed (0.7 

m.y.) and the Bailey (1.2 m.y.) ash over the 245-m stratigraphic interval that separates them and extrapolate 

this rate down to the stratigraphic position of the thin 

white ash. This calculation gives us about 1.5 m.y. for 

the thin white ash below the Bailey ash. We can also estimate the age of this ash by interpolating between the 

Bailey ash, above, and the lowermost gray ash, below, 

again on the basis of stratigraphic position of the three, 

assuming a 2-m.y. age for the lowermost ash 

(Huckleberry Ridge? ash bed, see below). Again, we estimate an age of about 1.5 m.y. for the thin white ash 

below the Bailey ash. Such estimates are subject to considerable error because sedimentation rates most likely 

have not been constant during these time intervals and 

also probably differed from site to site within the basin. 

An independent age estimate made on the basis of systematic compositional trends discussed below gives us 

an age of about 1.4 m.y.

The thin white ash below the Bailey ash is chemically most similar to the Bailey ash (samples 22 through 

26a; average similarity coefficient of 0.86 ±0.01; fig. 4) 

and to the upper, white ash in the Manix basin of the 

Mojave Desert (samples 28, 29; average similarity coefficient of 0.86 ±0.01; fig. 4).

LOWERMOST GRAY ASH, SOUTH MOUNTAIN 

AREA (HUCKLEBERRY RIDGE? ASH BED)

A 2.5-cm-thick fine gray vitric ash is interbedded 

with sand and silt beds of the Pico Formation where 

they are buttressed against deformed Modelo Formation a few meters above the Pico-Modelo contact, west 

of South Mountain (sample 43; figs. 1, 2; table 1). This 

ash is about 670 m below the stratigraphic level of the 

Bailey ash.

Glass in this ash contrasts sharply with glass in 

ashes of the Long Valley-Glass Mountain family in 

chemical composition but is very similar to tephra 

erupted from the Yellowstone area (Pearlette tephra 

family). The ash correlates well with a gray 40-cm-thick 

ash interbedded with lake beds of Pleistocene Lake 

Tecopa (ash C of Sheppard and Gude, 1968; our samples 

44, 44a, and 45; figs. 1, 2; table 1). The similarity coefficient among these samples ranges from 0.96 to 0.98 and 

averages 0.97 ±0.01 (fig. 4).

The age of this ash at this locality has not been determined. If we assume a constant sedimentation rate 

for the stratigraphic interval containing the Bishop, 

Bailey, and lowermost gray ashes in the Ventura 

Avenue anticline and South Mountain sections near 

Ventura, the age of the lowermost gray ash would be 2 

to 2.1 m.y. Again, the same cautions apply regarding 

uniformity of sedimentation rates and variation in rates 

from site to site in the basin.

The lowermost gray ash in the South Mountain area 

and its correlative in the Tecopa lake beds are chemically very similar to the Huckleberry Ridge ash bed 

(formerly the Pearlette type B ash bed), dated at about 

1.9 m.y. by the fission-track method (Naeser and 

others, 1971) and equivalent to the proximal 

Huckleberry Ridge Tuff in the Yellowstone area of 

Wyoming, where it has also been dated at 1.9 m.y. by 

the K-Ar method (Christiansen and Blank, 1972). The 

lowermost gray ash in the South Mountain area is not 

similar enough to the Huckleberry Ridge ash bed to be 

considered correlative on the basis of chemical analyses 

of glass alone (similarity coefficients of 0.92 to 0.94, with 

an average of 0.93 ±0.01; fig. 4). Christiansen and Blank 

(1972) report, however, that the Huckleberry Ridge 

Tuff is a composite emplacement unit produced by several eruptions. Perhaps here again we see the effect of 

multiple eruptions produced by an eruptive episode of 

short duration, which may account for small chemical 

differences in distal tephra units. Further work on this 

problem is currently underway. Identification of two 

Yellowstone-type ashes in the Ventura-South Mountain 

area of southwestern California (the Lava Creek B and 

Huckleberry Ridge? ash beds) marks the first time that 

these ashes have been found in marine strata, the westernmost exposures of these ashes, and important time 

horizons for reconciling continental and marine faunal 

chronologies.

