‘THE MARINE TERTIARY OF THE WEST COAST 593 
Climate.—The temperature conditions during the Oligocene time 
were fairly uniform along the West Coast as far north as Alaska. 
The waters of the Lower Oligocene, judging from the molluscan 
fauna, were subtropical to warm-temperate, while those of the 
Upper Oligocene sea were more temperate.t Thus the fauna of 
the San Lorenzo horizon (Upper Oligocene) is more closely related 
to that living off the coast of California, Oregon, and Washington 
at the present time than it is to that of the Lincoln. 
Paleogeography.—The distribution of the Lower Oligocene 
deposits (the Lincoln horizon) (Fig. 5) corresponds closely to that 
of the Tejon (Upper Eocene). In California there was a long 
inland trough corresponding closely to, though somewhat wider 
than, the present Great Valley of California. The presence of 
great thicknesses of organic shales of the Kreyenhagen formation, 
from which the oil of the Coalinga field is derived, indicates that 
the deepest portion of the Lower Oligocene trough was along the 
western border of the present San Joaquin Valley. 
The distribution of the Upper Oligocene (San Lorenzo) is very 
different from that of the Lower Oligocene. In California there 
were two limited basins of deposition, one in middle California in 
the vicinity of San Francisco, and one in the region of the southern 
end of the San Joaquin Valley. 
A fauna referred to the Oligocene which may be Upper Eocene.— 
The fauna of the Tejon (Upper Eocene) of the West Coast, as has 
already been stated, can probably be correlated with the upper 
Claiborne horizon of the Eocene of the Gulf province, but whether 
or not there is a fauna on the West Coast that is equivalent to 
the Jackson horizon of that province can only be proved by further 
detailed study. ; 
The possibility of referring the Molopophorus lincolnensis zone, 
now considered Lower Oligocene, to the Jackson stage has been 
considered. Dr. C. E. Weaver has listed a number of species 
tR. E. Dickerson, ‘‘Climate and Its Influence upon the Oligocene Faunas of 
the Pacific Coast,” Proc. Cal. Acad. Sci., Fourth Series, Vol. VII (1917), No. 6, 
PP. 157-92. 
2R. W. Anderson and R. W. Pack, ‘‘Geology and Oil Resources of the West 
Border of the San Joaquin Valley North of Coalinga, California,” U.S. Geol. Surv. 
Bull. 603 (1915), pp. 74-78. 
