Vol. VII] GESTER— GEOLOGY McKITTRICK DISTRICT 219 



porous Etchegoin sands separated by occasional shales or 

 marls and (werlain by clays of the Tulare naturally form ex- 

 cellent reservoirs for the accumulation of oil. 



Shale Series: Santa Margarita (?) 



Beneath the Etchegoin and occupying the a])ex of the anti- 

 cline is a series of organic shales. As previously stated the 

 shales may belong either to the Santa Margarita or to the 

 Monterey or to both. Both of these formations can be recog- 

 nized along the Mt. Diablo Range and both of theiu contain 

 organic shales, but from the general stratigraphic sequence, 

 the beds underlying the Etchegoin around McKittrick are 

 tentatively classed as Santa Margarita. The Santa Margarita 

 consists of a series of crushed and sharply folded silicious and 

 organic shales which in this area occupy a small depression 

 through the central part of Sec. 28 and across the S. \V. 34 

 Sec. 27 into the N. W. ^4 of 34. Westward through Section 

 29 the area widens out and joins the mass of organic shales 

 which forms the mass of the Temblor Range west of Mc- 

 Kittrick and Sunset. As only a small portion of the series is 

 exposed in this area no attempt was made to determine its 

 thickness, and the shales are furthermore so broken and so 

 uniform in quality that no statement of lithological secpience 

 is possil)le. Westward from McKittrick these shales are a 

 mile or more in thickness and within the area described there 

 are several hundred feet of uniformly bedded white shales ex- 

 posed. Interstratified with these shales are numerous thin 

 beds or hard calcareous layers. These limy beds are more 

 abundant in the lower part of the shale series than in the 

 upper. 



RELATIONS TO PETROLEUM 



In the upper part of the Santa Margarita the shales are fre- 

 quently found to be very white on the surface, but when 

 broken the fresh exposures are a dull chocolate color due to 

 the presence of bituminous matter. 'Jliis is usually found to 

 be very dry, but in one or two instances oil was found in 

 small vugs or holes in chunks of a very hard silicious shale. 

 The shale is frequently \'ery diatomaceous, in which casts of 