ASHES OF THE MANIX BASIN, MOJAVE DESERT

Four ash beds crop out in pluvial lake beds and deformed older alluvium of the Manix basin in the Mojave 

Desert, about 40 km east of Barstow. The uppermost 

ash, in pluvial lake beds, was not analyzed, because 

glass in the sample was devitrified. Since our study, 

outcrops of this ash have been found that contain fresh 

glass, and the ash has been correlated (Izett, 1981) with 

his Long Canyon ash, K-Ar dated at 0.185 m.y. on 

tephra near the source area in Long Canyon (Bacon and 

Duffield, 1981). The three other ashes, interbedded with 

older fluvial deposits in the basin and separated from 

the overlying pluvial lake beds by an angular uncon-
32 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

formity, had fresh glass and were analyzed. We refer to 

these ashes as the upper white ash, the middle white 

ash, and the Huckleberry Ridge ash bed (lowermost 

gray ash of Manix basin).

UPPER WHITE ASH

A fine white vitric ash about 8 cm thick crops out in 

low cliffs on the south side of the Mojave River (samples 

28, 29; figs. 1, 2; table 1). Only the basal 2 to 2.5 cm is 

massive pure air-fall(?) ash, the upper part being finely 

bedded water-laid tephra, probably locally reworked. 

This ash does not correlate with any other ash analyzed 

to date. It is most similar to ashes of Long Valley-Glass 

Mountain provenance and was probably erupted from 

that volcanic province. Although correlated with the 

Bishop Tuff on the basis of rapid-scan X-ray fluorescence analysis for rubidium, strontium, and zirconium 

by Merriam and Bischoff (1975), this ash is chemically 

different from the Bishop ash-bed group, particularly 

with respect to scandium, manganese, samarium, hafnium, tantalum, and thorium (table 1). Average similarity coefficients between this ash and the three chemical 

types of the Bishop ash-bed group are 0.88 ±0.02, 

0.91 ±0.01, and 0.91 ±0.01 (fig. 4).

MIDDLE WHITE ASH

A fine white vitric ash about 3 to 4 cm thick (samples 30-33; figs. 1, 2; table 1) underlies the upper white 

ash by about 12 to 15 m. Pure white ash, about 1.3 cm 

thick near the base, rests with sharp contact on alluvial 

silt and sand and grades upward into pinkish tuffaceous 

silt. The upper 2 to 3 cm consists of well-bedded or laminated water-laid ash. Samples 30 and 31 were collected 

on the south side of the Mojave River; samples 32 and 

33 were collected on the north side, about 0.8 km north 

of localities 30 and 31. Our chemical analyses correlate 

this ash over this short distance, across the river. This 

ash also correlates well with an ash, the second from the 

top of a sequence of four ashes interbedded with the late 

Cenozoic lacustrine Waucoba Beds of Hopper (1947) in 

eastern Owens Valley, about 270 km to the north of the 

Manix basin (sample 34; figs. 1, 2; table 1). The range of 

similarity coefficients for ashes of these two localities is 

from 0.95 to 0.96, with an average of 0.96 ±0.01 (fig. 4). 

The range of similarity coefficients for the entire group 

of five samples is from 0.95 to 0.98, with an average of 

0.97 ± 0.01 (fig. 4).

There is no direct isotopic age available for this ash 

at the Manix basin localities, but a K-Ar age of 2.3 m.y. 

was obtained on the ash in the Waucoba Beds of Owens 

Valley (Hay, 1966; our sample locality 34). This age appears to be somewhat too old, because the middle white 

ash locally overlies the Huckleberry Ridge ash bed in

the Manix basin (see below).

Although Merriam and Bischoff (1975) correlated 

this ash with the Bishop Tuff on the basis of rapid-scan 

X-ray fluorescence analysis for rubidium, strontium, 

and zirconium, neutron-activation analyses for trace and 

minor elements reveal large differences between these 

tephra units, particularly for scandium, manganese, 

iron, rubidium, cesium, samarium, terbium, dysprosium, ytterbium, lutecium, hafnium, tantalum, 

thorium, and uranium (fig. 3; table 1). Average similarity coefficients between the middle white ash and the 

chemical types of the Bishop ash-bed group are low: 

0.62 ±0.01, 0.65±0.01, and 0.68 ±0.01. Furthermore, 

the ash correlates well with an older, late Cenozoic ash 

in the Waucoba Beds (see above) and is underlain by the 

Huckleberry Ridge ash bed dated by others at about 2 

m.y. (see below).

