U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3321

Geologic Map of the Southern White Ledge Peak 

and Matilija Quadrangles, Santa Barbara 

and Ventura Counties, California
Cover Top, View looking west from west end of Rincon Mountain of eastern part of Santa Barbara coastal plain. Bottom left, View looking 

northeast of exposure in Devils Gulch of southeast-dipping beds of Rincon Shale (Tr) in footwall block of nearby Devils Gulch fault (not visible 

here; located to right of photograph view). Bottom right, Outcrop of gently dipping beds of conglomeratic sandstone of the Oligocene middle 

conglomerate and sandstone unit (Tspm) of the Sespe Formation. Lake Casitas and Laguna Ridge visible in background. Photographs by 

Scott A. Minor, U.S. Geological Survey.
Geologic Map of the Southern White Ledge 

Peak and Matilija Quadrangles, Santa Barbara 

and Ventura Counties, California

By Scott A. Minor and Theodore R. Brandt

Scientific Investigations Map 3321

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Minor, S.A., and Brandt, T.R., 2015, Geologic map of the southern White Ledge Peak and Matilija quadrangles, 

Santa Barbara and Ventura Counties, California: U.S. Geological Survey Scientific Investigations Map 3321, 34 p., 

1 sheet, 1:24,000, http://dx.doi.org/10.3133/sim3321.

ISSN 2329-132X (online)
iii

Contents

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

Previous Mapping..........................................................................................................................................2

New Mapping.................................................................................................................................................2

Fault-Kinematic Measurements

5

Geologic Summary.........................................................................................................................................5

Structural and Kinematic Framework ...............................................................................................8

Description of Map Units............................................................................................................................13

Surficial Deposits................................................................................................................................13

Man-Made Deposits...........................................................................................................................13

Alluvial Deposits..................................................................................................................................13

Marine-Shore Deposits......................................................................................................................15

Mass-Wasting Deposits ....................................................................................................................16

Bedrock Units......................................................................................................................................16

Acknowledgments.......................................................................................................................................30

References Cited..........................................................................................................................................30

Sheet

1. Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, 

Santa Barbara and Ventura Counties, California .............................................................. Link

Figures

1. Generalized location map of part of southwestern California showing the 

region of geologic mapping and major tectonic faults. Area of figure 2 is 

in orange rectangle ......................................................................................................................2

2. Regional physiographic map showing location of the current map area...........................3

3. Tectonic and physiographic map of the combined White Ledge Peak and 

Matilija quadrangles ....................................................................................................................4

4. Photograph of view looking west from west end of Rincon Mountain of 

eastern part of Santa Barbara coastal plain............................................................................5

5 Structural plots of slip observations of A, Map-scale and B, Mesoscale 

faults exposed in map area.........................................................................................................6

6. Close-up photograph of fault slip surface, formed in sandstone bed of 

the Rincon Shale (Tr)...................................................................................................................8

7. Photograph of outcrop of conglomeratic sandstone of the Oligocene middle 

conglomerate and sandstone unit (Tspm) of the Sespe Formation....................................8

8. Photograph of exposure in Devils Gulch of dipping beds of Rincon Shale 

(Tr) in footwall block of nearby Devils Gulch fault..................................................................9

9. Photograph of anticline formed in the upper siliceous unit of the Monterey 

Formation (Tmu)...........................................................................................................................9
iv

10. Photograph of Lion Creek exposure of conglomerate of Ojai (Qco) which 

unconformably overlies Rincon Shale (Tr)...............................................................................9

11. Photograph of Rincon Creek exposure of Rincon Creek fault...............................................9

12. Photograph of landslide (Qls) complex on north flank of Rincon Mountain....................10

13. Photograph of Lion fault exposed in cut bank of Lion Creek...............................................10

14. Photograph panorama looking across San Antonio Creek valley, of a faulted 

late Pleistocene alluvial terrace (Qia6) .................................................................................12

Conversion Factors

Multiply By To obtain

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)
Geologic Map of the Southern White Ledge Peak 

and Matilija Quadrangles, Santa Barbara and 

Ventura Counties, California

By Scott A. Minor and Theodore R. Brandt

of the Santa Barbara coastal plain to Ojai (figs. 1, 2, 3, and 

4). The Santa Ynez Mountains and large coastal hills border 

it on the north (figs. 2 and 3) and south, respectively. The 

Santa Ynez Mountains, the most prominent mountain block 

of the coastal WTR, extend for more than 100 km and rise 

abruptly as much as 1,225 meters (m) (4,000 feet [ft]) above 

the adjacent coastal alluvial plains, valleys, and hills.

The coastal terrain bordering the Santa Ynez Mountains, 

along with the adjacent Santa Barbara Channel, coincide with 

a zone of moderate seismicity that poses some risk to people 

living in the densely populated Santa Barbara-Ojai-Ventura 

metropolitan corridor. A major (~7 magnitude (M)) earthquake 

occurred in the Santa Barbara Channel in 1812, and other 

strong earthquakes have occurred offshore within 10 km of the 

Santa Barbara coastal plain in 1925 (M6.3), 1941 (M5.5), and 

1978 (M5.1) (for example, Yerkes and others, 1981; Yerkes 

and Lee, 1987). Numerous Quaternary landslide deposits 

along the steep slopes of the Santa Ynez Mountains (Bezore 

and Wills, 2000; Tan and Clahan, 2004; Tan and Jones, 2006) 

and adjacent coastal uplands indicate the potential for continued slope failures in developed areas.

Folded, faulted, and fractured sedimentary rocks in the 

subsurface of the coastal plains and hills within and south of 

the map area, including the adjacent Santa Barbara Channel, 

are sources and reservoirs for economic deposits of oil and 

gas (Tennyson and Isaacs, 2001), some of which are currently being extracted offshore. Shallow, localized, sedimentary aquifers underlying the Santa Barbara coastal plain 

and Ojai Valley-Ventura River area provide limited amounts 

of water for nearby urban areas (Upson, 1951; Muir, 1968; 

Kear, 2005).

The present map compilation provides a set of uniform 

geologic digital geodatabase and shape files that can be used 

for analysis and interpretation of these and other geologic 

hazards and resources in the map area.

The digital geodatabase for this map and a map plot file 

(PDF) are available on the Internet at: http://dx.doi.org/10.3133/

sim3321.

Introduction

This report presents a digital geologic strip map of 

the southern parts of the contiguous White Ledge Peak and 

Matilija 71⁄2′ quadrangles in coastal southern California at a 

compilation scale of 1:24,000 (map plate; figs. 1 and 2). The 

map depicts the distribution of bedrock units and surficial 

deposits and associated deformation adjacent to and south of 

the Arroyo Parida fault (including faults on trend with it east 

of the Ventura River) (fig. 3). The overall objective of the new 

mapping presented herein is to extend recent geologic mapping of the Santa Barbara coastal plain by the U.S. Geological 

Survey (USGS) (Minor and others, 2009) as far east as 

Sulphur Mountain and Ojai Valley (figs. 2 and 3).

This geologic map, combined with the recently published 

adjacent map to the west (Minor and others, 2009), completes 

a 69-kilometer (km)-long east-west transect between the cities 

of Goleta and Ojai (fig. 2). These geologic transect maps and 

the associated sedimentologic, biostratigraphic, stratigraphic, 

and structural data embedded within them, provide new insights 

to and constraints on Neogene-through-Quaternary tectonic 

deformation, uplift, syntectonic sedimentation, and consequent 

landscape change as well as geohazards in the urbanized coastal 

hills, plains, and valleys along the southern flank of the Santa 

Ynez Mountains. The present compilation builds on the earlier 

foundation geologic mapping by Thomas Dibblee, Jr. (Dibblee, 

1987a,b) and presents new detailed map data that refine geologic knowledge and interpretations along a key segment of 

the regional map transect where the Arroyo Parida and similar 

striking faults approach and interact with the tip regions of the 

potentially seismogenic Red Mountain and San Cayetano faults 

located to the southeast and east, respectively, of the map area 

(fig. 2) (Yeats, Lee, and Yerkes, 1987; Rockwell, 1988; Huftile 

and Yeats, 1995). The principal aim of the new mapping and 

associated fault-kinematic measurements (see below) is to document and constrain the nature of transpressional strain transfer 

between these various faults.

The map area, located in the western Transverse Ranges 

(WTR) physiographic province, forms a 22-km-long strip that 

extends eastward (inland) from Carpinteria at the east end 
2 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Previous Mapping

The earliest systematic geologic mapping in the map area 

was by Upson (1951), who mapped the Santa Barbara coastal 

plain region in reconnaissance at a scale of 1:31,680 as part 

of a water-resource study, and by Lian (1954), who mapped 

the eastern part of the coastal plain area at a scale of 1:62,500. 

As part of their thesis-dissertation research Clark (1982) and 

Rockwell (1983) mapped the geology of the Ojai Valley and 

upper Ventura River area at a scale of 1:24,000, with Rockwell’s 

mapping focused on the distribution and age of elevated late 

Pleistocene fluvial terraces. The Thomas Dibblee Foundation 

published geologic maps of the White Ledge Peak and Matilija 

71⁄2’ quadrangles at a scale of 1:24,000 (Dibblee, 1987a,b).

More recent “preliminary” geologic maps of these two 

quadrangles by the California Geological Survey (formerly 

California Division of Mines and Geology) (Tan and Clahan, 

2004; Tan and Jones, 2006) largely reproduce the Dibblee 

bedrock mapping but include extensive new mapping of landslide deposits and related features. The California Geological 

Survey also produced 1:24,000 scale landslide inventory and 

landslide potential maps of the Santa Barbara coastal plain 

region, which include the present map area west of Rincon 

Creek (Bezore and Wills, 2000).

New Mapping

Field-based geologic mapping and associated faultkinematic investigations in the map area were conducted by 

S.A. Minor chiefly in 2007 through 2011. T.R. Brandt assisted 

in the design and editing of the geographic information system 

(GIS) data that are used in the digital geodatabase and performed database integration. The present geologic map is based 

on new mapping from observations and interpretations made at 

the ground surface or in shallow surface excavations, analysis of 

aerial photographs (map plate), and new biostratigraphic data. 

Owing mainly to the questionable or conflicting stratigraphic 

picks in many of the drilling logs in the map area, no geologic 

cross sections are presented herein. The recently revised geologic time scale of the U.S. Geological Survey Geologic Names 

Committee (2010) was adopted for assigning geologic ages to 

the Tertiary map units in this report, whereas the chronostratigraphic chart of Cohen and others (2013) was used to assign 

ages to the subdivisions of the Quaternary. In the description 

of map units, sedimentary lithologic terms and rock naming 

conventions are largely from Williams and others (1982).

The new mapping of the White Ledge Peak and Matilija 

quadrangles broadly resembles the earlier Dibblee (1987a,b) 

mapping that has served as the principal geologic map reference in the area, but it differs significantly in the amount of 

Figure 1. Generalized location map of part of southwestern California showing major tectonic faults, the area of fig. 2 (in orange), 

and the two quadrangles containing the geologic mapped area (in yellow).

Area of fig. 2

Area

shown CALIFORNIA

FAULT

BIG PINE FAULT

MOJAVE DESERT

SOUTHERN COAST RANGES

SAN JOAQUIN VALLEY

SIERRA NEVADA

SUR-NACIMIENTO FAULT

PACIFIC

OCEAN

Santa Barbara Channel

SAN ANDREAS FAULT

SAN ANDREAS FAULT

GARLOCK

WESTERN TRANSVERSE RANGES

MAP LOCATION

Los Angeles

San Luis Obispo

Bakersfield

Santa Maria

Ventura

Santa

Barbara

0 30 MILES

0 30 KILOMETERS

121° 120° 119° 118° 117°

36°

35°

34°
Figure 2. Regional physiographic map showing location of the current map area (yellow shading), previously published geologic map of the Santa area; (Minor and others, 2009; green shading), 71⁄2’ topographic quadrangles overlapping geologic map areas (pink shading), and major tectonic fauFaults: SYF, Santa Ynez; SCF, San Cayetano; RMF, Red Mountain; VF, Ventura; APF, Arroyo Parida; MRF, More Ranch. Fault symbols: barbs, thrust faupaired opposing arrows, sense of strike-slip movement, dotted lines where concealed. The base map is derived from the U.S. Geological Survey Na(NED), 10-meter resolution elevation data, 2005; hillshading illuminated from the northwest; color ramping based on relative elevation, with dark greelevations and white indicating highest elevations.

SYF

APF

MRF

RMF

Ventur

Santa Barbara

Goleta

Carpinteria

Oja

Minor and others, 2009

VF PACIFIC OCEAN

S a n t a Y n e z

M o u n t a i n s

DOS PUEBLOS CANYON GOLETA SANTA BARBARA CARPINTERIA WHITE LEDGE PEAK MATILIJA

S a n R a f a e l M o u n t a i n s

Summerland

g

120°00’

34°30’

119°30’

00 5 10 KILOMETERS

5 10 MILES
Figure 3. Tectonic and physiographic map of the combined White Ledge Peak and Matilija quadrangles showing faults (black lines) and folds (magestudy and other major structural features in the vicinity (thick black and magenta lines). Location of town is labeled and marked with white square. This outlined in red. Structural lines and symbols are the same as those used on geologic map. The digital elevation model (DEM), hypsometric tint, and composing the base map are derived from the U.S. Geological Survey National Elevation Dataset (NED), 10-meter resolution elevation data, 2005.

? ?

? ?

?

?

?

?

ARROYO

PARIDA

ROAD

FAULT

MESA FAULT 

CREEK

FAULT

FAULT

ARROYO PARIDA LAGUNA LA DEVILSVIEW

Laguna Ridge anticline

Ayers Creek syncline

FAULT VILLANOVA V

RED MT

FAULT

OAK

GUL

FAULT

RIDGE

FAULT CHISMAHOO SHEPARD

RINCON

CARPINTERIA

SANTA YNEZ FAULT

?

?

?

?

?

?

?

Matilija overturn

?

WHITE LEDGE PEAK MATILIJA

34°30’

119°30’ 119°27’30” 119°25’ 119°22’30” 119°20’ 119°17’3

34°22’30”

34°25’

34°27’30”

Santa Ana

Valley

Map area border Map area border

L a g u n a R i d g e

R i n c o n M o u n t a i n Casitas Rincon Valley Point

S a n t a B a r b a r a C o a s t a l P l a i n Oak View

S a n t a Y n e z M o u n t a i n s

Ventura

River Coyote

Rincon

Lake

Casitas

PACIFIC 

OCEAN

Creek

 Creek S a n A

? ? ?

? ? ?

