Preliminary geologic map emphasizing bedrock formations 
in Alameda County, California:  A digital database

by R.W. Graymer, D.L. Jones, and E.E. Brabb

U.S. Geological Survey Open-File Report 96-252

Geologic Explanation

Introduction

This map database represents the integration of previously 
published and unpublished maps by several workers (see Sources of 
Data) and thousands of man-hours of new geologic mapping and field 
checking by the authors.  The data are released in a preliminary 
digital form to provide an opportunity for regional planners, local, 
state, and federal agencies, teachers, consultants, and others 
interested in geologic data to have the new data long before a 
traditional paper map is published.  The authors currently plan to 
produce a second version of the geologic map of Alameda County that 
would include subdivided Quaternary units and enhanced 
stratigraphic description and nomenclature, both as a digital product 
and as a traditional paper map.  The timing of release of these 
products, and indeed whether they will be produced at all, depends 
on a variety of factors, including funding, outside author control.

Stratigraphy

Lithologic associations in Alameda County are divided into nine 
assemblages; I, II, and V - XI (Assemblages III and IV occur only in 
Contra Costa County).  As defined in Graymer, Jones, and Brabb 
(1994), assemblages are large, fault - bounded blocks that contain a 
unique stratigraphic sequence.  The stratigraphic sequence differs 
from that of neighboring assemblages by containing different rock 
units (e.g. the freshwater limestone (Tlp) in Assemblage VIII is 
missing from the other Assemblages), or by different stratigraphic 
relationship among similar rock units (e.g. the Orinda Formation (Tor) 
overlies the Claremont Chert (Tcc) in Assemblage I, whereas in 
Assemblage VI three other formations (To, Tt, and Tbr) totaling more 
than 500 meters thick lie between the Orinda and Claremont).  These 
stratigraphic differences represent changes in depositional conditions 
in one or more large depositional basins.  The current adjacent 
location of the different assemblages reflects the juxtaposition of 
different basins or parts of basins by large offsets along the faults 
that bound the assemblages.
	In general, in Alameda County the Tertiary strata rest with 
angular unconformity on two complexly deformed Mesozoic rock 
complexes.  One of these Mesozoic complexes is made up of:  the 
Coast Range ophiolite, which includes serpentinite, gabbro, diabase, 
and basalt; keratophyre; and overlying Great Valley sequence.  
Within this complex in the Berkeley and Hayward areas the Great 
Valley sequence rests unconformably on ophiolite and volcanic rocks 
in several places.  This complex represents the accreted and 
deformed remnants of Jurassic oceanic crust, and overlying arc 
volcanic rocks and a thick sequence of turbidites.  
	The second Mesozoic complex is the Franciscan complex, which 
is composed of weakly to strongly metamorphosed graywacke, 
argillite, limestone, basalt, serpentinite, chert, and other rocks.  The 
rocks of the Franciscan complex in Alameda County were probably 
Jurassic oceanic crust and pelagic deposits, overlain by Late Jurassic 
to Late Cretaceous turbidites.  Although Franciscan rocks are 
dominantly little metamorphosed, high-pressure, low-temperature 
metamorphic minerals are common in the Franciscan complex 
(Bailey, Irwin, and Jones, 1964), and the presence of high grade 
metamorphic blocks in sheared but relatively unmetamorphosed 
argillite matrix (Blake and Jones, 1974) reflects the complicated 
history of the Franciscan.  The complex was subducted beneath the 
Coast Range ophiolite during Cretaceous time.  Because the Novato 
Quarry terrane (Kfn) forms the lowest in the stacked sequence of 
terranes in the Bay Area (Wakabayashi, 1992) subduction took place, 
at least in part, after the Late Cretaceous (Campanian) deposition of 
the sandstone of the Novato Quarry terrane.  Because of the 
subduction relationship, the contact between the two Mesozoic 
complexes is everywhere faulted (Bailey, Irwin, and Jones, 1964), 
and the Franciscan complex presumably underlies the entire county.  
	Tertiary rocks rest with angular unconformity on both 
Mesozoic complexes.  In Assemblages IX and X, Tertiary rocks are on 
the Franciscan complex.  The more usual situation is observed in all 
other assemblages, where Tertiary rocks overlie strata of the Great 
Valley sequence, although in most assemblages the contact is now 
faulted.
	Three types of intrusive rocks have been mapped in Alameda 
County.  One is a small stock of coarse-grained, crystalline granular, 
quartz diorite that intrudes the Coast Range ophiolite in the Cedar 
Mtn. quadrangle (KJqd).  Another type occurs as small rhyolite plugs 
intruding Cretaceous and Tertiary strata in the Sunol area (Tsv).  The 
third type forms a large body of fine grained quartz diorite in the 
Oakland area (Kfgm).  These rocks are not included in any 
assemblage because of their intrusive nature.

Paleontology

	Hundreds of fossil collections from Contra Costa County have 
been described in the literature during the past century, and 
thousands more have been collected by geologists working for 
petroleum companies.  A partial list of references is provided by 
Freeberg (1990).  Preparation of a digital database of this 
information is under way by scientists at the U.S. Geological Survey 
and the University of California, Berkeley.

Radiometric Ages

	A compilation of the radiometric ages of rocks in Contra Costa 
and other counties south of latitude 38 degrees is provided by 
Lindquist and Morganthaler (1991).  Additional data are provided by 
Wright (1974), Sarna-Wojcicki (1976, and written communication, 
1990), Sarna-Wojcicki and others (1979), and Curtis (1989).


