28 CALIFORNIA ACADEMY OF SCIENCES [Proc. 47u Ser. 
In their general features, faunal and other, the Coalinga 
beds resemble the San Pablo beds to some extent; and it is 
not impossible that in part the two may be equivalent, though, 
as will be shown later, it is hardly probable. 
THE PLIOCENE SERIES 
The Etchegoin Beds.—It is quite possible in many parts 
of the Mount Diablo range to recognize a marine series later 
than, if not always distinct from,’all of the preceding. This 
is the series called in the former paper the “Etchegoin Beds”. 
It must be admitted that no sharply defined line separates this 
series from that last described, though evidence is not lacking 
of a change in the physical conditions of their deposition. 
Generally the strata of the Etchegoin beds are conform- 
able in position with those of the Coalinga, and there is no 
great change in the lithology, such as is seen in some of the 
earlier formations. One of the most conspicuous character- 
istics of the later series is an enormous amount of bluish gray 
sand which is distributed throughout almost its entire length 
and thickness. In this feature these beds contrast strongly 
with the yellow or light brown sands of the Coalinga and 
earlier series. From its fauna it may be more easily recognized 
within limits, though there are species that continue upward 
from the Coalinga, and as yet there are not many species that 
individually are to be regarded as a sure sign of the Pliocene 
throughout the Coast or even the State. The exact thickness 
of the Etchegoin beds has not been measured at any point, 
though it has been estimated at a few places. West of the 
town of Coalinga it is hardly less than 1400 feet in the out- 
crop, but in some of the wells drilled along the base of the 
hills it must be somewhat less. Farther north, near the eastern 
part of the field, the thickness is greater, as seen both in the 
outcrop and in the wells, where the aggregate is not less than 
2500 feet, and may be more. North of the Avenal wells, 15 
miles southeast of Coalinga, the thickness is probably as great 
as 3500 or even 4000 feet. Bluish gray sands usually make 