?

?

?

?

?

?

?

?

?

0 3 KILOMETERS

0 3 MILES

1 2

1 2
Geologic Summary 5

stratigraphic and, especially, structural detail and in the resulting geologic interpretations and map depictions. The present 

compilation includes detailed description, differentiation, and 

mapping of Pleistocene marine and nonmarine units that bear 

on the Quaternary tectonic uplift and deformational history 

of the map region and the attendant interplay of marine and 

continental deposition. Structures are mapped in considerably 

greater detail than on the previously published maps, resulting 

in a more thorough and, in places, distinct documentation of 

faults and folds in Quaternary deposits.

Fault-Kinematic Measurements

As part of efforts to document the structural geology and tectonic evolution of the map area, 132 kinematic 

data (slip-surface orientation and slickenline rake measurements and slip-sense determinations) were collected from 73 

smaller-displacement (<5 m) “mesoscale” fault surfaces and 

19 larger-displacement (5 to >100 m) fault surfaces exposed 

in the map area within sedimentary rocks and deposits ranging 

in age from middle Eocene (Coldwater Sandstone, unit Tcw) 

to late Pleistocene (intermediate alluvial deposits, unit Qia, 

and marine-terrace deposits, unit Qmt) (fig. 5A,B). Slip 

lineation (mostly striation) bearing and rake measurements 

taken at exposures of larger-displacement faults are shown in 

red on the cartographic representation of the map, whereas 

all of the kinematic data (slip-lineation bearing, rake, slip 

sense, slip-sense certainty) from both the larger- and smallerdisplacement faults are embedded as “point” data in the 

geodatabase. The slip sense of faults that do not offset beds or 

other distinctive stratigraphic or structural features was determined or inferred using secondary fractures, mineral coatings, 

or other shear-sense indicators preserved on the principal slip 

surfaces (fig. 6) (Petit, 1987; Doblas, 1998).

Also recorded were relative-age observations of faults 

and fault slip, especially crosscutting relations of multiple sets 

of slickenlines on reactivated faults. These fault-kinematic data 

may provide important constraints for the timing and rates of 

uplift and movement histories of fault blocks, which may also 

reveal significant tectonic controls on the geomorphic evolution of Neogene to recent landscapes of the region. The faultkinematic data will also likely provide constraints for future 

regional seismic hazards models.

Geologic Summary

The western Transverse Ranges consist mainly of variably deformed marine and nonmarine sedimentary rocks and 

deposits that range in age from Jurassic to Holocene. These 

strata record a long history of continental-margin sedimentation, 

and deposits as young as late Pleistocene record considerable 

protracted deformation that includes Neogene and Quaternary 

transpressional faulting, folding, and clockwise verticalaxis rotations of crustal blocks (for example, Dibblee, 1966, 

1982; Hornafius and others, 1986; Namson and Davis, 1988; 

Luyendyk, 1991; Dickinson, 1995; Gurrola and others, 2014). A 

dramatic result of this deformation is the prominent Santa Ynez 

Mountains lying directly north of the map area (fig. 3), which 

were uplifted along a large homoclinal-to-anticlinal structure 

beginning in the Pliocene (Dibblee, 1982).

In the map area, the oldest stratigraphic units are Eocene 

and consist of resistant, southward-dipping, mostly marine sedimentary rocks that are only locally exposed. Just north of the 

map area, however, these rocks form a backdrop of prominent 

hogbacks and cuestas along the south flank of the Santa Ynez 

Mountains uplift (fig. 3). Less resistant but similarly-dipping 

and folded Oligocene through Pliocene terrestrial and marine 

sedimentary rocks make up most of the coastal hills and sea 

Figure 3.—Continued.

Figure 4. View looking west from west end of Rincon Mountain 

of eastern part of Santa Barbara coastal plain. City of Carpinteria 

and Rincon Point are visible in right and left center of photograph, 

respectively. Part of extensive landslide complex on south flank of 

Rincon Mountain is visible in lower left part of photograph (area 

of bright green vegetation). Southwest part of map area includes 

landscape visible in lower half of photograph.

?

?

EXPLANATION

?

?

Fault—Queried where uncertain; ball on downthrown side indicating 

 older normal slip; opposing arrows indicate sense of younger strike-

 slip component of movement

Thrust fault—Queried where uncertain, dashed where location 

 approximate; sawteeth on upthrown side

Reverse fault—Queried where uncertain, dashed where location 

 approximate, short dash where inferred, dotted where concealed; 

 exhibits reverse component of slip; boxes on upthrown side

Anticline—Queried where uncertain, dashed where location 

 approximate, short dash where inferred, dotted where concealed; 

 large arrowhead shows direction of plunge

Syncline—Queried where uncertain, dashed where location 

 approximate, short dash where inferred, dotted where concealed; 

 large arrowhead shows direction of plunge

Syncline, overturned—Queried where uncertain, dashed where 

 location approximate, short dash where inferred, dotted where 

 concealed; large arrowhead shows direction of plunge
6 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Figure 5. Structural plots of slip observations of A, Map-scale (plotted on map) and B, Mesoscale faults (see database for 

measurements and coordinates) exposed in map area. Upper circular plots are lower-hemisphere, equal-area projections of fault 

slip surfaces (great circles) and slickenlines (points); small arrows attached to points indicate slip sense (strike-slip-dominant faults) 

or hanging-wall movement direction (dip-slip-dominant faults); reverse and normal slip components indicated by open and filled 

points/arrows, respectively; N, north; n, number of fault-slip measurements. Lower histograms show fault strike and rake frequency 

distributions; frequency axis values are scaled to decimal fractions of the total number of measurements; strike azimuths are 90° 

counterclockwise from fault dip directions; rake values range from 0° to 360°, where 0° (=360°) is pure sinistral (sin) strike slip, 90° is 

pure normal (nor) slip, 180° is pure dextral (dex) strike slip, and 270° is pure reverse (rev) slip.

N

0 30 60 90 120 150 180 210 240 270 300 330 360

Strike azimuth (degrees)

Frequency

0

0.05

0.1

0.15

0.2

0.25

0.3

E dip S dip W dip N dip E dip

0

0.02

0.04

0.06

0.08

0.1

0.12

0 30 60 90 120 150 180 210 240 270 300 330 360

Rake (degrees)

Frequency

sin nor dex rev sin

FAULT STRIKE DISTRIBUTION FAULT RAKE DISTRIBUTION

n = 29 

A MAP-SCALE FAULTS
Geologic Summary 7

Figure 5. Structural plots of slip observations of A, Map-scale (plotted on map) and B, Mesoscale faults (see database for 

measurements and coordinates) exposed in map area. Upper circular plots are lower-hemisphere, equal-area projections of fault 

slip surfaces (great circles) and slickenlines (points); small arrows attached to points indicate slip sense (strike-slip-dominant faults) 

or hanging-wall movement direction (dip-slip-dominant faults); reverse and normal slip components indicated by open and filled 

points/arrows, respectively; N, north; n, number of fault-slip measurements. Lower histograms show fault strike and rake frequency 

distributions; frequency axis values are scaled to decimal fractions of the total number of measurements; strike azimuths are 90° 

counterclockwise from fault dip directions; rake values range from 0° to 360°, where 0° (=360°) is pure sinistral (sin) strike slip, 90° is 

pure normal (nor) slip, 180° is pure dextral (dex) strike slip, and 270° is pure reverse (rev) slip.—Continued

N

0 30 60 90 120 150 180 210 240 270 300 330 360

Strike azimuth (degrees)

E dip S dip W dip N dip E dip

0 30 60 90 120 150 180 210 240 270 300 330 360

0

0.02

0.04

0.06

0.08

0.1

Frequency

Rake (degrees)

sin nor dex rev sin

0

0.02

0.04

0.06

0.08

0.1

Frequency

n = 103 

FAULT STRIKE DISTRIBUTION FAULT RAKE DISTRIBUTION

B MESOSCALE FAULTS
8 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Figure 6. Close-up photograph of principal fault slip surface, 

formed in pebbly sandstone bed of the Rincon Shale (Tr), 

preserving carbonate mineral coatings (white patches) that were 

precipitated in the fault zone during its slip history. Slickenside 

striae (trending diagonally across photograph from upper 

right to lower left), along with distribution of mineral coatings 

preferentially on lower left sides of surface asperities, indicate 

that missing fault block slipped in direction of black arrow. Coin is 

about 2.5 cm in diameter.

Figure 7. Outcrop of gently dipping beds of conglomeratic 

sandstone of the Oligocene middle conglomerate and sandstone 

unit (Tspm) of the Sespe Formation. Lake Casitas and Laguna 

Ridge visible in background.

cliffs in the map area (figs. 7, 8, and 9). Less tilted, but moderately faulted, Pleistocene marine and terrestrial sediments 

underlie many of the smaller hills and mesas bordering the east 

end of the Santa Barbara coastal plain and in the Oak View-Ojai 

Valley area (figs. 3, 10, and 11). Undisturbed Holocene alluvial 

deposits underlie the floodplains of the Ventura River and larger 

stream valleys and Quaternary landslides and landslide complexes are common on steeper mountain flanks, particularly on 

Rincon Mountain and Sulphur Mountain (figs. 3 and 12).

Structural and Kinematic Framework

Structurally, the map area is dominated by an array of 

subparallel faults and lesser folds that is continuous with the 

Santa Barbara fold and fault belt transecting the Santa Barbara 

coastal plain area directly to the west (Minor and others, 

2009; Gurrola and others, 2014) (fig. 3). In the map area this 

structural belt is roughly arcuate in plan, containing structures 

that change in trend from west-northwest in the western part 

of the map area to east-northeast in the eastern part (map plate 

and fig. 3).

In the map area, the fault and fold belt is bounded on the 

north by the large-trace-length (30 km total; 20 km in map 

area) Arroyo Parida fault, which, near Pike Spring (western 

part of map area), abruptly changes ~20° in strike from westnorthwest (west of bend) to east-northeast (east of bend). The 

Arroyo Parida fault continues to the east of this bend for about 

8 km mostly as a single trace before it splays and eventually merges with other, smaller subparallel faults where it 

approaches and crosses the Ventura River. The Arroyo Parida 

can no longer be confidently traced as a single, distinct fault 

east of the river valley.

The Arroyo Parida fault has had a complex movement 

history in the Neogene and Quaternary involving significant, early (late Miocene?) normal(?) dip slip as well as later 

(Plio-Pleistocene) strike slip and reverse-oblique slip (Minor 

and others, 2009). Early normal movement on the Arroyo 

Parida is inferred from (1) its apparent north dip based on its 

trace over irregular topography in the western part of the map 

area, (2) common juxtaposition of stratigraphically older rock 

units on the south side of the fault, and (3) kinematic evidence of early normal slip on similarly oriented faults in the 

Santa Barbara coastal plain area west of the map area (Minor 

and others, 2009). Near-fault sinistral deflections (drag?) of 

bedding in bedrock (Eocene and Oligocene Sespe Formation, 

units Tspl, Tspm, and Tspu) suggest that sinistral strike slip 

accompanied or followed the normal slip. The Arroyo Parida 

fault likely accommodated a large component of sinistral 

strike slip in the Quaternary based on sinistral deflections of 

several stream channels that cross the fault trace in the map 

area (for example, Coyote Creek near its confluence with Lake 

Casitas) and north of Carpinteria and Summerland, 10 km 

west of the map area (figs. 2 and 3) (Dibblee, 1966; Gurrola 

and others, 2001; Minor and others, 2009). Vertically displaced late Pleistocene alluvial terraces (Qia4 and Qia3) on 

either side of the Ventura River suggest an additional component of youthful south-side-up dip slip along at least the easternmost part of the Arroyo Parida. Although direct kinematic 

characterization of the Arroyo Parida is precluded in the map 

area due to the lack of exposures of its principal slip surface, 

the prevalence of similar-striking reverse faults observed elsewhere in the area (see discussion below) suggest that the late 

Neogene and younger dip-slip components of movement may 

have been reverse along the Arroyo Parida.
Geologic Summary 9

Figure 8. View looking northeast of exposure in Devils Gulch of 

southeast-dipping beds of Rincon Shale (Tr) in footwall block of 

nearby Devils Gulch fault (not visible here; located to right of photograph view). Flat surface covered with grass and shrubs above gulch 

on left side is late Pleistocene intermediate alluvial strath terrace 

(Qia4) that is also cut by Devils Gulch and other subparallel faults.

Figure 9. View looking northeast along hinge of anticline formed 

in shale and mudstone of the upper siliceous unit of the Monterey 

Formation (Tmu). Fold is exposed in Highway 33 roadcut in 

southeastern part of map area about 1.5 km north of its southern 

border. Pick in lower center of photograph is about 0.5 m in length.

Figure 10. Lion Creek cutbank exposure (near central east border 

of map area) of moderately dipping boulder-, cobble-, and pebblebearing conglomerate of Ojai (Qco) which here unconformably 

overlies Rincon Shale (Tr) with minor angular discordance. Clasts in 

the middle(?) Pleistocene conglomerate of Ojai are mostly derived 

from the Eocene and Oligocene sedimentary units exposed along 

the south flank of the nearby Santa Ynez Mountains uplift.

Figure 11. View looking west of Rincon Creek cutbank exposure 

of Rincon Creek fault, here juxtaposing tilted Pleistocene strata of 

the Casitas Formation (Qca) in the upthrown (left) block against 

horizontally bedded upper(?) Pleistocene older alluvial deposits 

(Qoa) and unconformably underlying Casitas deposits (Qca). 

Fault principal slip surface excavated near top of exposure reveals 

reverse-sinistral oblique-slip kinematic indicators. Dotted line 

indicates the location is concealed. A, fault movement away from 

observer, T, toward the observer.

Qca

T A

Qoa

Qca

W

Qco

Tr
10 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Figure 12. View looking south of landslide (Qls) complex on north flank of Rincon Mountain. Landslide deposits, which have slid and 

flowed downslope in directions indicated by arrows, were sourced in mudrocks of the Rincon Shale (Tr) and lower calcareous unit of 

the Monterey Formation (Tml) that underlie upper slopes of Rincon Mountain. White dashed line delineates the approximate location of 

the composite headwall scarp of the slumped area.

Qls complex

Most map-scale faults defining the structural grain of 

the fault and fold belt in the map area are either inferred or 

directly observed to be reverse and oblique reverse in nature. 