Structure

	The faults of Alameda County are characterized by both strike-
slip and dip-slip components of displacement.  There are four major 
fault systems that display large right-lateral offsets, the Hayward, 
the Stonybrook-Palomares-Miller Creek-Moraga, the Calaveras, and 
the Greenville.  These fault systems trend roughly N30W.  Most of 
these fault systems include many fault strands in a broad (as much 
as 10 km wide) zone.  Offset is distributed on the various faults in 
the zones, and the locus of fault movement associated with a fault 
zone has changed through geologic time (see Graymer, Jones, and 
Brabb, 1995, for a description of the Hayward fault zone, 
Montgomery and Jones, 1992, for a description of part of the 
Calaveras fault zone).  All of the fault systems have strands which 
have been active during Quaternary time and some, such as the 
Hayward, Calaveras, and Greenville, have generated historic 
earthquakes or display active creep (Lienkaemper, 1992, Radbruch-
Hall, 1974, Herd, 1977a, 1977b and 1978, Cockerham and others, 
1980).  As much as 170 km of right slip has been taken up by the 
Hayward, Stonybrook-Palomares-Miller Creek-Moraga, and Calaveras 
fault systems since 8 Ma (McLaughlin and others, 1996).  Of this, 
about 43 km was probably taken up by the Hayward fault system 
(Fox and others, 1985).  These fault systems also form most of the 
boundaries of the assemblages.  The juxtaposition of rocks with 
different stratigraphic histories across these faults lends support to 
the idea of large offsets.  Note, however, that the Hayward fault 
system does not form an assemblage boundary.
	In addition to strike-slip faults, faults in Alameda County can 
be divided into three categories based on the fault-normal 
component of displacement and orientation.  The first of these 
categories comprises transpressional faults within the major strike-
slip fault zones.  These faults trend roughly parallel to the strike-slip 
faults discussed above, but display a large component of thrust or 
reverse displacement.  Examples of this type of fault are the Mission, 
Warm Springs, and Arroyo Aguague faults in the Hayward fault zone.  
The compressional component of deformation on these faults is 
caused by the small but important component of plate motion at 
right angles to the trend of the strike-slip fault zones (Jones and 
others, 1995), as well as fault-normal compression related to changes 
in trend of the strike-slip fault zone (Andrews and others, 1993).  
The transpressional faults also have a component of strike-slip offset, 
although the amount of offset is for the most part undetermined.  
	The second category of fault consists of thrust and reverse 
faults that trend at high angle to the strike-slip fault zones (N60E-
N60W).  Examples of this type include the Verona and Williams 
faults.  These faults reflect compression directed parallel to plate 
motion.  
	The third category of fault with a fault-normal component of 
offset in Alameda County comprises transtensional faults, or faults 
with oblique normal offset.  These faults occur within the major 
strike-slip fault zones (trending about N30W).  The best example of 
this type is the Chabot fault.  The transtensional faults reflect 
deformation during a period (late Pliocene to early Pleistocene, see 
Graymer, Jones, and Brabb, 1995) when regional stress contained a 
small but significant fault-normal extensional component.  
	Both types of faults with compressional deformation 
underwent late Quaternary deformation (Graymer, Jones, and Brabb, 
1995, Andrews and others, 1993, Herd and Brabb, 1980), but the 
amount of seismic hazard that they represent remains to be 
determined.  The transtensional faults, on the other hand, appear to 
have ceased moving for the most part by late Pleistocene time.
	Folds in Alameda county can be divided into three categories 
based on axial trend and style of deformation.  The first category 
includes tight folds and overturned folds with inclined axial planes 
whose axes trend obliquely to the major strike-slip fault zones 
(about N60W).  These folds were probably caused by the same 
component of regional stress that formed the strike-slip faults and 
the thrust and reverse faults of the second category discussed above.  
These folds occur in the north-central part of the county, in the 
region between the Calaveras and Moraga-Miller Creek-Palomares 
faults.
	The second category of fold contains tight, upright folds whose 
axes strike roughly parallel to the major strike-slip faults (about 
N30W).  These folds must have been formed by a component of 
regional compression perpendicular to the strike-slip faults (Jones 
and others, 1995).  For the most part, only synclines of this category 
are preserved, anticlines having been disrupted by faulting of the 
first category discussed above.  Folding of this type is present in the 
western part of the county between the Hayward and Moraga-Miller 
Creek-Palomares-Stonybrook faults and on either side of the 
Calaveras fault in the south part of the county.
	The third category of fold in Alameda County includes the 
broad anticline and related smaller folds of the Altamont anticline in 
the northeastern part of the county, east of the Greenville fault.  This 
fold trends roughly paralell to the major strike-slip faults, and 
therefore must be caused by regional compression perpendicular to 
the strike-slip faults, in a manner similar to that of the second 
category of folds.
	Preserved folds in Alameda County for the most part formed in 
late Miocene or later time, as late Miocene strata are involved in the 
folds.  Pre-late Miocene folding undoubtably occurred, associated 
with subduction of the Franciscan complex beneath the Coast Range 
ophiolite and subsequent deformation associated with the 
unconformity at the base of the Tertiary sequence.  These folds have 
been totally disrupted, being best preserved as homoclinal sequences 
of Cretaceous strata.  The youngest folding must postdate the 
Pliocene and Pleistocene deposition of the Livermore gravels (QTl), as 
those strata are folded in at least one area.  Late Pleistocene strata 
have not been observed to be folded, but are tilted and uplifted in 
several places in the west part of the county.

