Newly Discovered Paleocene and Eocene 

Rocks near Fairfield, California, and 

Correlation with Rocks in Vaca Valley and the 

So-Called Martinez Formation or Stage 

By Earl E. Brabb, Donn Ristau, David Bukry, Kristin McDougall, 

Alvin A. Almgren, LouElla Saul, and Annika Sanfilippo 

Open-File Report 2008-1228 

U.S. Department of the Interior 

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

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2008 

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Suggested citation: 

Brabb, E.E., Ristau, Donn, Bukry, David, McDougall, Kristin , Almgren, A.A., Saul, 

LouElla, and Sanfilippo, Annika, 2008, Newly discovered Paleocene and 

Eocene rocks near Fairfield, California, and correlation with rocks in Vaca 

Valley and the so-called Martinez formation or stage:, U.S. Geological Survey 

Open File Report, 2008-1228, 29 p. [http://pubs.usgs.gov/of/2008/1228/]. 

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imply endorsement by the U.S. Government. 

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this report 

Cover: Sandstone with Turritella infragranulata pachecoensis from locality 

03CB5241 on the southwest flank of Cement Hill; view of slab prepared by Skyler 

Phelps, Auburn. LouElla Saul identified and dated the fossils (from figure 1B). 

ii 
iii 

Contents 

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

Previous Work .............................................................................................1 

New Work in Cement Hill Area ..................................................................4 

Structural Blocks in the Area.......................................................................6 

Block A.....................................................................................................6 

Block B...................................................................................................13 

Block C...................................................................................................13 

Block D...................................................................................................13 

Block E ...................................................................................................14 

Block F ...................................................................................................14 

How Do the Blocks Fit Together? .............................................................14 

Can Landsliding Explain the Structures Observed? ..................................15 

Vacaville Junction Area.............................................................................16 

Vaca Valley Area.......................................................................................17 

Cretaceous Rocks in Vaca Valley ..........................................................17 

Paleocene Rocks in Vaca Valley............................................................21 

Eocene Rocks in Vaca Valley ................................................................21 

Summary for Vaca Valley Area .............................................................26 

Is the Name Martinez Formation Appropriate ?........................................26 

Conclusions................................................................................................27 

References Cited ........................................................................................28 

Figures 

1. Views of Turritella infragranulata pachecoensis ...............................2 

2. Index map .............................................................................................3 

3. Geologic Map for Lower Cement Hill Area ........................................4 

4. Original Stratigraphic Column for Lower Cement Hill Area ..............6 

5. Map Showing Fossil Collecting Localities ..........................................8 

6. Revised Geologic Map for Lower Cement Hill Area ........................11 

7. Division Into Structural Blocks .........................................................12 

8. Revised Stratigraphic Column for Lower Cement Hill Area ............16 

9. Geologic and Locality Map for Vaca Valley .....................................18 

10. Locality Map for the Oakdale School, Area ......................................19 

11. Stratigraphic Column Near Oakdale School ......................................20 

Tables 

1. Foraminifers from the Lower Cement Hill Area ............................9, 10 

2. Foraminifers from the Vaca Valley Area ................................23, 24, 25 
Newly Discovered Paleocene and Eocene 

Rocks near Fairfield, California, and Correlation 

with Rocks in Vaca Valley and the So-Called 

Martinez Formation or Stage 

By Earl E. Brabb, Donn Ristau, David Bukry, Kristin McDougall, Alvin A. 

Almgren, LouElla Saul, and Annika Sanfilippo 

Introduction

Discovery of a 3-foot thick sandstone bed with abundant Turritellid gastropods of late 

Paleocene age (fig. 1) about 4 miles northeast of Fairfield and on the southwest flank of 

Cement Hill, Solano County (fig. 2, area 1) provides an opportunity to reevaluate the 

relationships of lower Tertiary formations in this part of California. Cement Hill is 

named for travertine deposits in and on top of sandstone of Late Cretaceous age (Hart, 

1978). In this report, the current study area where the Paleocene fossils were recently 

discovered is referred to as lower Cement Hill and is located in section 7 of the U.S. 

Geological Survey Fairfield North 7.5’ minute quadrangle, Township 5 North, Range 1 

West. Lower Cement Hill is about 23 miles north of the so-called Martinez “formation” 

or stage area (Weaver and others, 1941) of late Paleocene age near Martinez (fig. 2, area 

2). The Martinez “formation” and stage have played a significant role in the development 

of early Tertiary stratigraphy in this part of California. The discovery of correlative rocks 

at Cement Hill was unsuspected and may be helpful in defining the extent of this 

so-called formation or stage. 

Coccolith identification and correlations are by David Bukry, foraminifer identifications 

and correlations by Alvin Almgren and Kristin McDougall, gastropod identification and 

correlation by LouElla Saul, and Radiolaria identifications and correlations are by 

Annika Sanfilippo. 