Inferences of reverse faulting are based on one or a combination of several of the following observations: (1) the presence 

of stratigraphically older rocks or deposits in the hangingwall block where the fault dip direction can be determined 

(fig. 13); (2) alluvial terrace cut by the fault is more elevated 

on the hanging-wall block; (3) abrupt steepening, overturning, 

or asymmetrical folding of beds on one or both sides of the 

fault, verging towards the down-dropped block. Reverse and 

oblique-reverse slip is confirmed by direct kinematic observations on exposed principal slip surfaces of mapped faults 

(fig. 5A). More than half (59 percent) of the slip lineation rake 

angles measured on the fault surfaces lie within the reverse–

oblique-reverse range (195°‒345°).

A majority of the measured mesoscale faults similarly 

have reverse components of slip, although these smaller 

faults have a much broader strike range (fig. 5B). Most of the 

directly measured fault surfaces dip moderately to shallowly 

to the south and south-southwest. Presumably the same is true 

for most of the inferred reverse faults, which are similarly 

upthrown on their southern sides. One prominent exception 

is the Chismahoo Road reverse fault in the western part of 

the map area, whose curving trace across rugged topography 

and overturned southern (downthrown) block imply a northnortheasterly dip. Kinematic observations indicate that some 

faults have experienced dominantly strike-slip movement 

(fig. 5A,B), in some cases either pre- or post-dating reverse 

movement on the same slip surface. No clear, consistent correlation of strike slip sense (that is, sinistral or dextral) with fault 

strike has been identified in the map area.

Strata in the map area predominantly dip gently to 

moderately (10°‒55°) to the south, the main exceptions 

being in the areally restricted north-dipping limbs and plunging noses of folds (figs. 8 and 9). This stratal tilt pattern is 

consistent with and likely genetically related to the regionally 

extensive south-dipping flank of the Santa Ynez Mountains 

uplift present north and northwest of the map area, which is 

grossly homoclinal but in detail characterized by domains 

of overturned strata with steep to moderate dips (Dibblee, 

Figure 13. View looking west of Lion thrust fault exposed in cut 

bank of Lion Creek. Here fault thrusts Miocene Rincon Shale (Tr) 

over tar-impregnated Pleistocene conglomerate of Ojai (Qco). 

Late Pleistocene alluvial terrace (Qia) overlies and postdates 

fault. Pick in center of photograph is about 0.5 m in length. Dashed 

line indicates contact location is approximate.

Colluvium

Tr

Qco

Qia
Geologic Summary 11

1966, 1982; Minor and others, 2009). A panel of moderately 

to steeply overturned, north-dipping Tertiary strata on either 

side of Rincon Creek (western part of the map area, fig. 3) 

forms the footwall block of the Chismahoo Road fault, with 

the vergence of the overturned strata consistent with southward displacement of the upthrown (hanging-wall) block of 

the fault.

Most folds are located in the eastern part of the map 

area, where they range in trend from west-northwest to 

east-northeast, subparallel to nearby fault traces, and generally plunge gently (<10°) to moderately (10°‒30°) eastward 

(figs. 3, 9). Two prominent folds with long (5–8 km) axial 

traces project across Lake Casitas, the Ayers Creek syncline 

and Laguna Ridge anticline (fig. 3). The north-vergent Laguna 

Ridge fold is a hanging-wall anticline probably associated 

with reverse slip on the adjacent Laguna Ridge fault to the 

north, and the fold seems to merge with a separate up-to-south 

reverse fault where it projects eastward into the low hills 

east of Lake Casitas (fig. 3). In contrast, the symmetric Ayers 

Creek syncline is not clearly related to slip on any adjacent, 

co-extensive fault exposed at the surface, but the north fold 

limb is cut by a reverse fault that merges westward with 

the fold’s axial trace where it crosses the east shore of Lake 

Casitas. Several smaller folds are present on the north side of, 

and trend subparallel to, the trace of the Arroyo Parida fault 

in the Santa Ana Valley area in the northeast part of the map 

area (fig. 3). Two notable folds are located in the western part 

of the map area: (1) a northwest-trending syncline whose axial 

trace is in rocks of the Monterey Formation (Tml) underlying 

the western ridge crest of Rincon Mountain (fig. 3), and (2) a 

west-trending and -plunging syncline formed in deposits of the 

Casitas Formation (Qca).

A series of reverse and oblique-reverse faults cutting 

Oligocene and Miocene sedimentary bedrock (units Tspu, 

Tv, Tr, Tml, and Tmu) and Pleistocene alluvial terrace deposits (units Qia6, Qia5, Qia4, Qia3, and Qia2) in the Ventura 

River-Oak View area (eastern part of map area, fig. 3) strike 

northeast and dip southeast, subparallel to bedding attitudes 

in the area (figs. 8, 13, and 14). These up-to-south reverse 

faults have been interpreted to have formed by flexural slip 

of underlying Tertiary strata accommodating late Neogene 

and Quaternary folding in the area, including development 

of the Ayers Creek syncline (Clark, 1982; Rockwell, 1983; 

Rockwell and others, 1984). Alternatively, or additionally, 

oblique-reverse faulting in this area may accommodate the 

eastward termination or transfer of sinistral slip on the Arroyo 

Parida fault.

Most faults in the map area cut Quaternary marine 

(Qsb and Qmt) and terrestrial (Qca, Qco, Qoa, and Qia6 

to Qia2) deposits as young as late Pleistocene, similar 

to that documented in the fault and fold belt to the west 

(Minor and others, 2009; Gurrola and others, 2014), indicating that much of the deformation is youthful. Such young 

deformation is perhaps best expressed geomorphically by the 

faulted Pleistocene deposits and alluvial terraces in the Oak 

View-San Antonio Creek areas (fig. 3), where reverse faults 

form a series of fault scarps where they vertically displace a 

sequence of late Pleistocene alluvial terraces (figs. 13 and 14). 

In the Carpinteria area at the east end of the Santa Barbara 

coastal plain (southwesternmost part of map area, fig. 3), the 

Carpinteria and Rincon Creek faults are also geomorphically 

well-expressed by locally prominent, north-facing, fault-fold 

scarps and broad anticlinal upwarps formed in middle and late 

Pleistocene deposits (Qca, Qoa, and Qmt) on their southern, 

upthrown blocks (fig.11).

Furthermore, the late Pleistocene sequence of marine 

terraces (Qmt) in this area gradually (but steadily) rises in 

elevation eastward from Carpinteria and lower Rincon Creek 

to the southern border of the map area and farther southeast 

towards Ventura, providing direct evidence of dramatic post 

45 ka (kilo-annum, thousand years) tectonic uplift in the 

region (Yerkes and Lee, 1987). The occurrence of earlier 

(pre-Quaternary?) stratal tilting in the map area, and possibly related folding and faulting, are indicated by small to 

moderate (<20° to >50°) angular unconformities that separate 

Tertiary sedimentary bedrock units from overlying early(?) 

and (or) middle(?) Pleistocene deposits (Qsb, Qca, and Qco) 

(fig. 10).
Figure 14. Panorama looking west-to-southwest across San Antonio Creek valley, of a faulted late Pleistocene alluvial strath terrace (Qia6). Ter

south-tilted “treads” visible along ridge crest in upper center and left parts of photograph, is cut by a series of intervening southwest-striking, soufaults expressed as north-facing slopes or “risers” visible in upper left, center, and right parts of photograph. Lower bench visible on far-right side grassy surface in center foreground are younger alluvial terraces (Qia3 and Qia2, respectively) that postdate faulting.
Geologic Summary 13

DESCRIPTION OF MAP UNITS

[Unit symbols are queried on map where the unit identification is questionable. The database contains 

additional features (minor folds and faults) that do not appear on the map]

SURFICIAL DEPOSITS

MAN-MADE DEPOSITS

af Artificial fill (Holocene)—Mappable areas of fill used for construction of highways, roads, 

buildings, and dams. Thickness mostly less than 10 m, but locally exceeds 30 m

ALLUVIAL DEPOSITS

Qa Active alluvium (Holocene)—Unconsolidated sediments, primarily pebble to boulder gravel, 

in floors and banks of modern stream and river channels and floodplains. Sediments subject to seasonal flooding and downstream transport. Active channels incised as much as 

5 m into older alluvial deposits (for example, Qya). Includes active alluvium of Ventura 

River in east part of map area. Thickness of unit generally less than 5 m

Qya Younger alluvium (Holocene)—Unconsolidated to weakly consolidated, poorly to moderately sorted silt, sand, and pebble to boulder gravel occupying the broad valley floors and 

floodplains of larger drainages. Unit typically forms extensive, non-dissected terraces that 

flank, and lie less than 3 m above, active stream and river channels and their associated 

alluvium (Qa). Younger alluvium present mainly along the Ventura River and within the 

San Antonio, Rincon, and Carpinteria Creek drainages, where it is rarely subject to flooding. Adjacent to valley and canyon margins unit locally includes subordinate colluvial 

deposits containing poorly sorted, angular clasts. Terrace surfaces formed by alluvium 

commonly contain poorly to moderately developed soil profiles and are sparsely to moderately vegetated with grasses, shrubs, and trees. Younger alluvium previously mapped as 

stream gravel and “abandoned meanders of San Antonio Creek” (Clark, 1982); modern 

river gravels and Oak View floodplain and terraces “Q1”, “Q2”, and “Qt3” (Rockwell, 

1983); alluvium (Dibblee, 1987a,b); alluvial deposits (Tan and Clahan, 2004); and alluvial and colluvial deposits (Tan and Jones, 2006). Younger alluvium deposits estimated to 

range in age from <250 years before present (yr B.P.) to about 5 kyr (thousand years) B.P. 

(Rockwell, 1983; Rockwell and others, 1984). Thickness of younger alluvium generally 

less than about 4 m

Qaf Alluvial fan deposits (Holocene and late Pleistocene?)—Weakly to moderately consolidated, poorly to moderately sorted silt, sand, and pebble to boulder gravel forming 

weakly to moderately dissected fans. Deposits form a broad fan-like apron in the town of 

Ojai, small fans along Rincon Creek, and a fan delta where Rincon Creek empties into the 

Pacific Ocean at Rincon Point. Thickness of fans in Ojai and at Rincon Point estimated to 

be at least 15 m

Qia Intermediate alluvial deposits, undifferentiated (late Pleistocene)—Undifferentiated unit 

mapped where poor exposures and geomorphic expression do not allow distinguishing 

deposits based on relative age. Deposits composed of pale-brown, -tan, and -gray, weakly 

consolidated silt, sand, and pebble, cobble, and boulder gravel. At most places proportion of gravel greatly exceeds that of sand and silt; a few meters of finer-grained sediments cap alluvial deposits in some exposures. Gravel commonly crudely stratified, and 

elongate clasts are locally imbricated. Variably rounded gravel clasts mostly composed of 

locally derived Eocene through Miocene sandstones, siliceous shales and mudstones, and 

rare reworked cobbles and pebbles derived from conglomerates of the Sespe Formation. 

Intermediate alluvial deposits form weakly to moderately dissected stream and river 

strath terraces as high as about 150 m above adjacent modern floodplains and broad, 

low-relief, piedmont alluvial aprons. In Oak View area strath terraces are cut into both 

Tertiary bedrock units and semi-consolidated deposits of conglomerate of Ojai (Qco). 

In piedmont areas average clast size in deposits generally decreases away from bedrock 

mountain fronts and uplands.
14 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Rockwell and others (1984) estimated late Pleistocene ages (~16–100 ka) for deposits 

forming elevated ancestral Ventura River terraces in eastern part of map area (units Qia2, 

Qia3, Qia4, Qia5, and Qia6 of the present map, described below) using radiocarbon ages 

and estimated rates of faulting of older elevated terraces. These radiocarbon ages were later 

confirmed, with minor refinements, using terrestrial cosmogenic nuclide dating techniques 

(DeVecchio and others, 2012). Late Pleistocene age of unit also likely near southwest 

corner of map area on coastal plain near Carpinteria, where southern edge of apron formed 

by intermediate alluvial deposits appears to grade into, or interfingers with, late Pleistocene 

(45? ka) marine-terrace deposits (Qmt) (Wehmiller and others, 1978). 

Intermediate alluvial deposits previously mapped as terrace deposits, younger 

alluvium, and older alluvium (Upson, 1951); alluvium, old alluvium, and Carpinteria 

Formation (Lian, 1954); old alluvium and Oak View terrace sequence (Clark, 1982); Oak 

View terraces “Qt3” through “Qt6c” (Rockwell, 1983; Rockwell and others, 1984); alluvium and older dissected surficial sediments (Dibblee, 1987a,b); alluvial deposits (Tan 

and Clahan, 2004); and alluvial and colluvial deposits (Tan and Jones, 2006). Thickness 

of intermediate alluvial deposits mostly less than 10 m and thins to a few meters or less 

where deposits form strath terraces; maximum thickness of deposits may be significantly 

greater where they underlie broad piedmonts in Ojai and Santa Ana Valleys and on the 

coastal plain near Carpinteria.

In Ventura River-San Antonio Creek area and along the Los Sauces and Rincon 

Creeks, terrace-forming intermediate alluvial deposits are subdivided into six age groupings (described below) based chiefly on relative levels (elevations) of terraces and secondarily on degree of erosional dissection and soil development. Terrace-level groupings 

in Ventura River area approximately follow those of Rockwell (1983) and Rockwell and 

others (1984), who determined that terrace relative elevations, amount of dissection, and 

soil maturity all increase with age. In general, terraces on east and west sides of Ventura 

River are progressively younger towards the modern river floodplain. Deposits assigned 

to any one terrace level are likely somewhat diachronous and may temporally overlap 

deposits of younger or older age assignment, both along a single large drainage (for 

example, Ventura River) and, especially, across breadth of map area

Qia1 Intermediate alluvial deposits, terrace level 1—Forms locally preserved terrace remnants 

a few meters above active (Qa) and Holocene (Qya) alluvial floodplains of San Antonio 

Creek, Ventura River, and Los Sauces and Rincon Creeks. Weak soil development, with 

little or no B horizon (Rockwell, 1983). Mostly mapped as Oak View terrace unit “Qt3” 

by Rockwell (1983)

Qia2 Intermediate alluvial deposits, terrace level 2—Forms small to large terrace remnants as 

much as 15 m above active (Qa) and Holocene (Qya) alluvial floodplains of San Antonio 

Creek, Ventura River, and Rincon Creek. Weak to moderate soil development (Rockwell, 

1983). Mapped as Oak View terrace unit “Qt5a” by Rockwell (1983) and Rockwell and 

others (1984), who estimated age of terrace level as 16–22 ka

Qia3 Intermediate alluvial deposits, terrace level 3—Forms small to large terrace remnants as much 

as 25 m above active (Qa) and Holocene (Qya) alluvial floodplains of San Antonio Creek, 

Ventura River, and Rincon and Gobernador Creeks. Moderate soil development (Rockwell, 

1983). Mostly mapped as Oak View terrace unit “Qt5b” by Rockwell (1983) and Rockwell 

and others (1984), who estimated age of terrace level as about 32 ka

Qia4 Intermediate alluvial deposits, terrace level 4―Forms small to large terrace remnants 

as much as 60 m above active (Qa) and Holocene (Qya) alluvial floodplains of Ventura 

River and Rincon, Gobernador, and Carpinteria Creeks. Moderate to strong soil development (Rockwell, 1983). Mapped as Oak View terrace unit “Qt6a” by Rockwell (1983) 

and Rockwell and others (1984), who determined age of terrace level as 40 14C cal ka B.P.

