Middle Miocene Foraminifera 

and Stratigraphic Relations 

in the Adelaida Quadrangle 

San Luis Obispo County 

California

GEOLOGICAL SURVEY BULLETIN 1271-A

Middle Miocene Foraminifera 

and Stratigraphic Relations 

in the Adelaida Quadrangle 

San Luis Obispo County 

California

By PATSY B. SMITH and DAVID L. DURHAM

CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1271-A

Foraminifera and rocks near 

the type areas of the Relizian 

and Luisian Stages are described 

and their age and environments 

inferred

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 20 cents (paper cover)
CONTENTS

Abstract __.________________._._.______----_-_. Al

Introduction. _________________________________________________ 1

Previous work__________________________________________________ 2

Geologic setting.____________________________________________ 3

Sedimentary rock units__._______________.________________________ 3

Foraminifera ______________________________________________ 7

Collection-locality descriptions._____________________________________ 11

References cited___________________________________________________ 13

ILLUSTRATIONS

Page

FIGURE 1. Index map showing location of Adelaida 7^-minute quadrangle and type areas of the middle Miocene stages of 

Kleinpell______________________________ A2 

2. Generalized geologic map of the Adelaida 7^-minute quadrangle showing approximate location of fossil localities.____ 4

TABLE

Page 

TABLE 1. Fossil Foraminifera from the Sandholdt Member of the Monterey

Shale. _______-_-_______._______________ A8

m

CONTRIBUTIONS TO GENERAL GEOLOGY

MIDDLE MIOCENE FORAMINIFERA AND STRATIGRAPHIC

RELATIONS IN THE ADELAIDA QUADRANGLE, SAN LUIS

OBISPO COUNTY, CALIFORNIA

BY PATSY B. SMITH and DAVID L. DURHAM

ABSTRACT

The Salinas Valley region contains the type areas of the Monterey Shale and 

and the Santa Margarita and Pancho Rico Formations, as well as the type areas 

of the Relizian and Luisian Stages of Kleinpell. Only in and very near the 

Adelaida 7%-minute quadrangle do strata representing all these stratigraphic 

units crop out in close proximity. In addition, beds that contain fossil marine 

mollusks of Paleocene age crop out in the quadrangle. Of particular significance 

in Coast Range stratigraphy are the wide range in Tertiary age of fossils found 

in the Adelaida quadrangle and the geographic position of the quadrangle between the type areas of the Relizian and Luisian Stages of Kleinpell.

INTRODUCTION

The Adelaida T^-minute quadrangle is in the southern Salinas Valley region on the northeast flank of the Santa Lucia Kange (fig. 1). 

It is of particular stratigraphic interest because fossiliferous marine 

beds of Late Cretaceous, Paleocene, Miocene, and Pliocene age crop 

out there in close proximity, a circumstance unusual in so small an 

area of the Coast Ranges. About one-third of the beds exposed in the 

quadrangle belong to the Sandholdt Member of the Monterey Shale. 

These rocks are particularly significant because they contain middle 

Miocene foraminiferal faunas of both the Eelizian and Luisian Stages 

of Kleinpell, and because they lie between the type areas of the two 

stages. This paper presents the results of studies on Foraminifera 

collected during mapping of the Adelaida quadrangle and summarizes 

stratigraphic relations determined by the mapping and by study of 

fossils. It includes only a generalized geologic map (fig. 2); a more 

detailed map is published separately (Durham, 1968b).

Al
A2 CONTRIBUTIONS TO GENERAL GEOLOGY

MONTEREY\COUNTY _ ___

OBISPO COUNTY" i

Type area of n, 

Luisian Stage

FIGURE 1. Index map showing location of Adelaida 7^-minute quadrangle and 

type areas of the middle Miocene stages of Kleinpell.

PREVIOUS WORK

Published records of previous work on fossil Foraminifera from 

the Adelaida T^-minute quadrangle are meager. Wilson (1931, p. 103) 

reported that "At Chimney Eock (sec. 9, T. 26 S., R. 11 E.), the 

Siphogenerina hughesi subzone of the Uvigerinella californica zone 

[of Kleinpell] occurs 514 feet above the base of the [Monterey] shale 

* * *" and (p. 104) "* * * at least part of the [Monterey] shale in the 

Adelaida district is the correlative of the lower part of the Monterey
FORAMINIFERA, ADELAIDA QUADRANGLE, CALIFORNIA A3

formation at its type locality." Kleinpell (1938, table 8) gave a check 

list of Foraminifera collected by Wilson at five localities in the Adelaida quadrangle, and (p. 116) mentioned that his "Siphogenerina 

transversa and Plectofrondicularm miocenwa, Zones [early Miocene 

Saucesian Stage] are well developed on * * * Las Tablas Creek 

* * *," which is partly in the Adelaida quadrangle. Kleinpell also 

mentioned (p. 121) that his Siphogenerina hughesi Zone (middle Miocene Kelizian Stage) "is well developed" at Chimney Kock in the 