Previous Work

The rocks that are the focus of this report were mapped by Weaver (1949) as Domengine 

Sandstone of Eocene age and by Sims and others (1973) as Late Cretaceous based partly 

on unpublished mapping by Exxon geologists Howard Sonneman and John Switzer. Part 

of the Sims and others map is shown in fig. 3. The dominance of Late Cretaceous rocks 

in the area, including the rocks regarded as Eocene by Weaver (1949), was supported by 

several collections of Late Cretaceous foraminifers identified by Chevron and Exxon 

paleontologists and virtually surrounding the lower Cement Hill area. The age of most of 

these samples was verified by Alvin Almgren from the original Chevron and Exxon 

slides. Except for the tiny outcrop of sandstone with Paleocene fossils, the existence of 
complexly folded and faulted Tertiary rocks would probably never have been discovered 

without the excavations that accompanied a preliminary geologic investigation for 

development of a housing area (Ristau,1966). 

A 

B 

Figure 1. Sandstone with Turritella infragranulata pachecoensis from locality 

03CB5241 on the southwest flank of Cement Hill. A, View of rock surface. B, View of 

slab prepared by Skyler Phelps, Auburn. LouElla Saul identified and dated the fossils. 

2 
Figure 2. Map showing localities discussed in this report: (1) Lower Cement Hill area 

northeast of Fairfield; (2) Type area for Martinez Stage; (3) Peabody Road, Vacaville 

Junction, and Travis Field area; (4) Vaca Valley and Oakdale School area; (5) Type area 

for Capay “shale” near Brooks; and (6) Potrero Hills. 

3 
Figure 3. Part of the geologic map by Sims and others (1973) showing the geologic 

setting of the Cement Hill area. The green areas have different formations of Cretaceous 

age. Purple areas have rocks of Paleocene age in the Vacaville Junction (3) and Vaca 

Valley-Oakville School areas (4); see also fig. 2). Black dots show places where Chevron 

and Exxon geologists and E. Brabb collected Late Cretaceous foraminifers with ages 

confirmed by A. Almgren. Lower Cement Hill is where rocks significantly younger than 

Cretaceous were recently discovered. 

New Work in Cement Hill Area

The current study area is part of a subdivision in the Fairfield North quadrangle for which 

grading commenced in 2002. Elevations within the subdivision development area vary 

4 
from approximately 100 to 200 feet above mean sea level, with the 200-foot contour 

elevation targeted as the upper limit of grading for roadway and subdivision 

improvements. 

Several samples of mudstone and siltstone from test pits and borings were sent to Alvin 

Almgren before grading began to determine the age of the rocks beneath the mapped 

alluvium. He provided ages of Late Cretaceous E and F-2 zones, late Paleocene E zone, 

and early Eocene C and B zone, all based on foraminifers (zones from Goudkoff, 1945 

and Laiming, 1940). Because the test pits and borings were scattered in an area with only 

a small ledge of sandstone containing the Turritella exposed, the structural relationships 

of these samples could not be determined. The Turritella was examined by LouElla Saul 

and determined to be Turritella infragranulata pachecoensis correlative with planktic 

foraminifer zone P4, the Martinez “stage” of Weaver (1953), and with other late 

Paleocene formations in California. 

As grading began in 2002 on roads and housing pads, more and more sandstone, 

siltstone, mudstone, and shale above and below the Turritella-bearing sandstone were 

exposed. At one point in time, nearly 2,000 feet of what seemed like nearly continuous 

section was present in various outcrops throughout the site, with the Paleocene sandstone 

marker bed in the approximate center of the section. Many of the finer-grained rocks had 

foraminifers clearly visible on the rock surfaces, offering the possibility that this section 

might become the “Rosetta stone” for Paleocene rocks in central California, an area 

where rocks of this age are uncommon and generally sparsely fossiliferous. Accordingly, 

dozens of samples were collected for possible microfossil analysis. A preliminary 

"stratigraphic section" was pieced together based on the rocks exposed in the cuts (fig. 4). 

A conglomerate in shale overlying the sandstone with Turritella and the presence of a 

white sandstone similar to the Domengine Sandstone provided the incentive to speculate 

that the conglomerate above the Turritella beds might represent the beginning of Eocene 

deposition. 

As grading progressed, more nannoplankton samples were collected and sent to David 

Bukry. About one-half of the 40 samples have nannoplankton that provided ages for the 

rocks (zones from Okada and Bukry, 1981; Bukry, 1991; and Bukry and others 1998). 

Additional samples for foraminifers were sent to Alvin Almgren and Kristin McDougall. 

The approximate location of the samples from preliminary scraper cuts, trenches, and 

other excavations are shown on figure 5. The rich character of the foraminifer faunas 

identified by K. McDougall is documented on table 1. All the fossils were used to make a 

new geologic map, shown in figure 6. For convenience in discussing this complex area, 

the geology is divided into 6 blocks, A through F shown on figure 7. Almost all of the 

rocks uncovered in the Lower Cement Hill area are now concealed by concrete roads, 

curbs, sidewalks, house foundations, and fill. 

5 
Figure 4. Original stratigraphic column for the lower Cement Hill area is based on 

limited paleontologic data and an assumption that faults in the section did not greatly 

displace the rocks. This column had to be completely revised when the rocks thought to 

be Eocene near the top of the column turned out to be partly overturned Late Cretaceous 

and Paleocene age and the rocks thought to be Paleocene below the Turritella bed turned 

out to be Eocene. Faulting with extensive displacement has disrupted the lower Cement 

Hill area into several different tectonic blocks. 