Qia5 Intermediate alluvial deposits, terrace level 5―Forms small to large terrace remnants 

as much as about 85 m above active (Qa) and Holocene (Qya) alluvial floodplains of 

San Antonio Creek, Lion Creek (near the Lion Fault), Ventura River, and Rincon Creek. 

Moderate to strong soil development (Rockwell, 1983). Mostly mapped as Oak View terrace unit “Qt6b” by Rockwell (1983) and Rockwell and others (1984), who estimated age 

of terrace level as 56±10 ka
Geologic Summary 15

Qia6 Intermediate alluvial deposits, terrace level 6—Forms small to large terrace remnants 

as much as about 140 m above active (Qa) and Holocene (Qya) alluvial floodplains of 

San Antonio Creek and Ventura River, and caps Shepard Mesa west of Rincon Creek. 

Moderate to strong soil development (Rockwell, 1983). Mapped as Oak View terrace 

unit “Qt6c” by Rockwell (1983) and Rockwell and others (1984), who estimated age 

of terrace level as 94±13 ka

Qoa Older alluvial deposits (late? and middle? Pleistocene)—Nonmarine brown, pale-gray, 

pale-tan, and reddish-brown, moderately consolidated, crudely stratified, poorly sorted, 

clayey to silty and pebbly sand and sandstone, silty to sandy pebble-cobble-boulder 

gravel, conglomerate, and breccia, and rare interbeds and partings of sandy to pebbly 

clay, silt, and mudstone. Sand and sandstone in places well bedded and cross laminated. 

Gravel and conglomerate typically occupy paleochannels or form lenticular beds, and 

contain subrounded clasts composed primarily of sandstone derived from Eocene formations (including Coldwater Sandstone [Tcw]) exposed in Santa Ynez Mountains north of 

and within map area. Clasts commonly are imbricated. Breccia deposits contain subangular clasts mainly of Eocene sandstone and typically form thick (>3 m), sheet-like, clastsupported beds probably deposited as debris flows.

Older alluvial deposits present chiefly in west part of map area where they form 

moderately steep and dissected uplands and lower, gently sloping hills along south flank 

of Santa Ynez Mountains and bordering eastern end of Santa Barbara coastal plain. 

Deposits interpreted as erosional remnants of old alluvial fans formed along lower flank 

of Santa Ynez Mountains. Clast size generally decreases and sorting increases away from 

mountain front. Finer-grained facies at places forms badlands topography. In west part of 

map area, older alluvial deposits are deformed by youthful faults and upwarps.

Older alluvial deposits also mapped in Santa Ana Valley in northeastern part of map 

area, where they are preserved as a discontinuous belt of low rounded hills whose surfaces are strewn with cobbles and boulders up to several meters in diameter of Eocene(?) 

sandstone. In the same area, base of map unit consists of rounded cobble-pebble gravel 

where it laps onto rocks of the Sespe Formation (Tspu) in a road cut exposure east of 

Poplin Creek. Nearby, unit inferred to be gently folded into east-plunging syncline near 

trace of Arroyo Parida fault at west end of valley, based on its arcuate map pattern. At 

most places in west part of map area, older alluvial deposits overlie dipping strata of 

the Casitas Formation (Qca) with little or no angular discordance. The deposits closely 

resemble, and may be partly correlative with, some sediments of the Casitas Formation 

and the conglomerate of Ojai (Qco). Older alluvial deposits can be distinguished from 

nearby Casitas deposits by the relatively lesser consolidation and competency of the 

former. Also, the older alluvial deposits generally contain a smaller percentage of Sespe 

sandstone clasts and reworked Sespe conglomerate clasts, are more uniform in color, and 

at some places are less tilted than directly underlying Casitas deposits. Most older alluvial 

deposits of this report previously mapped as terrace deposits and Casitas Formation 

(Upson, 1951); Casitas Formation and Carpinteria Formation (Lian, 1954); older dissected surficial sediments (fan gravel and fanglomerate deposits) (Dibblee, 1987a); and 

alluvial deposits (Tan and Clahan, 2004). Stratigraphic intervals within older alluvial 

deposits yield significant quantities of groundwater in wells on the Santa Barbara coastal 

plain west of map area, where unit forms one of the principal aquifer units (Upson, 1951; 

Muir, 1968).

Maximum age (middle(?) Pleistocene) of unit constrained by middle Pleistocene 

strata of uppermost Santa Barbara Formation (Qsb) that interfinger with deposits of 

the Casitas Formation (Qca) in map area, which in turn directly underlie older alluvial deposits; minimum age (late(?) Pleistocene) of unit constrained by elevated, late 

Pleistocene marine-terrace deposits (Qmt) that lap onto distal facies of older alluvial 

deposits near southwest corner of map area. Maximum exposed thickness approximately 

350 m beneath Shepard Mesa in western part of map area
16 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

MARINE-SHORE DEPOSITS

Qb Beach deposits (Holocene)—Modern, unconsolidated marine-shoreline beach sediment, 

mostly fine- to medium-grained, well-sorted, clean, light-grayish-tan sand composed 

predominantly of quartz, feldspar, and lithic grains. Includes subordinate wave-rounded 

pebbles, cobbles, and shell fragments, as well as plant remains and litter left by people. 

Thickness of deposits probably rarely exceeds 5 m and varies seasonally mainly due to 

storm-surge beach erosion; occasionally during the winter months sand is completely 

stripped away in places, exposing the underlying bedrock surface that is commonly littered with wave-rounded cobbles. Beach deposits present intermittently along shoreline 

near southwest corner of map area

Qmt Marine-terrace deposits (late Pleistocene)—Mostly pale- to medium-tan and -gray, weakly 

to moderately consolidated, crudely to moderately bedded, pebble-cobble gravel, pebbly 

to gravelly sand, and silt. Deposits unconformably overlie elevated marine wave-cut 

platforms abraded on bedrock. Lower part of marine-terrace sequences typically consists 

of thin (≤1 m) basal layer of fossiliferous rounded cobble and pebble gravel that locally 

grades upward into laminated to massive beach(?) sand and (or) estuarine organic-rich 

clay and silt. Some basal gravel clasts exhibit mollusk (pholad) borings. Upper two-thirds 

or more of terrace sequences consists of nonmarine eolian sand and silt, stratified alluvial 

pebble-cobble gravel, and minor colluvial deposits.

Marine-terrace basal-abrasion surfaces in map area are inferred to have formed during 

interglacial sea-level high stands, whereas the overlying terrace deposits most likely accumulated during marine regressions resulting from eustatic drops in sea level and (or) tectonic 

uplift (Rockwell and others, 1992; Muhs and others, 1992; Gurrola and others, 2001).

Marine-terrace deposits, exposed in upper part of sea cliffs and U.S. Highway 101 

road cuts near southwest corner of map area, are inferred to underlie small, locally dissected coastal mesas that extend inland from the cliffs. The first emergent marine terrace 

exposed in sea cliff at Carpinteria at 15 m (40–60 ft) elevation (just west of map area; see 

Minor and others, 2009) continues eastward into map area, where it gradually climbs in 

elevation eastward and projects across Highway 101 and Rincon Creek into a flight of 

terraces northeast of Rincon Point. The lower part of this terrace sequence and its associated marine-terrace deposits are expressed by four lower bench-like surfaces separated by 

subtle (<1 to 2 m height) risers or steps inferred to mark approximate positions of marine 

shoreline angles (that is, base of paleo sea cliffs); these shoreline angles have approximate 

elevations of 61 m (200 ft), 73 m (240 ft), 88 m (290 ft), and 116 m (380 ft) above modern 

sea level. More elevated and dissected, presumably older, marine-terrace deposit remnants 

present just to the north are bounded by at least two inferred shoreline angles ranging in 

elevation from 146 to 162 m (480 to 530 ft) (lower shoreline) and 183 to 226 m (600 to 

740 ft) (upper shoreline). Eastward-ascending lower part of terrace sequence spanning the 

Carpinteria-Rincon Point coastal strip has been correlated with the uplifted Punta Gorda 

terrace preserved east of the map area, which has an amino-acid-racemization estimated age 

of 45 ka (oxygen isotope stage 3) (Wehmiller and others, 1978; Lajoie and others, 1979; 

Yerkes and Lee, 1987).

Alluvial deposits typically present in upper part of marine terrace sequences are 

probably correlative with intermediate alluvial deposits (Qia). Marine-terrace deposits 

are inferred to grade into, or interfinger with, intermediate alluvial deposits just north 

of Highway 101 at east end of coastal plain near Carpinteria. Marine-terrace deposits of 

this report have been previously mapped as terrace deposits (Upson, 1951; Lian, 1954); 

Carpinteria Formation (Lian, 1954); older dissected surficial sediments (alluvial deposits) 

(Dibblee, 1987a); and paralic deposits (Tan and Clahan, 2004). Maximum thickness of 

lower, marine part of terrace deposit sequence approximately 5 m; composite thickness of 

marine-terrace deposits, including upper nonmarine part, typically ranges from 5 to 10 m

MASS-WASTING DEPOSITS

Qdf Debris-flow deposits (Holocene and late Pleistocene?)―Massive, weakly-to moderatelyconsolidated, poorly sorted, generally matrix-supported rock-debris breccia. Mainly 

located in southern part of map area on flanks of Rincon Mountain and smaller hills to 
Geologic Summary 17

the east. Chiefly composed of clay, silt, and shale, mudstone, siltstone, and (or) sandstone 

debris derived from Rincon Shale (Tr), Santa Barbara Formation (Qsb), and (or) Sespe 

Formation (Tspu, Tspm) exposed upslope.

Youthful lobate and hummocky geomorphic expression of most deposits suggests 

they are Holocene in age, but considerable erosional dissection of a few deposits suggest some debris flows were emplaced during the late Pleistocene. Most mapped deposits 

estimated to be less than 10 m thick

Qls Landslide deposits (Holocene and late? Pleistocene)—Deposits of diverse slope-movement 

processes including earth slides, earth flows, rock slides, debris slides, and rock slumps 

(Bezore and Wills, 2000; terminology of Cruden and Varnes, 1996). Deposits range from 

poorly sorted, disrupted mixtures of rock fragments and soil to relatively intact bedrock 

slide blocks. Surfaces of deposits commonly hummocky; downslope-facing breakaway 

or headwall scarps identifiable and mapped in places. Slopes underlain by Rincon Shale 

(Tr), Monterey Formation (Tml, Tmu), and relatively fine-grained intervals of the Sespe 

Formation (Tspu, Tspm, Tspl) and Santa Barbara Formation (Qsb) are particularly 

susceptible to sliding. Many of the mapped landslide deposits are actually a composite 

of several smaller overlapping and (or) inset slide units, each formed by one or more 

episodes of downslope movement. Partial or complete boundaries of slide units mapped 

where identified within large slide complexes on north and south flanks of Rincon 

Mountain (southwest part of map area) and on northwest flank of Sulphur Mountain 

(eastern part of map area). “Landslide” scarps mapped within bedrock units indicate 

places of incipient or partial break-away and downslope movement of bedrock; laterally most such scarps can be traced into intact (non-slide) bedrock, and bedrock below 

scarps does not appear to be noticeably disturbed and detached. Bedding attitudes shown 

on map within landslide deposits indicate places where semi-coherent bedding was 

measured within large bedrock slide blocks; landslide attitudes document disruption of 

local bedrock strata due to landslide movement. Slide complex located on south flank of 

Rincon Mountain along southern border of map area is part of the late Pleistocene Rincon 

Mountain “megaslide” as inferred by Gurrola and others (2010). Late Pleistocene age of 

some landslide deposits suggested by their relatively high degree of stream dissection that 

has locally resulted in perched (relative to modern valley floors) distal ends of the slide 

deposits. Maximum thickness of deposits in large slide complexes likely exceeds 50 m

BEDROCK UNITS

Qca Casitas Formation (middle? Pleistocene)—Nonmarine interbedded conglomerate and 

gravel, sandstone and sand, siltstone and silt, and rare mudstone forming mostly thin to 

thick lenticular beds. Formation typically moderately to well consolidated. Deposits in 

aggregate exhibit pale to medium shades of buff, tan, red, maroon, gray, brown, and, less 

commonly, green, yellow, and orange, and they commonly form badlands topography 

where exposed in cliffs.

Conglomerate and gravel contain subrounded to rounded pebbles, cobbles, and 

boulders, combined in various proportions, in a clayey, silty, and (or) sandy matrix; 

deposits are both clast-supported and matrix-supported. Conglomerate and gravel deposits are massive to moderately well stratified, in places appear to fill paleochannels, and 

form beds that locally exceed 5 m in thickness. Clasts composed chiefly of locally(?) 

derived Eocene and Oligocene (Tcw, Tspl, Tspm, and Tspu) sandstone and lesser siltstone, shale, and mudstone; clasts in upper part of unit east of Rincon Creek also include 

subangular-to-subrounded pebbles and cobbles of Monterey siliceous shale and mudstone 

(Tml?, Tmu). Subordinate well-rounded pebbles and cobbles of various other lithologies 

within the Casitas are probably reworked from conglomerates of the middle and lower 

units of the Sespe Formation (Tspm, Tspl).

Sandstone and sand are typically pale shades of buff, tan, gray, and greenish-gray, 

fine to coarse grained, silty, clayey and (or) pebbly, and massive to well bedded and laminated. Sandstone is mostly friable, but locally is well indurated where cemented with carbonate minerals. In places sandstone and sand contain conglomeratic and gravelly lenses.
18 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Siltstone and silt are commonly pale gray and pale greenish-gray, sandy to clayey, 

and thinly bedded and laminated. Mudstone is commonly brown and forms thin beds 

and partings. Finer-grained intervals in Casitas, dominated by fine-grained sandstone, 

siltstone, and mudstone, are as thick as 5 m.

Casitas Formation was first defined and mapped by Upson (1951), who designated 

type section in western part of map area near confluence of Rincon and Casitas Creeks. 