Despite the large differences in glass chemistry between the middle white ash at Manix basin and the 

Bishop ash-bed group, the middle white ash belongs to 

the Long Valley-Glass Mountain family of ashes, as can 

be seen in gross chemical similarities to other tephra 

units belonging to this group, as well as in systematic 

age-related elemental depletion trends that are a characteristic of this tephra family (figs. 3, 5, 10).

HUCKLEBERRY RIDGE ASH BED 

(LOWERMOST GRAY ASH)

A fine gray vitric ash 3 cm thick (sample 41) underlies the middle white ash (sample 32) by about 2 to 3 m 

in low hills on the north side of the Mojave River in the 

Manix basin (figs. 1, 2; table 1). This ash correlates very 

well on the basis of its glass composition with a sample 

of the Huckleberry Ridge ash bed (formerly called the 

Pearlette type B ash bed; sample 42; figs. 1, 2) from the 

Borchers faunal locality, Meade County, Kansas (table 

1; also see Izett and others, 1972). The similarity coefficient between these two samples is 0.97 (fig. 4). Furthermore, the Manix basin gray ash contains crystals of 

green to brown hornblende, clinopyroxene, allanite, zircon, apatite, ilmenite, and magnetite, minerals typical of 

the tephra of the Yellowstone family (Izett and others, 

1970). These data correlate a single tephra unit over a 

distance of about 1,500 km between sample localities 

and over a distance of about 1,200 km between the 

source area in Yellowstone National Park, Wyoming, 

and the Manix basin.

The similarity coefficient comparing analyses of the 

Manix basin gray ash (sample 41) with an analysis of the 

upper part of the Lava Creek B ash bed at Lake Tecopa 

(sample 38) is also high (0.95; fig. 4), but not as high as 

the coefficient comparing the former ash with the 

Huckleberry Ridge ash bed (0.97; fig. 4). Furthermore,
AVERAGE OF NORMALIZED CONCENTRATIONS OF 

FIVE ELEMENTS: Mn, Rb, Ta, Hf, and U

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34 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

Table 8. Analytical data on fission-traok ages of zircon crystals from an 

ash flow tuff in the Coso area (sample U8)

Analyst

C. E. Meyer

M. J. Woodward

Spontaneous

No . Counted

217

390

tracks

Density 1

7.1x105

5.3x105

Induced

No. Counted

2088

3754

tracks

Density

1.4x107

1.1x107

Neutron

flux2

9.59x10 14

9.59x10 1l>

Age

(m.y.)

2.98±0.28

2.91±0.20

^Tracks per cm2 . 

Neutrons per cm .

coarser fraction would be expected to contain a higher 

proportion of compound shards containing phenocrysts 

and microphenocrysts. As can be seen from table 1, 

there is very little difference between the two analyses 

within the limits of analytical precision of the neutronactivation method; consequently there is little or no 

sampling error in the analyses due to differences in degree of separation of phenocrysts from the glass.

ASH IN SEARLES VALLEY

An ash collected by G. I. Smith (oral commun., 

1976; sample 49; figs. 1, 2; table 1) from late Cenozoic 

lacustrine deposits exposed on the southeast side of 

Searles Valley does not correlate specifically with any 

tephra unit analyzed in this study. Glass of this ash is 

most similar to tephra units erupted from the southern 

Cascade Range of northern California, specifically the 

Nomlaki Tuff Member of the Tehama and Tuscan Formations, 3.4 m.y. old (Evernden and others, 1964), the 

Ishi Tuff Member of the Tuscan Formation, between 2.5 

and 3.5 m.y. old (Harwood and others, 1981), and the 

ash in the Merced Formation, about 0.45 m.y. old 

(Meyer and others, 1980).