Structural Blocks in the Area 

The six structural blocks are bounded by extensively brecciated shear zones, some of 

which have been partly filled with calcite. At least two of the blocks are overturned. The 

blocks are discussed from East to West. 

Block A 

This block in the eastern portion of lower Cement Hill has about 20 feet of overturned and 

highly sheared, dark-gray to black shale and siltstone, with Late Cretaceous coccoliths, 

foraminifers, and the following radiolarians at localities 02CB5401D and E.: 

Afens liriodes Riedel and Sanfilippo 

6 
Alievium superbum (Squinabol) 

Amphipyndax pseudoconulus (Pessagno) 

?Amphipyndax tylotus Foreman 

Archaeodictyomitra lamellicostata (Foreman) 

Clathropyrgus titthium Riedel and Sanfilippo 

Cryptamphorella conara (Foreman) 

?Dictyomitra crassispina (Squinabol) 

Lithomelissa hoplites Foreman 

Myllocercion acineton Foreman 

Pseudoaulophacus floresensis Pessagno 

Pseudoaulophacus lenticulatus (White) 

Stichomitra asymbatos Foreman 

?Theocampe salillum Foreman 

Theocapsomma comys Foreman 

Annika Sanfilippo believes that these are correlative with the Late Cretaceous Campanian 

Stage, Amphipyndax pseudoconulus Zone of Riedel and Sanfilippo (1974) emended by 

Foreman (1977) as the Amphipyndax enesseffi Zone. For additional reference, see the report 

by Sanfilippo and Riedel (1985). The shale with radiolarians also contains rare coccoliths of 

Late Cretaceous age. 

The rocks with Late Cretaceous fossils seemingly grade into a similarly-overturned 10-

foot thick siltstone, sandstone, and glauconitic sandstone and a 70-foot thick siltstone 

containing CP 4 late Paleocene coccoliths at locality 03CB5401C. These rocks are 

truncated by highly sheared siltstone in which the bedding is intensely deformed and 

distorted at the western boundary of Block A. The eastern boundary of Block A is 

concealed beneath alluvium but is assumed to be a fault because all the Cretaceous rocks 

uphill seem to be upright. 

7 
Figure 5. Subdivision layout along Manuel Freitas Parkway showing principal fossil 

locations relative to streets and lot lines. The gray squares indicate places where samples 

were collected but are barren of microfossils. The “T” shows places where Turritella sp. 

was observed and/or collected. 

8 
Table 1A Foraminifers from the lower Cement Hill area. Check list prepared by Kristin 

McDougall, shipment number WESP-03-04. Additional foraminifers examined and dated 

by Alvin Almgren but those are not on this chart and are summarized in the text. 

9 
Table 1B Foraminifers from the lower Cement Hill area. Check list prepared by Kristin 

McDougall, shipment number WESP-03-04. Additional foraminifers examined and dated 

by Alvin Almgren but those are not on this chart and are summarized in the text. 

10 
Figure 6. Revised geologic map for the lower Cement Hill area north of Manuel Freitas 

Parkway from extensive paleontologic, lithologic, and structural data. 

11 
Figure 7. Division of the lower Cement Hill area into six structural blocks labeled A 

through F in order to discuss each block separately. 

The overturned rocks with Late Cretaceous fossils in Block A seemingly grade into a 

similarly-overturned 10-foot thick siltstone, sandstone, and glauconitic sandstone and a 

70-foot thick siltstone containing CP 4 late Paleocene coccoliths at locality 03CB5401C. 

These rocks are truncated by highly sheared siltstone in which the bedding is intensely 

deformed and distorted at the western boundary of Block A. The eastern boundary of 

Block A is concealed beneath alluvium but is assumed to be a fault because all the 

Cretaceous rocks uphill seem to be upright. 

Foraminifers from the rocks with Late Cretaceous fossils in Block A were thought to be 

most likely Paleogene but could be as old as Cretaceous, according to K. McDougall. A. 

12 
Almgren examined foraminifers from the same locality and believes that they are Late 

Cretaceous E zone. Similar black shale that weathers white and contains abundant 

diatoms, radiolarians, and foraminifers of Late Cretaceous age has been mapped by 

Exxon geologists north of Vacaville Junction about 3 miles east of 02CB5401D and E 

(fig. 2, area 3) and along the west side of Vaca Valley northwest of Vacaville (fig. 2, area 

4). This shale has been given the local name “Sacramento” shale by petroleum geologists. 

 At those localities, discussed later in this report, the black shale also contains a prolific 

foraminifer fauna correlative with the Campanian Stage and E zone of Goudkoff (1945), 

according to Almgren (1986). 

Block B 

Most of the rock in block B is massive brown sandstone about 350 feet thick. A white 

sandstone about 50 feet thick forms the top of this sequence and is probably at least part of 

the Domengine Sandstone mapped by Sims and others (1973) in the Peabody Road and 

Travis Field areas east of Cement Hill (fig. 2 area 2). Locality 02CB5432 in the middle of 

the sequence contains early Eocene CP 10/11 coccoliths. 