Unit subsequently mapped in the Carpinteria-Rincon Creek area as Casitas Formation 

(Lian, 1954; Dibblee, 1987a; Tan and Clahan, 2004).

Deposits of Casitas Formation are mapped only in the western, coastal area near 

Rincon Creek and in low hills northeast of Carpinteria. Casitas deposits closely resemble, 

and may be temporally equivalent with, some of the older alluvial deposits (Qoa), 

particularly where the alluvial deposits directly overlie Casitas sediments in the low hills 

and mesas northeast of Carpinteria. The two units can be distinguished, however, by 

the generally greater amount of clay and silt in Casitas deposits, which results in their 

somewhat greater consolidation, induration, and competency. Also, Casitas deposits 

contain a greater percentage of Sespe sandstone clasts and reworked Sespe conglomerate 

clasts, exhibit a greater variety of colors, and at some places are more strongly tilted than 

directly overlying older alluvial deposits. Casitas sediments were likely deposited as alluvium shed off of the Santa Ynez Mountains and other nearby uplands. Casitas Formation 

may be correlative with the similar conglomerate of Ojai (Qco) exposed in eastern part 

of map area and with nonmarine deposits in the Ventura area (~10 km south of map area) 

mapped as upper part of San Pedro Formation (Yerkes and others, 1987) and Saugus 

Formation (Dibblee, 1988). Age of Casitas Formation in map area is bracketed by underlying and interfingering middle Pleistocene upper part of the Santa Barbara Formation 

(Qsb), and by late Pleistocene marine terrace (Qmt) and intermediate alluvial deposits 

(Qia) that unconformably overlie it west of Rincon Creek. Maximum exposed thickness 

~975 m in area of type section south of Casitas Creek and east of Rincon Creek. Unit also 

present in subsurface of the coastal plain in the Carpinteria area (Upson, 1951; Jackson 

and Yeats, 1982). The abandoned Summerland oil field 10 km west of map area produced 

from sand-rich intervals within Casitas Formation (Arnold, 1907), indicating potential for 

at least part of formation to serve as a subsurface hydrocarbon reservoir. Coarser-grained 

intervals within the Casitas yield significant quantities of groundwater in wells and the 

formation forms one of the principal aquifer units beneath the Santa Barbara coastal plain 

near and west of Carpinteria (Upson, 1951; Muir, 1968)

Qco Conglomerate of Ojai (middle? Pleistocene)—Nonmarine interbedded conglomerate and 

gravel, sandstone and sand, and subordinate siltstone and silt and rare mudstone forming mostly thin to thick lenticular beds. Deposits in aggregate typically exhibit pale to 

medium shades of tan, tannish-gray, and brown. Unit mostly moderately to well consolidated and poorly exposed, forming gullied slopes and rounded hills.

Conglomerate and gravel contain subrounded to well-rounded pebbles, cobbles, and 

boulders, combined in various proportions, supported in a silty and (or) sandy matrix. 

Conglomerate and gravel deposits are massive to moderately well stratified, in places 

forming beds and paleochannels that locally exceed 5 m in thickness. Clasts composed 

chiefly of locally(?) derived, Eocene and Oligocene (Tcw, Tspl, Tspm, and Tspu) 

sandstone and lesser siltstone, shale and mudstone; rare clasts of shale and mudstone of 

Monterey Formation (Tml, Tmu) also present locally. Subordinate well-rounded pebbles 

and cobbles of various other lithologies within the conglomerate of Ojai are probably 

reworked from conglomerates of middle and lower units of Sespe Formation (Tspm, 

Tspl). In some beds elongate cobbles and small boulders as much as 0.5 m diameter are 

crudely to strongly imbricated. Along Lion Creek near the eastern border of map area, 

conglomerate is anomalously cohesive and dark gray where it is impregnated with tar in 

the footwall of the Lion fault.

Sandstone and sand are typically pale shades of buff, tan, and tannish-gray, fine to 

coarse grained, silty, clayey and (or) pebbly, and massive to well stratified and laminated. 

Sandstone is mostly friable to weakly indurated. In places sandstone and sand contain 

conglomeratic and gravelly lenses. Sandy and sandstone-rich intervals in places exceed 
Geologic Summary 19

3 m in thickness. In lower 2‒3 m of Highway 33 cut at southern edge of Oak View, conglomeratic deposits of unit overlie massive, mottled (bioturbated?), friable, well-sorted, 

fine-grained sand atypical of sand layers elsewhere in map unit; this sand interval resembles sandy facies of Santa Barbara Formation (Qsb) exposed in western part of map area, 

but is lacking any fossil marine shell fragments; lower exposed sand not mapped separately due to its limited, isolated exposure.

Subordinate siltstone and silt are commonly pale gray and pale tannish-gray, sandy 

to clayey, and thinly bedded and laminated. Rare mudstone is commonly brown to tan 

and forms thin beds and partings. Finer-grained beds and intervals rarely exceed 1 m in 

thickness.

Deposits mapped herein as conglomerate of Ojai previously mapped as the Oak 

View terrace sequence (Clark, 1982); older gravel (Rockwell, 1983); older dissected fan 

gravel or fanglomerate (Dibblee, 1987b); undivided alluvial deposits (Tan and Jones, 

2006); and Saugus Formation (DeVecchio and others, 2012).

Conglomerate of Ojai is exposed only in the eastern part of map area chiefly in 

the gentle uplands between the Ventura River and San Antonio Creek. Deposits closely 

resemble, and may be temporally equivalent with, some of the older alluvial deposits 

(Qoa) mapped to the northwest in western Santa Ana Valley and in the western part of 

map area near Carpinteria. Conglomerate of Ojai may also be correlative with similar 

deposits of the Casitas Formation (Qca) mapped in western part of map area and with 

nonmarine deposits in the Ventura area (~10 km south of map area) mapped as upper 

part of San Pedro Formation (Yerkes, Sarna-Wojcicki, and Lajoie, 1987) and Saugus 

Formation (Dibblee, 1988). Conglomerate of Ojai was likely deposited as alluvium shed 

off of the Santa Ynez Mountains, Topatopa Mountains, and other nearby uplands. Age 

of conglomerate of Ojai in map area is not well constrained, bracketed by unconformably underlying Miocene Monterey Formation (Tml, Tmu), and by oldest preserved late 

Pleistocene intermediate alluvial deposits (Qia6) unconformably overlying it. Middle(?) 

Pleistocene age inferred from possible correlation with Casitas Formation deposits to 

west, which overlie middle and early Pleistocene Santa Barbara Formation (Qsb), and 

with deposits of the upper part of San Pedro Formation to south near Ventura having an 

estimated age of ~200 ka (Yerkes, Sarna-Wojcicki, and Lajoie, 1987). Maximum exposed 

thickness in map area ~130 m; a maximum unit thickness of 240 m was determined by 

McKay (2011), using water well data of Kear (2005), in subsurface of Ojai Valley about 

7 km northeast of the map area. Coarser-grained intervals within the conglomerate of Ojai 

have the potential to yield significant quantities of groundwater in wells and may form a 

significant aquifer beneath Ojai Valley and the Oak View-Ventura River area (Kear, 2005)

Qsb Santa Barbara Formation (middle and early Pleistocene)―Marine fossiliferous sandstone 

with subordinate siltstone, mudstone, and conglomerate. Sandstone is mostly pale-gray 

and cream-colored (fresh) to buff and shades of pale-tan, -yellow, and -gray (weathered), 

fine- to medium-grained, and includes silty, clayey, and pebbly beds and intervals. Sandstone ranges from bioturbated and massive to crudely or moderately bedded and planarto cross-laminated. Sandstone is mostly friable, but includes rare resistant sandstone beds 

that are cemented with carbonate minerals. White to gray fossil marine shell fragments 

are common within sandstone, both in isolated occurrences and concentrated in layers of 

shell hash.

Siltstone, mudstone, and rare shale weather pale-gray and pale-greenish-gray, are 

typically laminated, and form partings, interbeds, and thin-bedded intervals that are commonly accompanied by silty to clayey fine-grained sandstone beds.

Conglomerate and conglomeratic sandstone, which weather to tannish-red brown to 

rusty-orange brown, form paleochannels, lenses, beds, and intervals as thick as ~10 m. 

Conglomerates are polymict, containing generally well-rounded pebbles and subordinate 

cobbles composed of sandstone possibly derived from Eocene formations exposed in 

nearby Santa Ynez Mountains (including Tspl, Tcw), chert and intermediate-to-silicic 

volcanic rocks possibly reworked from conglomerates of the Sespe Formation (Tspm, 

Tspl), shale and mudstone of the Monterey Formation (Tmu?, Tml?), and other rock 

types of uncertain provenance.
20 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Diverse marine invertebrate fossil assemblages, dominated by mollusks, are concentrated in multiple stratigraphic intervals within exposed part of Santa Barbara section, 

ranging in thickness from less than 1 m to several tens of meters. Most shells are disarticulated, fragmented, and concentrated in beds and lenses in both sandstone and finergrained intervals. Unit includes rare, whitish beds of calcareous coquina.

Santa Barbara Formation is exposed only in Rincon Creek area in west part of 

map area, where a moderate to pronounced angular unconformity separates formation 

from underlying Miocene units (Tr, Tml, Tmu). Surface trace of this unconformity east 

of Rincon Creek, on lower western flank of Rincon Mountain, marks eastern limit of 

exposure (and possibly deposition) of unit. Upper contact of Santa Barbara Formation 

with overlying Casitas Formation (Qca) is gradational where exposed in low hills east of 

Rincon Creek, expressed by ~35-m-thick interval of interfingering or interstratified Santa 

Barbara-like marine (fossil-shell bearing) sandstones and Casitas-like conglomerates and 

sandstones. Upper contact mapped at top of stratigraphically uppermost bed of fossiliferous marine sandstone.

Molluscan fossils collected from Santa Barbara Formation in southwestern-most 

part of map area and on Santa Barbara coastal plain west of map area (Minor and others, 2009) examined by C.L. Powell, II (USGS, written commun., 2001) characteristically include bivalves Chlamys spp., Cyclocardia occidentalis (Conrad), C. californica

(Dall), Humilaria perlaminosa (Conrad), Lucinoma annulatum (Reeve), Patinopecten 

caurinus (Gould), Pecten bellus (Conrad), and gastropods Amphissa reticulata (Dall), 

Boreotrophon spp., Crepidula princeps (Conrad), Olivella biplicata (Sowerby), Neptunea 

tabulata (Baird), and Turritella cooperi Carpenter. The molluscan fauna are consistent 

with deposition at shelf water depths and a possible late Pliocene to middle Pleistocene 

age (C.L. Powell, II, written commun., 2001). Previously, Dibblee (1966) presented a list 

of molluscan fossils from the formation interpreted to indicate a “late Pliocene(?) to early 

Pleistocene” age.

Middle and early Pleistocene age provisionally assigned to Santa Barbara Formation in this report based partly on reconnaissance paleomagnetic data from Santa Barbara 

coastal plain west of map area. These data suggest that much of formation was deposited 

during the normal polarity epoch following the Brunhes-Matuyama geomagnetic reversal at about 780 ka (Keller and Gurrola, 2000; Gurrola and others, 2001; J.W. Hillhouse, 

USGS, written commun., 2007). Middle and early Pleistocene age also consistent with 

(1) a reported amino-acid racemization age of 500–600 ka for formation ~ 20 km west of 

map area (Wehmiller, 1992), (2) strontium isotopic data suggesting an age of 400–900 ka 

for formation near Santa Barbara Harbor ~20 km west of map area (Patterson and others, 

1990), (3) age of about 600 ka for planktic foraminifer Neogloboquadrina pachyderma 

within formation near Santa Barbara Harbor (Patterson and others, 1990), and (4) a 

1.2 Ma (Mega-annum, million years) age determination for the Bailey ash (Izett, Naeser, 

and Obradovich, 1974), which directly underlies Santa Barbara Formation in the Ventura 

area ~8 km south of map area (Yerkes, Sarna-Wojcicki, and Lajoie, 1987).

Unit typically is poorly exposed and forms subdued rounded hills except in some 

narrow, steep-walled stream canyons where soil and regolith have been stripped off of 

Santa Barbara rocks; silt- and clay-rich intervals locally erode into badlands topography. 

Formation has a minimum thickness of approximately 350 m east of Rincon Creek; upper 

part of section in this area is truncated by the Rincon Creek fault.

Unit was also mapped as Santa Barbara Formation by earlier workers (Upson, 1951; 

Lian, 1954; Dibblee, 1987a; Tan and Clahan, 2004). Coarser-grained intervals within the 

unit yield significant quantities of groundwater in wells and the Santa Barbara Formation 

forms one of the principal aquifer units beneath the Santa Barbara coastal plain (Upson, 

1951; Muir, 1968)

Tsq Sisquoc Formation (lower Pliocene and upper Miocene)—Marine diatomaceous mudstone and shale, and subordinate dolomite and conglomerate. Distinguished from the 

underlying upper siliceous unit of the Monterey Formation (Tmu) by abrupt upward 

change from generally hard, siliceous mudstone and shale to typically pale gray-brown, 

relatively soft diatomaceous mudstone and, locally, conglomerate.
Geologic Summary 21

Diatomaceous mudstone and shale are white to pale-gray and pale-gray-brown 

weathering, and gray to brown on freshly broken surfaces. Mudstone is generally soft 

to moderately hard; shale ranges from soft to, rarely, hard and fissile; where moderately 

hard, both rock types commonly exhibit dense hackly fractures. Both mudstone and shale 

are generally of conspicuously low density. Reaction in dilute hydrochloric acid (HCl) 

ranges from weak to strong, indicating the presence of variable amounts of carbonate 

minerals. Foraminifers, diatoms and diatom debris, and fish scales and other fragments 

are common to abundant, particularly along surfaces that are broken parallel to stratification; preservation of diatoms is generally poor in the Sulphur Mountain area. Most 

mudstone and shale beds are moderately to strongly laminated but some are massive and 

bioturbated. Laminations, generally 0.5–10.0 millimeters (mm) thick, are defined by light 

and dark color bands. At places, such as in railroad and highway cuts near Rincon Point, 

shale is impregnated with oil, and at other places densely fractured mudstone exhibits 

hydrocarbon staining and a petroliferous odor.

Dolomite constitutes less than 1 percent of the formation and forms laterally 

persistent beds generally less than 50 centimeters (cm) thick, ranging to 100 cm thick, 

and ellipsoidal to spheroidal concretions as much as about 100 cm in longest dimension. 

