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GEOLOGY. — Geology and oil resources of the west border of the San 

 Joaquin Valley north of Coalinga, California. RoBpmT Anderson 

 and R. W. Pack. U. S. Geological Survey Bulletin 603. Pp. 220, 

 with 15 plates and 5 figures. 1915. 

 The region described forms the eastern foothills of the Diablo Range, 

 which is the easternmost component of the Coast Ranges in central 

 California. In the higher parts of the range, altered sedimentary and 

 igneous rocks of probable Jurassic age outcrop. Overlying these rocks 

 are thick unmetamorphosed Cretaceous and Tertiary sedimentary for- 

 mations, with basaltic intrusives and flows in two very small areas. 

 The post-Jurassic sedimentary formations are mainly arkosic sand- 

 stones and shales, but there are two persistent shale formations, each 

 over 1000 feet thick, composed largely of the remains of diatoms and 

 f Oram inif era. One of these formations is of Upper Cretaceous age; 

 the other is probably Oligocene. The Cretaceous rocks all belong to 

 the Chico or Upper Cretaceous phase, and aggregate the astonishing 

 thickness of something over 23,000 feet. 



The structure of the region is predominantly monoclinal, forming 

 the eastern flank of the great anticlinal structure that determines the 

 Diablo Range. The regularity of the monoclinal structure is broken, 

 however, by several anticlinal folds that head in the central part of 

 the range and, trending obliquely to it, extend out toward the San 

 Joaquin Valley. Faults are relatively few and only locally dominate 

 the structure. 



The petroleum apparently originated in the diatomaceous shales, 

 and at present is found in, or in close association with, the two forma- 

 tions that are composed largely of that material. 



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