Adelaida quadrangle. Bramlette and Daviess (1944) showed on columnar sections that beds at the base of the Sandholdt Shale (Sandholdt Member of the Monterey Shale of this paper) at two localities in 

the Adelaida 7^-minute quadrangle belong to the early Miocene 

Saucesian Stage of Kleinpell.

GEOLOGIC SETTING

The diversity of Tertiary formations in the Adelaida quadrangle 

is due partly to the proximity of two unlike stratigraphic sequences 

separated by the Jolon fault. Figure 2 shows the distribution of rock 

units in the Adelaida 7^-minute quadrangle and their general structural relations. Southwest of the fault the oldest exposed rocks are 

strata of an unnamed formation of Cretaceous and Paleocene age. The 

Tierra Redonda Formation lies unconf ormably on this unnamed unit, 

and is succeeded by a conformable sequence comprising the Monterey 

Shale, Santa Margarita Formation, and Paso Eobles Formation, although at some places the Paso Robles lies unconformably on the 

Monterey. Granitic rocks of the pre-Tertiary basement complex crop 

out northeast of the Jolon fault, where a conformable sequence comprising the upper part of the Monterey Shale, the Pancho Kico Formation, and the Paso Robles Formation is also exposed. At some places 

the Paso Robles lies directly on the Monterey Shale or on the basement 

complex.

The occurrence of these unlike stratigraphic sequences in the Adelaida quadrangle is attributed to their juxaposition by lateral displacement along the Jolon fault. The regional distribution of both the 

Santa Margarita and Pancho Rico Formations indicates that the displacement was in a right-lateral sense and amounted to at least 11 

miles (Durham, 1965).

SEDIMENTARY ROCK UNITS

The unnamed formation of Cretaceous and Paleocene age is mainly 

medium- to coarse-grained arkosic sandstone and pebble to boulder 

conglomerate, although hackly mudstone is locally abundant in the 

unit. The base of the formation is concealed, but the unit is probably
A4 CONTRIBUTIONS TO GENERAL GEOLOGY

Mf82 

(MM). 

.-.-. . Chimney Rock 7 . "58

FIGURE 2. Generalized geologic map of the Adelaida 7%-minute quadrangle 

showing approximate location of fossil localities.

thicker than 10,000 feet. The formation contains the marine Paleocene 

fossils Amauropsis martinezensis Dickerson?, Cucullaea mathewsoni 

Gabb, Mesalia martinezensis (Gabb), Nemocardiwn cf. A7, linteum 

(Conrad), Priscoficus cf. P. caudata (Gould), Tornatella pinguis 

(Gabb), and Turritella infragranulata Gabb at fossil locality M2693 

(W. O. Addicott, written commun., 1967), and Schenck (1936, p. 48) 

reported the Late Cretaceous marine fossil Acila demessa Finlay from 

a locality within the formation 2 miles to the northwest.

The Tierra Redonda Formation is chiefly fine- to medium-grained, 

locally conglomeratic, arkosic sandstone that is generally nearly white
FORAMINIFERA, ADELAIDA QUADRANGLE, CALIFORNIA 

EXPLANATION

A5

Santa Margarita Formation

Tm, chiefly porcelaneous rocks

i- <

o

Basement complex

ucko: Q;UJ< 0.1-, 

Contact 

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X Mf867

Fossil locality 

Mf, locality for Foraminifera 

M, locality for larger invertebrates

Age or stage of foraminiferal faunas 

MM, middle Miocene 

K, Relizian Stage 

IK, lower Relizian Stage 

UK, upper Relizian Stage 

L, Luisian Stage 

LL, lower Luisian Stage 

UL, upper Luisian Stage

and that ranges from friable to well cemented. The unit, which is 

about 600 feet thick, lacks fossils. It is considered of early and middle 

Miocene age because northwest of the Adelaida quadrangle the Tierra 

Redonda lies conformably on the lower Miocene Vaqueros Formation

314-278 6S
A6 CONTRIBUTIONS TO GENERAL GEOLOGY

and conformably underlies and locally intertongues with middle Miocene beds of the Sandholdt Member of the Monterey Shale (Durham, 

1968a).

