The Miocene Topanga Group of Southern 

California—A 100-Year History of Changes in 

Stratigraphic Nomenclature 

By Russell H. Campbell, Thane H. McCulloh, and John G. Vedder 

Open-File Report 2007-1385, Version 1.1, revised 2009 

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior 

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Marcia K. McNutt Director 

U.S. Geological Survey, Reston, Virginia 2007 

Revised 2009 

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Suggested citation: 

Campbell, R.H., McCulloh, T.H., and Vedder, J.G., 2007, revised 2009, The Topanga 

Group; a 100-year history of changes in stratigraphic nomenclature: U.S. Geological 

Survey, Open-File Report 2007-1385, version 1.1, 36 p. 

[http://pubs.usgs.gov/of/2007/1385/].

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iii

Contents 

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

Introduction ......................................................................................................................................... 1

Summary .............................................................................................................................................. 5

Chronology of Usage........................................................................................................................ 12

Acknowledgments............................................................................................................................ 29

References Cited .............................................................................................................................. 29

Figures 

Figure 1. Index map of coastal southern California .........................................................4 

Figure 2. Distribution of Topanga Group .............................................................................8

Figure 3. Chronological chart showing ages of Miocene rocks..........................................11
1

The Miocene Topanga Group of Southern 

California—A 100-Year History of Changes in 

Stratigraphic Nomenclature

By R.H. Campbell1, T.H. McCulloh2, and J.G. Vedder3

Abstract 

A review of selected literature summarizes the origin and chronology of changes 

in usage of “Topanga” in the Miocene stratigraphic nomenclature of the Los Angeles 

Basin and adjacent areas in southern California. The review was done to summarize and 

reconcile some differences in Miocene stratigraphic nomenclature as applied to geologic 

map compilations of the Santa Ana (Morton, 2004), San Bernardino (Morton and Miller, 

2003), Long Beach (Saucedo and others, 2003) and Los Angeles (Yerkes and Campbell, 

2005) 30’ x 60’ quadrangles, all of which are products of the cooperative (California 

Geological Survey-U.S. Geological Survey) Southern California Areal Mapping Project 

(SCAMP). The deposition of the Topanga Group spans about 6 my (from as old as about 

18 ma to as young as about 12 ma), and the sequence of included strata records changes 

in provenance and depositional environments that are contemporaneous with part of a 

major Miocene tectonic episode in southern California -- the “basin-inception phase” in 

the evolution of the Neogene Los Angeles basin (Yerkes and others, 1965). The area of 

Topanga deposition extends to the southern, eastern, northern, and northwestern sides of 

the Los Angeles basin, as well as the southern part of the eastern Ventura Basin. 

Topanga beds are inferred to underlie the thick upper Miocene and Pliocene deposits of 

the central Los Angeles Basin and the southern part of the eastern Ventura Basin; 

however, they have been reached by drilling only in marginal areas, where the overlying 

deposits are relatively thin. Post-Topanga strata were deposited in more-restricted areas 

of rapid subsidence. Selected papers are summarized as they relate to the Topanga 

nomenclature, and are presented in chronological order. 

Introduction 

In the century since Arnold (1907) described a marine molluscan fauna from a 

locality near the head of Topanga Canyon, the name “Topanga” has become embedded in 

the geologic literature of southern California stratigraphy. That fossil locality was 

 

1

 U.S. Geological Survey Scientist Emeritus, c/o Department of Earth Sciences, University of California, 

Riverside, Riverside, CA 92521 2

 U.S. Geological Survey Scientist Emeritus, 7136 Aberdeen Avenue, Dallas, TX 75230 

3

 U.S. Geological Survey Scientist Emeritus, 285 Golden Oak Dr., Portola Valley, CA 94028 
2

included in a stratigraphic unit mapped by W.S.W. Kew (1924) along the north flank of 

the central Santa Monica Mountains as the Topanga Formation. (Kew had introduced the 

name in a short paper published in 1923; however, the map and unit descriptions in the 

1924 paper provide a more complete definition.) Within a few years of its introduction 

by Kew (1923), “Topanga Formation” was the name applied to middle Miocene marine 

strata in a wide area of the Los Angeles Basin and its margins (e.g., English, 1926). In 

the 1940’s and 1950’s, geologic mapping in the Santa Monica Mountains by Cordell 

Durrell and students at the University of California, Los Angeles, led Durrell (1954) to 

recognize that the type Topanga Formation in the Santa Monica Mountains included three 

units of formation rank, which he termed the “Upper Topanga, Middle Topanga, and 

Lower Topanga Formations.” Durrell’s terminology did not meet requirements 

subsequently established by the American Commission on Stratigraphic Nomenclature 

(1961), so Yerkes and Campbell (1979) named the Topanga Group to include the three 

Topanga formations of Durrell (1954), and introduced the names “Topanga Canyon 

Formation” and “Calabasas Formation” for Durrell’s “Lower Topanga Formation” and 

“Upper Topanga Formation”, respectively, in the central and western Santa Monica 

Mountains. Because the Middle Topanga Formation of Durrell (1954) includes volcanic 

strata named “Conejo Volcanics” by Talliaferro (1924) in the western Santa Monica 

Mountains, Yerkes and Campbell (1979) followed the usage of Blackerby (1965) and 

extended the Conejo Volcanics to the central Santa Monica Mountains. Yerkes and 

Campbell (1979) did not attempt specific correlations of the Topanga Group formations 

in the central and western Santa Monica Mountains with subdivisions of “Topanga 

Formation” rocks as mapped by Hoots (1931) in the eastern Santa Monica Mountains, 

nor to rocks mapped by others as “Topanga Formation” in the central Los Angeles Basin 

and around its northern, eastern and southern margins. 

The stratigraphic nomenclature currently used for Tertiary and Late Cretaceous 

rocks in and around the Los Angeles Basin has evolved from the work of many 

individual studies over the 20th Century. Early workers tended to extend formation 

names such as Chico, Martinez, Domengine, Vaqueros, Temblor, and Monterey from 

type localities in central and northern California, to southern California rock units on the 

basis of similar faunal elements and similar lithologies. Some of these names also 

became identified with molluscan faunal “Stages” (e.g., Weaver and others, 1944). 

Although some southern California map units, notably the Vaqueros Formation and the 

Monterey Formation (or Monterey Shale), still retain those names, others have 

subsequently received local names which reflect differences in lithofacies and 

relationships to adjacent units, or to discontinuities at some high-angle faults. For 

example, the widely recognized Monterey Shale has been discriminated from partly or 

wholly coeval units in southern California, such as the Puente and Modelo Formations 

and the Topanga Group, on the basis of lithology, dominant source terrain, depositional 

environment, and biogenic content. Intertonguing marine and nonmarine strata, 

representing shifting shorelines, have been assigned to hybrid names (e.g., the 

“undifferentiated Sespe and Vaqueros Formations” in the northern Santa Ana Mountains 

mapped by Schoellhamer and others, 1981, and described, p. 31-37), or to discrete 

members, for example the Piuma Tongue of the Sespe Formation in the Santa Monica 

Mountains – a nonmarine sandstone-siltstone tongue described by Yerkes and Campbell 

(1979, p. 10-11) that separates two marine sandstone beds that carry mollusks assigned to 

the “Vaqueros Stage”. 

This paper reviews the historic usages of the terms “Topanga fauna”, “Topanga 

Formation”, and “Topanga Group”, and attempts to reconcile an evolving terminology 
3

with ongoing map compilations; it is not intended as an extension or refinement of 

correlations. It was undertaken in order to summarize and reconcile some differences in 

Miocene stratigraphic nomenclature as applied to geologic map compilations of the Santa 

Ana (Morton, 2004), San Bernardino (Morton and Miller, 2003), Long Beach (Saucedo 

and others, 2003) and Los Angeles (Yerkes and Campbell, 2005) 30’ x 60’ quadrangles, 

all of which are products of the cooperative (California Geological Survey-U.S. 

Geological Survey) Southern California Areal Mapping Project (SCAMP). Figure 1 

shows (dashed outline) the approximate area of those four 30’ x 60’quadrangles and their 

relations to major physiographic features. 

As geologic work progressed through a century, changes in stratigraphic 

nomenclature have been accompanied by refinements and revisions of paleontological 

interpretations of stratigraphic zonations, development of new paleontologic and isotope 

dating tools for determining unit ages, and refinements in regional and world-wide 

correlations leading to changes in the geologic time scale. The publication in 1961 of the 

“Code of Stratigraphic Nomenclature” (American Commission on Stratigraphic 

Nomenclature, 1961), and subsequent revisions, offers a uniform set of guidelines for the 

nomenclature of lithostratigraphic, chronostratigraphic and geostratigraphic units. This 

paper does not attempt to fit the terminology of various authors, at various times, into the 

structure of current usage, and age-stratigraphic descriptors such as “Stage” and “zone” 

reflect the usages of published sources at the time of publication. For example, papers 

published over several decades in the middle 20th Century commonly referred to 

“Vaqueros”, “Temblor”, “Relizian”, and “Luisian”, as “Stages”, whereas current 

preferred usage emphasizes their geographically restricted usefulness for correlation, and 

would identify the “Vaqueros” and “Temblor” as “California Molluscan Stages” (CMS) 

(Bartow, 1992), and would identify the “Relizian” and “Luisian” as “Benthic 

Foraminiferal Stages” (BFS) (Barron and Isaacs, 2001). The transitions to this usage and 

the incorporation of nannofossil zonations and paleomagnetic reversal chronozones in the 

geologic time scale have not been abrupt and comprehensive, and we have not attempted 

to revise usages that appear in reports that predate current preferences. We have also 

avoided superimposing current chronostratigraphic usages on older correlations; and, 

within the scope of seeking uniformity in map unit labels for a large area, we have tried 

to retain the terminologies as they were applied by the various original authors. In 

addition, we have not attempted to update fossil nomenclature used by the cited authors 

to conform to current synonymy. 
Figure 1.

SMM

SIH

SGM

SBM

SJH

SAMSJM

OR SSM

SYM

MD

SNM

TTM

SJV CR

SS

LAB

SRI

SCZI

SCTI

SNI

SMI

SCMI

AI

V o

o LA

o LB

SD o

NB o

SB o

R o LSBM

o PS

EVB

VB

Fig. 2 area

100 50 0 100 200 Kilometers

Scale
5

Figure 1 (preceding page). Index map of coastal southern California showing selected 

physiographic features and area of Figure 2. Shaded relief image prepared by R.M. 

Alvarez. 

Islands (in italics): SMI, San Miguel Island; SRI, Santa Rosa Island; SCZI, Santa 

Cruz Island; AI, Anacapa Island; SNI, San Nicolas Island; SCTI, Santa 

Catalina Island; SCMI, San Clemente Island. 

Physiographic features (in white): LAB, Los Angeles Basin; VB, Ventura Basin; 

EVB, eastern Ventura Basin; CR, California Coast Ranges; SJV, San 

Joaquin Valley; SNM, southern Sierra Nevada Mountains; MD, Mojave 

Desert; SS, Salton Sea; SYM, Santa Ynez Mountains; TTM, Topatopa 

Mountains; SGM, San Gabriel Mountains; SBM, San Bernardino 

Mountains; SMM, Santa Monica Mountains; SAM, Santa Ana Mountains; 

LSBM, Little San Bernardino Mountains; SJM, San Jacinto Mountains; OR, 

Oak Ridge; SSM Santa Susana Mountains; SIH, Simi Hills; SJH, San 

Joaquin Hills. 