The rocks of Block B strike predominantly north to northwest and dip steeply to the 

northeast. A prominent zone of highly sheared sandstone interpreted as a fault zone about 

100 feet wide extends at least along the north-south extent of the outcrop area and marks 

the boundary between Blocks B and C. 

Block C 

Block C consists mostly of at least 400 feet of well-bedded sandstone and siltstone. 

Several interbeds of greenish-gray mudstone and shale contain foraminifers and 

coccoliths of early Eocene age. However, strata at the base of the sequence contain the 

youngest floras, indicating that Block C is overturned. Shale and mudstone at localities 

03CB5373 and 5434 contain early Eocene CP 10 coccoliths, whereas localities 

03CB5412 and 5436 contain early Eocene CP 11 coccoliths. Locality 03CB5412 also 

contains a rich foraminifer fauna correlative with the late Penutian Stage to early 

Ulatisian Stage, according to K. McDougall. Localites 02CB5422 and 5422A from the 

middle part of Block C have CP10 /11, undivided, coccoliths. 

Bedding in Block C strikes nearly north and is overturned to the east. Several small-scale 

folds and faults are present within Block C, and other folds and faults are suspected. 

Block D 

This block consists mainly of massive brown sandstone about 100 feet thick. Within this 

sandstone is a well-cemented 3-foot thick sandstone bed with abundant Turritella 

infragranulata pachecoensis. This bed was traced throughout the extent of Block D 

where it had to be removed or buried in order to create level building pads and streets. 

The eastern part of Block D is a highly sheared and contorted mixture of sandstone and 

shale with fault surfaces dipping from 30 degrees to vertical. The fault zone brings rocks 

of Paleocene age in Block D against Eocene rocks in Block C. The western boundary of 

Block D consists of a 20- to 25-foot thick zone of sheared siltstone and mudstone with 

numerous crosscutting shears. Bedding is highly contorted and disrupted. The bedding in 

the remaining part of the block strikes northwest and dips moderately to the northeast. 

13 
Block E 

The rocks in Block E are mainly well-bedded sandstone with many interbeds of siltstone, 

mudstone, and shale with a total thickness of at least 500 feet. One greenish-gray 

mudstone and glauconitic mudstone within Block E is about 200 feet thick and has 

localities 03CB5402, 5402A, 5402B, 5402C 03CB5391, 03CB 5411, 5411A and 

03CB5412 with early Eocene CP 10 coccoliths. Rich foraminifer faunas of early or 

middle Eocene age, late Penutian to early Ulatisian benthic foraminiferal stages, were 

found in these same samples, according to K. McDougall. 

The rocks at the western boundary of Block E are not exposed but are covered with 

alluvium that has extensive shear zones and secondary carbonate extending in a 

northeast-southwest direction. We interpret these shears and carbonate as masking a 

major fault truncating Blocks C, D, and E. 

Block F 

Approximately 300 feet of laminated sandstone with interbeds of siltstone comprise the 

lower part of Block F in the northwest part of the lower Cement Hill area. Some 

sandstone is thicker-bedded and has rip-up clasts of mudstone at a few localities near the 

western edge of the property where the oldest beds were concealed by houses in the 

adjacent subdivision and alluvium during our work. The rocks strike predominantly 

northeast-southwest and dip fairly steeply to the southeast. 

Localities 03CB5431B, 5431BB, 5431E, and 5431G from siltstones in the lower part of 

Block F yielded arenaceous foraminifers correlative with the Late Cretaceous F-1 zone of 

Goudkoff, according to A. Almgren. Localities 03CB5431F and 5431H have rare 

coccoliths of Late Cretaceous age. 

The upper part of Block F consists mainly of about 500 feet of thickly bedded to massive 

sandstone with interbeds of siltstone. These rocks strike and dip in about the same 

direction as those in the lower part of the Block. A sandstone grit at or near the base of 

this unit contains fragments of mollusks and what seemed from a brief examination to be 

a coral, but the exposure was covered before the material could be collected. The contact 

between the sandstone grit and the underlying sandstone beds could be a disconformity 

or a fault. 

Turritella infragranulata pachecoensi, was recovered from sandstone near the top of 

Block F. A sample containing foraminifers of late Paleocene E zone age was identified 

by A. Almgren from a test pit in the vicinity of the Turritella-bearing sandstone, but the 

rocks with the foraminifers could not be found after the hill was excavated so that the 

stratigraphic position of these fossils relative to the Turritella was not established. 

Shear zones occur near the contact between the lower and upper units of Block F, but the 

similar attitudes above and below this shear zone and the presence of what may be a 

disconformity made us reluctant to divide the unit into separate blocks. 

How Do the Blocks Fit Together?