The Monterey Shale is divided into two parts. The lower part, the 

Sandholdt Member, is mainly calcareous shale and mudstone with 

interbeds of cherty rock and dolomitic carbonate rock. The top of 

the member is concealed, but the unit probably is at least as thick 

as 2,000 feet. It contains abundant Foraminifera indicative of the 

middle Miocene Eelizian and Luisian Stages of Kleinpell. The upper 

part of the Monterey is porcelanite and porcelaneous mudstone with 

associated dolomitic carbonate rock and chert. The thickness of the 

upper part of the Monterey is unknown because the contact between 

the upper and lower parts is concealed. Fossils suitable for age datermination are lacking in the upper part of the formation.

The Santa Margarita Formation is fine- to coarse-grained or grantv 

litic arkosic sandstone that commonly contains grains of dark-colored 

chert. The rock is mainly calcareous and ranges from friable to well 

cemented. The formation is about 500 feet thick and contains abundant 

marine fossils of late Miocene age. According to W. O. Addicott 

(written commun., 1964), fossil locality USGS M204S contains: Forreria cf. F. carisaensis (Anderson), Chlainys hodgei (Hertlein), Lyropecten estrellanus (Conrad), and Mytilus cf. M. scfiencM Hanna and 

Hertlein; fossil locality M2049 contains: IForreria sp., Lyropecten 

estrellanus (Conrad), O street titan Conrad, Terebratalia arnoldi quaylei Hertlein and Grant, Astrodapsis cf. A. ma?*garitanus Kew, and 

Balanus gr eg arms (Conrad); and fossil locality USGS M2051 contains: Lyropecten estrellanus (Conrad), Ostrea titan Conrad, and 

Astrodapsis cf. A. margaritanus Kew.

The Pancho Rico Formation is fine- to coarse-grained arkosic sandstone that ranges from noncalcareous to calcareous and from friable 

to well cemented. The unit is probably no thicker than 50 feet. The 

apparent thickness of the Pancho Rico is exaggerated on the geologic 

map (fig. 2) in order to depict the unit at the scale of the map. The 

Pancho Rico contains marine fossils of early Pliocene age. Fossils 

identified by W. O. Addicott from localities USGS M2047 and M2050 

are listed elsewhere (Durham and Addicott, 1965, table 1).

The Paso Robles Formation is composed chiefly of poorly bedded 

friable conglomerate and arkosic sandstone. The conglomerate contains pebbles, cobbles, and some boulders of a variety of rocks, including porcelaneous and cherty rocks derived from the Monterey Shale. 

The sandstone is for the most part poorly sorted. Mudstone is locally 

common in the Paso Robles, and limestone beds 1-3 feet thick occur 

in the formation at some places. The thickness of the Paso Robles is
FORAMINIFERA, ADELAIDA QUADRANGLE, CAWFORNIA A7

unknown, but the unit may be as thick as several hundred feet. The 

Paso Eobles is considered of Pliocene and probably Pleistocene age 

because it conformably overlies the Pliocene Pancho Rico Formation 

and unconformably underlies Quaternary alluvial sediments. The unit 

is regarded as nonmarine because it lacks fossils and has the poor sorting, poor bedding, cross-stratification, and channeling that suggest 

fluviatile deposition.

FORAMINIFERA

Foraminifera were collected from the Sandholdt Member of the 

Monterey Shale at 2T localities in the Adelaida quadrangle (fig. 2 and 

collection-locality list). Localities shown in table 1 are listed by age; 

no precise stratigraphic sequence is implied as the scattered nature 

of the samples and complex structure make this impossible. Species 

are arranged alphabetically in the table.

Foraminiferal faunas older than middle Miocene are lacking in the 

Sandholdt Member of the Monterey Shale in the Adelaida 7i£-minute 

quadrangle, although Foraminifera of the lower Miocene Saucesian 

Stage occur near the base of the member about 11 miles northwest of 

the quadrangle along Copperhead Creek. Saucesian Foraminifera also 

occur in the lower part of the Sandholdt at its type area in Reliz 

Canyon. Thorup (1941), in his original definition of the Sandholdt as 

a formation, pointed out that the Sandholdt in Reliz Canyon contains 

Saucesian Foraminifera in the lower part and lower middle Miocene 

Foraminifera in the upper part. The Sandholdt, redefined as a member 

of the Monterey Shale (Durham, 1963, p. Q15), includes the Sandholdt Formation of Thorup and overlying calcareous shale beds, which 

contain Foraminifera of the upper middle Miocene Luisian Stage. At 

most places in the southern Salinas Valley area, the Sandholdt Member contains Foraminifera of only the middle Miocene Relizian or 

Luisian Stage.