PUMICE OVERLYING THE CAHUILLA 

BEDS, SALTON TROUGH

Large pumice cobbles up to 20 cm in diameter overlie the informally named Cahuilla beds of the Salton 

trough. The Cahuilla beds, in turn, overlie the strongly 

deformed Borrego Formation with marked angular unconformity. The pumice was most likely derived by erosion of young pumice domes of late Pleistocene (Muffler 

and White, 1969) or Holocene (Friedman and Obradovich, 1981) age situated at the south shore of the 

Salton Sea; the cobbles then floated northward along the 

shore. The highest extent of these cobbles probably defines a former high stand of the lake in this area. Glass 

from one of these cobbles (sample 50; fig. 1; table 1) was

analyzed. The chemical composition of this glass is quite 

distinct from that of the Bishop ash-bed group in the 

Borrego Formation, especially with respect to iron, 

rubidium, cesium, the rare-earth elements, and hafnium, indicating that there is no genetic relation between the ashes in the Borrego Formation and the local 

pumice domes, despite their close geographic proximity. 

This, pumice is also easily distinguished from other 

tephra families on the basis of its chemical composition 

(figs. 4, 5; table 1).

PROVINCIAL RELATIONS OF TEPHRA

OF THE LONG VALLEY-GLASS

MOUNTAIN FAMILY

The Long Valley-Glass Mountain family of tephra is 

defined on the basis of gross chemical similarities that 

distinguish these tephra units from tephra of other 

families. The Bishop ash-bed group, Glass Mountain-D 

ash bed, and Glass Mountain-G ash bed beneath it were 

all erupted from sources just east of the central Sierra 

Nevada, as indicated by thickness and clast-size gradients of these units. Because of chemical similarities 

(figs. 3, 4, 5), the Bailey ash and the thin white ash 

below it are also presumed to have been erupted from 

this general area, although no near-source outcrops of 

these ashes have been found. The younger, voluminous 

deposits of the Bishop Tuff and younger deposits in the 

down-faulted Long Valley caldera and other basins east 

of the Sierra Nevada may cover near-source correlatives 

of the older ashes. The upper white ash and middle 

white ash of the Manix basin and the subsurface ash obtained from lake beds of Searles Valley also belong to 

this family (figs. 4, 5).

In general, greatest similarity is observed between 

tephra units of this family that are close in age or 

stratigraphic position to each other, while greater differences are observed between units that are farther 

separated in time and space (fig. 3). These relations
RECOGNITION OF PROVINCIAL CHARACTERISTICS OF TEPHRA 35

suggest that there is a systematic compositional variation in this tephra family that is related to time. Isotopic 

or relative ages of six of these units (the Bishop ash-bed 

group, Glass Mountain-D ash bed, Glass Mountain-G ash 

bed, the Bailey ash, the thin ash beneath the Bailey, and 

the middle white ash of the Manix basin) are known. 

These six units show systematic elemental depletion 

with decreasing time for a number of elements (fig. 3). 

Five elements, manganese, rubidium, tantalum, hafnium, and uranium, show the most consistent depletion 

trends with decreasing age (fig. 10). Isotopic ages of 

three of these ashes, the Bishop, the Bailey, and the ash 

in the Waucoba Beds (equivalent to the middle white 

ash of the Manix basin), have been determined, while 

ages of two others, the Glass Mountain-D ash bed and 

Glass Mountain-G ash bed, can be fairly closely bracketed at between about 0.8-0.9 and 1.0-1.1 m.y., respectively, from stratigraphic relations to the other ashes 

and magnetic polarity (fig. 10). As mentioned above, the 

2.3-m.y. age of the ash in the Waucoba Beds is considered to be somewhat too old, because this ash closely 

overlies the 1.9-m.y.-old Huckleberry Ridge ash bed. 

