Guidebook for Structural transect along Highway 33, Ventura to the Cuyama Badlands, California (April 2, 2017) Leader: Thom Davis, www.thomasldavisgeologist.com; www.geologicmapsfoundation.org.

Participants: Coast Geological Society

COPYRIGHT 2017 © by Thomas L. Davis, Geologist: any commercial use of this guidebook is

prohibited without prior permission.

Start: 8:00 AM sharp, April 2, 2017. Meet at the west end of parking lot behind Century 10 Movie

Theater (555 Main St.) in downtown Ventura. Parking lot is downhill of Poli Street and between

California and Chestnut Avenues. We will return to Ventura by 4:00 PM. This trip is along paved

roads. We will drive to Stop 1 first.

Figure 1. Map of a portion of the western Transverse Ranges, southern California, showing cross section lines 6-6’ and 7-7’ and the April 2, 2017 Coast Geological Society field trip stops. Cross sections are available for download at: www.thomasldavisgeologist.com.

Regional cross Section 6-6’ and 7-7’:

Regional cross section 6-6’ (Figure 2A) starts at the eastern end of the Santa Barbara

Channel near Port Hueneme, crosses the Oak Ridge fault, the deep Pliocene age

sedimentary trough of the Ventura basin, the Ventura Avenue anticline, Sulphur

Mountain and Ojai Valley, Santa Ynez Range, Pine Mountain ridge, and ends at the Big

Pine fault. The structural interpretation shown in cross section 6-6’ is from Namson

(1986 and 1987) where it first appeared in publication as cross section C-C’ (Plate II in

the 1986 publication). The cross section restoration is shown in Figure 2B. Cross

section 7-7’ (Figure 4), crosses many of the same structures as cross section 6-6’, and

the two sections reveal the variation in geometry and kinematics of the various

structures along strike. Cross section 7-7’ was incorporated into Namson and Davis’s

cross section across the entire western Transverse Ranges (Namson and Davis, 1988).

A generalized stratigraphic column of the Ventura basin is included at the end of this

guidebook (Figure 7). See Dibblee (1982a, b) for additional field descriptions.

Southern portion of regional cross Section 6-6’:

The southern portion of cross section 6-6’ (Figure 3) begins on a structural shelf just

south of the West Montalvo oil field which is part of the 60 km long Oak Ridge-Montalvo

anticlinal trend. On the basis of the asymmetric shape of the anticlinal fold trend it is

interpreted to be part of a north-vergent, fault-propagation fold above the postulated

South Mountain thrust. The Oak Ridge fault is the southern boundary of the deep trough

of the Pliocene and Pleistocene Ventura basin and the fault cuts the north limb of the

anticlinal trend. The Oak Ridge fault is interpreted to be a Pliocene age normal fault

whose shallow portion has been rotated northward and into a reverse-fault geometry by

folding of the Oak Ridge-Montalvo anticlinal trend. Excess slip from the deeper South

Mountain thrust has reactivated shallow segments of the Oak Ridge fault. This

structural interpretation can be applied to all of the Oak Ridge-Montalvo fold trend which

contains anticlinal oil traps at Sheills Canyon, Bardsdale, South Mountain, and West

Montalvo oil fields.

Cross section 6-6’ shows how convergent deformation within the deep trough of the

Ventura basin and along its southern margin is linked to San Cayetano thrust system.

Southward directed slip along the Lion Mountain detachment extends across the deep

Ventura basin and cuts and translates the shallow portion of the Oak Ridge normal fault

southward. Approximately 4.7 km of back slip coming off the Lion Mountain detachment

and up the South Mountain thrust creates a thrust wedge between the south-dipping

thrust and the deeper detachment. Northward and deeper the 4.7 kms of offset of the

Oak Ridge fault creates a structural shelf just below the Lion Mountain detachment and

between the two portions of the older normal fault. This structural shelf along the

southern margin of the deep Ventura basin and between the offset shallow and deep

segments of the Oak Ridge fault is shown in the other regional cross sections by

Namson to the east (Davis, et al, 2015). This structural shelf is a regional feature of the

southern margin of the deep Ventura basin and extends eastward to at least the Aliso

Canyon area of the eastern Ventura basin.