Cities (black): V, Ventura; LA, Los Angeles; SB, San Bernardino; R, Riverside; PS, 

Palm Springs; LB, Long Beach; NB, Newport Beach; SD, San Diego. 

Summary 

The Topanga Formation was first named and mapped by Kew (1923; 1924), who 

described it as a sedimentary and volcanic map unit, bounded by the overlying Modelo 

Formation and the underlying Sespe or Vaqueros Formations. The name was taken from 

the Topanga anticline area, near the head of Topanga Canyon, on the north flank of the 

Santa Monica Mountains. The map unit includes the fossil locality from which Arnold 

(1907) had reported a molluscan assemblage that became widely known as the “Topanga 

fauna”. As mapped by Kew (1924), the Topanga Formation includes the Fernwood and 

Cold Creek Members of the Topanga Canyon Formation, the Conejo Volcanics, and the 

Calabasas Formation, all of which were assigned to the Topanga Group by Yerkes and 

Campbell (1979). Kew (1924) also comments that strata earlier mapped as part of the 

Vaqueros Formation in the Simi Valley area (Kew, 1919) ought to be considered as part 

of the Topanga Formation. On the south flank of the Santa Monica Mountains, beds of 

the Calabasas Formation, the Conejo Volcanics, and the Topanga Canyon Formation are 

juxtaposed against different lithofacies of the same ages by the Malibu Coast Fault. 

Arnold (1907) described his fossil locality as “... at the head of Topanga Canyon, 

three miles south of Calabasas ...”, and a more precise geographic and stratigraphic 

position is not known to us. Since the middle of the 20th Century, the best-known locality 

in that vicinity has been a road cut on Old Topanga Road, in a tributary to Dry Canyon, in 

the Malibu Beach 7.5’ quadrangle, near its northern boundary with the Calabasas 7.5’ 

quadrangle (see, especially, Susuki, 1951). As mapped by Kew (1924), that locality is 

stratigraphically near the middle of the Topanga Formation, but below the volcanic rocks 

and post-volcanic strata that he included in his Topanga Formation. Yerkes and 

Campbell (1980) place the locality within the middle part of the Cold Creek Member of 

the Topanga Canyon Formation. Kew (1924, p. 47-48) states, “... the Topanga 

formation is characterized by a fauna similar to that of the ‘Temblor formation’ of the 

San Joaquin Valley, whereas the Vaqueros contains a markedly different fauna at its type 

locality on Vaqueros Creek, Monterey County.” This comment characterizes the 
6

Topanga Formation as a biostratigraphic unit (in addition to its description as an 

allostratigraphic unit) and in the context of the North American Stratigraphic Code 

(2005), it seems to be an “assemblage biozone”. The dual characterization of the 

Topanga Formation, as both allostratigraphic and biostratigraphic, probably contributed 

to the subsequent use of the name in the Los Angeles Basin and vicinity. 

Deposition of the Topanga Group spans the time interval identified by Yerkes and 

others (1965, p. A17 and figure 9, p. A31) as the “basin-inception phase” in the evolution 

of the Los Angeles Basin. The earliest deposits of the Topanga Group in the central 

Santa Monica Mountains and the Santa Ana Mountains appear to reflect a continuation of 

the shifting shoreline conditions evidenced in the underlying Vaqueros and Sespe 

Formations and their intertonguing relationships. Deposition continued during block 

faulting that initiated the formation of localized basins and uplifted areas, some of which 

exposed basement rocks to erosion. Eruptions from one or more volcanic centers locally 

and temporarily interrupted continuing sedimentation. Volcanism ceased before the 

uppermost Topanga Group beds were laid down unconformably over the volcanics and 

older rocks. Before the end of Topanga deposition, the outlines of the ancestral Los 

Angeles and eastern Ventura Basins can be recognized. The central parts of these basins 

subsequently subsided rapidly, and received thick late Miocene and Pliocene marine 

sedimentary deposits. 

The stratigraphic changes recorded in Topanga Group deposition represent a 

disruption of earlier depositional conditions. Reconstructed Paleogene shorelines appear 

to mark a continuous west- or southwest-facing margin of the North American continent 

(e.g.: Yerkes and others, 1965; Yerkes and Campbell, 1971; Wright, 1991; McCulloh and 

others, 2000). The subsidence of the Los Angeles and Ventura basins (which received 

thick marine sedimentary deposits in the late Miocene and Pliocene), and the formation 

of discrete marine basins and ridges in the southern California borderland, appear to have 

begun in the Miocene (e.g.: Yerkes and others, 1965; Wright, 1991, fig. 36). The 

structural rearrangement is probably associated with breakup of the oceanic Farallon 

plate and the attachment of parts of the Pacific margin of the North American continental 

plate to the Pacific oceanic plate, as described by Atwater (1970), and updated by 

Atwater and Stock (1998). Topanga deposits record some effects of this structural 

upheaval by local differences in depositional environments that reflect the initial stages of 

subsidence of the Los Angeles and Ventura Basins, and by changes in source terrains as 

represented by changes in detrital characteristics of Topanga-age deposits. For example, 

chips of slate basement rocks, volcanic detritus, and fossil-bearing clasts of Paleocene, 

Eocene and Miocene strata are found locally within the Calabasas Formation of the 

central Santa Monica Mountains. 

Topanga-age deposits in the San Joaquin Hills contain the earliest appearance of 

Catalina Schist detritus in the Tertiary sedimentary record of that area. In the San 

Joaquin Hills the San Onofre Breccia (Relizian and older Luisian benthic foraminiferal 

stages -- BFS), a unit containing large angular blocks of Catalina Schist, overlies strata 

that Vedder (1975) assigned to the “Topanga Formation.” Vedder (1975) recognized 

three members of his “Topanga Formation”, the Paularino, Los Trancos and Bommer, 

youngest to oldest, respectively. Morton and Miller (2006) elevated the members to 

formation status as parts of the Topanga Group. The upper two (the Paularino and Los 

Trancos Formations) contain interbeds with varying amounts of Catalina Schist detritus 

(Vedder, 1975); but Catalina Schist detritus is not reported from the lowest unit, the 

Bommer Formation. In the San Joaquin Hills area, east of the Newport-Inglewood Fault 

Zone (fig. 2), Topanga-age beds overlie strata of the Vaqueros and Sespe Formations and 
7

are overlain by San Onofre Breccia, in turn, succeeded by Monterey Shale which also 

contains lenses with blueschist detritus. In the subsurface west of the NewportInglewood Fault Zone, some strata containing Catalina Schist detritus have been assigned 

to the Topanga Formation by some workers. However, on the Palos Verdes Peninsula, 

also west of the Newport-Inglewood Fault Zone, beds containing Catalina Schist detritus 

occur as interbeds in the Monterey Shale (middle and upper Miocene), which is underlain 

there by a Catalina Schist basement without intervening Paleogene strata (Woodring and 

others, 1946). Further northwest, Catalina Schist detritus is common south of the Malibu 

Coast Fault in sandstone and conglomerate interbeds in strata ranging from Saucesian 

BFS to upper Mohnian BFS – early Miocene to late Miocene in age. The oldest of these 

beds overlie inferred Catalina Schist basement. In the far western Santa Monica 

Mountains (fig. 1) detrital glaucophane is present in some Vaqueros (?) Formation 

sandstone (Oligocene-lower Miocene) north of the Malibu Coast Fault. Vedder and 

Howell (1976) reviewed the distribution of Miocene detritus from the Catalina Schist in 

the California Continental Borderland islands, coastal areas, and available subsea data, 

and examined implications for the sources of the detritus. 

The section to the south of the Malibu Coast Fault in the central and western 

Santa Monica Mountains consists of Catalina Schist basement overlain directly by 

Miocene basaltic volcanic rocks (chiefly submarine), the Zuma Volcanics of Yerkes and 

Campbell (1979). The volcanics are succeeded by marine mudstone, sandstone, and 

conglomerate of the Trancas Formation, which is succeeded by calcareous and dolomitic 

shales of the Monterey Shale. Catalina schist detritus occurs in sandstone and 

conglomerate interbeds in both the Monterey Shale (‘Relizian or Luisian’ and Mohnian 

BFS’s in this area) and the Trancas Formation (Saucesian and ‘Relizian or Luisian’). In 

general, this section resembles the section in the Palos Verdes Peninsula, and lacks the 

Cretaceous and Paleogene strata recognized in the Santa Monica Mountains to the north 

of the Malibu Coast Fault. The San Joaquin Hills is the northernmost area where 

Catalina Schist detritus is recognized in beds of middle Miocene age that are assigned to 

the Topanga Group and that clearly overlie Paleogene strata associated with an eastern 

basement source terrain. Blake’s (1991, Fig. 2.) columnar section for the San Joaquin 

Hills suggests that the lower part of the Bommer Formation is older (possibly as old as 

Saucesian BFS) than the base of the Topanga Group (Relizian BFS) in the Santa Monica 

and Santa Ana Mountains sections. To the north of the San Joaquin Hills, the San Onofre 

Breccia (in the restricted usage of Yeats, 1973, p. 123) occurs in the subsurface only as 

far north as the Huntington Beach oil field (Yeats, 1973, Fig. 1). Further north, beds in 

the subsurface that contain Catalina Schist detritus are referred to as “schistconglomerate” (as contrasted with poorly-sorted sedimentary breccia containing abundant 

large clasts of Catalina Schist). Schist-conglomerate beds are interbedded with sandstone 

derived from eastern sources (Yeats, 1973, p. 123), and lie below siltstone from which 

Luisian microfossils were reported by Wissler (1943). Because most subsurface 

correlations with the “Topanga Formation” have been based on the presence of Relizian 

or lower Luisian foraminifers, it seems likely that any equivalents of a Saucesian BFS 

Bommer Formation would not have been included in subsurface strata assigned to the 

“Topanga Formation.” Figure 2 shows the distribution of outcrops that have been 

assigned to the “Topanga Formation” (Group) and of coeval strata commonly assigned to 

the middle Miocene part of the Monterey Shale. 
LAB

EVB

Long Beach 30' x 60' quadrangle

Los Angeles 30' x 60' quadrangle San Bernardino 30' x 60' quadrangle

Santa Ana 30' x 60' quadrangle

SC

OR SS

SF

SM

SR

SI

NH

V

SYC

BM

MC

BC

SM

H

N-I

PV

T-H

RC

PH

SG

W

E

SA

PB

VT

SJ

o LA

o LB

o RIV

SFV

o StC

SPB

o WH

FM o

SA o

o SB

SM o

SG

SA

VT

SC

AN

TA RV

34o 30' 

0'

33o  30' 

117o 00'

117o 00' 

9o 00'

19o 00'

o G

CR

0 50 75 Kilometers

Scale

25 25
9

Figure 2 (preceding page). Distribution of Topanga Group outcrops and of coeval beds in 

the vicinity of the Los Angeles and eastern Ventura Basins. Map shows selected 

features, city centers, and faults. 