Almost none of the rocks in the various blocks have distinctive marker beds that allow us 

to piece the blocks together to make a continuous section. The Turritella-bearing 

14 
sandstone is present in Blocks B and F but was not found in Block A. The white 

sandstone in Block B and the relative ages of coccoliths in various blocks allowed us to 

tentatively piece together a section (figure 7) about 2,000 feet of largely sandstone with 

many siltstone, shale and mudstone inter-beds ranging in age from Late Cretaceous 

Campanian Stage to early Eocene Cp 11. Blocks A and D are not shown because at least 

some or all of the rocks are duplicated in Block F. However, the Cretaceous rocks in 

Block A are different in age from those in Block F, suggesting that more faulting is 

present than we recognized. The presence of many additional shears than described and 

several small-scale folds should make readers cautious that the so-called section is 

probably duplicated in part and even more complex in structure than we realized. 

Can Landsliding Explain the Structures Observed?

The alluvium in the Lower Cement Hill area before grading had a somewhat hummocky 

appearance and is downhill from crescent-shaped valleys that could be landslide scarps, 

providing the possibility that the overturned beds and faulted blocks were produced by 

landsliding. The outcrops uphill from the part that was graded, however, are all 

Cretaceous rocks seemingly in place and not overturned. No rocks of Tertiary age were 

found uphill from the graded area. Moreover, no alluvium was mixed in with the 

overturned and faulted bedrock blocks as might be suspected if landsliding produced the 

mixed structure. We conclude that the structures seen in Lower Cement Hill were 

produced by tectonic forces, not landsliding. 

A glance at the regional structure north and south of lower Cement Hill (Fig. 3) provides 

clues about the complicated structure. North of Vacaville for at least 35 miles, 

Cretaceous rocks are part of a monocline dipping moderately to the east. About 5 miles 

south of lower Cement hill, however, Paleocene and Eocene rocks have been folded into 

a broad anticline with nearly an East-West strike in the Potrero Hills (Fig. 2, area 6, and 

Sims and others, 1973). The Potrero Hills and the complex structure in the lower Cement 

Hills area could have been produced by drag along a strike-slip fault. Which fault and 

how the structure developed is beyond the scope of this paper, but complicated structures 

in the Potrero Hills and adjoining areas produced by contraction, strike-slip, and thrust 

faults, as proposed by Unruh and Hector (2007); these could explain lower Cement Hills. 

 

We have hesitated to use the term thrust fault for most of the faulting observed at lower 

Cement Hill because of the complex structure. Many high-angle faults were observed, 

but few thrusts were documented. We believe that compression and thrusting dominated 

the development of lower Cement Hill, but the evidence is not conclusive. 

15 
Figure 8. A new stratigraphic column for the lower Cement Hill area showing the 

different fault blocks, collecting localities, and an interpretation of how the faulted and in 

some places overturned blocks fit together. Unrecognized faulting and folding may 

further complicate this overview of the stratigraphic sequence 

Vacaville Junction Area

The Cretaceous rocks at lower Cement Hill are exposed again along Peabody Road about 

one-half mile north of Vacaville Junction (fig. 3, area 3), where the white-weathering 

“Sacramento” shale forms conspicuous outcrops and contains abundant foraminifers and 

radiolarians. The foraminifers are Late Cretaceous E zone of Goudkoff (1945), according 

to A. Almgren. Among the foraminifers is the topotype for Reussella szajnochae var. 

californica (Cushman) described by Almgren (1959). This shale with similar faunas also 

crops out in a drainage ditch about 3,500 feet northeast of the Peabody Road exposures. 

16 
The shale at that locality, though, is overlain by glauconitic sandstone and olive-gray 

mudstone with foraminifers correlative with the late Paleocene E zone of Laiming 

(1940), according to A. Almgren. E. Brabb resampled these outcrops in 1992 at which 

time they yielded Late Cretaceous (92CB3531C and D) and late Paleocene CP7 

coccoliths (92CB3531B). 

At least 9 of the holes for seismic surveys in the area from about one mile southeast of 

Cement Hill to areas around and in Travis Field plus two surface samples yielded late 

Paleocene E zone faunas, according to A. Almgren (unpublished notes). This eastward 

extension of the Paleocene rocks from the lower Cement Hill area has been incorporated 

into the map by Graymer and others (2004). 

Vaca Valley Area 

Exxon, Chevron, and Unocal geologists all recognized rocks of Paleocene age in the 

Vaca Valley area northwest of Vacaville (fig. 2, area 4, and fig. 9) about 6 miles north of 

lower Cement Hill where the mapping by Exxon geologists H. Sonneman and J. Switzer 

was used for the map by Sims and others (1973). This map has two units of Paleocene 

age: a lower unit of massive quartz sandstone and an upper unit of silty mudstone and 

shale. These units were considered members within the Martinez Formation by Sims and 

others (1973). Field investigations in 1997 and 2002 were focused on determining the 

lithologic character of the Paleocene rocks, the relationships with the underlying 

Cretaceous sequence and overlying “Vacaville shale” of Boyd 1998), and whether these 

rocks have the same age, lithology, and relationships as the rocks in lower Cement Hill. 

Cretaceous Rocks in Vaca Valley 

The white-weathering siliceous shale called informally the “Sacramento” shale by 

petroleum geologists in the lower Cement Hill and Vacaville Junction areas (fig. 2, areas 

1 and 3) has been mapped as a separate unit less than 50 feet thick by Sims and others 

along the western side of Vaca Valley (fig. 3, area 4, and fig. 9. No fossils have been 

recovered from the “Sacramento shale” in the southern part of this area, but the unit is 

bracketed by samples 03CB5352 and 03CB5353 from shale near Alamo Creek. A. 