Normalized values of the five elements plotted against 

their ages have a nearly linear trend. A straight-line extrapolation of the age-composition trend between the 

Bishop and the Bailey ashes (fig. 10) would intersect the 

normalized composition of the middle white ash of the 

Manix basin (equivalent to the ash in the Waucoba 

Beds) at about 2 m.y. Using this linear relation, we can 

estimate the age of the thin ash below the Bailey ash at 

about 1.4 m.y. (fig. 10). Estimates of the age of this ash 

based on extrapolation and interpolation between dated 

ash horizons in the Ventura-South Mountain area, assuming uniform sedimentation rates (see above), both 

gives similar results of about 1.5 m.y.

Two ashes of this tephra family, the upper white 

ash of the Manix basin and the ash obtained from the 

subsurface in Searles Valley, do not appear to fall on 

this age-composition trend, but isotopic ages have not 

been determined for them. The upper white ash of the 

Manix basin (samples 28, 29; figs. 1, 2; table 1) is 

younger than the middle white ash at that locality and 

older than the uppermost white ash in pluvial lake beds 

of the Manix basin. The age of this uppermost ash has 

not been determined directly, although it has been correlated (Izett, 1981) with a young dome dated from KAr at about 185,000 yr B.P. in Long Canyon west of the 

Coso volcanic field (Bacon and others, 1981). The age of 

the ash in the subsurface from Searles Lake (sample 35; 

figs. 1, 2; table 1) is also not known but is estimated to 

be about 3 m.y. from stratigraphic and paleomagnetic 

data (Liddicoat and Smith, 1979).

The younger ashes, such as the Bishop ash-bed 

group and Glass Mountain-D ash bed, are associated

with roughly coeval pyroclastic and flow rocks of widely 

ranging compositions. The ash-flow phases of the Bishop 

Tuff itself have chemical variations that are much greater than the variations in the air-fall ash (Hildreth, 1979) 

and encompass the range of several plinian tephras derived from the Long Valley-Glass Mountain province. 

For this reason, we believe that each of the six tephra 

units shown in figure 10 may represent initial plinian 

eruptions from about the same source area, each a culmination of a relatively short-term differentiation cycle. 

Thus, these widespread air-fall ashes were probably derived from the uppermost, highly differentiated parts of 

one magma chamber or a succession of spatially and 

genetically related magma chambers within the same 

volcanic province. The long-term, roughly linear depletion trend may represent an envelope curve for some 

long-term magmatic evolution process superimposed on 

shorter term cyclic eruptive episodes, such as that represented by the Bishop Tuff and associated volcanic 

rocks of approximately coeval age. Similar cyclic variations in trace-element chemistry of tephra and associated flows have been documented by Smith (1979) 

for the Valles caldera complex of the Jemez Mountains, 

New Mexico. Depletion trends such as those observed 

for the Long Valley-Glass Mountain tephra family could 

be used as an independent method of estimating or 

cross-checking ages of tephra erupted from this volcanic 

province, but because reversals with time in such trends 

have been noted for other volcanic provinces (Smith, 

1979) and because not all tephra layers of this family fall 

on the age-composition trend, this method should be 

viewed with skepticism pending further testing.

RECOGNITION OF PROVINCIAL 

CHARACTERISTICS OF TEPHRA

Because of gross chemical similarities in trace- and 

minor-element glass composition, eruptive source areas 

of individual tephra layers can be recognized. For instance, average similarity coefficients within the Long 

Valley-Glass Mountain tephra family among tephra 

layers of different age range from 0.62 to 0.94. Average 

similarity coefficients among tephra layers of the Yellowstone family range from 0.84 to 0.93, whereas average similarity coefficients between tephra layers of 

these two families are much lower, from 0.44 to 0.56, 

demonstrating the large compositional contrast among 

tephra layers from different source areas (figs. 3, 4, 5).

In this study, three main tephra families have been 

recognized on the basis of trace- and minor-element 

composition of the volcanic glass: the Long Valley-Glass 

Mountain, the Yellowstone (Pearlette), and the Coso. 

Sample 50, correlated with the pumice domes at the 

south shore of the Salton Sea, represents a fourth vol-
36 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

canic province (although no tephra unit is associated 

with this source), while sample 49, from Searles Valley, 

probably represents a fifth, south Cascade Range province. In other studies (Izett and others, 1972; SarnaWojcicki and others, 1979) six other major late Cenozoic 

tephra families have been identified in the western conterminous United States on the basis of chemical composition of volcanic glass. Each of these families is associated with a specific source area. Within several 

tephra families, subgroups can be distinguished, while 

several families (for instance, those of Cascade Range 

volcanic sources) can be grouped into larger supergroups on the basis of gross similarities.