Description of Units

Surficial deposits (Quaternary).  Overlying all assemblages:

Qar	Artificial deposits (Holocene).  Clay, silt, sand, gravel, 
cobbles, and boulders used to construct dams.

Qu	Surficial deposits, undivided (Holocene and Pleistocene).

Qls	Landslide deposits (Holocene and Pleistocene).  Landslides 
are intentionally omitted from most of this map because 
they are so numerous they would conceal much of the 
information on bedrock geology.  Only a few of the large 
landslide areas are shown.  For more comprehensive reports 
of landslides in the area, see Nilsen and others (1979)

Qt	Terrace deposits (Holocene(?) and Pleistocene).  Clay, silt, 
sand, gravel, and cobbles forming geomorphically distinct 
terraces.  This unit is only differentiated in a few places.

Qoa	Older alluvium (Pleistocene).  Alluvial clay, silt, sand, gravel, 
and cobbles.  This unit is only differentiated in a few places.

Tertiary Intrusive Rocks

Tsv	Silicic volcanic rocks (Miocene or younger).  Rhyolite and 
dacite plugs, dikes, and sills.  The mapped outcrop of these 
rocks is limited to a small area north and south of Sunol.

Mesozoic Intrusive Rocks

KJqd	Quartz diorite (Jurassic or younger).  Coarse-grained, 
crystalline-granular quartz diorite.  Feldspars are more or 
less altered.  Outcrop is limited to one small stock (several 
hundred meters in diameter) near Cedar Mountain in the 
Diablo Range.

Rocks that presumably underlie the entire area

KJf	Undivided Franciscan complex (Jurassic and Cretaceous).  
More or less sheared and metamorphosed graywacke, shale, 
mafic volcanic rock, chert, ultramafic rock, limestone, and 
conglomerate.  Highly sheared sandstone and shale forms 
the matrix of a melange containing blocks of many rock 
types, including sandstone, chert, greenstone, blueschist, 
serpentinite, eclogite, and limestone.  Locally divided into:

Kfn	Novato Quarry terrane of Blake and others (1984) (late 
Cretaceous).  Distinctly bedded to massive, fine- to coarse-
grained, mica bearing, lithic wacke.  Where distinctly 
bedded, sandstone beds are about one meter thick, and 
siltstone interbeds are a few centimeters thick.  
Sedimentary structures are well preserved.  At the type 
area in Marin County, fossils of Campanian age have been 
discovered, but none have yet been collected in Alameda 
County.  In north Oakland, the sandstone is associated with a 
one kilometer diameter body of fine-grained quartz diorite 
(Kfgm).  Although the margins of the intrusive body are 
pervasively sheared, the diorite was probably originally 
intruded into the sandstone, judging from the extensive 
hydrothermal alteration in many parts of the sandstone 
outcrop area.

KJfs	Franciscan sandstone, undivided (Late Jurassic to Late 
Cretaceous).  Undivided graywacke and meta-graywacke.

KJfm	Franciscan melange (Late Jurassic and/or Early Cretaceous).  
Sheared black argillite, graywacke sandstone, and minor 
green tuff, containing blocks and lenses of meta-graywacke 
(fs), chert (fc), shale, metachert, serpentinite (sp), 
greenstone (fg), amphibolite, tuff, eclogite, quartz schist, 
greenschist, basalt, marble (fl), conglomerate, and 
glaucophane schist.  Blocks range in size from pebbles to 
several hundred meters in length.  Only some of the largest 
blocks are shown on the map.

KJfe	Eylar Mountain terrane of Crawford (1976) (Late Jurassic 
and/or Early Cretaceous).  More or less sheared and 
metamorphosed mudstone, siltstone, graywacke, 
conglomerate, chert, and minor pillow basalt.  Mudstone is 
almost everywhere metamorphosed to slate or chlorite 
phyllite.  Sedimentary structures are well preserved locally.  
Graywacke ranges from massive, coarse-grained and 
conglomeratic sandstone to distinctly bedded, medium- and 
coarse-grained sandstone.  Although most Eylar Mountain 
terrane graywacke in Alameda County is little foliated, 
locally it displays foliation as pronounced as textural zone 
2A.  The depositional contact of clastic sedimentary rocks on 
chert is preserved in several locations.  Chert is mostly thin-
bedded, red and green, more or less recrystallized, 
containing a few well preserved radiolarians locally.  In 
some places chert has been altered to white meta-chert.  
Widely dispersed, small outcrops of basalt are distinctly 
pillowed, amygduloidal, and lacking phenocrysts.  In many 
locations the basalt is converted to bright green meta-basalt.

KJfg	Franciscan greenstone (Late Jurassic and/or Early 
Cretaceous).  More or less metamorphosed basalt, generally 
pervasively altered.  Pillow structure is well preserved 
locally.  In places the basalt is amygduloidal.

Assemblage I

Tbp	Bald Peak Basalt (late Miocene).  Massive basalt flows.  
Ar/Ar ages of 8.37+0.2 and 8.46+0.2 Ma have been obtained 
from rocks of this unit (Curtis, 1989).

Tst	Siesta Formation (late Miocene).  Non-marine siltstone, 
claystone, sandstone, and minor limestone.

