PETROLEUM RESOURCES AND INDUSTRIES 

 The principal formations involved in the Cali- 

 fornia oil districts, in order of age, beginning with 

 the oldest, are: 



Jurassic or pre- Jurassic crystalline rocks; occurrence of 

 oil rare. 



Franciscan formation, probably of Jurassic age, of meta- 

 morphosed sediments with associated serpentine dikes; 

 very minor quantities of oil in northern California. 



Knoxville-Chico Cretaceous conglomerate, sandstones, and 

 shales; commercial quantities of paraffine-asphalt base 

 oil at Coalinga. 



Tejon or Eocene sandstone and shale; minor quantities 

 of paraffine oil at Coalinga. 



Sespe or Oligocene red conglomerate, sandstone and shale; 

 commercially petroliferous in Ventura County. 



Vaqueros, lower Miocene, and Monterey, middle Miocene, 

 sandstones and shales; the reservoir for much of the 

 oil in the Coalinga, Santa Maria, Santa Clara Valley 

 and Puente Hills districts. 



Fernando and equivalent formations, upper Miocene- 

 lower Pilocene, conglomerates, sandstones and shales; 

 carrying commercial quantities of oil in nearly every 

 district in the State. 



The great bulk of the oil comes from the Miocene forma- 

 tions. 



ORIGIN OF THE OIL. The oils of the California 

 fields are believed to have been derived largely 

 from the organic shales which are associated with 

 the oil-bearing beds in all of the fields of the State. 

 It is believed that the oil originated from the organic 

 matter, both vegetable and animal, once contained 

 in these beds. Probably the principal source of the 

 oil has been the diatomaceous deposits, which make 

 up a large percentage of the Tejon or Eocene forma- 

 tion in the Coalinga district, and the Monterey or 

 lower Miocene formation throughout the balance of 

 the districts. Other organisms that may also be the 

 source of some of the oil are plants, foraminifera, 

 bryozoa, and possibly molluscs and fish. A great 

 deal of evidence can be advanced favoring the 

 organic origin of the oil in California, and enough 

 demonstrating the impossibility of its inorganic 

 origin locally to practically prove the former theory 

 by the process of elimination. 



RELATION OF GEOLOGIC STRUCTURE TO OIL DE- 

 POSITS. Commercial quantities of petroleum occur 

 at one place or another in the California oil fields 

 in practically every form of geologic structure 

 known to the Coast Ranges. When it is remembered 

 that the Coast Ranges of this State afford some very 

 involved folds and faults, complicated by igneous 

 intrusions, the significance of this statement is 

 apparent. In the San Joaquin Valley fields the 

 occurrences are usually associated with moderately 

 low-dipping monoclines, local areas of maximum 

 concentration being determined by cross anticlines, 



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