The unique chemical characteristics associated with 

each eruptive source area are undoubtedly related to 

the parent materials from which magma was formed and 

the magmatic differentiation processes that operate 

within these source areas. These, in turn, are probably 

related to the tectonic setting of the source area itself.

CONCLUSIONS

Tephra correlation and age data provide five 

categories of information that are useful in resolution of 

problems relating to the Quaternary geology of southern 

California, as well as in other areas:

(1) Recognition of a tephra layer at a specific 

locality provides age data for the tephra layer and 

stratigraphically associated deposits. For example, 

recognition of the Lava Creek B ash bed in the marine 

San Pedro Formation within the Ventura area dates 

stratigraphically associated sediments at about 0.6 m.y.

(2) Correlation of a particular tephra layer at two or 

more localities documents the temporal equivalence of 

deposits at these locations and permits .correlation of diverse depositional environments such as marine and 

continental. For example, the identification of the Lava 

Creek B ash bed within the deposits of the Ventura 

Basin and Pleistocene Lake Tecopa enables temporal 

correlation of marine with lacustrine sediments. Alternatively, correlation of a single ash layer among several 

separate basins can document synchroneity of depositional conditions. For instance, pluvial conditions must 

have existed about 0.6 m.y. ago in the Lake Tecopa 

basin, Searles Valley basin, and southern San Joaquin 

Valley, because Lava Creek B ash is found in lake beds 

in all three areas.

(3) Identification of an ash sequence within a continuous stratigraphic section makes it possible to 

bracket specific intervals within stratigraphic sections, 

provides information on deposition rates and rates of 

organic evolution and migration, and makes it possible 

to estimate durations of unconformities. For instance, 

within the Ventura basin, nine ashes have been

identified within a composite stratigraphic section that 

represents continuous deposition spanning an age range 

of 0.6 to 1.9 m.y. The age of the uppermost beds in this 

section have been estimated at 0.2 m.y. by amino-acid 

stereochemistry on marine mollusks (Wehmiller and 

others, 1977; Lajoie and others, 1978). These age data 

enable us to calculate depositional rates and to bracket 

marine fauna! stages previously developed within this 

basin (Yerkes and others, 1983).

(4) Correlation of ash sequences between basins 

makes it possible to compare depositional rates between 

different tectonic provinces, as well as to reconcile 

marine and continental faunal chronologies. For example, the stratigraphic separation between the Lava 

Creek B and Huckleberry Ridge? ash beds in the marine 

Ventura basin is about 2,800 m. The stratigraphic separation between these same two ashes in the lacustrine 

Lake Tecopa section is about 30 m (J. W. Hillhouse, 

written commun., 1981). Calculated net sedimentation 

rates in the two areas are thus 2.2 mm/yr and 0.02 mm/ 

yr, a difference of about two orders of magnitude. Correlation of the two sequences, furthermore, permits 

comparison on the basis of planktic foraminifers (Natland, 1952; Ingle, 1967; Yerkes and others, 1983) of 

marine faunal stages with land vertebrate stages (for 

instance, with the recently developed faunal chronology 

based on rapidly evolving microtine rodents (C. R. 

Repenning, oral commun., 1981).

(5) Dated tephra layers provide time horizons by 

which directions and rates of crustal motion can be 

measured. An extensive tephra layer defines a paleosurface of a portion of the Earth. By determining the displacement of this surface from its original position relative to a reference point, line, or surface (for instance, 

sea level), we can determine amounts of crustal uplift, 

subsidence, horizontal translation, or complex differential deformation such as faulting and folding. For instance, the presence of the Bailey ash on both flanks of 

the west-trending Ventura Avenue anticline of the Ventura basin and of the South Mountain anticline makes it 

possible to determine a minimum rate of north-south 

crustal shortening within this tectonic province over the 

last 1.2 m.y. Combined with paleobathymetric data obtained from paleontological evidence, the relative uplift 

or subsidence of any particular site where this ash is 

found can also be determined.