Tmb	Moraga Formation (late Miocene).  Basalt and andesite flows, 
minor rhyolite tuff. Ar/Ar ages obtained from rocks of this 
unit range from 9.0+0.3 to 10.2+0.5 Ma (Curtis, 1989).  
Interflow sedimentary rocks (Tmbs) are mapped locally.

Tor	Orinda Formation (late Miocene).  Distinctly to indistinctly 
bedded, non-marine, pebble to boulder conglomerate, 
conglomeratic sandstone, coarse- to medium-grained lithic 
sandstone, and green and red siltstone and mudstone.  
Conglomerate clasts are sub-angular to well rounded, and 
contain a high percentage of detritus derived from the 
Franciscan complex.

Tcc	Claremont Chert (middle to late Miocene).  Laminated and 
bedded chert, minor brown shale and white sandstone.  
Chert occurs as distinct, massive to laminated, gray or brown 
beds as much as 10 cm thick with thin shale partings.  
Distinctive black, laminated chert occurs locally in the 
Berkeley Hills.  Interbedded sandstone (Tccs) mapped 
locally.

Tush	Unnamed gray mudstone (early Miocene).

Tsm	Unnamed glauconitic mudstone (Oligocene(?) and Miocene).  
Brown mudstone is interbedded with sandy mudstone 
containing prominent glauconite grains.  Both rock types 
locally contain phosphate nodules up to one centimeter in 
diameter.  Brown siltstone and fine-grained sandstone 
(Tsms) are locally interbedded.  The unit is bounded below 
and above by faults.  It was mapped as Sobrante(?) 
Formation by Radbruch (1969).

Tes	Unnamed mudstone (Eocene).  Green and maroon, 
foraminifer rich mudstone, locally interbedded with hard, 
distinctly bedded, mica bearing, quartz sandstone.  This unit 
is bounded above and below by faults.

Ta	Unnamed glauconitic sandstone (Paleocene).  Coarse-grained, 
green, glauconite rich, lithic sandstone with well preserved 
coral fossils.  Locally interbedded with gray mudstone and 
hard, fine-grained, mica bearing quartz sandstone.  Outcrop 
of this unit is restricted to a small, fault - bounded area in 
the Oakland hills.


Assemblage II -

QTl	Livermore gravels (Pliocene and Pleistocene).  Poorly to 
moderately consolidated, indistinctly bedded, cobble 
conglomerate, gray conglomeratic sandstone, and gray 
coarse-grained sandstone.  Also includes some siltstone and 
claystone.  Clasts contain mostly graywacke, chert, and 
metamorphic rocks probably derived from the Franciscan 
complex. 

	Mullholland Formation of Ham (1952) (late Miocene and 
Pliocene).  Divided into upper and lower members, outcrop of 
the upper member is restricted to Contra Costa County.
Tmll		Lower member; sandstone and mudstone.  Includes 
	sandstone marker beds (Tmls), mapped locally.

Tus	Unnamed sedimentary and volcanic rocks (late Miocene).  
Includes conglomerate, sandstone, siltstone, and limestone 
(Tusl) mapped locally.

Tn	Neroly Sandstone (late Miocene).  Blue, gray, and brown, 
volcanic - rich, shallow marine sandstone, with minor shale, 
siltstone, tuff, and andesitic conglomerate. 

Tbr	Briones Formation (middle and late Miocene).  Sandstone, 
siltstone, conglomerate and shell breccia.  The Briones 
Formation in this assemblage contains a tuffaceous layer with 
a K/Ar age of 14.5+0.4 Ma (Lindquist and Morganthaler, 
1991).  
	Divided locally into:
Tbi		I member of Wagner (1978).  Massive feldspathic 
		sandstone.
Tbg		G member of Wagner (1978).  Massive sandstone, pebble 
		conglomerate, and shell breccia.  Locally subdivided into:
Tbgc			Conglomerate.
Tbgl			Limestone.
Tbf		F member of Wagner (1978).  Fine -grained feldspathic 
		sandstone and locally prominent brown shale.
Tbe		E member of Wagner (1978).  Medium - grained 	
		sandstone with abundant shell breccia beds; lithologically 
		similar to unit Tbg.
Tbd		D member of Wagner (1978).  Massive, medium - grained 
		sandstone with local conglomerate layers.

Tro	Rodeo Shale, Hambre Sandstone, Tice Shale, and Oursan 
Sandstone, undivided (middle Miocene)

Tr	Rodeo Shale (middle Miocene).  Brown siliceous shale with 
yellow carbonate concretions.

Th	Hambre Sandstone (middle Miocene).  Massive, medium - 
grained sandstone, weathers brown.

Tt	Tice Shale (middle Miocene).  Brown siliceous shale

To	Oursan Sandstone (middle Miocene).  Greenish gray, medium 
- grained sandstone with calcareous concretions.

Tcs	Claremont Shale (middle Miocene).  Brown siliceous shale 
with yellow carbonate concretions and minor interbedded 
chert.  Also includes interbeds of light gray and white quartz 
sandstone and siltstone (Tccs) mapped locally.

Ts	Sobrante Sandstone (middle Miocene).  Massive white, 
medium - grained calcareous sandstone.

	Great Valley sequence (Cretaceous)

Ku	Unnamed sedimentary rocks (Late Cretaceous, Cenomanian 
and Turonian).  Massive to distinctly bedded, biotite bearing, 
brown weathering, coarse- to fine-grained graywacke and 
lithic wacke, siltstone, and mudstone.  Also contains lenses of 
pebble to boulder conglomerate (Kc), mapped locally.