Fig

ure

2A

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Stop #1, Ventura Avenue Anticline oil field and Red Mountain fault:

Stop is near the axis of the Ventura Avenue Anticline that at the surface has folded

deep-marine clastic deposits of the Pico Formation (Figure 3). To the northwest and

across the Ventura River wash are outcrops of north-dipping sandstone, siltstone, and

shale of the Pico Formation. Further northwest and on the ridge above the Pico

outcrops are red beds of the Sespe Formation that are thrust southward over the Pico

beds by the Red Mountain fault. The Red Mountain fault is a major east-west trending,

north-dipping, reverse fault just north of the Ventura Avenue anticlinal trend. To the

north and along the Ventura River course the surface trace of the Red Mountain fault

bends northward towards the western termination of the Sulphur Mountain anticline, and

the fault’s surface trace dies out in beds of the lower Monterey Formation. At the bend

Sespe, Vaqueros, and lower Monterey beds dip eastward towards the wide south-limb of

the Sulphur Mountain anticline (a smaller anticline on the Lion Mountain anticline). The

subsurface geometry and structural cause of this northward bend is poorly understood.

Red Mountain fault dies-out in the subsurface before reaching cross section 6-6’. The

deep Canada Larga syncline separates the Lion Mountains and Ventura Avenue

anticlines and along the south limb of the Lion Mountain anticline +5 km of Pliocene

marine strata are exposed.

Figure 3 shows the Ventura Avenue anticline is a very large east-west trending fold

between the Canada Larga syncline to the north and the thick Pliocene and Quaternary

age Ventura basin trough to the south. Both anticlinal limbs have steep dips and in map

view the north limb has a much narrower north-south extent than the south limb. The

anticline has a steep east-plunge into the Ventura trough where it terminates, but to the

west the anticlinal structure continues for some distance and, eventually, into the

offshore. Onshore the Ventura Avenue anticline traps the Ventura and San Miguelito oil

fields. Further westward the anticlinal trend continues and traps oil offshore at three

culminations: Rincon (partially offshore), Carpinteria Offshore, and Dos Cuadras

(offshore).

Ventura anticline portion of regional cross Section 6-6’:

Figure 3 shows Namson interpretation (1986) of the deep structure at Ventura Avenue

anticline and the anticline’s geometric and kinematic connection to the San Cayetano

thrust system and the Lion Mountain fault that is exposed along the north flank of

Sulphur Mountain. In this interpretation the Ventura Avenue anticline is shown as a

detached fold above the Lion fault that is a detachment fault at the base of the Rincon

Formation, and also a higher thrust flat to the San Cayetano thrust system. The Ventura

Avenue anticline is shown to be folded and uplifted by a series of wedge-shaped

imbricated thrust faults that step up from the Lion Mountain fault detachment surface.

Under the Canada Larga syncline, that is just north of Ventura Avenue anticline, the

lower splay of the San Cayetano thrust (SCT 1) intersects the Lion Mountain detachment

to form a southward-directed fault wedge in the front limb of the Lion Mountain anticline.

Stop #2, Overview of the Ojai Valley, Topa-Topa Range, Matilija overturn, and San

Cayetano fault:

Stop is in a large parking area along the northwest side of Highway 150 with an excellent

overview of the Ojai Valley and town of Ojai. Adjacent outcrops are Sespe Formation

red beds along the north flank of the Lion Mountain anticlinal trend. East of the stop the

Lion Mountain anticline plunges eastward under upper Ojai Valley. Small amounts of oil

have been produced from sandstone beds in the Coldwater and lower Sespe Formations

at the Lion Mountain area located about two miles west of the stop. The south-dipping

Santa Ana fault whose surface trace is along the southern margin of Ojai Valley is not

shown in cross section 6-6’ (Figure 3). At that location the Santa Ana fault is either not

present or a very small fault within the Sespe Formation.

From the stop, and looking northward across Ojai Valley, is the south flank of the

Topatopa Range. The various Eocene formations are overturned to a north-dip with the

Oligocene Sespe Formation red beds exposed along the base of the range. This

structure is well known, at least geologically, as the Matilija overturn. The Matilija

overturn is the frontal structure to the Santa Ynez Mountains anticlinorium (Figure 3).

The overturn is the easternmost segment of a steeply-folded panel of rocks that to the

west is generally south-dipping. The panel consists of a thick sequence of Cretaceous

and Tertiary formations and extends from here to Point Conception (a distance of about

60 miles). Eastward, the Matilija overturn merges into a more complex series of smaller

folds: the Echo Canyon and Santa Paula Ridge anticlines, and several unnamed

anticlines with overturned south limbs. There the overturn is broken by the San

Cayetano thrust which places the Eocene section over Miocene and Pliocene strata

along the north flank of the Lion Mountain anticline.