The foraminiferal faunas listed in table 1 are all middle Miocene in 

age. The oldest faunas, collected as close to the base of the Sandholdt 

as possible, are assigned to the lower Relizian Stage. The Saucesian 

faunas found in the Sandholdt in Reliz Canyon and at Copperhead 

Creek to the north are absent. The Relizian faunas are characterized 

by such species as Siphogenerina hughesi, Robulus laimingi, Planulina 

baggi, Plectofrondicularia catifornica, Valvulineria califomica 

appressa, and Baggina cancriformis. They are similar to faunas of the 

type Relizian Stage. The lower Luisian is characterized by the highest 

occurrence of V. depressa, Nonionella incisa, V. califomica obesa, and 

the lowest occurrence of Pullenia miocenica globula. These faunas 

differ from the type section of the Luisian Stage, 20 miles to the south-
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FORAMINIFERA, ADELAIDA QITADRANGILB, CALIFORNIA A9

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A10 CONTRIBUTIONS TO GENERAL GEOLOGY

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Dell ___________
FORAMINIFERA, ADELAIDA QUADRANGLE, CALIFORNIA All

east (Smith, 1968), in lacking the abundance of V. californica s. 1. 

Upper Luisian faunas are characterized by Siphogenerina collomi, 

Uvigerina hootsi, U. subperegrina, Epistominella capitanensis, E. 

gyroidinafonnis, Eponides rosaformis, and Planularia luciana. This 

stage also differs from that in the type area owing to the relatively 

rare occurrences of V. calif ornica.

Using the species criteria of Bandy and Arnal (1960), most of the 

samples from the Kelizian and Luisian Stages would indicate a bathyal 

environment, probably lower and middle bathyal (2,000±1,000 ft to 

4,000±2,000 ft). Bandy and Arnal suggest that the Valvulineria 

faunas are probably upper bathyal (100±600 ft), which may mean 

that the faunas from the Adelaida quadrangle were deposited in water 

slightly deeper than that at the type area of the Luisian Stage.

Two samples, USGS Mf856 and Mf824, both from middle Miocene 

undifferentiated, indicate an outer shelf or upper slope environment. 

These faunas are dominated by small Bolivinas, Globigerinas, and 

Uvigerinellas. No specific age assignment can be given them.

COLLECTION-LOCALITY DECRIPTIONS

U.S. Geological Survey (USGS) Cenozoic localities

Mf821. Roadcut on Gamp Roberts, 1,300 ft S., 2,375 ft W. of NE cor. sec. 24, T. 25 

S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, upper 

Luisian Stage. Collectors: D. L. Durham and R. J. McLaughlin, 1964.

Mf822. Camp Roberts, 725 ft N., 1,075 ft W. of SE cor. sec. 32, T. 25 S., R. 11 E. 

Sandholdt Member of Monterey Shale, middle Miocene, upper Luisian Stage. 

Collectors: D. L. Durham and R. J. McLaughlin, 1964.

Mf823. Camp Roberts, 1,450 ft N., 1,600 ft W. of SE cor. sec. 32, T. 25 S., R 11 E. 

Sandholdt Member of Monterey Shale, middle Miocene, upper Luisian Stage. 

Collectors: D. L. Durham and R. J. McLaughlin, 1964.

Mf824. Camp Roberts, 525 ft N., 2,025 ft W. of SE cor. sec. 4, T. 26 S., R 11 E. 

Sandholdt Member of Monterey Shale, middle Miocene. Collectors: D. L. 

Durham and R. J. McLaughlin, 1964.

Mf855. Cut on ranch road just above base of Monterey Shale, 400 ft S., 1,475 ft W. 

of NE cor. sec. 16, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, 

middle Miocene, upper Relizian Stage. Collectors: D. L. Durham and T. L. 

Winder, 1965.

Mf856. Cut on ranch road, 250 ft S., 1,100 ft W. of NE cor. sec. 16, T. 26 S., 

R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene. Collectors: 

D. L. Durham and T. L. Winder, 1965.

Mf857. 2,300 ft N., 600 ft W. of SE cor. sec. 10, T. 26 S., R. 11 E. Sandholdt 

Member of Monterey Shale, middle Miocene, lower Luisian Stage. Collectors : D. L. Durham and T. L. Winder, 1965.