Physiographic and geologic features: EVB, eastern Ventura Basin; LAB, Los 

Angeles Basin; SFV, San Fernando Valley; TA, Topanga Anticline area; RV, 

Russell Valley area. 

Cities: FM, Fillmore; StC, Santa Clarita; SB, San Bernardino; LA, Los Angeles; SM, 

Santa Monica; WH, Whittier; RIV, Riverside; SA, Santa Ana; LB, Long 

Beach; G, Glendora. 

Faults – SC, San Cayetano; OR, Oak Ridge; SS, Santa Susana; SF, San Fernando; 

SM, Sierra Madre; SG, San Gabriel; PB, Punchbowl; SA, San Andreas; VT, 

Vincent Thrust; SR, Santa Rosa; SI, Simi; SYC, Sycamore Canyon; BM, 

Boney Mountain; AN, Anacapa; SM, Santa Monica; BC, Benedict Canyon; 

H, Hollywood; W, Whittier; SJ, San Jacinto; E, Elsinore; SC, Shady Canyon; 

PH, Pelican Hills; N-I, Newport-Inglewood; T-H, Thums-Huntington Beach; 

PV, Palos Verdes; RC, Redondo Canyon; SPB, San Pedro Basin. 

Hachured line north of the Malibu Coast Fault is the approximate limit of an 

area where outliers and windows in Cretaceous through middle Miocene strata 

indicate complex low-angle faulting in late-middle Miocene, possibly extending 

into early-late Miocene. 

Dashed line between the Newport-Inglewood zone of faulting and folding 

and the Palos Verdes fault (from Wright, 1991, Figure 5) indicates subsurface 

boundary separating eastern facies assigned to the Topanga Group from western 

facies including “schist conglomerate” (beds containing conglomerate clasts 

consisting of greenschist or blueschist, or both, metamorphic facies, but which 

are not assigned to the San Onofre Breccia). 

Compiled from digital source maps (Los Angeles, San Bernardino, Santa 

Ana, and Long Beach 1:100,000-scale geologic maps), with supplemental data from 

Wright (1991). 

While the Topanga nomenclature was being extended to correlative units, the 

tools for geologic correlation were also evolving. The last half of the 20th century saw 

significant refinements and revisions of the geologic time scale for the Miocene Epoch. 

New correlation tools, including zonation by diatoms and calcareous nannofossils, and a 

paleomagnetic time scale, were combined with isotope age data to provide an improved 

correlation of provincial and world-wide geologic ages. Figure 3 (after McCulloh and 

others, 2002, Figure 4) illustrates these correlations for the southern California Miocene. 

 As a result of these revisions, “Topanga Formation” strata assigned to a “middle 

Miocene age” in some earlier studies are now recognized as of early and middle Miocene 

age; the underlying Vaqueros Formation strata are now recognized as ranging from 

Oligocene to early Miocene in age; and the overlying Modelo Formation is recognized as 

of middle and late Miocene age. The isotope ages of Miocene volcanic rocks, as 

summarized by McCulloh and others (2002), indicate that many of volcanics found 

around the margins of the Los Angeles Basin fall within the age range of the Conejo 
10

Volcanics, and are mostly within the middle Miocene. However, some volcanics from 

the southern California Borderland may be of early Miocene age. The age-range 

embraced by the entire Topanga Group (late Saucesian to early Mohnian BFS), as shown 

on Figure 3, is correlative with paleomagnetic chrons C5D through C5A, and is about 18 

ma to about 12 ma. The tectonism that accompanied Topanga deposition is associated in 

time with the capture of the Monterey microplate by the Pacific plate, which Atwater and 

Stock (1998, p. 392) place at about 18 ma. 

The Monterey microplate is a fragment of the Farallon Plate that became attached 

on the east to the Pacific Plate, at which time it ceased subducting eastward beneath the 

North American Plate (Atwater and Stock (1998). This probably marks the earliest time 

that part or all of the Salinian Block (a fragment of the North American Plate) could 

begin to move with the Pacific Plate. The Salinian block is now bounded on the east by 

the San Andreas Fault and on the west by the continental slope, where it is attached to 

Pacific Plate oceanic crust. The southern boundary lies within the western Transverse 

Ranges. Further south, the Farallon Plate continued subduction eastward. The area south 

of and adjacent to the Salinian Block was subjected to extensional deformation in middle 

Miocene to earliest Pliocene time, followed by compressional deformation in later 

Pliocene, Pleistocene, and Holocene time (Campbell and Yerkes, 1976, p. 552 and fig. 5). 

With the possible exception of some northward overlap in the northern part of the eastern 

Ventura Basin, Topanga Group deposition was entirely south of the southern margin of 

the Salinian Block, during the early stages of extensional deformation. 

Even though contiguous deposition and common provenance were not 

everywhere demonstrated, the name Topanga Formation has been extended, chiefly by 

biostratigraphic correlation, from the allostratigraphic unit initially mapped and described 

by Kew. It has been applied to age-correlative units based on molluscan fossils for 

littoral and shelf depositional environments (e.g., Durham, 1954), and also on foramiferal 

fossils in shelf, slope, and bathyal depositional environments (e.g., Kleinpell, 1938; 

Wissler, 1943). In the subsurface of the Los Angeles basin, strata correlated with the 

“Topanga Formation” on the basis of Relizian BFS and lower Luisian BFS Foraminifera 

have been assigned to the Topanga Group or the “Topanga Formation”. In regional 

summary publications, some authors have used “Topanga Group” (e.g., Blake, 1991; 

Wright, 1991), but have not been comprehensive in reassigning previously designated 

members to formation status. Other workers, however, have continued to use the term 

“Topanga Formation” (e.g., Schoellhamer and others, 1981; Morton, 2004). In 

addressing a need for uniformity in stratigraphic nomenclature for the purpose of edgematching geologic map compilations for the Southern California Areal Mapping Project 

(SCAMP) we chose to use the term “Topanga Group” for the middle Miocene shelf, 

paralic, volcanic, and bathyal fan strata; however, we recognize that some older 

formations within the group may have begun to deposit as early as the Saucesian BFS, 

and some younger units may not have ceased their deposition until early Mohnian BFS 

(fig. 3). 
Figure 3. Chronological chart showing published ages of Miocene volcanic rocks in 

 and around the Los Angeles basin, from McCulloh and others (2002). 

 References to pre-2002 publications are shown beside rows; ages in the 

 last three rows are from the study by McCulloh and others (2002).

11
12

Figure 3 (preceding page). Chronological chart showing ages of Miocene rocks in and 

around the Los Angeles Basin, from McCulloh and others, (2002, fig. 4, p. 10). 

The chart compares isotope ages of Miocene volcanic rocks and shows their 

correlation with Miocene subdivisions, paleomagnetic chrons, magnetic polarity, 

calcareous nannofossil (nannoplankton) zones, benthic foraminiferal stages, California 

molluscan stages, and terrestrial vertebrate stages. Solid lines represent volcanic ages 

with uncertainties and dashed lines represent less-certain age ranges. (The 

chronostratigraphic and biostratigraphic data were adapted from the compilation by 

Barron and Isaacs, 2001.) 

Chronology of Usage 

The following chronologic list of publications outlines a history of the usage of 

“Topanga Formation” and “Topanga Group” as applied in and around the margins of the 

Los Angeles Basin. The chronological list includes references to some relevant 

paleomagnetic and isotope age information, as well as to some revisions of the age ranges 

of Miocene biostratigraphic units. 

1907 – Arnold (1907) described fossil mollusks from “lower Miocene” at the head of 

Topanga Canyon, 3 miles south of Calabasas, Los Angeles County, California. 

(At this time, the recognized Miocene subdivisions were “lower” and “upper”; 

“middle” was a later revision.) New species at this locality were shown to be 

accompanied by previously known species including Turritella ocoyana Conrad. 

This locality is one where many mollusk species are preserved in abundance in a 

relatively thin stratigraphic interval. (Although the range of Turritella ocoyana

extends to subjacent and superjacent strata, it is abundant at the locality and in 

contiguous strata in many parts of the Santa Monica Mountains.) Since the early 

1950’s, the best known fossil locality is not within the Topanga Canyon drainage 

area, but is a road cut on Old Topanga Canyon Road, just northwest of the divide 

between Old Topanga Canyon and a tributary to Dry Canyon. Old Topanga 

Canyon is an east-southeast flowing tributary to Topanga Canyon, and the present 

route of Topanga Canyon Road follows a south-flowing tributary further to the 

east.) 

1923 – In a short paper summarizing stratigraphic observations in a large part of southern 

California, Kew (1923) named the Topanga Formation as a middle Miocene 

marine series, and restricted the name, Vaqueros Formation, to lower Miocene 

series. The paper proposed revisions of some terminology used by Eldridge and 

Arnold (1907), and extends the name, Topanga Formation, to similar stratigraphic 

units exposed in the Puente Hills, Santa Ana Mountains, and San Joaquin Hills, 

also providing a brief description of each section. Kew’s (1923) nomenclature of 

Miocene formations as Vaqueros (lower Miocene), Topanga (middle Miocene), 

Mint Canyon (upper Miocene), and Modelo (upper Miocene) was subsequently 

used by many workers in southern California. 

1924 – Kew (1924) published the first map showing a stratigraphic unit named the 

Topanga Formation. The map shows the Topanga Formation in the Topanga 

Anticline area underlying an unconformity at the base of the Modelo Formation, 

with its base on the Sespe Formation. As mapped, the formation includes a thin 

interbed of basaltic volcanic rocks. The map also shows the base of the formation 

further west, in the Russell Valley-Conejo Valley area, as a volcaniclastic 
13

conglomerate underlain by volcanics, which he describes as “...the lower 

Miocene igneous series.” 

The southern boundary of Kew’s map area is north of most of the western 

Santa Monica Mountains. He mapped the base of the Modelo Formation only in 

the area of the Topanga Anticline (on the east) and the Russell Valley area (on the 

west), and did not delineate the rocks that lie below the Modelo between these 

areas. As a result, Kew did not recognize that the volcanics he mapped in the 

Russell Valley area were stratigraphically equivalent to the thin volcanic member 

he mapped as within the Topanga Formation (middle Miocene) in the Topanga 

Anticline area, instead referring to the volcanic rocks of the Russell Valley area as 

a “... lower Miocene igneous series.” Subsequent mapping (Durrell, 1954) 

showed that the thin volcanic member mapped by Kew in the Topanga Anticline 

area becomes very much thicker progressively westward (the Middle Topanga 

Formation of Durrell, 1954; the Conejo Volcanics of Yerkes and Campbell, 

1979), that the post-volcanic Topanga (Upper Topanga Formation of Durrell, 

1954; Calabasas Formation of Yerkes and Campbell, 1979) becomes very thin in 

the Russell Valley area, and that the base of the Modelo Formation becomes 

progressively more conformable westward over the underlying Topanga. 

Kew also comments (1924, p. 47-48) about earlier work: “In the report on 

Simi Valley (Kew, 1919) the series of strata here named Topanga formation were 

included in part in the Vaqueros formation and in part in the Modelo formation. 