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Journal of Science, v. 281, p. 1-34.

Bailey, R. A., Dalrymple, G. B., and Lanphere, M. A., 1976, Volcanism, structure, and geochronology of Long Valley Caldera, 

Mono County, California: Journal of Geophysical Research, v. 81, 

no. 5, p. 725-744.
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Dalrymple, G. B., Cox, Allan, and Doell, R. R., 1965, Potassiumargon age and paleomagnetism of the Bishop Tuff, California: 

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38 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

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APPENDIX 39

APPENDIX

SAMPLING METHODS

We examined ash and tuff outcrops at collecting localities and sampled the purest or least contaminated 

layers or zones. For air-fall or water-deposited tephra, 

these layers or zones are usually situated at or near the 

base of the tephra units. We "high-graded" the least 

contaminated material from the exposures, obtaining 

between several hundred grains and several kilograms, 

depending on the thickness of the tephra unit, the ease 

of obtaining the purest available material, and the type 

of analyses planned for each sample. Samples of 0.5 to 2 

kg were collected for chemical and petrographic 

analyses. At several localities, we collected larger samples of 10-20 kg for fission-track age determinations. At 

some outcrops, we took multiple samples vertically 

where the presence of multiple emplacement units "was 

suspected, or to determine vertical variability within 

each tephra unit. In a number of instances, we took replicate samples laterally within individual emplacement 

units to determine their lateral variability.

SAMPLE PREPARATION

Previous experience (Sarna-Wojcicki, 1971, 1976; 

Sarna-Wojcicki and others, 1979) indicates that purity of 

glass separations is reflected favorably in the quality of 

analytical results and facilitates data interpretation. For 

this reason, special care was exercised in glass separations for chemical analyses.

We disaggregated samples by hand or crushed 

them in a mullite mortar and sieved them in plastic 

sieves fitted with nylon filament screens to avoid contamination with metals. We treated the 100-200 mesh 

size fraction (0.14-0.08 mm) with 10 percent reagent 

grade HC1 for about 1 minute, rinsed several times in 

distilled water, treated it with 8 percent reagent-grade 

HF for about 30 seconds, rinsed it several times again, 

vibrated it in an ultrasonic cleaner, wet-sieved it again, 

and then dried it. We then separated the glass from 

other components of tephra in a Frantz magnetic 

separator and in acetone-bromoform and acetonemethylene iodide liquid solutions using a density- gradient column.

ANALYTICAL METHODS

NEUTRON-ACTIVATION ANALYSIS

Bowman and others (1973) and Sarna-Wojcicki and 

others (1979) describe the analytical methods for 

neutron-activation analysis. In this study, neutronactivation analyses of glass samples were done by two 

laboratories, Lawrence Berkeley Laboratory of the 

University of California at Berkeley and the 

Radiochemistry Laboratory of the U.S. Geological 

Survey at Reston, Virginia. To correct for 

standardization and instrumental differences between 

the laboratories, we calculated conversion factors by 

least-square fits for 22 samples split and analyzed by 

both laboratories. Elemental concentrations determined 

by the U.S. Geological Survey laboratory (tables 1, 9) 

are predicted y values from regression analysis.

[The USGS 

Equations

ilyzed splits of 22 samples. 

;o LBL analyses. ]

Parameter Sc Ce

(1)

a2 -0.035 0.012 4.849 0.571 0.258 -108.901 0.443 -1.758 0.635 -0.271 0.002 -0.018 -0.091 0.032 -0.051 -0.002 -0.154 0.129

b3 0.935 0.998 0.785 0.946 0.882 1.136 1.113 1.018 1.030 1.150 0.981 1.113 1.037 0.953 0.934 1.189 1.011 1.102

r2 0.999 0.999 0.958 0.980 0.985 0.976 0.999 0.997 0.993 0.994 0.991 0.993 0.998 0.993 0.997 0.997 0.996 0.973

a 0.042 -0.011 -4.190 2.202 -0.183 115.07 -0.367 1.912 -0.416 0.256 0.002 0.023 0.094 -0.030 0.069 0.008 0.196 0.037

b 1.068 1.001 1.219 1.036 1.117 0.859 0.898 0.981 0.970 0.869 1.011 0.892 0.963 1.043 1.068 0.8382 0.987 0.883

r 2 0.998 0.999 0.964 0.980 0.985 0.976 0.999 0.997 0.992 0.996 0.991 0.993 0.998 0.993 0.997 0.997 0.996 0.973