Mf858. Cut on county road south of Adelaida, 1,125 ft S. of NE cor. sec. 27, T. 26 

S., R. 10 E., on section line. Sandholdt Member of Monterey Shale, middle 

Miocene, upper Luisian Stage. Collectors: D. L. Durham and T. L. Winder, 

1965.
A12 CONTRIBUTIONS TO GENERAL GEOLOGY

Mf859. Cut on Paso Robles Road, 2,200 ft S., 2,425 ft W. of NE cor. sec. 26, T. 26 S., 

R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, upper 

Relizian Stage. Collectors: D. L. Durham and T. L. Winder, 1965.

MfS60. Cut on Paso Robles Road by Las Tablas Creek, 2,575 ft S., 900 ft E. of 

NW cor. sec. 25, T. 26 S., R. 10 E. Sandholdt Member of Monterey Shale, 

middle Miocene, lower Relizian Stage. Collectors: D. L. Durham and T. L. 

Winder, 1965.

MfS61. Cut on Paso Robles Road by Las Tablas Creek, 2,425 ft N., 1,450 ft E. of 

SW cor. sec. 30, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, 

middle Miocene, lower Relizian Stage. Collectors: D. L. Durham and T. L. 

Winder, 1965.

Mf862. Cut on Paso Robles Road, 850 ft S., 2,200 ft E. of NW cor. sec. 22, T. 26 S., 

R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, lower 

Relizian Stage. Collectors: D. L. Durham and T. L. Winder. 1965.

Mf863. Cut on Paso Robles Road, 225 ft S., 2,225 ft E. of NW cor. sec. 22, T. 26 S., 

R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, lower (?) 

Relizian Stage. Collectors: D. L. Durham and T. L. Winder, 1965.

Mf864. 1,250 ft N, 2,450 ft E. of SW cor. sec. 24, T. 25 S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, lower Relizian Stage. Collectors: 

D. L. Durham and T. L. Winder, 1965.

Mf865. 1,625 ft N, 300 ft E. of SW cor. sec. 11, T. 26 S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, Relizian Stage. Collectors: D. L. 

Durham and T. L. Winder, 1965.

Mf866. 1,175 ft S., 1,400 ft W. of NE cor. sec. 23, T. 26 S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, upper Relizian or lower Luisian Stage. 

Collectors: D. L. Durham and T. L. Winder, 1965.

Mf867. 2,550 ft S., 1,025 ft E. of NW cor. sec. 24, T. 26 S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene. Collectors: D. L. Durham and T. L. 

Winder, 1965.

Mf868. Cut along oil pipeline, 225 ft N., 50 ft E. of SW cor. sec. 24, T. 26 S., R. 10. 

E. Sandholdt Member of Monterey Shale, middle Miocene, upper Relizian 

Stage. Collectors: D. L. Durham and T. L. Winder, 1965.

Mf869. 275 ft N., 2,250 ft E. of SW cor. sec. 19, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, Relizian Stage. Collectors: D. L. 

Durham and T. L. Winder, 1965.

Mf870. 400 ft S., 1,400 ft E. of NW cor. sec. 29, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, Relizian Stage. Collectors: D. L. 

Durham and T. L. Winder, 1965.

M£87L 1,750 ft S., 2,250 ft E. of NW cor. sec. 32, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, Relizian or lower Luisian Stage. 

Collectors: D. L. Durham and T. L. Winder, 1965.

Mf872. Cut on Willow Creek Road, 750 ft N, 350 ft W. of SE cor. sec. 26, T. 26 

S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene, lower 

Luisian Stage. Collectors: D. L. Durham and T. L. Winder, 1965.

Mf873. 1,875 ft N, 950 ft W. of SE cor. sec. 25, T. 26 S., R. 10 E. Sandholdt Member of Monterey Shale, middle Miocene. Collectors: D. L. Durham and T. L. 

Winder, 1965.

Mf895. Cut on Peachy Canyon Road, 2,450 ft S., 1,450 ft W. of NE cor. sec. 33, 

T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, 

lower Luisian Stage. Collector: D. L. Durham, 1966.

Mf896. 1,950 ft S., 2,700 ft W. of NE cor. sec. 33, T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene. Collector: D. L. Durham, 1966.
FORAMINIFERA, ADELAIDA QUADRANGLE, CALIFORNIA A13

Mf897. Cut on Peachy Canyon Road, 2,100 ft S., 400 ft W. of NE cor. sec. 34, T. 