Almgren considers the age of sample 03CB5352 as Late Cretaceous E zone of Goudkoff 

(1945) and the other sample to be probably the same age. 

17 
Figure 9. Geologic units and localities in the Vaca Valley area northwest of Vacaville. 

Dunns Peak and the hamlet of Bucktown are shown in the east-central part of the map. 

The general area of Bucktown and Ulatis Creek is where Mallory (1959) established the 

type locality for the Ulatisian stage. Numbers and letters refer to foraminifer samples 

collected by A. Almgren, Chevron geologists, and E. Brabb. 

18 
Figure 10. Locality map for the Oakdale School area and reference section for the Capay 

Shale. This map is a short distance north of figure 9. 

19 
Figure 11. Stratigraphic column near Oakdale School. This column is generalized and 

constructed from attitudes on the map by Sims and others (1973) and from additional 

fieldwork. 

Two samples collected by Exxon and Chevron geologists pin down the age of the 

“Sacramento” shale north of Vaca Valley near Oakdale School (fig. 10). Sample HSS 

483 from the “Sacramento” shale is Late Cretaceous, probably lower E zone of Goudkoff 

(1945), according to A. Almgren. Sample C636 found in a gully about 1,600 feet 

southwest of Oakdale School (fig. 10) has foraminifers correlative with the Late 

Cretaceous E zone of Goudkoff, according to Brabb and Parker (2005). This dark-gray 

shale sample is about 100 feet above the “Sacramento” shale and less than 200 feet below 

the concealed base of a shale with Eocene fossils (see fig. 11). No samples younger than 

Late Cretaceous E zone were found in the Cretaceous rocks of the Vaca Valley area. 

20 
Paleocene Rocks in Vaca Valley 

Paleocene rocks are generally poorly exposed in the Vaca Valley area, but the general 

lithology, thickness, and age were established from small outcrops in the hills between 

Alamo Creek and an unnamed reservoir about 3 miles to the north (fig 9). Glauconitic 

sandstone, probably less than a few tens of feet thick and with late Paleocene CP4 

coccoliths crops out at 03CB5341. Nearly a mile north of 03CB5341, at 97CB4684, a 

gray mudstone below a glauconite sandstone contains late Paleocene CP7 coccoliths. No 

upper mudstone unit mapped by Sims and others (1973) could be found. 

Chevron Petroleum Company kindly made available their foraminifer slides and notes for 

three samples they consider Paleocene on the west side of Vaca Valley (fig. 9). A. 

Almgren confirmed a late Paleocene E zone of Laiming (1940) age for samples 11100, 

11101, and 11104. He also collected sample AAWC-40 in about the same stratigraphic 

position as the Chevron samples and obtained a similar E zone age. 

Two samples from mudstone overlying the Paleocene rocks show that the Paleocene is 

quite thin, probably less than 100 feet thick, much thinner than Paleocene strata at lower 

Cement Hill. Glauconitic mudstone at 03CB5333 (fig. 9) has early Eocene CP11 

coccoliths. Sample 11106 collected 800 feet north of Benchmark 328 is early Eocene D 

zone of Laiming (1940), according to A. Almgren, and restricts the areal extent of 

Paleocene rocks to a thin band along the west side of Vaca Valley. No contact with the 

underlying rocks of Cretaceous age has yet been seen. 

A much thicker outcrop width of Paleocene rocks is shown on the map by Sims and 

others (1973) in the Oakland School area (fig. 10), but these rocks are of Eocene age, as 

documented below. No rocks of Paleocene age have been found north of locality 

97CB4684 (fig. 9) where the Capay shale of Eocene age is believed to rest 

disconformably or unconformably on Cretaceous rocks, similar to the situation at lower 

Cement Hill. We support the unpublished mapping by Chevron geologists which shows 

Paleocene rocks as missing north of the locality where 97CB4684 was collected. 

Eocene Rocks in Vaca Valley 

About 400 feet of Eocene shale on the east side of Vaca Valley southeast of Bucktown 

(fig. 9) and adjacent to Ulatis Creek was named informally the “Vacaville shale” in a 

thesis by Boyd (1949). This informal name was maintained in a later publication of his 

thesis (Boyd, 1998). He estimated that 1,600 feet or more of unnamed rocks lie beneath 

the Vacaville shale and alluvium in the central part of Vaca Valley, and about 1,000 feet 

of unnamed sandstone and shale are on the western side. The lower part of Boyd’s 

“Vacaville shale” was used by Mallory (1955) as the type for his Ulatisian Stage. 

The rocks reported as concealed in Boyd’s thesis area are exposed in a nearly continuous 

shale section near Oakdale School (fig. 10) where the name Capay Shale was used by 

Sims and others (1973). A stratigraphic column was constructed for this area (fig. 11) 

based on attitudes and contacts on the Sims map, as modified by the reduced thickness 

and absence of the Paleocene rocks reported above, and additional fieldwork. The Capay 

Shale is estimated to be about 1,800 feet thick in this section, compared to 1,938 feet in a 

similar unpublished section constructed by Chevron Petroleum geologists. 