(2)

based on 16 sample pairs only 

y intercept 

3 slope of line 

correlation coefficient
40 CHEMICAL ANALYSES AND AGES OF PLIOCENE AND PLEISTOCENE ASH LAYERS, CALIFORNIA

ELECTRON MICROPROBE ANALYSIS

We determined major- and minor-element 

concentrations of 12 elements in glass of tephra samples 

by means of an electron microprobe using a 15-kv 

excitation potential, a 0.010 nm specimen current, and a 

l-jjum beam diameter. When possible, the beam was 

swept over a 10 by 10 jjum area to minimize volatilization 

of sodium and water. As standards, we used natural 

glasses and silicate minerals that were analyzed by 

conventional wet-chemical methods. We took X-ray 

counts on a total population of 60 to 80 shards per 

sample to evaluate homogeneity. Each glass shard 

selected for analysis was inspected visually to avoid vesicles, crystalline material, or abnormally fluorescent 

areas under the beam. We made corrections for background, atomic number, absorption, and fluorescence 

using a modified on-line data reduction program 

(Yakowitz and others, 1973). We give results of electron 

microprobe analyses in table 2.

ENERGY-DISPERSIVE X-RAY FLUORESCENCE ANALYSIS

Powdered glass separated from tephra samples was 

analyzed by means of an energy-dispersive X-ray 

fluorescence spectrometer. Integrated peak intensities 

within two spectral regions were determined for potassium, calcium, titanium, manganese, iron, copper, and 

zinc (for the spectral region between 2.96 and 9.01 keV) 

and for rubidium, strontium, yttrium, zirconium, and 

niobium (for the spectral region between 12.32 and 17.00 

keV). Peak intensities for each element were normalized 

by dividing by total number of counts (peak intensities 

plus background) for each of the two spectral regions 

studied and were multiplied by 10,000 to convert normalized counts to whole integers. Standards were not 

run for this type of analysis; consequently, we did not 

obtain information on elemental concentrations in the 

glass, only relative peak intensity data. These data,

however, are sufficiently precise to distinguish among 

most of the tephra units we have studied. By using 

spectral intensity data alone to compare tephra samples, 

we avoided an extra step and its associated error in the 

analytical procedure.

PETROGRAPHIC ANALYSIS

Sized separates of the 100-200 mesh (0.14-0.08 mm) 

fractions and the 200-325 mesh (0.08-0.03 mm) fractions 

for fine tephra beds were separated in a magnetic 

separator at high- and low-amperage settings. We 

further processed the intermediate magnetic fraction, 

containing mostly magnetic glass, for separation of volcanic glass (see above). We separated the magnetic fraction, containing the bulk of minerals rich in transition 

elements, in heavy liquid solutions having a specific 

gravity of approximately 2.85, and examined the heavy 

separate in optic oils under a petrographic microscope. 

We recorded the presence of transparent mineral 

species for each sample and calculated relative frequencies of the various species present from line counts using 

a mechanical stage (table 5). We also noted presence of 

glass coatings on specific minerals. We consider glasscoated minerals to be cogenetic; that is, they were probably contained in the magma chamber from which the 

tephra unit was erupted, and they usually help distinguish such minerals from other minerals present in the 

tephra owing to detrital or accidental contamination.

Many of the tephra layers found in the southern and 

southwestern parts of California were undoubtedly 

situated at great distances from their sources because 

they are very thin and fine grained. In such layers the 

characteristic heavy minerals are usually very small or 

absent owing to winnowing by wind. Heavy-mineral 

separates from such units consist mostly of detrital minerals. In such instances, we have relied on the chemistry of volcanic glasses and stratigraphic data to determine correlations.

GPO 787-042/116