THE MARINE TERTIARY OF THE WEST COAST 589 
Jurassic. To the west there was a positive area covering the 
present western side of the Coast: ranges of middle California. 
Apparently throughout the entire Eocene period this area to the 
west was a positive block; the absence of either continental or 
marine deposits in this area is the chief basis for the conclusion. 
Fic. 2.—Martinez (Lower Eocene) 
The smaller positive and negative areas which existed during the 
Oligocene, Miocene, and Pliocene in this western area were not 
differentiated during the Eocene. 
One of the most permanent positive areas of the Tertiary was 
that which existed in the region now occupied by the Tehachapi 
and San Emigdio Mountains (Fig. 1). This area formed the east— 
west peninsula which separated the northern from the southern 
basins. The extent of this peninsula varied considerably during 
the different epochs of deposition. The area now covered by the 