Dolomite is very hard, gray to brown on freshly broken surfaces, weathers pale-gray to 

light orange, light brown, or ocher, is aphanitic to sugary in texture, and reacts slowly or 

not at all in dilute HCl. Laminations, mostly 1–10 mm thick but as much as 20 mm thick, 

are defined by alternating light and dark color banding.

Conglomerate consists mainly of angular to subrounded clasts of mudstone, shale, 

dolomite, and porcelanite apparently derived from underlying Monterey Formation (Tml

and [or] Tmu). Generally, clasts range up to boulders as much as 1 m across, but the 

largest blocks are more than 5 m across. Laminated clasts typically are oriented at various angles to each other and bedding. However, some large, elongate clasts are parallel 

or subparallel to stratification. The matrix between the clasts is massive to laminated 

diatomaceous mudstone. Conglomerate is recognized only in basal ~20-m-thick interval 

of Sisquoc Formation where exposed in abandoned railroad cut above sea cliff west of 

Rincon Point; its presence elsewhere within unit is uncertain due to generally poorly 

exposed nature of unit. In railroad cut, matrix-supported blocks in basal conglomerate include a large (~7-m-wide) block(?) of buff, massive, fine-grained sandstone of 

unknown provenance.

Sisquoc Formation samples from a coastal exposure near and east of the University 

of California, Santa Barbara, campus about 30 km west of map area yielded diatoms of the 

Thalassiosira miocenica/Nitzschia miocenica Assemblage Zone (upper Miocene, about 

6.2–6.7 Ma) (basal Sisquoc) and of the Thalassiosira oestrupii Zone (lower Pliocene, 

younger than 5.5 Ma) (upper part of Sisquoc) (J.A. Barron, oral and written commun., 

2001, 2002, 2005) (see also Minor and others, 2009). In the map area, samples of mudstone and shale from sea cliff and railroad cut near Rincon Point yielded diatoms of the 

Thalassiosira praeostrupii subzone (uppermost Miocene, ca. 5.9–5.5 Ma) (J.A. Barron 

and R.G. Stanley, written communs., 2005).

Rocks mapped in this study as Sisquoc Formation previously mapped as Monterey 

Shale (Upson, 1951); Santa Margarita Formation (Lian, 1954); Sisquoc Shale (Dibblee, 

1987a,b; Tan and Jones, 2006); and Sisquoc Formation (Tan and Clahan, 2004).

Thickness of Sisquoc Formation in map area is uncertain; where unit is exposed 

near Rincon Point upper contact is concealed by alluvial fan deposits (Qaf) and (or) is 

offshore, and where it is present south of Sulphur Mountain upper contact lies outside 

(south) of map area. Sisquoc is at least 280 m thick in the Rincon Point area and at least 

400 m thick on the south upper flank of Sulphur Mountain.

Organic content in Sisquoc is locally great enough in region for unit to qualify as a 

potential hydrocarbon source (Tennyson and Isaacs, 2001). Sisquoc Formation is generally weakly resistant to erosion and poorly exposed except in cuts and sea cliffs near 

Rincon Point
22 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Monterey Formation (Miocene)—Marine, predominantly well-bedded, siliceous and calcareous mudstone and shale with subordinate porcelanite and dolomite. The Monterey 

Formation is well exposed in sea cliffs west of Rincon Point near the southwestern corner 

of map area and along a small stretch of shoreline it underlies on the west side of Lake 

Casitas. However, the Monterey generally is poorly exposed and highly weathered, with 

many original lithologic details obscured, where it crops out inland on the northwest spur 

of Rincon Mountain, on the northwest flank of Sulphur Mountain, and in low hills on 

the east side of Lake Casitas and in the Oak View area. The Monterey Formation is of 

Miocene age on the basis of abundant biostratigraphic data from microfossils (Dibblee, 

1966; Ingle, 1980, and references therein; Arends and Blake, 1986; Barron, 1986; 

DePaolo and Finger, 1991; Blake, 1994; Hornafius, 1994a,b, and references therein). No 

complete, continuous, tectonically undisrupted sections of the Monterey Formation are 

exposed in map area; thickest partial sections of Monterey in map area are about 550 m 

near the mouth of Rincon Creek and about 340 m on the north flank of Sulphur Mountain. Organic contents in rocks of the Monterey Formation are generally high and the unit 

is a major potential hydrocarbon source in the region (Tennyson and Isaacs, 2001). Also, 

highly fractured zones within the formation form localized oil reservoirs (Tennyson and 

Isaacs, 2001).

The Monterey Formation is divided into two subunits in map area that are distinguished from each other by lithology and age: an upper siliceous unit and a lower calcareous unit. The upper siliceous unit (Tmu) consists mainly of diatomaceous mudstone and 

shale, siliceous shale, and porcelanite. The lower calcareous unit (Tml) consists mainly 

of calcareous mudstone and shale. Microfossil assemblages, mainly diatoms, calcareous 

nannofossils, and benthic foraminifers, indicate that the upper unit is of late and middle 

Miocene age and the lower unit of middle and early Miocene age

Tmu Upper siliceous unit (upper and middle Miocene)—Consists mainly of diatomaceous 

mudstone and siliceous shale with subordinate porcelanite and lesser dolomite and 

calcareous mudstone and shale. Mudstone and shale generally weather white, cream, and 

pale tan and are generally pale brown to gray on fresh surfaces. Most rocks are soft to 

moderately hard, less resistant to weathering than dolomite and porcelanite, and noticeably low density. Generally weak or no reactions to dilute HCl indicate the presence of 

mostly small to negligible amounts of carbonate minerals. In places, mudstone and shale 

contain abundant, well-preserved microfossils visible with hand lens, including diatoms, 

foraminifers, and fish scales and bone fragments. Mudstone and shale generally form 

flaggy and platy to tabular, thin to medium beds; most beds are less than 30 cm thick, but 

some are 100 cm thick or more. Mudstone and shale are typically well laminated; laminations are generally planar and 0.5–20 mm thick. Rarely, beds include cream phosphatic 

laminations and (or) oblate phosphatic nodules as thick as 1 cm, with the longest dimension usually parallel to bedding. Phosphatic laminae and nodules increase in frequency 

down section towards base of upper siliceous unit. In places, mudstone and shale exhibit 

hydrocarbon staining and a strong petroliferous odor. Diatomaceous mudstone and shale 

decrease in abundance down section relative to other lithologic components. Siliceous 

mudstone and shale present on northwest flank of Sulphur Mountain are harder and more 

brittle, porcelaneous, and fissile (shale) than elsewhere in map area. Also in this area, 

rare, thin (<2 cm) layers of black, glassy chert are locally present near base of upper 

siliceous unit.

Porcelanite and porcelaneous mudstone form isolated, resistant beds as much as 

10 cm thick that are sporadically interstratified with diatomaceous mudstone and shale. 

Porcelanite is hard and brittle, gray to brown on fresh surfaces, weathers pale gray and 

tan to white, and exhibits conchoidal fracture and porcelaneous luster. Porcelanite is generally well laminated. In places, it is densely fractured and stained by hydrocarbons with 

a strong petroliferous odor; locally porcelanite is brecciated.

Rare dolomite forms concretions and beds that increase in frequency down section 

towards basal contact of upper siliceous unit. Concretions are ellipsoidal to spheroidal, 

generally 10–50 cm thick and less than 2.5 m long, and usually oriented with the long 

axis parallel to stratification. Beds are generally laterally persistent and mostly about 
Geologic Summary 23

10–100 cm thick. Dolomite is very hard and brittle, commonly fractured, relatively resistant, brown to gray on fresh surfaces, generally weathers pale orange or yellow orange, 

and aphanitic to sugary in texture. Reaction of the dolomite in dilute HCl ranges from 

none to weak.

Calcareous shale and mudstone weather white, cream, and pale gray, tan, and 

brown, and are generally brown to gray on fresh surfaces. Rocks generally react vigorously in dilute HCl. Most calcareous beds are well laminated; laminations are mostly 

planar. Calcareous shale and mudstone form thin to medium flaggy to tabular beds that 

increase in frequency down section towards base of upper siliceous unit.

A single thin (4-cm-thick), pinkish-gray weathering tuff layer is exposed at, or a few 

meters stratigraphically above, the basal contact of upper siliceous unit in the sea cliff 

1.5 km northwest of Rincon Point.

Published biostratigraphic studies of assemblages of diatoms and foraminifers, 

summarized by Hornafius (1994a,b), show that Monterey rocks approximately equivalent 

to the upper siliceous unit (as mapped herein) exposed along the coast about 45 km west 

of map area (Dos Pueblos Canyon area) were deposited about 8.0–14.5 Ma. Samples of 

upper part of the upper siliceous unit collected in the Santa Barbara area about 17 km 

west of map area yielded late Miocene diatoms ranging in age from ca. 8.5 to 9.9 Ma 

(Minor and others, 2009). Within map area in the Rincon Point area, shale samples 

from uppermost part of upper siliceous unit yielded late Miocene diatoms that are likely 

younger than 8.6 Ma (that is, lacking Denticulopsis) (J.A. Barron and R.G. Stanley, 

written commun., 2004). Samples of the middle shale unit of the Monterey Formation 

as mapped by Minor and others (2009) (equivalent to lower part of upper siliceous unit 

mapped herein) from coastal exposures about 20 km west of map area yielded benthic 

foraminiferal assemblages indicative of the Mohnian Stage of Kleinpell (1938, 1980) 

and mostly middle bathyal (500–2,000 m) water depths, as well as calcareous nannofossils of probable late Miocene age (R.S. Boettcher and S.A. Kling, Micropaleo 

Consultants, written communs., 2001) (see also Minor and others, 2009). Shale and 

mudstone samples collected in eastern part of map area (northwest flank of Sulphur 

Mountain) from approximate base of upper siliceous unit yielded middle Miocene benthic 

foraminiferal assemblages indicative of the Luisian Stage to upper part of Luisian Stage 

of Kleinpell (1938, 1980) and upper bathyal (150–500 m) water depths (K.A. McDougall, 

USGS, written commun., 2012).

The upper siliceous unit rests conformably on the lower calcareous unit (Tml). In 

the sea cliff west of Rincon Point, the contact between the upper and lower units of the 

Monterey Formation is placed at, or just stratigraphically below, a single conspicuous tuff 

bed where there is a marked upward increase in the frequency and thickness of siliceous 

and porcelaneous beds. Inland within the map area the base of upper unit, although 

poorly exposed, is mapped at a similar abrupt change in lithology.

Rocks assigned herein to the upper siliceous unit previously mapped as Monterey 

Shale (Upson, 1951; Lian, 1954); upper shale unit of the Monterey Formation (Dibblee, 

1987a,b); Monterey Formation (Tan and Clahan, 2004); and upper section of the 

Monterey Formation (Tan and Jones, 2006). Upper siliceous unit mapped herein equivalent to both the upper siliceous and middle shale units of the Monterey Formation as 

mapped by Minor and others (2009) on the Santa Barbara coastal plain west of map area; 

these two units are combined on the present map because field exposures are generally 

inadequate to differentiate the middle and upper units. Thickness of the upper siliceous 

unit decreases eastward, from about 360 m near the mouth of Rincon Creek to about 

190 m on the northwest flank of Sulphur Mountain. Upper siliceous unit is variably resistant to erosion and moderately to highly susceptible to landsliding. East of San Antonio 

Creek, on the lower northwest flank of Sulphur Mountain, the upper siliceous unit is 

involved in several large landslides and landslide complexes (mapped as Qls), many of 

which compose large translated and partly rotated blocks of internally intact bedrock 

in which remnants of pre-landslide stratigraphy are preserved. In inland upland areas, 

upper siliceous unit is generally poorly exposed and mostly covered by colluvium and 

dense vegetation
24 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Tml Lower calcareous unit (middle and lower Miocene)—Calcareous, siliceous, and phosphatic mudstone and shale, with subordinate dolomite, porcelanite, and sandstone. 

Distinguished from the underlying Rincon Shale (Tr) mainly by its well-bedded character, white-to-tan color, and greater proportion of siliceous shale and mudstone, which 

typically are harder and more resistant to weathering than Rincon Shale.

Mudstone and shale range from moderately hard to very hard, weather white, pale 

cream, and pale gray, and are pale brown, brown, and gray brown on fresh surfaces. 

Mudstone and shale are well stratified and form laterally persistent beds generally 3–30 cm 

thick, but some beds are as thick as 100 cm. Beds vary considerably in relative resistance 

to weathering; more resistant beds are commonly tabular or flaggy. Reaction in dilute HCl 

varies from none to strong and indicates that many beds are moderately to highly calcareous. Most beds exhibit laminations ranging from 0.5 to 10 mm thick, which are defined 

by subtle variations in color and texture; some beds are massive to bioturbated. Microfossils are locally abundant and consist mainly of calcareous foraminifers and fish scales 

and fragments. In places, white-to-cream phosphatic nodules and laminae are abundant, 

generally about 1–10 mm thick and 5–25 cm in longest dimension, which is always parallel 

to bedding. Intervals of mudstone with abundant phosphatic nodules and laminae appear 

to be more frequent in the upper part of the unit. These intervals weather white to pale tan, 

are dark gray to brown on fresh surfaces, and generally are less resistant to weathering than 

calcareous and siliceous mudstones.

Dolomite is very hard, resistant, weathers yellow gray, orange gray, orange tan, and 

ocher, and is gray to gray brown on freshly broken surfaces. Dolomite constitutes less than 

5 percent of the unit and generally forms beds and concretions about 10–50 cm thick. Concretions are ellipsoidal to irregular in shape and about 1–2 m in longest dimension, which 

usually parallels stratification. Most dolomite reacts slowly with dilute HCl, but some 

weathered dolomite reacts strongly. Dolomite beds are commonly densely fractured.

Porcelanite is hard, brittle, resistant, exhibits conchoidal fracture, weathers light 

gray to white, and is gray to brown on freshly broken surfaces. Porcelanite is present at 

irregular intervals in the unit as massive to well-laminated beds about 5–20 cm thick that 

increase in thickness and abundance upward in the unit. Some intervals of porcelanite 

contain subordinate dolomite interbeds. Thin (1‒2 cm) lenses and seams of black, glassy 

chert are present locally in the lower calcareous unit in the Sulphur Mountain area.