Assemblage V -

QTl	Livermore gravels (Pliocene and Pleistocene).  Poorly to 
moderately consolidated, indistinctly bedded, cobble 
conglomerate, gray conglomeratic sandstone, and gray 
coarse-grained sandstone.  Also includes some siltstone and 
claystone.  Clasts contain mostly graywacke, chert, and 
metamorphic rocks probably derived from the Franciscan 
complex. 

Tgvt	Green Valley and Tassajara Formations of Conduit (1938), 
undivided (Pliocene and Miocene).  Non - marine sandstone, 
siltstone, and conglomerate.  A 5 meter thick tuff marker bed 
(Tgvtt) is mapped locally.  This tuff is correlated with the 
Pinole Tuff of Assemblage II, which has a K/Ar age of 5.2+0.1 
Ma.  Another tuff in this unit has a K/Ar age of 4.0+1.0 Ma, 
while a tuff layer lower in the unit has been correlated with 
the Roblar tuff in Sonoma County which has K/Ar ages of 
5.7+0.5 Ma and 6.1+0.1 Ma (Sarna-Wojcicki, 1976).

Tn	Neroly Sandstone (late Miocene).  Brown, massive, marine 
sandstone with abundant clasts of volcanic rocks.

Tc	Cierbo Sandstone (late Miocene).  Light - gray, massive 
sandstone with marine fossils.  Contains sandstone and 
conglomerate near the base.

Kss	Unnamed sandstone (Late Cretaceous, Campanian and 
Maastrichtian).  Massive to distinctly bedded, coarse- to fine-
grained, biotite- and quartz-bearing lithic wacke and 
siltstone.  Also includes lenses of pebble to cobble 
conglomerate and minor amounts of mudstone.

Kslt	Unnamed siltstone (Late Cretaceous, Campanian).  Siltstone 
interbedded with minor shale, claystone, and sandstone.

Ku	Unnamed mudstone (Late Cretaceous, Cenomanian and 
Turonian).  Massive to distinctly bedded, gray mudstone and 
fine siltstone.  Also includes minor amounts of biotite- and 
quartz-bearing lithic wacke.

	Coast Range ophiolite (Jurassic).  Consists of:

Jb		Massive basalt and diabase

Jgb		Gabbro and diabase

sp		Serpentinite

Assemblage VI

Tol	Oro Loma Formation of Briggs (1953) (Pliocene).  Poorly 
consolidated reddish silt, sand, and gravel.

Tn	Neroly Sandstone (late Miocene).  Blue sandstone, minor 
siltstone, shale, tuff, and andesite-pebble conglomerate.

Tc	Cierbo Sandstone (late Miocene).  Distinctly thick-bedded, 
fine- to coarse-grained, moderately consolidated, light gray 
to white quartz sandstone with minor lithic and biotite 
grains.  Locally the unit contains beds of highly fossiliferous, 
coarse-grained sandstone.  The fossils are predominantly of 
the genus Ostrea.  The unit also contains minor pebble 
conglomerate locally.

	Great Valley sequence (Cretaceous).  In Alameda County, the 
sequence in this Assemblage consists of:

Kel	Unit E, lower member (Late Cretaceous).  Light gray to gray-
brown, foraminifer bearing siltstone and mudstone.  
Reddish-brown weathering and iron concretions are 
conspicuous.

Kd	Unit D - Sandstone (Late Cretaceous).  Medium to coarse 
grained, light gray, clean sandstone.  Grains include quartz, 
feldspar, and biotite.  Spherical weathering is common.  In 
places the clean sandstone is interbedded with fine to 
medium grained, biotite and muscovite bearing wacke with 
mudstone rip-up clasts.  Sandstone beds form packages up 
to 10 meters thick with 1 to 2 meters of interbedded 
siltstone and mudstone.  The unit also locally includes:
Kds	Shale member.  Brown to gray, micaceous mudstone and 
brown micaceous siltstone.  One layer is dark gray-brown 
to dark gray, massive, foraminifer rich, siliceous 
mudstone.

	Unit C - Sandstone and shale (Late Cretaceous).  Consists of:
Kcu	Upper member, shale and siltstone.  Also includes 
sandstone interbeds (Kcus) mapped locally.
Kcm	Middle member.  Medium grained, brown to gray, biotite 
rich wacke with some mudstone rip-up clasts.  Contains 
interbeds of siltstone, shale, and conglomerate.
Kcl	Lower member, shale and siltstone with minor sandstone.  
Also includes sandstone interbeds (Kcls) mapped locally.

Kbsh	Unit B, shale member (Late Cretaceous).  Olive-gray 
mudstone and micaceous siltstone.  Forms reddish soil.  
Contains sandstone interbeds.


Assemblage VII

QTi	Irvington Gravels of Savage (1951) (Pliocene(?) and 
Pleistocene).  Poorly to well consolidated, distinctly bedded 
pebbles and cobbles, gray pebbly sand, and gray, coarse-
grained, cross-bedded sand.  Cobbles and pebbles are well- to 
sub-rounded, and as much as 25 cm in diameter, and consist 
of about 60 percent micaceous sandstone, 35 percent 
metamorphic and volcanic rocks and chert probably derived 
from the Franciscan complex, and 5 percent black laminated 
chert and cherty shale derived from the Claremont 
Formation.  A large suite of early Pleistocene vertebrate 
fossils from this unit was described by Savage (1951).