As shown in cross section 6-6’ (Figures 2A, 3) the Santa Ynez Mountains anticlinorium is

asymmetric and south-vergent. The crest and north limb of the anticlinorium are

deformed by several small folds and faults that dip steeply to the south. Namson (1987)

interprets the anticlinorium as the result of two phases of deformation: one during the

late Eocene and early Oligocene (Ynezian orogeny) and the other during the late

Cenozoic. The late Cenozoic deformation is interpreted to result from fault-bend folding

and fault-propagation folding. The fault-bend fold is related to a ramp in the lower splay

of San Cayetano thrust (SCT 1) that extends from the basal detachment at about 12 km

depth upward to a higher-level detachment in the Cretaceous section. The slip on the

SCT 1 is 17.7 km which is transferred upward and southward along the thrust ramp

causing the Lion Mountain anticline. At the top of the ramp is another detachment that is

the same mid-level detachment under the Ventura Avenue anticline. The shallower-level

fault-propagation fold above the upper splay of the San Cayetano thrust fault (SCT 2)

has 3.3 km of slip. In Namson’s 1987 interpretation the shallow-level folding has

deformed and rotated the older Santa Ynez fault which was originally a north-vergent

back-thrust associated with a south-vergent Oligocene thrust system that uplifted the

ancestral San Rafael Mountains (Figure 5) (Reed and Hollister, 1936).

Regional cross section 7-7’:

Cross section 7-7’ (Figure 4A) lies about 15-20 km east of cross section 6-6’ (Figure 2A).

Cross section 7-7’ crosses many of the same structures as cross section 6-6’ and

comparison of the two sections shows their gross similarity and the geometric and

kinematic variations along strike. Cross section 7-7’ begins offshore at the western end

of the Santa Monica Mountains and crosses South Mountain, Topatopa Range, Pine

Mountain, Frazier Mountain and ends at the San Andreas fault (In the Namson and

Davis 1991 report the cross section is labeled 6-6’). Cross section 7-7’ was incorporated

into Namson and Davis’s cross section across the entire western Transverse Ranges

(Namson and Davis, 1988).

The first structure shown on the south end of cross section 7-7’ is the Santa Monica

Mountains anticlinorium. The geometry of the anticlinorium is constrained by the surface

geology of the Santa Monica Mountains and some subsurface drilling. The fold structure

is asymmetric with a steep south limb that is only partially onshore and extends into the

offshore. The crest of the fold occurs along the south flank of the Santa Monica

Mountains and the moderately-dipping north limb is well exposed along the crest of the

range and northward in the Conejo Valley. The Santa Monica Mountains anticlinorium is

interpreted to be a fault-propagation fold caused by the Elysian Park thrust (Davis, et al.

1989) which ramps up from a basal detachment at 15 km depth and terminates in an

offshore synclinal axis at about 9 km depth. The slip on the Elysian Park thrust is 11.3

km. Within the anticlinorium are several older, down-to-the-north normal faults that

probably controlled deposition of the thick section of lower and middle Miocene

volcaniclastic and other clastic rocks that occur throughout the Santa Monica Mountains.

The Malibu Coast fault is projected offshore into the cross section, where it cuts the

south limb of the anticlinorium. The fault juxtaposes contrasting stratigraphic sections:

south of the fault the Miocene strata lie unconformably on metamorphic basement rock

and north of the fault is a thicker Miocene section as well as lower Tertiary and

Cretaceous strata which rest unconformably on metamorphic or Franciscan basement.

These relationships suggest that the Malibu Coast fault had older Miocene movement

that was down-to-the-north, and had a similar basinal control as the previously

mentioned normal faults located further north. The Malibu Coast fault has been

reactivated as a reverse fault during late Cenozoic convergence and uplift of the Santa

Monica Mountains anticlinorium.

The next structures to the north and intersected by cross section 7-7’ are a pair of

anticlines that include the Oak Ridge-Montalvo anticlinal trend and an unnamed anticline

to the south that underlie the western portion of the Simi Hills. The Oak Ridge-Montalvo

anticlinal trend is defined by surface geology and subsurface drilling and is asymmetric

with a gently-dipping south limb and steeply-dipping north limb. The north- limb is cut by

the steeply, south-dipping Oak Ridge fault. The unnamed anticline is primarily defined

by subsurface data. The fold has moderately dipping limbs and the crest is broken up by

several normal faults. The normal faults are predominantly down-to the-south and

control thick accumulations of volcaniclastic and clastic strata. The cross section

interpretation shows the two anticlines to be related to ramps on the South Mountain

thrust which is a back-thrust off the lower splay in San Cayetano thrust fault (SCT 1).