At places along sea cliff and railroad cuts west of Rincon Point the lower calcareous 

unit includes intervals as thick as 30 m in which beds are gently to moderately folded, 

faulted, stretched, and brecciated; these intervals exhibit outcrop-scale, disharmonic 

folds with wavelengths and amplitudes as much as 10 m, discontinuous faults with small 

offsets, and beds that are stretched and thinned. Breccia consists of angular to subrounded 

clasts of mudstone, shale, dolomite, and porcelanite in a mudstone matrix; breccia is both 

clast-supported and matrix-rich, the latter having a mélange-like appearance. Although 

some of this breccia may have formed due to tectonic deformation well after sediment 

deposition and lithification, much of it may have formed during downslope, gravitydriven slumping and flow of soft to partly lithified sediment shortly after deposition, possibly in a submarine slope environment (Garrison and Ramirez, 1989).

Sandstone constitutes much less than 1 percent of lower calcareous unit. Sandstone 

beds weather pale tan to gray, are shades of brown and gray on freshly broken surfaces, 

and are generally more resistant to weathering than the underlying and overlying horizons 

of mudstone and shale; beds are tabular to flaggy and range from 10-to-100 cm thick. 

Sandstone is medium to coarse grained, feldspathic to lithic, and commonly stained with 

oil; rounded pebbles of dolomite and (or) other lithologies observed in one sandstone bed. 

Mostly forms single, isolated beds, but one thin (~3 m) mudstone/shale interval exposed 

in the sea cliff about 2 km northwest of Rincon Point contains three sandstone beds; a 

separate sandstone bed nearby is accompanied by a small sandstone dike.

Samples of mudstone and shale from the lower calcareous unit in the sea cliff 

about 1 km west of the map area yielded benthic foraminifers indicative of the Relizian 

and Saucesian Stages of Kleinpell (1938, 1980) and lower middle bathyal to upper 

middle bathyal (500–2,000 m) water depths (K.A. McDougall, written commun., 2004), 

and calcareous nannofossils of lower middle to lower Miocene zones CN4 to CN1 
Geologic Summary 25

(R.S. Boettcher and S.A. Kling, written communs., 2002, 2003) (see also Minor and 

others, 2009). In same sea cliff to east within southwestern corner of map area, samples 

of mudstone and shale from the lower unit yielded benthic foraminifers indicative of the 

lower part of the Relizian to lower part of Luisian Stages of Kleinpell (1938, 1980) and 

upper middle to upper bathyal (150–1,500 m) water depths (K.A. McDougall, written 

commun., 2004), and calcareous nannofossils of lower middle to upper lower Miocene 

zone CN3 (R.S. Boettcher and S.A. Kling, written communs., 2002, 2003). Farther to 

the east along same sea cliff, mudstone samples from upper part of lower calcareous unit 

yielded benthic foraminifers indicative of the Luisian Stage to upper part of Luisian Stage 

of Kleinpell (1938, 1980) and upper bathyal (150–500 m) water depths (K.A. McDougall 

and R.G. Stanley, written commun., 2012). In eastern part of map area, a mudstone sample from lower part of lower unit exposed east of Ventura River (just south of Oak View) 

yielded benthic foraminifers indicative of the Saucesian to Relizian Stages of Kleinpell 

(1938, 1980) and upper middle bathyal (500–1,500 m) water depths (K.A. McDougall, 

written commun., 2012). Shale and mudstone samples collected in Sulphur MountainSan Antonio Creek area (eastern part of map area) from approximate stratigraphic top of 

lower calcareous unit yielded middle Miocene benthic foraminiferal assemblages indicative of the Luisian Stage to upper part of Luisian Stage of Kleinpell (1938, 1980) and 

upper bathyal (150‒500 m) water depths (K.A. McDougall, written commun., 2012).

The conformable contact between the lower calcareous unit and the underlying Rincon 

Shale (Tr) is placed at abrupt lithologic transition from well-bedded, white- to creamweathering calcareous and siliceous mudstone and shale (typical of the lower calcareous 

unit) to the underlying massive, pale-gray mudstone (typical of the Rincon Shale). In most 

of map area, however, contact between the lower calcareous unit and the Rincon Shale is 

covered or poorly exposed.

Strata mapped in this report as the lower calcareous unit previously mapped as 

Monterey Shale (Upson, 1951; Lian, 1954); lower shale unit of Monterey Formation 

(Dibblee, 1987a,b); upper shale unit of Monterey Formation (Dibblee, 1987a); Monterey 

Formation (Tan and Clahan, 2004); and lower section or upper section of the Monterey 

Formation (Tan and Jones, 2006). Only minimum thicknesses of the lower calcareous 

unit can be determined in map area due to structural truncations and complications affecting the lower Monterey section; lower unit has a minimum thickness of about 190 m 

near the mouth of Rincon Creek, about 150 m on the north flank of Sulphur Mountain, 

and about 250 m in a fault block west of San Antonio Creek. The lower calcareous unit 

is well exposed along sea cliff and railroad cuts west of Rincon Point, but generally is 

poorly exposed where present inland on the flanks of Rincon Mountain, in the low hills 

east of Lake Casitas, in the Oak View area, and on the north flank of Sulphur Mountain. 

Lower calcareous unit generally is weakly resistant to erosion and moderately to highly 

susceptible to landsliding. East of San Antonio Creek, on northwest flank of Sulphur 

Mountain, and on south flank of Rincon Mountain (“Rincon Mountain Megaslide” of 

Gurrola and others [2010]), the lower unit is involved in several large landslides and 

landslide complexes (mapped as Qls), many of which compose large translated and partly 

rotated blocks of internally intact bedrock in which remnants of pre-landslide stratigraphy 

are preserved. In inland upland areas, lower calcareous unit is generally poorly exposed 

and mostly covered by colluvium and dense vegetation

Tr Rincon Shale (lower Miocene)—Marine mudstone, with subordinate dolomite, sandstone, 

and conglomeratic sandstone; locally fossiliferous. More than 90 percent of the Rincon 

Shale is composed of mudstone that is gray to gray brown on freshly broken surfaces, 

weathers pale gray, olive gray, greenish gray, and rusty brown, is generally hard to moderately hard, and generally shows a moderate to weak reaction in dilute HCl. Mudstone 

typically exhibits dense hackly and, less commonly, spheroidal fractures and forms a 

distinctive pale greenish-gray, granular, clay-rich soil. At places, the mudstone contains 

abundant microfossils including calcareous foraminifers and fish scales, and some mudstone and sandy mudstone beds near basal contact with Vaqueros Formation (Tv) contain 

fossil oyster and other marine shells. Rare red-brown ferruginous(?) mudstone beds present in some exposures. Mudstone is generally massive and bioturbated and thick bedded, 

with beds generally 30–200 cm thick.
26 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

Dolomite is hard, resistant to weathering, gray to gray brown on freshly broken 

surfaces, weathers to shades of orange, yellow orange, and orange brown, has aphanitic 

to sugary texture, and reacts slowly or not at all in dilute HCl. Dolomite forms laminated 

to massive, laterally-persistent beds as thick as 100 cm, and also spheroidal to ellipsoidal 

concretions that range in size from a few centimeters to nearly 3 m across. The long axes 

of the dolomite concretions commonly parallel bedding.

Sandstone forms sparse to rare interbeds within thick sequences of mudstone. 

Sandstone chiefly weathers shades of gray and is medium to fine grained and commonly 

clayey and calcareous. Sandstone interbeds are generally tabular, resistant, 5–40 cm 

thick, laterally persistent, and increase in frequency both eastward and down section as 

contact with Vaqueros Formation (Tv) is approached. Some thick (~3 m) sandstone beds 

near San Antonio Creek in eastern part of map area are coarse grained and conglomeratic, 

containing rounded pebbles and small cobbles possibly reworked from Sespe (Tspm) 

conglomerates; other sandstone beds and intervals in this area are fossiliferous, containing abundant oyster, gastropod, and other shells.

Tuff layer(s) exposed in the Rincon Shale at two localities in the Summerland 

area (about 10 km west of the map area; see Minor and others [2009] for specifics and 

references) yielded 40Ar/39Ar and K-Ar ages ranging from 16.5 to 17.3 Ma. The age of 

the Rincon Shale in the map area is considered to be early Miocene on the basis of these 

isotopic ages and previously reported Saucesian benthic foraminifers and other biostratigraphic evidence from: (1) the Rincon type section along Los Sauces Creek in and 

directly south of south-central part of map area (Kleinpell, 1938), and (2) a measured 

stratigraphic section in Cañada de la Pila, about 63 km west of map area (Stanley and 

others, 1992, 1994). Base of the Rincon Shale is considered to be coincident with the 

Oligocene-Miocene boundary (David Bukry, USGS, oral commun., 1994).

Upper contact of the Rincon Shale is mapped at base of lowermost bed or interval of white- to cream-weathering shale and mudstone of conformably overlying lower 

calcareous unit of the Monterey Formation (Tml). Basal contact is mapped at top of 

uppermost bed or interval of feldspathic sandstone typical of the conformably underlying 

Vaqueros Formation (Tv).

Unit previously mapped as Rincon Formation (Lian, 1954) and Rincon Shale 

(Upson, 1951; Dibblee, 1987a,b; Tan and Clahan, 2004; Tan and Jones, 2006). The 

Rincon Shale is about 470 m thick near its type section south of Casitas Valley along 

Los Sauces Creek. Organic contents in the Rincon Shale are generally high enough for 

the unit to qualify as an important potential hydrocarbon source in the region (Tennyson 

and Isaacs, 2001). The unit is generally poorly exposed and covered by vegetation where 

present in the uplands along the southern border of the map area, east of Lake Casitas, 

and south of Ojai Valley. The Rincon Shale is extremely susceptible to landsliding 

(Bezore and Wills, 2000), for example on the northwest flank of Rincon Mountain in the 

southwest part of map area, where a large landslide complex is mapped

Tv Vaqueros Formation (upper Oligocene)—Shallow-marine sandstone; pale tan, gray, and 

greenish-gray, moderately to well indurated, feldspathic, and locally fossiliferous. Sandstone is typically cemented with carbonate and moderately to strongly resistant to erosion, locally forming prominent ledges, cliffs, and ridges; commonly weathers to pale-tan 

and -gray, rounded sandstone outcrops and distinctive, pale-tan, sandy soils; some outcrops exhibit cavernous weathering. Sandstone locally is mottled tan and greenish gray. 

Sandstone ranges from massive and bioturbated to laminated, from thick to thin (tabular) 

bedded, and from fine to coarse grained. Both planar and cross laminations are common. 

Rare thin (5–15 mm) partings of gray siltstone and mudstone also present. Uppermost 

part characterized by interbedded, thinly laminated sandstone, siltstone, and mudstone; 

ratio of mudstone-siltstone to sandstone increases towards stratigraphic top of Vaqueros; 

some sandstone beds near top of unit are coarse grained, pebbly (including chert clasts), 

and rich in shell fragments. Upper contact mapped at top of uppermost prominent bed or 

interval of relatively pure (that is, low clay content) sandstone. Base of unit is typically 

marked by a distinctive thin (0.5‒2 m) interval of well-indurated and flaggy, thinly bedded and laminated, pale-gray, calcareous sandstone containing abundant pelecypod and 

other shell fragments and, locally, rounded pebbles of chert and other lithologies. Basal 
Geologic Summary 27

contact is sharp and recognized by abrupt change from thick, tan-gray sandstone and 

basal gray, shell-rich sandstone of the marine Vaqueros to underlying maroon to greenishgray, interbedded, tabular sandstone and mudstone of the nonmarine Sespe Formation.

Late Oligocene age of Vaqueros Formation is inferred from stratigraphic position of 

unit, which overlies upper Oligocene upper part of Sespe Formation and underlies lower 

Miocene Rincon Shale. Base of overlying Rincon Shale is considered to be approximately 

coincident with the Oligocene-Miocene boundary (David Bukry, oral commun., 1994). 

Rigsby (1998) reported a strontium-isotope date of 24±1 Ma from oyster shells in Vaqueros 

Formation in Hollister Ranch area 85 km west of map area, consistent with late Oligocene 

(or earliest Miocene) age.

Unit previously mapped as Vaqueros Sandstone (Upson, 1951; Lian, 1954; Dibblee, 

1987a,b; Tan and Jones, 2006) and Vaqueros Formation (Tan and Clahan, 2004). In map 

area unit increases in thickness eastward, from about 25 m in Casitas Valley and Lake 

Casitas area to about 90 m just west of Ventura River; a regional thickness of about 

100 m was reported by Dibblee (1982). Some oil in the region is produced from Vaqueros 

sandstone reservoirs (Tennyson and Isaacs, 2001)

Sespe Formation (Oligocene and upper Eocene)—Nonmarine, fluvial sandstone, mudstone, 

and conglomerate; predominantly maroon, reddish-brown, and greenish- to pinkish-gray. 

The poorly to moderately exposed Sespe Formation is present over a large portion of the 

map area in the foothills north of Carpinteria, in the Laguna Ridge area, and in the hills and 

uplands surrounding Santa Ana and Ojai Valleys. The Sespe is divided into three subunits 

that are distinguished from each other mainly by differences in lithology, provenance, and 

age: an upper sandstone and mudstone unit (Tspu), a middle conglomerate and sandstone 

unit (Tspm), and a lower conglomerate and sandstone unit (Tspl). A major distinguishing feature of the upper unit is its lack of conglomerate, whereas the conglomeratic middle 

and lower units are distinguished mainly by their differing clast compositions and colors of 

weathered sandstone and conglomerate beds (mostly maroonish shades in middle unit and 

pinkish- to tannish-gray shades in lower unit). In the map area, the middle unit composes 

well over half of the total thickness of formation. Overall thickness of Sespe Formation 

is more than 1,600 m in the Laguna Ridge area. Some oil in the region is produced from 

Sespe sandstone and conglomerate reservoirs (Tennyson and Isaacs, 2001).

Age of Sespe Formation in the map region is considered late Eocene and Oligocene 

by Howard (1995), with an intraformational unconformity representing much or all of 

early Oligocene time. This unconformity (erosional disconformity) coincides with the 

mapped contact separating the lower conglomerate and sandstone unit (Tspl) from the 

middle conglomerate and sandstone unit (Tspm). Rocks below unconformity have been 

interpreted as part of an upper Eocene to lowermost Oligocene fluvial sequence composed of clastic detritus derived primarily from bedrock now exposed in the Mojave 

Desert, whereas overlying rocks have been interpreted as part of a lower(?) and upper 

Oligocene fluvial sequence containing chert, graywacke, and other clasts derived from 

Franciscan Complex source terrane(s) (Howard, 1995)

Tspu Upper sandstone and mudstone unit (upper Oligocene)—Sandstone, siltstone, and mudstone interbedded in proportions that vary both laterally and through the section; sandstone to mudstone-siltstone ratio in a given exposure typically ranges from ~5:1 to ~1:10. 