Later work has shown that these rocks, which are well exposed along the Topanga 

anticline, should be separated as a distinct formation. Wherever recognized they 

are unconformably overlain by the Modelo formation as here restricted.” His 

observations from the Simi Valley area probably led him to include the Vaqueros 

Formation (as well as the Sespe Formation) as a lower limiting horizon for the 

Topanga. Kew (1924) also recognized that many molluscan fossils were similar 

to those in the Temblor Formation of the central California Coast Ranges, and 

restricted the usage of Vaqueros Formation to underlying beds. 

1926 – English (1926) mapped and described the Topanga Formation in the Puente Hills 

and Santa Ana Mountains north of latitude 33o

 45’. He assigned a middle 

Miocene age to the formation and stated that it “... belongs to the Turritella 

ocoyana faunal zone.” 

1931 -- Hoots (1931) mapped the Santa Monica Mountains east of Topanga Canyon 

Road; the map does not extend westward to the area where Kew (1924) described 

the type section containing Arnold’s (1907) “Topanga fauna”. Note that the 

“Topanga Canyon Road” that marks the western boundary of Hoots’ map is not 

the “Old Topanga Road” where Arnold (1907) reported the “Topanga fauna” 

locality. Hoots (1931) used the name “Topanga Formation” to include prevolcanic, volcanic, and post-volcanic “middle Miocene” rocks. He recognized 

that both intrusive and extrusive volcanics are present, but included both in the 

same map unit with the same label. Hoots’ map locations and fossil lists indicate 

that nearly all of the molluscan collections assigned to the “Temblor Stage” are 

from beds intruded by, interbedded with, or stratigraphically below volcanics. In 

the post-volcanic strata assigned to the Topanga Formation, mollusk species are 

rare, and only one collection contained an assemblage indicating a “Temblor 

Stage”. 

1932 – Gale’s (1932) introductory chapter to a guidebook that contains contributions 

from many authors includes a correlation chart by W. P. Woodring that applies 
14

the name “Topanga formation” to strata in the San Pedro Hills (Palos Verdes 

Peninsula). The chapter by H. W. Hoots, “General Geology of the Los Angeles 

Basin”, includes a stratigraphic chart that describes the “known distribution” of 

the “Topanga formation” as including the San Joaquin Hills, Santa Ana 

Mountains, Puente Hills, Repetto Hills, San Pedro Hills, Santa Monica 

Mountains, and beneath the Los Angeles Basin. The chapter by W.S.W. Kew 

(1932) describes an excursion route from Los Angeles to Santa Barbara, and 

includes a map showing the distribution of the “Topanga formation” north of the 

34th parallel. 

1932 – Loel and Corey’s (1932) classic volume on the Vaqueros Formation includes a 

check list (p. 168-174) of the “Fauna of the Temblor Horizon ...” indicating 

extensive collections from the Santa Monica Mountains from beds called Topanga 

Formation by Kew (1924). Their discussion of the relationship of the “Vaqueros 

fauna” to the “Temblor fauna” (p. 139-156) recognizes an overlapping of ranges 

they identified as a “Vaqueros-Temblor transition faunule and zone”; however, 

they assert (p. 139) that “...The Temblor fauna assemblage invariably occurs 

stratigraphically above that of the Vaqueros, although in some sections there is a 

minor intermediate association of a few forms otherwise confined to one or the 

other formation....” Their chapter, “Historical Review of the Paleontology of the 

Vaqueros Formation”, (Loel and Corey, 1932, p. 46-50) provides an excellent 

summary of literature on the California lower and middle Miocene Paleontology 

and stratigraphic nomenclature from 1849 through 1930, and discusses conflicting 

conclusions of different authors about distinguishing between the Vaqueros and 

Temblor as stratigraphic units on the basis of their macrofossil contents. Their 

correlation chart (Loel and Corey, 1932) suggests that the pre-volcanic beds that 

Kew (1924) included in his Topanga Formation fall in the “Vaqueros-Temblor 

transitional zone”, astride the boundary between lower Miocene and middle 

Miocene series. The chart also refers the age of the “Temblor fauna” to middle 

Miocene, whereas many earlier workers considered it an “upper part” of the lower 

Miocene at a time when the California Miocene series was subdivided into only 

upper and lower parts. 

1938 – Kleinpell (1938, p. 92) coined new names for six “California Miocene Stages” 

and subdivided each “Stage” into “Zones” based on benthic foraminiferal 

assemblages. Kleinpell’s correlation chart (his figure 14) equates the base of the 

Zemorrian Stage with the base of the lower Miocene Series, equates the 

Saucesian-Relizian Stage boundary with the approximate base of the middle 

Miocene Series, and equates the Luisian-Mohnian Stage boundary with the 

approximate base of the upper Miocene Series. Kleinpell’s biozone of Turritella 

inezana extends from the base of the Zemorrian Stage to the middle of the Luisian 

Stage, and the biozone of Turritella ocoyana extends from the base of the 

Saucesian Stage to the Luisian-Mohnian Stage boundary.) 

Kleinpell (1938) chose not to include the Topanga Formation of the Santa 

Monica Mountains in his correlation chart (his figure 14), citing “...the vagueness 

of its’ stratigraphic limits...”, instead showing overlapping Vaqueros and 

Temblor Formations. This is difficult to reconcile with an upper limit marked by 

the unconformity at the base of the Modelo Formation and a lower limit imposed 

by nonmarine redbed sandstone of the Sespe Formation; however, it may relate to 

some lithologic similarities between the Modelo Formation and the upper part of 

the Topanga Formation as mapped by Hoots (1931). 
15

1938 – Soper (1938) extended mapping about 5 miles westward from the western edge of 

Hoots’ (1931) map to Malibu and Las Virgenes Canyons, filling the gap between 

the maps of Kew (1924) and Hoots (1931) and mapping the Topanga Anticline 

area in more detail. His map and text recognize the three-fold subdivision of the 

Topanga Formation, into lower and upper members of marine sandstone, siltstone 

and shale, separated by a middle member of volcanic rocks. His map includes the 

name locality for the Topanga Formation. His base maps (and, presumably, his 

compilation sheets) were the Dry Canyon (northern) and Las Flores (southern) 6-

minute USGS topographic quadrangles at a scale of 1:24,000. 

1943 –Wissler (1943, p. 209-234), in the multiple-authored California Division of Mines 

Bulletin 118, “Geologic formations and economic development of the oil and gas 

fields of California”, described the stratigraphic formations of producing zones in 

Los Angeles Basin oil fields and their correlations using foraminifers from wells 

and some surface outcrops in peripheral mountains and foothills. He correlated 

foraminiferal-based zones recognized in subsurface sections with Hoots’ section 

of the Modelo Formation on Topanga Canyon Boulevard. He did not consider the 

pre-Modelo Topanga Formation of Hoots to contain Luisian foraminifers. Strata 

in oil fields of the west-side of the Los Angeles Basin that contain Luisian 

foraminifers were correlated with the Monterey Formation as exposed in the Palos 

Verdes Hills (including beds containing Catalina Schist detritus). He found strata 

containing Luisian foraminifera probably absent from east-side fields; and 

identified the Topanga Formation as containing Relizian and upper Saucesian 

foraminiferal assemblages. 

Wissler’s views apparently represented those of many 

micropaleontologists engaged in zoning Miocene subsurface strata in producing 

oil fields. Foraminifera recovered from drill cores and cuttings were the basis for 

detailed correlations of producing zones, most of which were in Pliocene or 

“upper Miocene” strata, and only a few in “middle Miocene” strata. In that 

scheme, most of the subsurface “Topanga” reported in the Los Angeles Basin, 

from east of the Newport-Inglewood zone and north of the San Joaquin Hills, 

probably excludes correlatives of the Calabasas Formation. 

In the same volume (Jenkins, 1943), reports on the oil fields of the 

Ventura Basin do not use the term, Topanga Formation. Instead, formation names 

used for middle Miocene marine strata are Rincon Formation or Temblor 

Formation. 

1944 -- The correlation chart (widely referenced) and discussions by the Western 

Cenozoic Subcommittee (Weaver and others, 1944) does not include the name 

Topanga nor describe its’ stratigraphic position. Key molluscan elements are 

named as evidence of inclusion in the “Temblor Stage”. 

1951 – In a definitive paleontological study of the type area of the Topanga Formation, 

Susuki (1951) listed 103 species from a section about 8,150 feet thick and figured 

39 of them. He identified a lower fossiliferous zone, succeeded by a thick 

unfossiliferous zone, a second fossiliferous zone, extrusive basalt, and a third and 

fourth fossiliferous zones separated by alternating sandstone and shale. The 

nomenclature proposed by Yerkes and Campbell (1979) placed Susuki’s lower 

two fossiliferous zones in the Saddle Peak Member and Cold Canyon Member, 

respectively, of the Topanga Canyon Formation, separated by the nonmarine and 

paralic Fernwood Member of the Topanga Canyon Formation. The extrusive 

basalt is contiguous with the thick section of Conejo Volcanics further to the west, 
16

and the upper two fossiliferous horizons of Susuki (1951) lie within the Calabasas 

Formation of Yerkes and Campbell (1979). Although Susuki’s results were not 

published, his documentation of the fossil elements in the type Topanga 

Formation influenced many workers in their assignment of strata containing those 

species assemblies to the Topanga Formation in southern California. 

1954 – California Division of Mines Bulletin 170, R.H. Jahns, ed., contains several map 

sheets, charts, and reports that use “Topanga Formation” 

The map and text discussion by Woodford and others (Chapter II, p. 71 

and Plate 1) referred middle Miocene strata in and around the margins of the Los 

Angeles Basin to the “Topanga Formation”, the “Monterey shale”, or the “San 

Onofre Breccia.” Differences in provenance of sandstone interbeds in deep water 

shales distinguished the upper Miocene Puente and Modelo Formations from the 

coeval parts of the Monterey shale. They report a mollusk (Aequipecten 

andersoni) from the “Buzzard Peak conglomerate member of the Topanga 

Formation” in the San Jose Hills, in the northeastern part of the Los Angeles 

Basin; except for that locality, their correlation appears to be based on middle 

Miocene foraminifera from interbedded (intertonguing) deep-water, fine-grained 

facies (especially in subsurface strata). 

Durrell’s map (Map Sheet 8) summarizes Santa Monica Mountains' 

stratigraphy and recognizes that three divisions of middle Miocene strata are 

extensive enough to be of formation rank. He named these units the “Upper, 

Middle and Lower Topanga Formations” respectively. His map shows 

continuous contacts for base and top of each formation, which demonstrate that 

the base of the Topanga Formation as mapped by Kew in the west (Russell 

Valley-Conejo Valley area) is stratigraphically equivalent to the contact at the top 

of Kew’s “volcanic member” at the Topanga Anticline. The map also shows the 

unconformity at the base of the Modelo Formation extending west of Hoots’ 

(1931) map from Topanga Canyon Road (the western edge of Hoots’ map) as far 

as Las Virgenes Canyon, including the area north of the type “Topanga 

Formation”. The informal nomenclature proposed by Durrell (1954) was used by 

subsequent mappers until the 1961 publication of the North American 

Stratigraphic Code (more recently updated; The North American Commission on 

Stratigraphic Nomenclature, 2005) made some revisions advisable. 