The unnamed anticline is interpreted to be a fault-bend fold associated with a ramp that

steps up from a lower detachment at 8 km to an upper detachment at 6 km. The Oak

Ridge-Montalvo anticlinal trend is interpreted to be a fault-propagation fold associated

with the second ramp on the South Mountain thrust. The Oak Ridge fault is shown as a

rotated normal fault that was active during late Miocene and Pliocene time and originally

dipped to the north. The South Mountain thrust translated slip up the rotated segment of

the normal fault reactivating the fault as a high-angle reverse fault. The slip translated

up the ramp for the unnamed fold is 4.0 km and slip translated up the ramp below the

Oak Ridge-Montalvo anticlinal trend is 3.9 km.

Cross section 7-7’ crosses the Santa Ynez Mountains anticlinorium north of the deep

trough of the Ventura basin. The anticlinorium includes the structures underlying

Sulphur Mountain and the Topatopa Range. In cross section 7-7’ Sulphur Mountain lies

above the Sisar thrust fault, and the thrust is north-vergent with an asymmetric anticline

in the hanging wall. The Sisar fault, which is similar to the Lion Mountain fault to the

west, is interpreted to be a back-thrust off the San Cayetano thrust, and the hanging wall

anticline under Sulfur Mountain is interpreted to be a fault-propagation fold. At the

surface the Sisar thrust is truncated by the upper splay of the San Cayetano thrust

system. The Santa Ynez Mountains anticlinorium is composed of several stacked folds

and complicated faults that are observed at the surface and encountered in subsurface

drilling. The deepest structure is a fault-bend fold that is in the footwalls of the Sisar

thrust and upper San Cayetano thrust splay (SCT 2). The fault-bend fold is associated

with a ramp in the deeper San Cayetano thrust splay (SCT 1). The ramp connects a

lower detachment near the base of the Eocene strata to the upper detachment at the

base of the Rincon shale. The SCT 1 cuts and translates the Big Canyon fault and the

Oak Ridge fault which are older normal faults. The Big Canyon fault is translated and

folded as it moved from the lower part of the ramp onto the upper detachment whereas

the Oak Ridge fault is only translated along the upper detachment. Approximately 8.0

km of slip on the upper detachment of the SCT 1 is divided and consumed equally

between two back thrusts, the South Mountain thrust and Sisar thrust.

The surface geology of the Santa Ynez Mountains anticlinorium along cross section 7-7’

(Figure 4A) is dominated by a thick Eocene section that is deformed into an overturned

fold in the hanging wall of the SCT 2. This overturned fold is interpreted to be an older

fault-propagation fold that has been cut and translated on the San Cayetano thrust

system that breaks through to the surface. The ramp making the fault-propagation fold

steps up from a basal detachment within the Franciscan basement at about 13 km to the

top of the Eocene. The upper part of the ramp has been cut and translated by the SCT 1

and continued slip on SCT 2 fault ruptured to the surface up the frontal synclinal axis of

the fault-propagation fold. Approximately 19.1 km of slip has been translated up the

ramp on the San Cayetano thrust system. In Namson’s 1987 interpretation the Santa

Ynez fault is shown to be a late Eocene fault associated with the Ynezian orogeny

(Figure 5). This interpretation shows it as a north-verging back thrust from a south-

verging fold and thrust structure. Subsequent late Pliocene and Quaternary folding in

the hanging wall of the San Cayetano thrust system further deformed the Santa Ynez

fault geometry.

Along cross section 7-7’ (Figure 4A) and north of the Santa Ynez anticlinorium and

Sespe Creek synclinorium are Pine Mountain and Frazier Mountain. Late Cenozoic

uplift and folding of Pine Mountain and Frazier Mountain are interpreted to be related to

the Pine Mountain fault. The Pine Mountain fault probably has two phases of movement.

