Vol. 6] Jones: The Geology of the Sargent Oil Field. 



65 



Faulting of the Monterey shale is frequent. The numerous 

 small faults were not mapped. The active San Andreas fault 

 cuts, of course, all the formations of the region through which 

 it passes. The Pescadero anticline is broken down by a fault 

 of considerable magnitude with the downthrow on the north. 



SAN PABLO FORMATION. 



The San Pablo formation is by far the most interesting 

 terrane in the region studied. The section is accessible and well 

 developed and its stratigraphic relations to both the underlying 

 and overlying formations are exceedingly clear in the field. The 

 writer very much regrets that time and lack of knowledge of 

 Coast Kange faunas prevented him from making a closer 

 palaeontological study of this formation as here developed. 



The formation is called the San Pablo because it possesses 

 the widespread lithologic characteristics and the structural 

 relations of that formation noted elsewhere. 



The tj^pical azure blue sandstones are here prominent and 

 well developed. It is believed that this formation is the equiva- 

 lent of most, if not all, of the Santa Margarita, Jacalitos, and 

 Etchegoin formations described by R. Anderson 7 . 



For purposes of discussion and the better to illustrate 

 structure in mapping, the San Pablo formation is here divided 

 upon a lithologic basis into five divisions: A, B, C, D, and E. 

 This division is not expected to stand from a stratigraphic 

 point of view but is simply made for convenience. That the 

 formation is divisible into members on palaeontologic grounds 

 is certain and a more detailed study of the fossil horizons in 

 this region may lead to a convenient and permanent subdivision. 



The different members, especially the lower ones, vary in 

 thickness ; so that while the maximum thickness of the formation 

 as a whole is about 1200 feet, taking the maximum thickness of 

 each of the five members the total thickness is 3000 feet in this 

 region. 



Member A. — This member consists of a series of coarse con- 

 glomerates and dark brown, in some cases almost black, sand- 

 stones. Exposed surfaces of these beds are light gray in color. 



- U. 8. Geol. Surv., Bull. No. 357, 1908, pp. 35-55. 