QTl	Livermore Gravels (Pliocene and Pleistocene).  Poorly to 
moderately consolidated, indistinctly bedded pebbles and 
cobbles, gray pebble and cobble bearing sand, and gray, 
coarse-grained sand.  This unit is similar to the Irvington 
Gravels, but lacks clasts derived from the Claremont 
Formation.

Tv	Unnamed volcanic rocks (late Miocene and/or Pliocene).  
White to gray rhyolite, dacite, and andesite tuff, breccia, and 
volcanoclastic conglomerate, and massive, black and red, 
plagioclase, pyroxene, and olivine porphyry basalt.

Tor	Orinda Formation (late Miocene).  Distinctly to indistinctly 
bedded pebble to boulder conglomerate, conglomeratic 
sandstone, and coarse- to medium-grained lithic sandstone.  
Conglomerate clasts include red, green, and black chert, 
quartzite, greenstone, diorite, lithic sandstone, and minor 
andesite.  The formation contains interlayered plagioclase 
porphyry dacite (Torv), mapped locally.

Tbr	Briones Formation (late Miocene).  Distinctly to indistinctly 
bedded, gray and white, fine- to coarse-grained, quartz-lithic 
sandstone and shell breccia.  Pebble and cobble conglomerate 
lenses are present in a few places.  Conglomerate clasts 
include black and red chert, quartzite, andesite, argillite, 
siltstone, basalt, felsic tuff, and quartz.  The formation also 
includes distinct, thin interbeds of hard white to light gray 
sandstone and gray siltstone near its base. 

Tt	Tice Shale (middle or late Miocene).  Distinctly bedded, dark 
brown, gray, and tan siltstone, mudstone, and siliceous shale.  
The shale contains numerous fish scales and poorly 
preserved foraminifers in places.  Bright orange weathering 
lenses of tan dolomite are present in the shale locally.

To	Oursan Sandstone (middle or late Miocene).  Distinctly 
bedded black mudstone, and foraminifer bearing, brown to 
tan siltstone and fine-grained sandstone.  The unit also 
contains large (as much as 2 meters long) lenses of bright 
orange weathering, tan dolomite, similar to those found in 
the overlying Tice Shale.  The Oursan Sandstone in 
Assemblage VII occupies the same stratigraphic position as 
the type Oursan in Contra Costa County, but differs from the 
type in color, presence of dolomite lenses, and absence of 
invertebrate fossils.

	Claremont Formation (middle and/or late Miocene).  Divided 
informally into:
Tcs	Chert and siliceous shale member.  Distinctly bedded, 
massive, gray and black, laminated chert, and dark brown to 
gray, finely laminated siliceous shale.  Some of the shale 
contains poorly preserved fish scales and foraminifers.  
Bright orange weathering lenses of tan dolomite occur locally.  
This unit is distinguished from the overlying Tice Shale by 
the presence of chert beds and lack of non-siliceous 
mudstone.
Tccs	Sandstone and siltstone member.  Light brown, gray, and 
white, fine-grained quartz sandstone and siltstone.

Ts	Sobrante Sandstone (middle Miocene).  White, fine- to 
medium-grained quartz sandstone.

Tsh	Unnamed shale, sandstone, chert and dolomite (early 
Miocene).  Massive, orange weathering, medium-grained 
quartz sandstone, interbedded laminated gray chert and 
dolomite, dark gray, concretionary siltstone and mudstone, 
and conglomerate.  Conglomerate contains pebbles of 
varicolored chert, andesite, and quartzite in a dolomite 
matrix.

	Tolman Formation of Hall (1958) (Eocene?).  Divided into:
Ttls	Gray, algal limestone, interbedded with white, 
calcium carbonate matrix pebble conglomerate, and 
clean, medium- to coarse-grained sandstone with 
calcite cement.  Sandstone grains include quartz, 
feldspar, and lithic fragments, and in places include 
a large percentage of algal debris.  Sandstone 
weathers orange.

Tts	Dark gray to dark greenish-gray, indistinctly 
bedded, glauconite bearing, medium- to coarse-
grained lithic sandstone.  Locally interbedded with 
minor amounts of fine-grained sandstone and 
siltstone.
	The Tolman Formation is bounded above by a fault.  It 
overlies Redwood Creek Formation sandstone and Pinehurst 
shale along an obscured contact.

Tps	Unnamed siltstone and sandstone (Paleocene).  Dark gray, 
indistinctly to distinctly bedded siltstone, claystone, and 
shale, in places containing abundant, poorly preserved 
foraminifers.  Grades downward into indistinctly bedded, 
dark brown to green, coarse-grained, glauconite bearing lithic 
sandstone.

	Great Valley sequence (Late Jurassic to Late Cretaceous).  In 
Assemblage VII, the sequence consists of:

Kp	Pinehurst Shale (Late Cretaceous, Campanian).  Siliceous 
shale with interbedded sandstone and siltstone.  This unit 
also includes maroon, concretionary shale at base.  This 
formation was originally considered to be Paleocene, but 
it contains foraminifers and radiolarians of Campanian 
age in its type area and throughout its outcrop extent.

Kr	Redwood Canyon Formation (Late Cretaceous, 
Campanian).  Distinctly bedded, cross-bedded to massive, 
thick beds of fine- to coarse grained, biotite and quartz-
rich wacke and thin interbeds of mica rich siltstone.  This 
formation is conformably overlain by the Pinehurst Shale.

