Vor. IIT] ANDERSON—FURTHER STRATIGRAPHIC STUDY 5) 
Coalinga, and elsewhere, the Pleistocene peneplains have been 
extensively dissected by recent stream erosion and their de- 
posits are left covering the mesa-like ridges or hills interven- 
ing between stream valleys. In such cases it is not unusual 
to find unstratified deposits of boulders covering the top of a 
ridge, or even resting cap-like on the crest of a conical hill. 
Among the boulders and pebbles of these deposits may be 
recognized fragments of all the earlier marine deposits of 
the range including metamorphics, Cretaceous sandstones, 
Eocene and Miocene limestones, and even many fragments of 
the immense oysters of the Coalinga beds as well as later 
fossils. 
The fragments of Ostrea titan have often proved mislead- 
ing to prospectors who have regarded them as a guide for the 
location of oil sands, with which, in their original position, 
they are often associated. 
In those deposits that are most clearly of Pleistocene origin, 
it is apparent that there is an unconformable relation between 
them and the underlying formations, and that a period of 
erosion has intervened. In other words, much of the denuda- 
tion and base-leveling has antedated the boulder deposits. 
_ These deposits are associated with, or more properly include, 
extensive beds of asphaltum at both McKittrick and Sunset; 
and in these asphaltum beds have been found the remains of 
a number of Pleistocene mammals, including the elephant, the 
horse, and an extinct species of wolf, doubtless representing 
a fauna belonging to the latter part of the Pleistocene period. 
It is evident, therefore, that it is to the early or middle epochs 
of the Pleistocene that the most extensive denudation is due. 
STRATIGRAPHIC RELATIONS 
As a result of more extended study and closer attention to 
details it is found to be desirable to revise in some points the 
stratigraphic classification offered in the preceding paper; 
although as there stated, the essentials are fairly well shown. 
Undoubtedly there is evidence of unconformity between the 