Durham’s stratigraphic chart (Chapter 3, p. 24), which is keyed to the time 

scale used by Weaver and others’ (1944), includes the “Topanga Formation” in 

both eastern and western parts of the Los Angeles Basin. The chart does not 

subdivide the Miocene, but shows “Vaqueros Stage” entirely in the lower part of 

the Miocene, succeeded by the “Temblor Stage”. 

Oakeshott and others’ correlation chart (Chapter 3, Plate 1) of sedimentary 

formations in southern California recognizes “Topanga fm.” in coastal San Diego 

and Orange Counties, Santa Ana Mountains and Puente Hills, Santa Monica 

Mountains, and eastern Ventura Basin (Simi Valley area). The chart places the 

Vaqueros Formation in the early Miocene and the Topanga Formation in the 

middle Miocene, as in earlier usage. 

1954 – The geologic map of the northern Santa Ana Mountains by Schoellhamer and 

others (1954) shows substantial revisions of English’s (1926) mapping of the 

Topanga Formation, and extends his mapping of the formation southeastward 

nearly six miles. 
17

In 1954 “Topanga Formation” was widely accepted usage for shallow 

marine rocks containing the “Turritella ocoyana fauna” (Temblor CMS fossil 

assemblage) around the margins of the Los Angeles Basin. In parts of the basin 

where strata represent a deeper-water environment, finer-grained strata containing 

foraminifers referred to the middle Miocene were also assigned to the “Topanga 

Formation”, particularly where they show evidence of source areas to the north 

and east. In the western part of the Los Angeles Basin, deep marine strata of the 

same age were referred to the Monterey Formation. (The Monterey may include, 

in part, distal equivalents from the some of the same terrigenous sources as the 

Topanga, but is notable for interbeds containing clastic detritus from a “western” 

sediment sources (i.e., Catalina Schist detritus) and a greatly increased relative 

volume of marine organic material, which predominates in some sections. 

Sandstone intervals in the Monterey Formation also generally include a higher 

proportion of quartz relative to more-easily altered minerals and rock-fragments.) 

This usage of the name, Topanga Formation, was embedded in reports by the U.S. 

Geological Survey, the California Division of Mines, academia (as represented by 

faculty from UCLA, UCB, Pomona College, Caltech, etc.), and by most 

petroleum exploration and production geologists and paleontologists. 

1955 – Shelton’s map and discussion of the Glendora volcanic rocks (Glendora-AzusaPomona-San Jose Hills area) assigned strata overlying the volcanics to “...the 

middle Miocene Topanga formation...”, and notes that although coarse-grained 

sandstones predominate, some with boulders of San Gabriel Mountains basement 

rocks, the fossil control reported is entirely from foraminifers in fine-grained 

interbeds. Interbeds included in the Glendora Volcanics yielded collections of 

foraminifers and fish scales of which “... all indicate Luisian (upper middle 

Miocene) age” (Shelton, 1955, p. 79). The overlying “Topanga Formation” was 

assigned to uppermost Luisian or possible lowest Mohnian Stages of Kleinpell 

(1938). 

1957 – Vedder and others (1957) described three members of the Topanga Formation in 

the San Joaquin Hills. The map explanation shows an upper member, the 

Paularino Member, as lower Luisian or Relizian Stage, and includes andesite flow 

breccia and pods of sedimentary breccia in which the predominant clasts are 

andesite. The Paularino Member overlies the Los Trancos Member, which 

contains sparse Relizian foraminifers and consists of dark gray siltstone with 

interbeds of light gray medium-grained sandstone that is locally tuffaceous and 

contains clasts of glaucophane schist. The Los Trancos Member overlies the 

Bommer Member, which contains Turritella ocoyana and other early to middleMiocene mollusks. The Bommer Member is composed chiefly of coarse-grained 

sandstone, containing thin lenticular pebble conglomerate, interbedded in the 

middle and upper parts of the unit and thin beds of fine- to medium-grained 

sandstone. Catalina Schist detritus is present in the Paularino and Los Trancos 

Members, but not in the Bommer Member (Vedder, 1957; Vedder, 1975). 

Unlike the section on the Palos Verdes Hills, where detrital glaucophane 

schist is found in beds overlying Catalina Schist basement, the parts of the section 

in the San Joaquin Hills that carry schist detritus overlie the Bommer Member of 

Vedder (1957), which, in turn, overlies older Tertiary and Upper Cretaceous 

strata. 

1960 -- Sullwold (1960) recognized bathyal fan depositional characteristics in the 

Modelo Formation (Tarzana Fan). Apparently he did not recognize that the 
18

“Upper Topanga Formation” of Durrell (1954; Calabasas Formation of Yerkes 

and Campbell, 1979) is also dominated by submarine fan deposits in parts of the 

Santa Monica Mountains, and some strata from the “Topanga Formation” may 

have been included in his description of the Tarzana Fan. 

1961 -- American Commission on Stratigraphic Nomenclature releases first version of 

the “Code of Stratigraphic Nomenclature” published in the American Association 

of Petroleum Geologists Bulletin, v. 45, no. 5, p. 645-665. Constraints imposed 

by the code, and subsequent changes and additions, flag a need for substantial 

revision of informal and formal stratigraphic nomenclature regarding the Topanga 

Formation of Kew (1924) and the Upper, Middle, and Lower Topanga Formations 

of Durrell (1954). 

1961-1973 – A series of preliminary geologic maps (scale 1:12,000) of parts of the 

Malibu Beach, Topanga, and Point Dume 7.5’ quadrangles were open-filed by the 

U.S. Geological Survey as progress reports on mapping in the Santa Monica 

Mountains, under a cooperative program with the Los Angeles County Engineer 

Department. These maps used Durrell’s informal stratigraphic nomenclature, 

“Upper, Middle, and Lower Topanga Formations.” Mollusk and foraminifer 

fossils collected from these strata were reported as “middle Miocene” (see, for 

example, Schoellhamer and Yerkes, 1961; Schoellhamer and others, 1962; Yerkes 

and others, 1964; Campbell and others, 1970; Yerkes and others, 1973. Their 

earlier experience mapping in the Santa Ana Mountains quickly led R. F. Yerkes 

and J. E. Schoellhamer to recognize many close similarities in the stratigraphic 

sections of the Santa Ana and Santa Monica Mountains). 

1964 -- Durham and Yerkes (1964) list fossil mollusks from the Topanga Formation in 

the Puente Hills, whereas the earlier work (English, 1926) had found none. 

1965 -- Yerkes and others (1965), in summarizing the geology of the Los Angeles Basin, 

generally avoided using formation names in their text, instead referring to a timestratigraphic nomenclature; however, their correlation chart (Plate 1) lists the 

Topanga Formation, and shows its age as spanning the Relizian and Luisian 

Stages of Kleinpell, 1938), which they equate with a middle Miocene age. Their 

assignment correlates Topanga deposition with a “basin-inception phase” in the 

evolution of the Los Angeles Basin, during which a persistent Late Cretaceous 

through early Miocene “prebasin phase of deposition” was disrupted by an 

episode of emergence and erosion that probably varied in degree and duration 

from one part of the area to another (Yerkes and others, 1965, p. A16-A19). In 

that framework, deposition of middle Miocene strata represents the transition 

from a relatively quiet tectonic state, dominated by broad regional features, to a 

different tectonic regime including accelerated subsidence and deposition in 

restricted areas during late Miocene through early Pleistocene time. (At the time 

this report was published, the “Vaqueros” CMS was still considered early 

Miocene and the Topanga molluscan fauna was considered middle Miocene.) 

1965 – Campbell and others (1965) used Durrell’s informal stratigraphic nomenclature in 

developing structural interpretations of rock distributions in the central Santa 

Monica Mountains. 

1970 – The preliminary geologic map (scale 1:12,000) of the Point Dume quadrangle by 

Campbell and others (1970) used the informal nomenclature “Upper, Middle, and 

Lower Topanga Formations of Durrell (1954)” for middle Miocene strata north of 

the Malibu Coast Fault. South of the Malibu Coast Fault they used informal 

nomenclature: “unit b” for mudstones and interbedded sandstone and 
19

conglomerate (Trancas Formation of Yerkes and Campbell, 1979) and “unit bv” 

for volcanics (Zuma Volcanics of Yerkes and Campbell, 1979) underlying and 

intertonguing with the mudstone unit. Cretaceous, Paleogene, and Neogene 

conglomerates north of the Malibu Coast Fault contain clast compositions that 

indicate an eastern basement source terrain, and sandstone units are dominated by 

arkoses and arkosic wackes. South of the Malibu Coast Fault, coarse clastic 

interbeds contain Catalina Schist detritus as well as more-durable kinds of eastern 

basement clasts, and sandstone beds are generally quartz arenites. (Color 

publication of the map was deferred until the stratigraphic nomenclature for units 

in the central and western Santa Monica Mountains could be brought into 

conformity with the Code of Stratigraphic Nomenclature.) 

1970 -- Lamar (1970) mapped and described three lithologic subdivisions in strata he 

assigned to the “Topanga Formation” at the east end of the Santa Monica 

Mountains, the southern end of the Verdugo Mountains, and the Elysian Hills, as 

well as an undivided subsurface “Topanga” unit at a depth of about 6,000 ft on the 

north flank of the Los Angeles Basin. Foraminifera and fish fossils indicate 

Luisian and Relizian ages for the Topanga map units; most beds appear to 

postdate extrusive Miocene volcanics, but some predate probable intrusive 

diabase. The overlying late Miocene beds are referred to the Puente Formation 

(Lamar, 1970). 

The map and sections by Lamar (1970) indicate that the “Topanga 

Formation” overlaps San Gabriel Mountains basement rocks, as represented by 

the Wilson Quartz Diorite, and the Santa Monica Mountains basement as 

represented by the Santa Monica Slate. The map and section relationships 

indicate that significant parts of the Topanga Group section in Lamar’s map area 

postdate much of the major fault displacement that is inferred to have resulted in 

the juxtaposition of the two basement terrains. 

1971 – Yerkes and Campbell (1971, p. 222-223) correlated Late Cretaceous and Tertiary 

strata, particularly Paleogene and early Neogene shoreline facies, in the Santa 

Monica Mountains with those in the Santa Ana Mountains. (This work was an 

attempt to reconcile relations and offsets along the Malibu Coast Fault and its 

eastward extension, including connected structures.) They recognized correlative 

shoreline facies in the Vaqueros and Topanga Formations which, at that time, 

were equated with early and middle Miocene ages, respectively. 

Subsequent paleomagnetic studies developed evidence that significant 

rotation of crustal blocks had occurred in the western Transverse Ranges (e.g., 

Kamerling and Luyendyk, 1979; Hornafius and others, 1986). The translational 

fault offsets proposed by Yerkes and Campbell (1971) are not, by themselves, 

adequate to explain the structural evolution of the present rock distribution. 

Although the Cretaceous, Paleogene and early Neogene shoreline correlations are 

probably still correct, the initial positions have not been satisfactorily 

reconstructed. Although the basement rocks of the Santa Ana and Santa Monica 

Mountains are similar, sparse paleontologic collections from the thick Jurassic 

slates of the two areas are, at least in part, of different ages (Jones and others, 

1976), raising some uncertainty about their equivalence.) 