26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, lower 

Luisian Stage. Collector: D. L. Durham, 1966.

Mf898. Cut on Peachy Canyon Road, 1,550 ft S., 3,000 ft E. of NW cor. sec. 35, 

T. 26 S., R. 11 E. Sandholdt Member of Monterey Shale, middle Miocene, 

lower Luisian Stage. Collector: D. L. Durham, 1966.

M2047. Camp Roberts, 550 ft N., 225 ft W. of SE cor. sec. 19, T. 25 S., R. 11 E. 

Pancho Rico Formation, fauna of late Miocene or early Pliocene age. Collectors : W. O. Addicott, D. L. Durham, and R. J. McLaughlin, 1964.

M2048. Cut along oil pipeline, 2,250 ft S., 875 ft E. of NW cor. sec. 19, T. 25 S., 

R. 11 E. Santa Margarita Formation, probably late Miocene. Collectors: 

W. O. Addicott, D. L. Durham, and R. J. McLaughlin, 1964.

M2049. Cut along oil pipeline, 2,300 ft S., 500 ft E. of NW cor. sec. 19, T. 25 S., 

R. 11 E., stratigraphically below M2048. Santa Margarita Formation, late 

Miocene. Collectors: W. O. Addicott, D. L. Durham, and R. J. McLaughlin, 

1964.

M2050. Camp Roberts, 2,225 ft N., 1,250 ft W., of SE cor. sec. 29, T. 25 S., R. 11 

E. Pancho Rico Formation, early Pliocene. Collectors: W. O. Addicott, D. L. 

Durham, and R. J. McLaughlin, 1964.

M2051. Camp Roberts, 1,725 ft S., 150 ft W. of NE cor. sec. 32, T. 25 S., R. 11 E. 

Santa Margarita Formation, late Miocene. Collectors: W. O. Addicott, D. L. 

Durham, and R. J. McLaughlin, 1964.

M2693. 2,050 ft N., 1,975 ft W. of SE cor. sec. 5, T. 26 S., R. 11 E. Unnamed formation, Paleocene. Collectors: D. L. Durham and T. L. Winder, 1965.

REFERENCES CITED

Bandy, O. L., and Arnal, R. E., 1960, Concepts of foraminiferal paleoecology:

Am. Assoc. Petroleum Geologists Bull., v. 44, no. 12, p. 1921-1932. 

Bramlette, M. N., and Daviess, S. N., 1944, Geology and oil possibilities of the

Salinas Valley, California: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map

24, scale 1:125,000. 

Durham, D. L., 1963, Geology of the Reliz Canyon, Thompson Canyon, and San

Lucas quadrangles, Monterey County, California: U.S. Geol. Survey Bull.

1141-Q, p. Q1-Q41.

 1965, Evidence of large strike-slip displacement along a fault 

in the southern Salinas Valley, California: U.S. Geol. Survey Prof. Paper 

525-D, p. D106-D111.

 1968a Geology of the Tierra Redonda Mountain and Bradley quadrangles, 

Monterey and San Luis Obispo Counties, California: U.S. Geol. Survey 

Bull. 1255 (in press).

1968b Geologic map of the Adelaida quadrangle, San Luis Obispo County,

California: U.S. Geol. Survey Geol. Quad. Map GQ-768, scale 1:24,000

(in press). 

Durham, D. L., and Addicott, W. O., 1965, Pancho Rico Formation, Salinas

Valley, California: U.S. Geol. Survey Prof. Paper 524-A, p. A1-A22. 

KLeinpell, R. M., 1938, Miocene stratigraphy of California: Tulsa, Okla., Am.

Assoc. Petroleum Geologists, 450 p. 

Schenck, H. G., 1936, Nuculid bivalves of the genus Acila: Geol. Soc. America

Spec. Paper 4,149 p.
A14 CONTRIBUTIONS TO GENERAL GEOLOGY

Smith, P. B., 1968, Paleoenvironment of the phosphate-bearing Monterey Shale

in the Salinas Valley, California: Am. Assoc. Petroleum Geologists Bull.

(in press). 

Thorup, R. R., 1941, Vaqueros Formation (Tertiary) at its type locality, Junipero

Serra quadrangle, Monterey County, California [abs.]: Geol. Soc. America

Bull., v. 52, no. 12, pt 2, p. 1957-1958. 

Wilson, R. R., 1931, Miocene shales of the Adelaida quadrangle, San Luis Obispo

County, California: Micropaleontology Bull., v. 2, no. 5, p. 102-104.

O