Ksc	Shephard Creek Formation (Late Cretaceous, Campanian).  
Distinctly bedded mudstone and shale, mica rich siltstone, 
and thin beds of fine-grained, mica-rich wacke.  This 
formation is conformably overlain by the Redwood 
Canyon Formation.

Kcv	Unnamed sandstone, conglomerate, and shale of the 
Castro Valley area (Late Cretaceous, Turonian and 
younger(?)).  The lower part of the unit is composed of 
distinctly bedded, mica bearing siltstone, fine-grained 
mica bearing wacke, shale, and, locally, one thin pebble 
conglomerate layer.  The middle part of the unit is 
composed of distinct, thick beds of medium- to coarse-
grained, mica-rich wacke and pebble to cobble 
conglomerate.  The middle part grades upward into the 
upper part, which is composed of distinctly to indistinctly 
bedded, medium- to fine-grained, mica-rich wacke and 
siltstone.  This unit is bounded above and below by 
faults.

Ko	Oakland Sandstone (Late Cretaceous, Cenomanian and/or 
Turonian).  Massive, medium- to coarse-grained, biotite 
and quartz-rich wacke and prominent interbedded lenses 
of pebble to cobble conglomerate.  Conglomerate clasts 
are distinguished by a large amount of silicic volcanic 
detritus, including quartz porphyry rhyolite.  
Conglomerate composes as much as fifty percent of the 
unit in the Oakland hills, but it becomes a progressively 
smaller portion of the unit to the south.

Kjm	Joaquin Miller Formation (Late Cretaceous, Cenomanian).  
Thinly bedded shale with minor sandstone.  The shale 
grades into thinly bedded, fine-grained sandstone near 
the top of the formation.  The contact with the overlying 
Oakland Sandstone is gradational.

Ksh	Unnamed shale (Early Cretaceous)

Ks	Unnamed sandstone and shale (Cretaceous).  Distinctly 
bedded, gray to white, hard, in places cross-bedded, mica 
bearing, coarse- to fine grained sandstone, siltstone, and 
shale.  Sandstone is granitic (quartz, feldspar, and biotite 
grains) or lithic, and forms discontinuous outcrops on 
ridges and uplands.  Siltstone and shale outcrop only in 
canyons.

KJk	Knoxville Formation (Late Jurassic and Early Cretaceous).  
Mainly dark, greenish-gray silt or clay shale with thin 
sandstone interbeds.  Locally includes thick pebble to 
cobble conglomerate beds in its lower part (KJkc).  Locally 
at the base the formation contains beds of angular, 
volcanoclastic breccia (KJkv) derived from underlying 
ophiolite and silicic volcanic rocks.  The depositional 
contact of Knoxville Formation on ophiolite and silicic 
volcanic rocks can be observed at several locations in 
Alameda County.

Volcanic Rocks overlying Coast Range ophiolite

Jsv	Keratophyre and quartz keratophyre (Late Jurassic).  
Highly altered intermediate and silicic volcanic and 
hypabyssal rocks.  Feldspars are almost all replaced by 
albite.  In some places, closely associated with (intruded 
into?) basalt.  This unit includes rocks previously mapped 
as Leona and Northbrae rhyolite, erroneously considered 
to be Tertiary (Dibblee, 1980, 1981, Radbruch and Case, 
1967, Robinson, 1956).  Recent biostratigraphic and 
isotopic analyses have revealed the Jurassic age of these 
rocks (Jones and Curtis, 1991).  These rocks are probably 
the altered remnants of a volcanic arc deposited on 
ophiolite during the Jurassic Period.

Coast Range ophiolite (Jurassic).  Consists of:

Jpb	Pillow basalt, basalt breccia, and minor diabase.
Jb	Massive basalt and diabase.
Jgb	Gabbro 
sp	Serpentinite.  Mainly sheared serpentinite, but also 
includes massive serpentinized harzburgite.  In places, 
pervasively altered to silica carbonate rock.

Assemblage VIII

QTl	Livermore Gravels (Pliocene and Pleistocene).  Poorly to 
moderately consolidated, indistinctly bedded cobbles and 
pebbles, gray pebble and cobble bearing sand, and gray, 
coarse-grained sand.
Tlp	Unnamed freshwater limestone (Pliocene(?))

Tss	Unnamed sandstone (late Miocene and/or Pliocene).  
Distinctly to indistinctly bedded, poorly consolidated, white, 
fine-grained sandstone and siltstone, interbedded with 
diatomite, gray diatomaceous chert, and tan, freshwater 
limestone.

Tbr	Briones Formation (late Miocene).  Distinctly to indistinctly 
bedded, gray and white, fine- to coarse-grained, quartz-lithic 
sandstone and shell breccia.  Pebble and cobble conglomerate 
lenses are present in a few places.  Conglomerate clasts 
include black and red chert, quartzite, andesite, argillite, 
siltstone, basalt, felsic tuff, and quartz.  Shell breccia beds 
form erosion resistant ridges and peaks.

Tt	Tice Shale (late Miocene).  Thin, distinct beds of dark brown 
shale and claystone.  Weathers reddish brown.

To	Oursan Sandstone (late Miocene).  Indistinctly bedded, fine- 
to medium-grained, olive sandstone, siltstone and claystone.  

Ks	Unnamed sandstone and shale (Cretaceous).