1972 – Addicott (1972) reported his stratigraphic studies in the Temblor Range which 

showed the type Temblor Formation to include members as old as Refugian (early 

Oligocene) and as young as Relizian, spanning the age range of the entire 
20

“Vaqueros Stage”. As a consequence, he recognized that the age range of the 

“Temblor Stage” is more restricted than the age range of the Temblor Formation. 

 1972 – Ingle (1972) documented the paleobathymetric and paleoecological implications 

of the Paularino, Los Trancos, and Bommer Members of the Topanga Formation 

in the San Joaquin Hills area. He assigned the entire sequence to the Relizian and 

lower Luisian Stages. 

1974 – In a landmark paper, Berggren, W.A., and Van Couvering, J.A. (1974) presented 

a Neogene time scale correlating zones based on planktonic microfossils, 

calcareous nannoplankton, radiolaria, and coccoliths with paleomagnetic 

reversals, European stages, New Zealand marine stages, European stages, North 

American Mammalian stages, and west coast (California) marine stages. The 

paper presents a world-wide correlation framework for the Cenozoic Period which 

has formed the basis for continuing work to refine and modify these correlations. 

California marine stages are identified with the names of the benthic foraminiferal 

stages erected by Kleinpell (1938); molluscan stages were not included. 

1975 – Vedder (1975) revised the 1957 geologic map of the San Joaquin Hills-San Juan 

Capistrano area, and included expanded descriptions of the members of the 

Topanga Formation. He also added extensive subsurface data from wells drilled 

in the area (Vedder, 1975). 

The Topanga Formation of Vedder (1975) in the San Joaquin Hills 

includes beds containing blueschist detritus, whereas the Topanga Formation of 

Schoellhamer and others (1981) in the northern Santa Ana Mts. does not. The 

earliest appearance of blueschist detritus in the San Joaquin Hills is in the Los 

Trancos Formation. Strata in the type locality for the Topanga Formation of Kew 

(1924), in the Santa Monica Mountains, do not contain blueschist detritus. In the 

Santa Monica Mountains, south of the Malibu Coast Fault, blueschist detritus is 

found in interbeds in the Monterey Shale (Mohnian and ‘Relizian or Luisian’) and 

in the underlying Trancas Formation (Saucesian and ‘Relizian or Luisian’). In 

several places along the Malibu Coast Fault, the Trancas is juxtaposed against 

Topanga and Vaqueros Formation strata that do not contain blueschist detritus, 

and which differ in other lithologic characteristics. However, further west, in the 

Triunfo Pass quadrangle, detrital glaucophane is present in some sandstone beds 

of the Vaqueros or Topanga Canyon Formations, or both. 

1976 – Campbell and Yerkes (1976) illustrate a structural disruption in strata of the Santa 

Monica Mountains and Simi Hills, contemporaneous with deposition of Conejo 

Volcanics and lower parts of the Calabasas Formation. This structural episode is 

approximately the same age as the “basin-inception phase” in Yerkes and others 

(1965) discussion of the evolution of the Neogene Los Angeles Basin. 

 1977 – Addicott (1977, p. 158) identifies the “Vaqueros Stage” as correlative with the 

upper part of the Zemorrian Stage and the lower part of the Saucesian Stage; notes 

that the Saucesian-Zemorrian boundary, which falls within the middle part of the 

“Vaqueros Stage” ...has been dated at about 22.5 m.y. B.P. (Turner, 1970)”. 

Accordingly, he places the Oligocene-Miocene boundary within the “Vaqueros 

Stage” and not at the base as shown in earlier reports (such as Addicott, 1972). 

He notes that the “Temblor Stage” is coeval with the upper part of the Saucesian 

Stage, as well as the Relizian and Luisian Stages of the California foraminiferal 

chronology, even though previous reports regarded the “Temblor Stage” as 

entirely of middle Miocene age. In part, the adjustment seems a result of the 15 to 

16 m.y. B.P. dating for the early-middle Miocene boundary (Berggren and Van 
21

Couvering, 1974; Ryan and others, 1974), which would also make the lower part 

of the “Temblor Stage” early Miocene in age. Addicott (1977) establishes 

significant changes in the time scale for the molluscan stages. However, changes 

like this can take a variable number of years to affect subsequent publications by 

different authors. 

Addicott (1977, p. 157) identifies the “California Neogene Stages” as 

“unnamed”, “Vaqueros”, “Temblor”, “Margaritan”, “Jacalitos”, “Etchegoin”, and 

“San Joaquin”; referring to each as a Stage. He used quotation marks for the 

stage names to avoid confusion with formations bearing the same names. 

1979 – Yerkes and Campbell (1979) elevated the Topanga formation to Group status and 

assigned formation names that meet the criteria of the 1961 and subsequent 

versions of the North American Code of Stratigraphic Nomenclature (American 

Commission on Stratigraphic Nomenclature, 1961; American Commission on 

Stratigraphic Nomenclature, 2005). They identified significant differences in 

lithofacies among the three formations; i.e.: the lower unit, the Topanga Canyon 

Formation, is dominated by a westward-deepening marine shelf depositional 

environment, contains a distinctive mollusk fauna, and has been variably affected 

by intrusive dikes and sills related to the overlying volcanics; the middle unit, the 

Conejo Volcanics, is chiefly extrusive basalt and andesite, much of which was 

erupted into a submarine environment; the upper unit, the Calabasas Formation, is 

dominated by bathyal fan turbidites with interbedded silty shales, and is 

lithologically distinct from the pre-volcanic strata. The Calabasas Formation is 

generally not intruded by the basalt and diabase that commonly intrudes the prevolcanic and syn-volcanic Topanga Group strata. However, the low-angle Malibu 

Bowl fault, which carries Calabasas strata in its upper plate, appears to be 

intruded by basalt along the west side of Malibu Canyon and in many places to 

the east, between Malibu and Santa Ynez Canyons. Many Calabasas sandstones 

and conglomerates contain significant proportions of detrital volcanic (andesitic 

and basaltic) rock fragments. 

Near Agoura, the lower part of the Calabasas Formation contains a few 

discontinuous masses of basalt and andesite, some of which are flows and 

volcaniclastic beds, and none show clear evidence of intrusive origin. The 

relations in the eastern Santa Monica Mountains, where volcanics are 

discontinuous and may not be directly related to the Triunfo Pass-Conejo Grade 

eruptive center for the Conejo Volcanics, have not been determined. Hoots 

(1931) did not discriminate extrusive from intrusive volcanics and mapped both 

pre- and post-volcanic sedimentary strata as Topanga Formation. Future mapping 

should attempt to discriminate post-volcanic from pre-volcanic sedimentary strata 

to assist in correlating the subunits of the Topanga Group in eastern Santa Monica 

Mountains with the formations identified to the west. 

Sedimentary breccias containing reworked fossils (including clasts of 

sandstone with imbedded Paleocene, Eocene, and Miocene mollusks) have been 

mapped in the Calabasas Formation; locally, they also contain basaltic and 

andesitic volcanic clasts derived from the Conejo Volcanics and large clasts of red 

sandstone and conglomerate derived from the Sespe Formation. Sedimentary 

breccias occur at more than two stratigraphic levels within the formation (Yerkes 

and Campbell, 1979; Yerkes and Campbell, 1980; Campbell and others, 1996). 

Many of the reworked fossil mollusk specimens show well-preserved form and 

ornamentation. 
22

Only one assemblage of possibly unreworked middle Miocene mollusks is 

known from the Calabasas Formation in the Santa Monica Mountains, and most 

of the Calabasas foram collections have not yielded assemblages diagnostic of a 

single stage; they are reported as “middle Miocene, Relizian or Luisian”. One 

well-documented Luisian foram assemblage was reported from near the base of 

the Calabasas at a locality east of Russell Valley and south of the Ventura 

Freeway. One unqualified and one questioned Mohnian assemblage were 

collected in the area west of Topanga Canyon Boulevard from Calabasas strata 

that lie below the basal Modelo unconformity as extended west (see Yerkes and 

Campbell, 1980) from the exposure that Hoots (1931) mapped from Topanga 

Canyon Boulevard eastward. (The unconformity exposed on Topanga Canyon 

Boulevard was subsequently used by Kleinpell (1938) as the base of his type 

Mohnian Stage.) 

1980 – The stratigraphic nomenclature proposed by Yerkes and Campbell (1979) was 

applied to a geologic map of an area combining the Malibu Beach and western 

part of the Topanga 7.5’ quadrangles (Yerkes and Campbell, 1980). That map 

refers the Topanga Group to Middle Miocene and the Vaqueros Formation to 

Lower Miocene (Yerkes and Campbell, 1980). Users of the map should be aware 

that the age assignments should be revised to accommodate updates to the 

geologic time scale (see fig. 3.) 

1981 – Schoellhamer and others (1981) describe the geology of the northern Santa Ana 

Mountains (most of their field mapping and laboratory work was done in the 

1950’s and 1960’s.) They refer to the Topanga as a formation, and note that the 

Topanga Formation contains a molluscan fauna of “provincial middle Miocene 

age.” Sparse microfossil collections were questionably referred to the Relizian 

Stage of Kleinpell (1938). Their generalized section (Schoellhamer and others, 

1981, Figure 3, p. D-5) places the locally unconformable base of the Topanga 

Formation at the base of the middle Miocene series, and equates the unconformity 

at the base of the overlying Puente Formation with the top of the middle Miocene 

series. Underlying strata, consisting of interbedded marine and nonmarine beds 

of late Eocene (?) to early Miocene age, were mapped together as “Sespe and 

Vaqueros Formations, undifferentiated.” (In a 2006 written communication, 

McCulloh reports that subsurface data from the area west of the northern Santa 

Ana Mountains indicate that equivalent beds there include microfossils as old as 

the Saucesian BFS, early Miocene.) 

The description of lithologies in the Topanga Formation makes no 

mention of detrital glaucophane, or of schistose clasts derived from the Catalina 

Schist. However, they describe glaucophane schist detritus in the Soquel Member 

of the overlying Puente Formation. 

 1981 – Poore, Barron, and Addicott (1981) present a revised correlation of provincial 

molluscan stages for California that restricts the “Vaqueros Stage” to early 

Miocene, extends the succeeding “Temblor Stage” to early and middle Miocene, 

in turn succeeded by the “Margaritan Stage” of middle and late Miocene age. 

 1986 -- Hornafius and others (1986) summarized paleomagnetic evidence of rotation and 

ages of rotated rocks for the western Transverse Ranges. From plots showing 

ages of rocks sampled against paleomagnetic declination, they conclude (p. 1482) 

that rapid clockwise rotation of 50-60 degrees occurred throughout the western 

Transverse Ranges in middle Miocene time (1-16 m.y.). Using the correlations of 

Barron and Isaacs (2001), this would indicate that the deposition of the latest 
23

Relizian through early Mohnian parts of the Topanga Group were being deposited 

while rotation was occurring, and that rotation may have continued during 

deposition of the late Miocene parts of the Modelo, Puente, and Monterey 

Formations. 