21 
The oldest sample in the Capay Shale is from a glauconitic mudstone at locality 03CB 

5343 near the base of the exposed section where coccoliths are early Eocene CP10. 

Foraminifers at 97CB4692, 97CB4693 and 97CB4693A are not distinctive but suggest an 

early Eocene to possibly middle Eocene age according to K McDougall (see fig. 11 and 

table 2). McDougall also believes that the faunas were deposited at lower bathyal depths 

or abyssal depths. No nannoplankton were recovered from these samples. 

Rich foraminiferal faunas (table 2) and nannoplankton floras were recovered from 

greenish-gray mudstone in the middle part of the Capay. Faunas at localities 97CB4694, 

97CB4695 and 97CB4695A are correlative with the Penutian Stage and were deposited 

at baythal or abyssal depths, according to K McDougall. Early Eocene CP11 coccoliths 

were recovered at 02CB5342, 03CB5312, 97CB4695A, and 03CB5311. The last locality 

plus 02CB5321, 02CB5313, and 03CB5355 have foraminifers correlative with the B-4 

zone of Laiming (1940), according to A. Almgren. 

The upper part of the Capay at localities 97CB4701, 97CB4702, 93CB5303, and 

93CB5302 has early Eocene CP11 coccoliths. Foraminifer faunas diagnostic of the late 

Penutian to early Ulatisian stage, according to K McDougall, were recovered at at 

97CB4701 and 97CB4702 and are believed to have been deposited at lower bathyal 

depths . Sample 02CB5355 has foraminifers correlative with the B-4 zone of Laiming 

(1940), according to A. Almgren. 

The Capay Shale, therefore, has similar faunas and floras to those in lower Cement Hill. 

However, the Cement Hill section has much more sandstone whereas the Paleocene 

sandstone has been removed by erosion or was never deposited in the Oakdale School 

area. 

The Capay Shale is overlain by the lower informal shale member of the Nortonville 

member of the Kreyenhagen formation, according to Sims and others (1973). This name 

is probably not appropriate, however, because the Nortonville and Kreyenhagen 

formations were deposited in different basins and are only partly the same age. The lower 

shale member is overlain in turn by the informal sandstone member and an upper shale 

member. The shale-on-shale contact of two formations is difficult to recognize, but the 

uppermost Capay beds are gray mudstone whereas the shale in the Nortonville is darkbrownish-gray mudstone. 

22 
Table 2A. Foraminifera collected in the Vaca Valley area. Identified by Kristin 

McDougall. 

23 
Table 2B. Foraminifera collected in the Vaca Valley area. Identified by Kristin 

McDougall. 

24 
Table 2C. Foraminifera collected in the Vaca Valley area. Identified by Kristin 

McDougall. 

Four samples were collected in the lower shale member of the Nortonville shale member. 

Localities 02CB5361 and 02CB5362 (fig. 10) and 02CB5362C (not on fig. 10 but 3 feet 

above 02CB5362) all contain middle Eocene CP13 coccoliths. Sample 02CB5362A was 

collected 3 feet below 5362 and it contains middle Eocene CP12 coccoliths. Locality 

97CB4705 2.5 miles north of 02CB5362 in Pleasants Creek and 1,800 feet northeast of 

Pioneer Ranch (not on map) is CP13. This sample is in the uppermost part of the 

Nortonville shale member. 

25 
Sims and others (1973) mapped the lower member of the Nortonville shale in a 

continuous band southward from the Oakdale School area to the area of Boyd’s thesis 

about one-half mile southeast of Bucktown (fig. 9). The lower shale member of the 

Nortonville is the upper part of the type “Vacaville” shale of Boyd. In Boyd’s area (1998, 

fig. 1), the “Vacaville” shale is overlain by the “Dunns Peak” sandstone, which in turn is 

overlain by more shale assigned to the Markley Formation. No fossils were found in the 

“Dunns Peak” sandstone and no distinctive fossils have yet been found in the overlying 

so-called Markley shale near Dunns Peak. 

The upper part of the type “Vacaville shale” has a 3-foot thick pebbly and glauconitc 

sandstone bed that marks a change from bluish-gray mudstone to chocolate-brown 

mudstone, a change similar to that found in the Oakdale School area between the Capay 

and Nortonville shales. The glauconitic sandstone also marks a substantial change in the 

character of the fauna and in the age, from early Eocene B-2 to B-4 zone of Laiming 

below the glauconite to middle Eocene A-2 zone of Laiming above the glauconite. This 

observation makes the use of the term “Vacaville shale” superfluous. The lower part 

below the glauconite is Capay Shale. The upper part above the glauconitic sandstone is 

the lower part of the Nortonville shale member. 

Unfortunately, the use of the rock unit Capay Shale is a misnomer, because most of the 

Capay in the type area is sandstone and conglomerate, according to Boyd (1956), Baker 

(1975), and Crook and Kirby (1935). The type area for the Capay is in the Brooks 7.5’ 

quadrangle, about 6 miles west of the town of Capay (fig. 2, area 5) and about 22 miles 

north of Oakdale School. However, the Capay is widely recognized as a shale unit of 

early Eocene age in subsurface well correlations throughout this part of California. 