Assemblage IX

Tbr	Briones Formation (late Miocene).  Distinctly to indistinctly 
bedded, gray and white, fine- to coarse-grained, quartz-lithic 
sandstone and shell breccia.  Pebble and cobble conglomerate 
lenses are present in a few places.  Conglomerate clasts 
include black and red chert, quartzite, andesite, argillite, 
siltstone, basalt, felsic tuff, and quartz.  Shell breccia beds 
form erosion resistant ridges and peaks.

Tt	Tice Shale (late Miocene).  Thin, distinct beds of dark brown 
shale and claystone.  Weathers reddish brown.

To	Oursan Sandstone (late Miocene).  Indistinctly bedded, fine- 
to medium-grained, olive sandstone, siltstone and claystone.  
Pebble and shell fragment conglomerate is present near the 
base.  

Tcc	Claremont Formation (middle and/or late Miocene).  
Distinctly bedded, massive, gray and black, laminated chert, 
and dark brown, black, or gray, finely laminated siliceous 
shale.  Some of the shale contains poorly preserved fish 
scales and foraminifers.  The unit also contains locally 
interbedded, light colored, calcareous sandstone, and 0.3 to 2 
meter thick beds of limestone.

Ttem	Temblor Sandstone (middle Miocene).  Thickly and 
indistinctly bedded, olive, fine- to coarse-grained sandstone 
and pebble conglomerate.  Vertebrate and invertebrate 
fossils are common in many parts of this unit.  The Temblor 
Sandstone unconformably lies on the Franciscan melange in 
this Assemblage.

Assemblage X

Tn	Neroly Sandstone (late Miocene).  Medium-grained, blue, 
quartz, feldspar, and mica-bearing sandstone.  This unit also 
contains green, glauconite bearing, pebble conglomerate 
layers, mapped locally (Tnc).

Tbr	Briones Formation (late Miocene).  Distinctly to indistinctly 
bedded, gray and white, fine- to coarse-grained, quartz-lithic 
sandstone and shell breccia.  Pebble and cobble conglomerate 
lenses are present in a few places.  Conglomerate clasts 
include black and red chert, quartzite, andesite, argillite, 
siltstone, basalt, felsic tuff, and quartz.  Shell breccia beds 
form erosion resistant ridges and peaks.  This unit 
unconformably overlies Franciscan greenstone (KJfg) and 
melange (KJfm) in the east part of this Assemblage.

Assemblage XI

Tol	Oro Loma Formation of Briggs (1953) (Pliocene).  Poorly 
consolidated reddish silt, sand, and gravel.

Tn	Neroly Sandstone (late Miocene).  Blue sandstone, minor 
siltstone, shale, tuff, and andesite rich pebble and boulder 
conglomerate.

Tc	Cierbo Sandstone (late Miocene).  Distinctly thick-bedded, 
fine- to coarse-grained, moderately consolidated, light gray 
to white quartz sandstone with minor lithic and biotite 
grains.  Locally the unit contains beds of highly fossiliferous, 
coarse-grained sandstone.  The fossils are predominantly of 
the genus Ostrea.  The unit also contains minor pebble 
conglomerate locally.

Tte	Tesla Formation (Eocene).  White and buff sandstone, 
siltstone, anauxitic claystone, and carbonaceous shale, with 
minor coal.

Great Valley sequence (Cretaceous).

Ksuh	Unnamed shale (Late Cretaceous).

Ksus	Unnamed sandstone (Late Cretaceous).

Ksu	Unnamed sandstone and shale (Late Cretaceous).

Kkh	Horsetown Formation of Huey (1948) (Early Cretaceous).  
Dark shale and thin beds of sandstone.



Sources of Data

1.	New mapping by the authors, 1992-1995 using maps and 
information in the following reports as a foundation:  Blake 
and others (1974), Dresen (1979), Whiteley (1978), 
Lienkaemper (1992), Turnbull (1976), Herd (1978), Hall 
(1958), Robinson (1956), Radbruch (1969), Case (1968), 
Radbruch (1957), California Division of Mines and Geology 
(1972-1989),  Dibblee (1972, 1973, 1980b, d-h, l, 1981a-b), 
Estes and others (1983), Liniecki (1983), Graham and others 
(1983), Hill (1983), Bauder (1975), Bauder and Liou (1978), 
Cotton (1972), Crawford (1976), Gokce (1978), Perkins 
(1974), and Aarons (1958).

2.	Wagner (1978), Haltenhoff (1978), Dibblee (1980e-f, h), 
California Division of Mines and Geology (1982c), and some 
new mapping by the authors (1992-95).

3.	Dibblee (1980i), Herd (1977a), California Division of Mines 
and Geology (1982d), and some new mapping by the authors 
(1995).

4.	Dibblee (1980m)

5.	Sonneman and Switzer (unpublished maps, EXXON, 1961-62), 
Sweeney and Springer (1981), Carpenter and others (1980), 
Carpenter and others (1984), Dibblee (1980a), California 
Division of Mines and Geology (1982a), and some new 
mapping by the authors (1995).  See also Huey (1948), Herd 
(1977a), and Oakshott (1980).

6.	Sonneman and Switzer (unpublished maps, EXXON, 1961-62), 
Huey (1948), California Division of Mines and Geology 
(1982b), and some new mapping by the authors (1995).  See 
also Dibblee (1980c, j), Throckmorton (1988), and Brabb and 
others (1971).

7.	Atchley and Dobbs (1960).  See also Snetsinger (1976).

8.	Graymer and others (1994).  See also Dibblee (1980k), Hall 
(1958), California Division of Mines and Geology (1980), and 
Herd (1977b).


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