The fault juxtaposes the Salinian and Franciscan basement terranes. This juxtaposition

must have occurred prior to Eocene time because the Eocene units occur

unconformably on both blocks. Late Cenozoic movement on the Pine Mountain fault

ruptured though the steep north limb of the syncline to the surface. There is

approximately 2.4 km of shortening associated with the blind thrust and fault propagation

fold and about 1.0 km on the Pine Mountain fault splay that rupture to the surface. The

Pine Mountain fault is interpreted to root into a north-verging ramp on the Pleito thrust

system which causes the uplift and folding of the San Emigdio Mountains north of the

San Andreas fault and offset of the San Andreas in the deep crust. The relationships

between thrusts of the western Transverse Ranges and San Andreas fault were first

discussed in Namson and Davis (1988). In this interpretation the San Andreas fault and

the thrust systems share a common displacement surface that dips at low angles and

offsets shallow and deep crustal parts of the plate boundary. In the big bend segment of

the San Andreas fault this displacement surface is a south-dipping fault that has

accommodated both right lateral strike-slip on the San Andreas fault and north-directed

convergence along the Pleito thrust system during the late Cenozoic. Gravity data and

the high topography of the Mount Pinos and Frazier Mountain areas support this model

(Namson and Davis, 1988). Fuis, et al. (2012), unaware of Namson and Davis’ 1988

work, proposed that the San Andreas fault is dipping southwest from 55-75 degrees

along the western big bend segment based on studies of potential field data, active-

source imaging, and seismicity.

The present-day length of regional cross section 7-7’ (Figure 4A) is 95.2 km and the

restored cross section length is 128.4 km (Figure 4B) which yields 33.2 km of

convergence. The convergence rate from the western Santa Monica Mountains to the

San Andreas fault is 8.3-16.6 mm/yr., assuming convergent deformation started between

2.0-4.0 Ma.

Fig

ure

4A

. C

ross s

ection

7-7

’ fr

om

th

e w

este

rn S

anta

Mo

nic

a M

oun

tain

s t

o t

he S

an A

ndre

as fa

ult (

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mso

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avis

, 1

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ss s

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how

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ld a

nd

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tyle

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tation

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Fig

ure

4B

is th

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ross s

ectio

n r

esto

ration

. C

ross s

ection

re

sto

ration

re

ve

als

tw

o e

arlie

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f defo

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: la

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on th

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ak R

idge

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ield

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.3-1

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/yr

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.0 M

a.

Stop #3, Santa Ynez Range and Santa Ynez fault:

Stop is along Matilija Creek Road and west of Hwy 33. Good exposures of the Santa

Ynez fault occur along the road-cuts. Probable Cretaceous Jalama Formation

conglomerate (south block) is faulted against Eocene Juncal Formation (north block).

McCulloh (1981) hypothesized that the Santa Ynez fault had 37 km of left-lateral

displacement mostly during the Miocene. In contrast Hall (1981) suggested the fault has

significant right-lateral displacement during the Miocene. Gordon (1978) and Dibblee

(1982) believed the fault displacement was primarily dip-slip and dismissed the large

strike-slip displacements as the fault terminated at both western and eastern ends of the

Santa Ynez-Topatopa Mountains.

Figure 5. In Namson’s 1987 interpretation the Santa Ynez fault is shown to have two

phases of activity: Late Eocene and Oligocene movement associated with the Ynezian

orogeny and late Cenozoic movement associated with the Pasadenan orogeny. This

interpretation shows it as a north-verging back thrust from a south-verging fold and

thrust structure. Subsequent late Pliocene and Quaternary folding in the hanging wall

of the San Cayetano thrust system further deformed the Santa Ynez fault geometry.

This interpretation explains the origin of the regional angular unconformity between the

upper Oligocene through Miocene strata and the upper Mesozoic through Eocene

strata, and provides a structural explanation for the Ynezian orogeny (Dibblee, 1982).

Stop #4, Overview of the Sespe Creek synclinorium and Pine Mountain fault and

anticlinorium:

Stop is along the east side of Highway 33 just south of Sespe Creek (Figure 1). Road-

cut outcrops just west of the stop are north-dipping Matilija Sandstone and Cozy Dell

Shale along the north limb of the Santa Ynez Mountains anticlinorium. To the north and

east is the Sespe Creek drainage. Prominent light-colored sandstone outcrops north of

Sespe Creek are Sespe and Coldwater Formations along the trough of an east-plunging

syncline. The steeply-dipping north-limb of the syncline is interpreted as a portion of the

lower limb of a fault-propagation fold cut by the Pine Mountain thrust (Figure 6). The

high ridge above (north) the syncline is Pine Mountain Ridge which is underlain by a

thick sequence of Eocene strata in the hanging wall of the Pine Mountain fault. Our

location is between the Neogene age Ventura and Cuyama basins. Older rocks

exposed along this portion of Highway 33 are forearc deposits predating the Ynezian

orogeny and belong to the regional forearc basin that covered much of central and

southern California from Cretaceous to Eocene time.