Solution of this problem is beyond the scope of this report, other than to suggest that the 

Capay of the Oakdale School area might be used as a supplementary reference section to 

define and correlate surface exposures of the Capay Shale. 

Summary for Vaca Valley Area 

Paleocene rocks in Vaca Valley consist of glauconitic sandstone and mudstone less than 

100 feet thick resting on Late Cretaceous shale beneath and overlain by Capay early 

Eocene glauconitic mudstone. The rocks are much thinner and lack the mollusks found 

in the lower Cement Hill area. In the Oakdale School area, the Paleocene rocks were 

never deposited or have been removed by erosion or faulting. 

Is the Name Martinez Formation Appropriate ?

The lower Cement Hill localities are only a few tens of kilometers north of Martinez (fig. 

1, area 2) where this formation was first named by Whitney (in Gabb, 1869, p. xiii) and 

considered to be Cretaceous. The subsequent evolution of the name is well described by 

Smith (1957, p. 130-135) and will not be repeated here. The term has been used mostly as 

a stage for rocks with Paleocene fossils, not as a lithologic unit. As Smith (1957, p. 134) 

points out, "no really satisfactory description of a type Martinez formation has ever been 

given." Even the use of "Martinez Formation, restricted" on the map by Brabb, 

Sonneman and Switzer (1971) and Sims and others (1973) is not good practice because 

of likely confusion with the Martinez Stage. 

26 
Weaver (1953) used the name Vine Hill sandstone as a substitute for Martinez Formation 

in the vicinity of Martinez. This glauconitic sandstone and minor siltstone has abundant 

mollusks including Turritella pachecoensis of Paleocene age indicating that it has similar 

lithology and is correlative with the rocks at Cement Hill and Vaca Valley. However, 

enough differences in the stratigraphic succession and detailed lithology in the two areas 

warrant caution in extending the Vine Hill to the Cement Hill and Vaca Valley areas. 

Conclusions

Unnamed sandstone and siltstone of late Paleocene age with gastropods of the Martinez 

Stage and foraminifers correlative with the E zone of Laiming (1940) are probably 

faulted against sandstone of Late Cretaceous age, F-2 zone of Goudkoff (1945) in the 

western part of lower Cement Hill. In the eastern part of lower Cement Hill, overturned 

siliceous mudstone locally called “Sacramento” shale contains radiolarians correlative 

with the Late Cretaceous Campanian Stage, Late Cretaceous coccoliths, and foraminifers 

correlative with the E zone of Goudkoff (1945). These rocks are overlain by overturned 

glauconitic sandstone and siltstone with late Paleocene CP4 coccoliths. Reconstruction of 

the Tertiary section before it was faulted suggests that the late Paleocene is represented 

mainly by sandstone and siltstone about 500 feet thick, and the early Eocene section has 

about 1,500 feet of sandstone, siltstone and mudstone with CP10 and CP10/11 coccoliths, 

and about 100 feet of mainly shale with CP11 coccoliths. 

In contrast, late Paleocene sandstone and siltstone in Vaca Valley are only a few tens of 

feet thick and overlie Late Cretaceous E zone shale. Almost all the Eocene rocks in Vaca 

Valley are mudstone and shale, lacking the sandstone present in lower Cement Hill. 

Although the thickness of the Eocene rocks in both areas is comparable, the Vaca Valley 

section has mostly CP10 coccoliths whereas the lower Cement Hill section has mainly 

CP11 coccoliths. We conclude that the Paleocene and Eocene rocks in Vaca Valley are 

not simply offset by lateral faulting from lower Cement Hill, but must have originated in 

different parts of the depositional basin. 

Work by K McDougall (see tables 1 and 2 of this report) on 18 samples from lower 

Cement Hill and Vaca Valley has provided a list of at least 202 benthic foraminifer 

species. The diversity and abundance of this fauna must compare favorably with other 

Eocene and Paleocene areas in California. Although lower Cement Hill is no longer 

exposed, the Vaca Valley will provide challenges for paleontologists for decades to 

come. We took mainly small samples to document the age of the different geologic units. 

A project to document the character of the faunas would probably double or triple the 

number of species that could be collected. 

Acknowledgments

We are grateful to Robert Tooby who provided unlimited access to the Cement Hill area 

during the entire period of this study. MCK Consulting provided extensive support and 

technical interest during the initial aspects of this investigation. Charles Powell III, U. S. 

Geological Survey, kindly arranged for LouElla Saul to examine the Paleocene 

gastropods. Skyler Phelps donated assistance and support for collecting and cutting large 

slabs of the Turritella beds. Wallace Kuhl Associates provided the subdivision base map 

used for determining the fossil sample collection localities. We are very grateful to 

27 
management people and paleontololgists with Unocal Company of California, Exxon 

Petroleum Company, and Chevron Petroleum Company for making samples and notes 

available for the Vaca Valley, Cement Hill, and Peabody road areas. 

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