TERTIARY DEPOSITS NEAR COALINGA OIL FIELD BL 
is sharply defined. ‘There are numerous borings in the top of the 
Chico sandstone which are filled with the fine gravel and sand of 
the Martinez, and covering the surface is a layer of glauconitic 
sandy material.with imprints of small shells, which is the base 
of the Martinez. This grades upward into the sands and sandy 
shales with concretions and nests of Martinez fossils. 
With this section in mind, the tracing of the contact in the area 
north of Coalinga is not so difficult. The top of the Chico comprises 
purple shales and concretionary sands, and the base of the Martinez, 
while of much more argillaceous character than at Oil Canyon, is 
yet distinct. 
MARTINEZ FORMATION 
To Messrs. Stanton, Merriam, Weaver, and Dickerson’ is due 
the credit of demonstrating in the Mount Diablo region the exist- 
ence below the Tejon of a series of beds of Eocene age, which is 
clearly distinguishable from that terrane by its characteristic fauna 
and unconformable relationship. This has been named _ the 
Martinez, but only meager accounts of its stratigraphy are available 
and its existence was recognized at only a few localities. 
Our work now proves that this lower member of the Eocene is 
of very considerable extent southward on the west side of San 
Joaquin Valley; that it consists of three or more clearly defined 
members, and that, in addition to the unconformity already 
described between it and the Cretaceous, there also exists a decided 
unconformity between it and the overlying Tejon. 
The Martinez is well developed in Townships 17 and 18 South, 
Ranges 13 and 14 East, in the Salt Creek-Cantua region, and com- 
prises a basal bed of chocolate shales with glauconitic sands over- 
lain by yellow sands and conglomerates and these overlain in turn 
by other chocolate shales. The generalized section of the Martinez 
in this particular area may be stated as follows: 
*T. W. Stanton, ‘‘The Faunal Relations of the Eocene and Upper Cretaceous 
on the Pacific Coast,” 17th Rep. U.S. Geol. Survey (1895-96), pp. 1011-60. 
J. C. Merriam, “‘The Geologic Relations of the Martinez Group of California 
at the Typical Locality,’ Jour. Geol., V (1897), 767-75. 
C. E. Weaver, ‘Contribution to the Paleontology of the Martinez Group,”’ 
Univ. Calif. Publ. Bull. Dept. Geol., TV (1905), 101-23. 
Roy E. Dickinson, “Stratigraphic and Faunal Relations of the Martinez Forma- 
tion to the Chico and Tejon North of Mt. Diablo,” Univ. Calif. Publ. Bull. Dept. 
Geol., VI (1911), 171-77. 
