THE MARINE TERTIARY OF THE WEST COAST 601 
Monterey series, the San Pablo is divisible into minor units on the 
basis of stratigraphy and fauna. The faunal changes and discon- 
formable relationships of the beds indicate that the sea advanced 
and retreated three times in middle California, during this period. 
It is only in middle California that we find the complete sequence 
of the Upper Miocene series. The two lower divisions of the San 
Fic. 6.—Vaqueros (lower Monterey, Miocene) 
Pablo series, the Briones and Cierbo groups," have been recognized 
only in the general region of San Francisco Bay. 
Stratigraphic relationships.—In certain sections immediately east 
of or in the Salinas Valley, a distance of not more than too miles 
1 The use of the term San Pablo for the Upper Miocene series of deposits on the 
West Coast makes it necessary to dispense with the term San Pablo within the group. 
The name Cierbo is therefore used in this paper in referring to the middle group of 
the San Pablo series. The type section of the Cierbo is in the south side of the Canada 
del Cierbo near Carquinez straits. Santa Margarita is a name in common use for 
the upper portion of the section in the southern part of the state of California and 
will be applied as a general name for the upper member of the San Pablo series. 
