Santa Clara valley : sespe formation. 
11 
RELATION OF UPPER SESPE BEDS TO VAQUEROS SHALE. 
No sharp lines of distinction separate the upper Sespe terrane from 
the underlying red beds or the overlying Vaqueros. On the contrary, 
there is a perceptible tendency for the terranes to shade one into 
another. Fossils of value have not yet been collected from this tran¬ 
sitional zone. There is, therefore, some uncertainty as to whether 
the beds in question should be referred to the Eocene or the Miocene. 
The red beds proper are commonly regarded as of Eocene age. In 
Sespe Canyon fragments of grayish-yellow sandstone, coming either 
from some horizon unrecognized but well up in the red beds or from 
a horizon corresponding to that of the rusty beds just described, have 
been found bearing well-marked Eocene fossils, among which are the 
forms Venericardia planicosta Lamarck (PI. XXV, fig. 1) and Turri- 
tella uvasana Conrad (PI. XLI, figs. 2 and 3). Beds of a similar 
nature, with an abundance of Tejon (Eocene) fossils, also occur along 
the northern edge of the Silver Thread oil field, west of Santa Paula 
Canyon, overlying certain pink and gray sandstones that are believed, 
on lithologic grounds, to belong to the Sespe. The following species 
have been found at this locality. With one exception they were iden¬ 
tified by the late J. G. Cooper.® 
Sespe ( Eocene) fossils from north side of Sisar Creek, west of Santa Paula Creek . 
Anatina sp. 
Cardium linteum Conrad. 
Corbula n. sp. 
Dentalium cooperi Gabb. 
Leda gabbi Conrad. 
Leda n. sp. 
Meretrix californiana Conrad. 
Nassa cretacea Gabb. 
Neaera dolabriformis Gabb. 
Nucula truncata Gabb. 
Nucula solitaria Gabb. 
Pecten calkinsi Arnold. 
Pecten interradiatus Gabb. 
Solen parallelus Gabb. 
Spirocrypta pileum Gabb. 
Tellina hoffmaniana Gabb. 
Tellina longa Gabb. 
Tellina parilis Gabb. 
Thracia semiplanata Whiteaves. 
Turbonilla n. sp. 
Yoldia arata Whiteaves. 
Yoldia nasuta Gabb. 
It may be, therefore, that the rocks in question represent the upper¬ 
most member of the Eocene in the region of the Santa Clara and the 
mountains to the north. On the other hand, the resemblance of sev¬ 
eral of the beds of this transitional zone to others a little higher in 
horizon, that bear identified Oligocene or lower Miocene forms, is to 
be borne in mind. To determine satisfactorily the limits not only of 
this, but of all the other formations in the Santa Clara district, a large 
amount of field work will be required. The difficulty will be enhanced, 
too, by the highly disturbed condition of the rocks and the compli¬ 
cated structural relations which they bear one to another, unless 
distinctly characteristic fossils are found to correlate the beds of the 
a Bull. California State Mining Bureau No. 11, 1897, pp. 84-85. 