 1987 -- Henry (1987, p. 3) indicates that four of the 62 Los Angeles Basin oilfields 

produced from the Topanga Formation. It is not clear whether the four include 

the Huntington Beach and Wilmington fields, where Wissler indicates the Luisian 

age beds are better correlated with the Monterey Formation. In his series of 

paleogeographic diagrams, Henry shows both Relizian and Luisian intertidal shelf 

deposition over the areas of most of the Los Angeles Basin fields, except for the 

west side fields north and northwest of Wilmington and south of Inglewood. 

Along the Newport-Inglewood zone, he shows Relizian present in the Potrero 

field (but the basis is not clearly cited) and absent to the south and west. The 

Luisian also is apparently absent from the Potrero field. The diagrams also 

indicate that both Relizian and Luisian are absent in the southwestern part of the 

West Newport field, an area contiguous with the San Joaquin Hills. 

1990-1993 – Dibblee and Ehrenspeck (1990, 1992a, 1992b, 1992c, 1993a.1993b) 

geologic maps in the central and western Santa Monica Mountains refer the 

Modelo Formation and parts of the Calabasas Formation (in the nomenclature of 

Yerkes and Campbell, 1979) to the Monterey Formation, obscuring lithologic 

differences with the Monterey Formation which crops out south of the Malibu 

Coast Fault. They referred parts of the Calabasas Formation of Yerkes and 

Campbell (1979) to the “Upper Topanga Formation” and, in eastern areas where 

volcanics are discontinuous, include parts of the Calabasas Formation and Conejo 

Volcanics of Yerkes and Campbell (1979) as part of a “Middle Topanga 

Formation.” They did not recognize a distinction between the Topanga Canyon 

and Vaqueros Formations of Yerkes and Campbell (1979), and referred the 

combined Topanga Canyon and Vaqueros Formations to a “Lower Topanga 

Formation.” Although their usage resembles the “Upper, Middle, and Lower 

Topanga Formations” nomenclature of Durrell (1954), the map units are not 

everywhere the same. As with the nomenclature proposed by Durrell (1954), the 

use of “Upper”, “Middle”, and “Lower” as an intrinsic part of a formation name 

does not follow the guidelines of the North American Stratigraphic Code, which 

was first published in 1961 and most recently updated in 2005 (The North 

American Commission on Stratigraphic Nomenclature, 2005). Dibblee and 

Ehrenspeck (1993c) also assign pre-Monterey strata to the south of the Malibu 

Coast Fault to the “Upper Topanga Formation”, including beds with Catalina 

Schist detritus (San Onofre Breccia), which are interbedded with mudstone 

containing Saucesian BFS foraminifera, and to dolomitic and cherty marls 

assigned to the Monterey Shale by Yerkes and Campbell (1979). 

1991 – Smith’s (1991) geochronology of giant pectinids places Vertipecten kernensis

(Hertlein) in the “Vaqueros Stage” (Smith, 1991, Fig. 10). This species is 

abundant at the horizon taken by Yerkes and Campbell as the base of the Topanga 

Canyon Formation in the Santa Monica Mountains. 

1991 – In his review of the Neogene stratigraphy of the Los Angeles Basin, Blake (1991) 

uses “Topanga Group” in the sense of Yerkes and Campbell (1979) for columns 

in the Santa Monica Mountains, San Joaquin Hills, Puente Hills, and Santa Ana 

Mountains, western Los Angeles Basin subsurface, and eastern Los Angeles 

Basin subsurface. Where not subdivided, “Topanga Group” is substituted for 
24

“Topanga Formation”. He designates (Table 3) Paularino, Los Trancos, and 

Bommer as Formations in the Topanga Group. Ages are listed as: Paularino, 

middle to early Miocene (lower Luisian to upper Relizian Stages), Los Trancos, 

early Miocene (Relizian Stage), Bommer, early Miocene (Relizian Stage). In the 

text description (p. 143-146) however, he continues to use their old designation as 

“Members”. 

Blake’s Figure 2 (p.139) correlates sections for the Santa Monica 

Mountains, Palos Verdes Hills, San Joaquin Hills, Puente Hills-Santa Ana 

Mountains area, west side Los Angeles Basin subsurface, and east side Los 

Angeles Basin subsurface. Blake’s sections show the Zemorrian Stage at the top 

of the Oligocene, the Saucesian Stage as the lower part of the early Miocene, the 

Relizian Stage as mostly early Miocene but partly middle Miocene, the Luisian 

Stage as middle Miocene, and the Mohnian Stage as middle and late Miocene. 

1991 – Wright’s (1991) summary of the structural geology and tectonic evolution 

generally agrees with the usage of Blake in the same volume; i.e., he uses 

Topanga Group, except that some sections and an Appendix listing stratigraphic 

terms use “Topanga Formation”, and he includes the Bommer, Los Trancos, and 

Paularino as “Members” (Wright, 1991). Wright (1991, Fig. 5, p. 42) also 

illustrated the extent and thickness of the Topanga Group in and around the 

margins of the Los Angeles Basin. In his discussion of the Topanga Group, 

Wright (1991, p. 43) discusses “Predecessor Basins” as including: 

a) “...the Late Cretaceous and Paleogene fore-arc basins that extended along the 

entire western edge of the North American plate. Figure 4 (p. 42) shows the 

known distribution of this sequence (designated as “Sedimentary”) in the Los 

Angeles area. Its presence or absence beneath the deeper parts of the present Los 

Angeles Basin has not yet been demonstrated.” 

b) “... volcanic and sedimentary rocks (the Topanga Group of Figure 5) (p. 42) 

deposited during the early to middle Miocene rifting that opened the basins of the 

borderland province and rotated the blocks within the Transverse Ranges.” 

c) “... regional subsidence during the late middle and late Miocene that 

facilitated the widespread deposition of biogenic sediments and clays of the 

Monterey and related formations.” 

Wright concludes that the basin inception may have begun as early as the 

Zemorrian Stage, early Miocene, and that volcanism, rifting, and rotation all 

occurred during Topanga Group deposition. (However, most of the rotation 

paleomagnetic data are from volcanic rocks, indicating that they record only postvolcanic rotation. If rotation began before volcanism, the measured rotations are 

minima.) 

1991 --Yeats and Beall (1991, p. 222) cite the usage of Barbat (1958) in restricting their 

usage of the term “Los Angeles Basin” to “...the structural configuration that was 

not fully achieved until close to the beginning of Repetto deposition, about 4 Ma, 

although the central trough first appeared during the late Mohnian, about 8 Ma.” 

The emphasis of the Yeats and Beall paper is on the Pico Formation 

stratigraphy, late Miocene to early Pliocene, but in summarizing the pre-basin 

stratigraphy of the area the “Topanga Formation” is grouped with older 

(Paleogene and early Miocene) strata as showing “...no tendency to thicken 

toward the center of the Los Angeles Basin.” 

1992 -- Bartow (1992) compiled Paleogene and Neogene time scales for southern 

California and shows the base of the Miocene at nearly 24 Ma, above the base of 
25

the “Vaqueros Stage” (about 30 Ma); it places the “Vaqueros-Temblor” boundary 

between 17 Ma and 18 Ma; and shows the top of the “Temblor Stage” between 13 

Ma and 14 Ma, at about the top of the Luisian benthic foramiferal Stage. 

1993 – In a guidebook article and map, Dibblee and Ehrenspeck (1993c) extend Topanga 

terminology to strata south of the Malibu Coast Fault, applying the term “Upper 

Topanga Formation” to mudstone and sandstone called “Trancas Formation” by 

Yerkes and Campbell (1979) and to dolomitic and cherty marls assigned to the 

Monterey Shale by Yerkes and Campbell (1979). They also do not recognize the 

Zuma Volcanics of Yerkes and Campbell (1979) as associated with a different 

suite of strata than the Conejo Volcanics, extending the term “Conejo Volcanics” 

to volcanic rocks south of the Malibu Coast Fault. However, they retain 

“Monterey Formation” for some strata on Point Dume. 

The usage of Dibblee and Ehrenspeck (1993c) would extend the age of the 

“Upper Topanga Formation” (Calabasas Formation) downward from the Luisian 

BFS to include strata containing Relizian BFS and Saucesian BFS foraminifera. 

In addition, assigning Mohnian BFS strata (Modelo Formation) on the north flank 

of the Santa Monica Mountains to the “Monterey Formation” blurs distinctions of 

the age and provenance of both units. 

1993 – Fritsche (1993) proposed a stratigraphic nomenclature that combines the 

sandstone members of the Vaqueros and Topanga Canyon Formations of Yerkes 

and Campbell (1979) together as an “Unnamed Sandstone.” He also proposed 

combining the Encinal Member of the Topanga Canyon Formation with the 

Danielson Member of the Vaqueros Formation to be termed the “Rincon Shale”, 

with a “Danielson Tongue” below a lower Miocene tongue of the “Unnamed 

Sandstone”, and an “Encinal Tongue” above it. Fritsche does not address the 

stratigraphy south of the Malibu Coast Fault. 

Although not explicitly stated, the effect of Fritsche’s proposal would be 

to abandon the allostratigraphic limits of the Topanga Formation as defined by 

Kew (1924), except for a very restricted part of the Topanga Canyon Formation of 

the Topanga Group of Yerkes and Campbell (1979). His proposed combination 

of the Vaqueros and Topanga Canyon Formations (based on lithologic 

similarities) does not recognize mappable field relations – that the stratigraphic 

sequence can be consistently identified from the molluscan assemblages they 

contain, and a horizon separating the two can be mapped using the continuity of 

overlapping individual beds. His proposal also leads to a sequence wherein 

Rincon Shale lies below sandstone carrying “Vaqueros” CMS mollusks; however, 

in the type area for the Rincon, in the Santa Ynez Mountains, the Rincon lies 

entirely above recognized “Vaqueros” CMS strata. 

1996 – Campbell and others (1996) use the nomenclature of Yerkes and Campbell 

(1979), Vaqueros Formation and Topanga Group, for map units in the Point 

Dume quadrangle geologic map. They also used the age assignments of Yerkes 

and Campbell (1979); i.e., the Vaqueros Formation is identified as lower Miocene 

and the Topanga Group is labeled middle Miocene. (An updated age assignment 

for the Vaqueros Formation is early Miocene, Oligocene, and late Eocene; and the 

Topanga Group ranges in age from early Miocene to late Miocene.) 

1998 – Atwater and Stock (1998) update Miocene plate motions and correlations with 

evolution of southwest North American structure; their calculations of PacificAntarctic-Africa-North America plate circuit yield reconstructions for times since 

chron 13 (33 Ma). Their quantitative comparison of reconstructed oceanic plate 
26

motions to structural displacements within the continental plate in the 

southwestern U.S. shows that the attachment of the Salinian Block to the Pacific 

plate was probably not completed until about chron 5E (~18 Ma), even though the 

breakup of the Farallon plate probably began at about 28 Ma (Atwater and Stock, 

1998, p. 391). 

The ~18 Ma age is contemporaneous with the “Vaqueros-Temblor” CMS 

boundary suggested by Bartow (1992) and reported by McCulloh and others 

(2002, fig. 4; reproduced herein as fig. 3). It approximates the beginning of 

deposition of the Topanga Group. 