San Rafael Mountains portion of regional cross Section 6-6’: Immediately north of

the Sespe Creek synclinorium there are two anticlines: one in the hanging wall and one

in the footwall of the Pine Mountain fault (Figure 6). The asymmetric, subthrust anticline

in the footwall of the Pine Mountain fault is interpreted to be a fault- propagation fold

caused by a ramp in a deeper thrust with 3.5 km of slip. This deeper thrust ramps up

from an intermediate detachment at the top of the Cretaceous section and terminates in

the subsurface at the axis of Sespe Creek synclinorium and within Eocene strata. The

Pine Mountain fault is interpreted to be a higher splay that ramps up across the back

limb of the fault-propagation fold. The slip on the Pine Mountain fault is 2.4 km.

Figure 6. Portion of cross section 6-6’ across the San Rafael Mountains, Sespe

Creek drainage, Pine Mountain, and Lockwood Valley (Namson, 1986, 1987).

Coast Geological Society field trip stops 3-5 are shown above the topographic

profile. Geologic unit abbreviations are shown in Figure 2A.

Stop #5, Lunch and crest of the Pine Mountain Ridge:

Stop is within Matilija sandstone and shale beds along the north limb (backlimb) of the

Pine Mountain anticline (Figure 6). The Pine Mountain anticline lies in the hanging wall

of the Pine Mountain fault and much of its south limb has been removed by erosion

where cross section 6-6’ crosses the anticline. Several miles west of the stop the Pine

Mountain thrust merges with the left-lateral Big Pine fault (Figure 1).

Stop #6, Overview of the Cuyama basin and Badlands, Big Pine fault, and north

limb of the Pine Mountain anticlinorium:

Directly below the stop is the trace of the Big Pine fault that has had about 13 km of left

lateral displacement, mostly during the Quaternary (Davis, et al, 1987). In the distance

is the easternmost portion of the Cuyama basin and Badlands. The basin is mostly

Cenozoic nonmarine rocks of the Simmler, Caliente, Quatal, and Morales Formations.

The nonmarine strata consist of a thick sequence of alluvial fan, fluvial and lacustrine

deposits of Oligocene through Pliocene age. To the west is the Sierra Madre which is

being uplifted by the southwest-dipping Ozena reverse fault. The hanging wall of the

Ozena fault consists of a +10 km thick clastic section of upper Cretaceous through

Eocene marine rocks. The thick section is folded, partially eroded by an angular

unconformity, and capped by mid-Tertiary strata. Left-lateral displacement of 13 km on

the Big Pine fault may have offset the eastern Cuyama basin (Cuyama Badlands) from

the small Lockwood basin and the Ozena fault from the south-dipping San Guillermo

reverse fault (Dibblee, 1982b). Both basins share a similar stratigraphy and history and

the Ozena and San Guillermo faults have a similar geometry, movement, and timing.

Northern portion of regional cross Section 6-6’:

Cross section 6-6’ lies several miles east of stop 6 and ends at the Big Pine fault (Figure

1). The present-day length of the cross section is 67.6 km and the restored cross

section is 99.0 km which yields 31.4 km of convergence (Figures 2A & B). The

convergence rate from Port Hueneme to the Pine Mountain fault is 7.9-15.7 mm/yr.,

assuming convergent deformation started between 2.0 and 4.0 Ma. Cross section 7-7’

(Figure 4A) extends northward to the San Andreas fault and is part of crustal-scale cross

section across the western Transverse Ranges published in Geology (Namson and

Davis, 1988).

Comment on rotation of the Transverse Ranges:

Jay Namson and I are asked occasionally about how the large, clockwise rotation of the

Transverse Ranges, supported by paleomagnetic data, impacts our cross sections and

restorations. There is nothing in our work that supports or denies the rotations, as long

as most of the rotation is completed before 4.0 ma. It is curious to us that we have

found no structural record of such large-scale block motions recorded in the folds and

faults in the cross sections and in the field and subsurface data and mapping used to

make the cross sections.

Figure 7. Generalized stratigraphic column of the Ventura basin showing ages,

stratigraphic nomenclature, rock column, water depth, and tectonic events (Martin

Lagoe, unpublished).

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