Sandstone-rich units are commonly broadly lenticular and thin to thick bedded, and in 

places they appear to occupy paleochannels. Sandstone beds are as thick as 10 m but 

mostly less than 2 m. Sandstone is mostly fine to medium grained, silty, feldspathic, and 

locally arkosic. On weathered surfaces sandstones display various shades of maroon, pale 

green, tan, and gray. Horizontal lamination and cross lamination, including trough cross 

lamination, are common. Sandstone is typically well indurated and forms resistant tabular, flaggy, or ledgy outcrops and, where steeply tilted, dip slopes and hogbacks. Small 

pebbly lenses are locally present in sandstone beds, and some thin (≤1 m thick) sandstone 

intervals, commonly near the base of beds, contain subrounded mudstone rip-up clasts.

Mudstone is typically silty to sandy and locally grades into siltstone and, rarely, 

fine-grained sandstone. Mudstone and siltstone are typically pale to dark maroon, reddish 

maroon, and brownish maroon, but in some places they are pale green or olive green. 

Mudstone is thin to very thin bedded and commonly laminated. Intervals of nearly pure 
28 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

mudstone range from less than 10 cm to at least 10 m thick. Some mudstone and siltstone 

bedding planes contain fossil mud cracks, ripple marks, worm burrows and (or) other 

trace fossils. Mudstone exhibits hackly to spheroidal fracturing on weathered surfaces. 

Most mudstone-rich intervals are poorly exposed and form gentle slopes.

Late Oligocene age of upper unit is based on Arikareean vertebrate fossils reported from 

the underlying middle unit 16‒26 km west of map area (Weaver and Kleinpell, 1963; Howard, 

1995) and on the Miocene-Oligocene boundary recognized at the base of the Rincon Shale 

(Tr) farther up section (David Bukry, oral commun., 1994).

Environment of deposition of Sespe upper sandstone and mudstone unit, which is 

equivalent to lithofacies D of Howard (1995), has been interpreted as progressing upward 

from braided to meandering river channels and interchannels (Howard, 1995). Unit 

previously mapped as part of the Sespe Formation (Upson, 1951; Lian, 1954; Dibblee, 

1987a,b; Tan and Clahan, 2004; Tan and Jones, 2006). Upper unit decreases in thickness 

from about 920 m in the Casitas Valley area to about 700 m north of Lake Casitas. Upper 

Sespe unit is locally prone to landsliding, particularly on steeper slopes

Tspm Middle conglomerate and sandstone unit (Oligocene)—Conglomerate, sandstone, and 

mudstone interbedded in proportions that vary both laterally and down section; relative 

proportion of conglomerate increases towards base of unit, but conglomerate is strongly 

subordinate to sandstone and mudstone in some intervals. Conglomeratic depositional 

units range from laterally extensive to narrowly lenticular and thin to thick bedded (as 

thick as 15 m), and in some places they appear to occupy paleochannels. Conglomerate and conglomeratic sandstone typically contain subangular to well-rounded pebbles 

and cobbles supported in a medium- to coarse-grained sand and silty sand matrix. Clasts 

are polymict and include abundant chert (red, green, and black), greenstone, and lithic 

sandstone derived from Franciscan Complex terrane(s), arkosic sandstone derived from 

Coldwater Sandstone (Tcw), and quartzitic, metamorphic (including augen gneiss), and 

granitoid rocks derived from Mojave Desert terrane(s) (Howard, 1995). Sandstone is 

mostly medium to coarse grained, pebbly, silty, and feldspathic to lithic; rare sandstone 

beds are arkosic. On weathered surfaces, conglomerates and sandstones display various 

shades of maroon and, less commonly, tan and pale greenish gray. Horizontal lamination and cross lamination, including trough cross lamination, are common, particularly in 

sandstones. Rarely, sandstone beds exhibit evidence of soft-sediment deformation, and 

sediment-filled fossil burrows are apparent on some sandstone bedding planes. Commonly, conglomerates and sandstones are moderately indurated and resistant and form 

tabular, flaggy, or ledgy outcrops.

Mudstone is typically silty to sandy and locally grades into siltstone and, more 

rarely, fine-grained sandstone. Mudstone is thin to very thin bedded and commonly 

laminated. Ripple marks are common. Mudstone-rich intervals range in thickness from 

thin partings to 20 m, and in some intervals proportion of mudstone greatly exceeds that 

of sandstone and conglomerate. Mudstone is maroon, maroonish red, reddish brown, 

and, rarely, pale greenish gray and exhibits hackly to spheroidal fracturing on weathered 

surfaces. Most mudstone-rich intervals are poorly exposed and form gentle slopes.

Upper contact of middle unit mapped at stratigraphically highest conglomerate bed. A disconformity at base of middle unit generally expressed by abrupt change 

from maroonish sandstone and conglomerate of mixed provenance (middle unit) to pale 

pinkish-gray sandstone and conglomerate of largely granitic and metamorphic provenance (lower Sespe unit). Lowermost part of middle Sespe unit locally contains one or 

more beds of sandstone and (or) conglomerate that strongly resemble those characterizing 

the lower Sespe unit; lower contact of middle Sespe unit mapped at base of lowermost 

maroon, middle Sespe-like conglomerate or sandstone bed.

Middle conglomerate and sandstone unit is primarily equivalent to Sespe lithofacies 

C of Howard (1995). Oligocene age of middle unit based on Arikareean vertebrate fossils 

(Sespia nitida Leidy) reported from the unit above disconformity in foothills north of 

Santa Barbara 16–26 km west of map area (Weaver and Kleinpell, 1963; Howard, 1995).

Middle unit previously mapped as part of the Sespe Formation (Upson, 1951; Lian, 

1954; Dibblee, 1987a,b; Tan and Clahan, 2004; Tan and Jones, 2006). Middle unit has 
Geologic Summary 29

a thickness of about 750 m west of Rincon Creek and in the Laguna Ridge area. Unit is 

moderately susceptible to landsliding particularly on steeper slopes along the lower flanks 

of the Santa Ynez Mountains and Laguna Ridge

Tspl Lower conglomerate and sandstone unit (lower Oligocene? and upper Eocene)—

Conglomerate, conglomeratic sandstone, sandstone, mudstone, and minor shale interbedded in proportions that vary both laterally and vertically through the section. Conglomeratic depositional units range from laterally extensive to narrowly lenticular and medium 

to thick bedded, and at some places, appear to occupy paleochannels. Conglomerate 

and conglomeratic sandstone contain pebbles, cobbles, and rare boulders supported in a 

medium-grained to very coarse-grained, locally arkosic sandstone matrix. Clasts are polymict and include abundant subrounded to well-rounded quartzitic, granitoid, metamorphic, and volcanic clasts derived from Mojave Desert source terrane(s) (Howard, 1995). 

Sandstone is mostly medium to very coarse grained, pebbly, feldspathic, and locally 

arkosic. On weathered surfaces, conglomerates and sandstones mostly exhibit distinctive 

shades of salmon gray, reddish gray, pale-pinkish gray, and pale tan; reddish-brown ironoxide staining is locally prevalent. Horizontal lamination and cross lamination, including 

trough cross lamination, are very common, particularly in sandstones. Conglomerates and 

sandstones are moderately to well indurated, resistant, and form flaggy, blocky, and ledgy 

outcrops and hogbacks.

Mudstone is typically silty to sandy and locally grades into siltstone and, more 

rarely, fine-grained sandstone. Intervals of fissile shale are locally present. Mudstone 

is thin to very thin bedded and commonly laminated. Mudstone-rich intervals range in 

thickness from thin partings to 5 m. Mudstone is maroon, maroonish red, gray, greenishgray, and reddish brown and exhibits hackly to spheroidal fracturing on weathered surfaces. Most mudstone-rich intervals are poorly exposed and form gentle slopes.

Disconformable upper contact of lower conglomerate and sandstone unit is commonly expressed by 3- to 10-m-thick interval of conspicuous deep-reddish-brown, 

massive-to-bedded, silty to sandy claystone and mudstone; upper contact mapped at base 

of lowermost maroon, middle Sespe-like conglomerate or sandstone bed. Basal contact 

of lower unit, exposed in northwestern map area, generally marked by sharp change from 

pinkish- and reddish-gray, laminated sandstone and conglomerate (Sespe) to pale yellowtan to buff, massive, locally oyster-shell-bearing sandstone of the underlying Coldwater 

Sandstone (Tcw). Locally lower contact is gradational, expressed by an interval of 

Coldwater-like sandstone containing Sespe-like maroon mudstone and siltstone interbeds; 

in such areas basal Sespe contact is mapped at top of uppermost Coldwater-like sandstone 

bed. The gradational nature of the basal contact is consistent with a late Eocene age for 

part or all of the lower conglomerate and sandstone unit.

The lower unit is primarily equivalent to Sespe lithofacies A of Howard (1995). Unit 

previously mapped as part of the Sespe Formation (Upson, 1951; Dibblee, 1987a,b; Tan and 

Clahan, 2004; Tan and Jones, 2006); as the lower member of the Sespe Formation (Lian, 

1954); and as pink sandstone and red claystone of the Sespe Formation (Dibblee, 1987a). 

The lower conglomerate and sandstone unit is exposed along strike for several kilometers 

near the northwestern border of the map area, and the upper part also in a separate, small 

strip along the northeastern border just west of the Ventura River; in the northwestern exposures the unit decreases in thickness eastward from about 150 m west of Rincon Creek to 

less than 60 m near Laguna Ranch (about 1 km south of La Granada Mountain)

Tcw Coldwater Sandstone (upper? and middle Eocene)—Shallow-marine sandstone with 

subordinate interbeds and thin intervals of siltstone, shale, and mudstone. The unit is 

present near the northwest border of map area where it forms ridges, spurs, and steep dip 

slopes and hogbacks along the Santa Ynez Mountains front. Sandstone is mostly fine- to 

medium-grained, feldspathic and partly arkosic, locally silty to clayey or micaceous, and 

locally weakly cemented with calcium carbonate. Sandstone forms thin, tabular beds 

as well as medium to thick beds, some of which are massive and bioturbated whereas 

others contain planar, wavy, or cross laminations. Some sandstone beds contain rare, thin 

siltstone and shale partings. Sandstone is typically pale gray and greenish gray on fresh 

surfaces and weathers to distinctive, pale shades of buff, greenish-buff, yellowish-tan, 
30 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

tan, and brown. Some beds and intervals as thick as 3 m, especially in the upper part of 

the unit, contain rare to conspicuously abundant oyster shells and shell fragments (Ostrea 

idriaensis, Weaver and Kleinpell, 1963), and numerous other fossil mollusks have been 

previously identified throughout the unit (for example, Weaver and Kleinpell, 1963). 

Other beds and intervals contain rare to common fossil wood fragments that in places 

contrast visually with the surrounding rock due to their dark-gray to reddish-brown color. 

Lenses and thin intervals of conglomeratic sandstone are locally present in the uppermost 

Coldwater near its contact with the overlying lower unit of the Sespe Formation (Tspl). 

Sandstone beds and sandstone-rich intervals typically crop out as resistant, blocky ledges 

and cliffs that form prominent hogbacks where steeply dipping.

Siltstone, shale, and mudstone form interbeds as thin as 1 cm and bedded intervals 

as thick as 5 m. These fine-grained rocks mostly exhibit pale to dark shades of gray, olive 

gray, greenish gray, and olive tan. Some siltstone beds are micaceous and contain fossil 

wood fragments. Siltstones and finer-grained rocks of the Coldwater are considerably 

less resistant and more poorly exposed than the sandstones. Some siltstone, shale, and 

mudstone intervals in uppermost part of unit are maroon, suggesting that contact with 

overlying nonmarine beds of the Sespe Formation is gradational. Upper Coldwater contact mapped at top of uppermost Coldwater-like sandstone bed.

Regionally, age of Coldwater has been determined to be late and (or) middle Eocene 

(Narizian) (Kleinpell and Weaver, 1963; Dibblee, 1966; Howard, 1995; Campion and 

others, 1996; Prothero, 2001) on basis of paleontologic, magnetostratigraphic, and sequence 

stratigraphic correlations. Unit previously mapped as Tejon Formation (Upson, 1951) and 

Coldwater Sandstone (Lian, 1954; Dibblee, 1987a; Tan and Clahan, 2004). Base of Coldwater 

is not exposed in map area; unit is about 750 to 1,000 m thick regionally (Dibblee, 1982)

Acknowledgments

The new mapping effort was funded by the USGS 

National Cooperative Geologic Mapping Program’s BALANCE (BAsins and LANdscape Co-Evolution) and BIGFOOT (BIG-storm FOOTprint on California and future 

hazards) Projects. The support and encouragement of BALANCE project co-chiefs Jonathan Matti and Robert Powell 

and BIGFOOT project chief Kevin Schmidt allowed the 

mapping effort to continue smoothly to completion. I am 

grateful to Rick Stanley (USGS) for his expert stratigraphic 

and biostratigraphic advice and contributions both in the field 

and from afar. Kris McDougall and John Barron (both USGS) 

conducted key paleontologic and biostratigraphic analyses 

for several of the map units. Discussions in the field with 

Richard Heermance (California State University, Northridge) 

during early stages of the mapping effort were helpful in elucidating and interpreting the Quaternary map units. Numerous 

discussions with Larry Gurrola about the geology of the map 

area throughout the mapping project were invaluable. Privateland access kindly granted by landowners too numerous to list 

individually was critical to complete the mapping. Constructive reviews by Larry Gurrola, Dave Lidke, and Paco Van 

Sistine improved the quality of the map, map text, and digital 

map database. The late Tom Dibblee is acknowledged for his 

numerous pioneering and far-reaching contributions to our 

understanding of the geology of the region surrounding and 

including the map area, and of southern California in general.

References Cited

Arends, R.G., and Blake, G.H., 1986, Biostratigraphy and 

paleoecology of the Naples Bluff coastal section based 

on diatoms and benthic foraminifera, in Casey, R.E., and 

Barron, J.A., eds., Siliceous microfossil and microplankton 

studies of the Monterey Formation and modern analogs: 

Los Angeles, Society of Economic Paleontologists and 

Mineralogists, Pacific Section, Book 45, p. 121–135.

Arnold, Ralph, 1907, Geology and oil resources of the 

Summerland district, Santa Barbara County, California: 

U.S. Geological Survey Bulletin, no. 321, 93 p. [Also 

available at http://pubs.er.usgs.gov/publication/b321.]

Barron, J.A., 1986, Updated diatom biostratigraphy for the 

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34 Geologic Map of the Southern White Ledge Peak and Matilija Quadrangles, California

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