2000 – McCulloh and others (2000) conclude that outcrop and subsurface data on the 

distribution of Paleogene depositional environments in the area that now adjoins 

the northeastern part of the Los Angeles Basin indicate a nearly east-west trend 

for the base-of-Neogene unconformity that marks the depositional edge of the Los 

Angeles Basin. This appears to be well south of the rock boundary between the 

Peninsular Ranges and San Gabriel basement complexes as mapped by Morton 

and Miller (2003), and indicates a pre-Miocene topographic configuration that is 

more complex than a simple, continuous, southwest-facing shelf. 

2001 – McCulloh and others (2001) use the term “Topanga Group of Wright (1991)” and 

indicate that it may not be the exact stratigraphic equivalent of the “Topanga 

Group of Yerkes and Campbell (1979)”. They identify the middle Miocene 

volcanic rocks of the northeastern Los Angeles Basin (chiefly basalt and basaltic 

andesite, rarely more-silicic volcanic rocks) as part of the “Topanga Group” as 

used by Wright (1991). 

In a careful reconstruction of the northeastern margin of the Los Angeles 

Basin, using outcrop and subsurface data, McCulloh and others (2001) conclude 

that the Mountain Meadows Dacite of the San Jose Hills is consanguineous and 

contemporary (Oligocene) with many intrusive bodies in the eastern San Gabriel 

Mountains. Therefore, its’ area of emplacement transcends the (suture) boundary 

between the Mesozoic basement terrain of the Peninsular Ranges and the preCambrian-Mesozoic basement terrain of the San Gabriel Mountains. The 

reconstruction indicates that Paleocene and late Luisian BFS shorelines lie in 

approximately the same positions, but with the late Luisian BFS shoreline more 

embayed to the northeast (see their Figure 11). 

2001 – Barron and Isaacs (2001) updated the chronostratigraphic framework for the 

California Miocene, indicating that an early Miocene age for a significant part of 

the Relizian benthic foraminiferal Stage and a middle Miocene age for a 

significant part of the Mohnian benthic foraminiferal Stage were firmly 

established. 

2002 -- McCulloh and others (2002) apply the geologic time framework of Barron and 

Isaacs to correlate isotope ages of volcanic rocks with early, middle, and late 

subdivisions of the Miocene Epoch, published and new isotope ages (Ma), 

magnetic chronology and polarity, calcareous nannofossil zones, benthic 

foraminiferal stages, provincial molluscan stages, and terrestrial vertebrate stages 

(fig. 3). 

The correlation chart (fig. 4, p. 10 of McCulloh and others, 2002; 

reproduced here as fig. 3) indicates that the “Vaqueros-Temblor” CMS boundary 

falls at about 17.6 Ma, which is near the middle of the late Saucesian benthic 

foram Stage. It shows the Saucesian-Relizian boundary at about 17.1 Ma, the 

Relizian-Luisian boundary at 15.7 Ma, and the Luisian-Mohnian boundary at 
27

about 13.6 Ma. It places the boundary between early and middle Miocene at 16.4 

Ma, and the boundary between middle and late Miocene at 11.2 Ma. From this, 

the age of the Topanga Group is inferred to range from as old as late Saucesian 

BFS (~17.6 Ma) to as young as late Luisian BFS (~13.6 Ma). 

2003 – The compilation by Morton and Miller (2003) of the San Bernardino 30’ x 60’ 

quadrangle avoids use of Topanga (whether Formation or Group) by assigning 

rocks in the vicinity of Azusa to “sedimentary rocks of the Azusa area.” Earlier 

workers (e.g., Shelton, 1955) had referred the sequence to the Topanga 

Formation. The rocks consist of sandstone, conglomerate, and interbedded 

siltstone and shale with basalt. Some sandstone beds contain Turritella ocoyana

and finer-grained interbeds have yielded Luisian BFS foraminifers. 

2004 – Morton’s geologic map (Morton, 2004) of the Santa Ana 30’ x 60’ quadrangle 

uses “Topanga Formation.” Because the three members of the Topanga 

Formation in the Santa Ana 30’x 60’ quadrangle, have not been correlated with 

the Topanga Group formations recognized by Yerkes and Campbell (1979) he 

chose to retain the nomenclature of the source maps for the Santa Ana quadrangle. 

2004 – McCulloh and Beyer (2004) use formation nomenclature of various authors in 

different localities, and do not discuss the Topanga Group as a stratigraphic unit. 

In their Northwest Sector, the central and western Santa Monica Mountains 

sections do not extend above the Conejo Volcanics and do not include the 

Calabasas Formation, which is the uppermost formation in the type Topanga 

Group of Yerkes and Campbell (1979). In the western Santa Monica Mountains, 

lower and middle Miocene strata are referred to the Vaqueros Formation, the 

Lower Topanga Formation, and to the Conejo Volcanics. In the central Santa 

Monica Mountains, lower and middle Miocene rocks are referred to the Vaqueros 

and Topanga Canyon Formations, and to the Conejo Volcanics. In the eastern 

Santa Monica Mountains, middle Miocene strata are assigned to the Topanga 

Formation, for which the base rests on volcanic beds having isotope ages that 

predate those of the oldest Conejo Volcanics. 

The Modelo Formation, which lies unconformably above the type 

Topanga Group (Yerkes and Campbell, 1979) in the central Santa Monica 

Mountains, is not shown on the sections for the central Santa Monica Mountains, 

but is shown as unconformably above the Topanga (Group?) in the section for the 

eastern Santa Monica Mountains (McCulloh and Beyer, 2004, fig. 2, p. 3). In 

their Southeast Sector, the Topanga Formation and “Topanga with volcanics” are 

overlain by the Puente Formation (middle and late Miocene), or by Monterey 

Shale (middle Miocene) succeeded by Puente Formation (middle and late 

Miocene), are shown extending downward to include early Miocene strata. The 

Vaqueros Formation in the Santa Ana Mountains and the San Joaquin Hills may 

not extend below the (ca. 24 ma) Oligocene-Miocene boundary. 

McCulloh and Beyer (2004, Fig. 2, p. 3) show the “Vaqueros-Temblor” 

Stage boundary at about 19.5 Ma, and the “Temblor-Margaritan” Stage boundary 

at about 12 Ma. The early Miocene is shown ranging from about 24 Ma to about 

16.5 Ma, and the middle Miocene from about 16.5 Ma to about 11 Ma. They put 

the Vaqueros Formation in early Miocene and the pre-Conejo parts of the 

Topanga Group (Formation) almost entirely in early Miocene, though the 

uppermost parts of the pre-Conejo Topanga strata may extend into the middle 

Miocene. The Conejo Volcanics is shown with a base at about 16.5 Ma and a top 

at about 13.5 Ma in the central and western Santa Monica Mountains. The age of 
28

the oldest and youngest of the Conejo Volcanics varies from place to place within 

the Santa Monica Mountains, and the actual range may be greater than is 

indicated by the limited number of localities that have yielded isotope ages. 

2005 – Yerkes and Campbell, in their (2005) compilation of the geology of the 30’ x 60’ 

Los Angeles quadrangle, refer the Topanga Group to the middle Miocene; but the 

Calabasas Formation (the uppermost formation in the Topanga Group) is referred 

to early late Miocene and late middle Miocene. The Conejo Volcanics is referred 

to the mid-middle Miocene, and the Topanga Canyon Formation is referred to 

early middle Miocene. The Vaqueros Formation is referred to early Miocene. (An 

updated age assignment for the Vaqueros Formation is early Miocene, Oligocene, 

and late Eocene; and the Topanga Group ranges in age from early Miocene to late 

Miocene.) Their map (Yerkes and Campbell, 2005) shows that the base of the 

Calabasas Formation is of different ages in different areas. In the area south and 

west of Calabasas, the formation is thick, basal beds are nearly accordant with the 

underlying Conejo Volcanics (minor discordance could reflect deposition on an 

uneven surface of volcanic deposits), and there is no clear evidence of subaerial 

erosion of the underlying volcanics. South and west of Agoura the Calabasas 

Formation appears generally accordant with the underlying Conejo, but is much 

thinner; and further west, at Westlake Village and Thousand Oaks, the base is a 

volcaniclastic conglomerate. A similar conglomerate is also mapped along the 

south flank of the Simi Hills, where the contact is strikingly discordant with 

underlying Cretaceous sandstone and conglomerate. 

2006 – Morton and Miller (2006) discuss the Topanga Group in their description of the 

map units in the combined San Bernardino-Santa Ana 30’ x 60’ quadrangles. 

In the San Joaquin Hills, Morton and Miller (2006) have followed the 

usage of Blake (1991, Fig. 2, p. 139) in using the term Topanga Group. Morton 

and Miller (2006) also elevated the three members identified by Vedder and 

others (1957), to formation rank as the Paularino, Los Trancos, and Bommer 

Formations. 

Elsewhere, they describe the Topanga Group in the Azusa area of the San 

Gabriel Valley as consisting of mostly marine sandstone and conglomerate that 

locally includes volcanic rocks. In an earlier publication (Morton and Miller, 

2003) they referred to these rocks as “sedimentary rocks of the Azusa area.” The 

section in the Azusa area is about 760 m thick (Shelton, 1955), and includes 

conglomeratic beds having clasts as large as about 1 m. Most of the clasts 

resemble rocks in the adjacent San Gabriel Mountains, and some volcanic rock 

clasts resemble the Glendora Volcanics. Most of the exposed rocks are coarsegrained sandstone, some of which are cross-bedded, fine-grained, thin-bedded 

sandstone and siltstone, and diatomaceous, fissile, and partly silicified shale. 

Fine-grained rocks contain foraminifers indicative of the Luisian BFS and the 

highest beds contain fish scales that probably are uppermost Luisian or lowermost 

Mohnian (Shelton, 1955). The section also includes a basalt layer about 30 m 

thick (Shelton, 1955); this mappable basalt unit, where well exposed, consists of 

pillow basalt (Photo 219 in the report by Morton and Miller, 2006) indicating a 

submarine origin. This basalt appears similar to pillow basalts included within 

the Conejo Volcanics of Yerkes and Campbell (1979) in the Santa Monica 

Mountains. 

Most of the Topanga Group in the South Hills, just south of Glendora, is 

massive and well bedded sandstone that commonly contains conglomerate lenses. 
29

It is about 600 m thick, about 35 to 40 percent of which consists of interbedded 

Glendora Volcanics. 

Acknowledgments 

Many workers have contributed to the literature and unpublished discussions 

describing the stratigraphy and spatial distribution of the Topanga Group and associated 

strata. The references that are cited in the above chronology are a small sample; they 

were selected to represent our view of how the current stratigraphic nomenclature 

developed. Over the past five decades, continuing discussions with our late colleague, 

Robert F. Yerkes, have had a strong influence on our perceptions. We wish to thank F. 

K. Miller, D. M. Morton, and C. L. Powell, II, for thoughtful and constructive reviews. 

Rachel M. Alvarez kindly provided the digital shaded relief map we annotated for an 

index (fig. 1). The work was supported by the U.S. Geological Survey, Western Earth 

Surface Processes Project, Basin and Landscape Co-evolution (BALANCE). 

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