786 REVIEWS 



Geology and Oil Resources of the West Border of the San Joaquin 

 Valley North of Coalinga, California. By Robert Anderson 

 and Robert W. Pack. U.S. Geol. Surv., Bull. No. 603, 1915. 

 Pp. 220, pis. 14, figs. 5. 



The region described in this bulletin is a strip 8 to 20 miles wide and 

 130 miles long lying along the east flank of the Diablo Range and the 

 adjacent western edge of the San Joaquin plain. This foothill belt was 

 studied with a view to determining whether or not oil fields exist, as in 

 the Coalinga and other districts farther south. In so far as finding 

 new oil fields is concerned, the examination proved disappointing. 

 Organic shales were found in great quantity, but there are few spur 

 folds running out toward the valley. The presence of oil pools to the 

 south is determined by such folds. 



The oldest rocks in the Diablo Range belong to the Franciscan 

 formation, of supposed Jurassic age, which is separated from the oldest 

 Cretaceous rocks by a great unconformity. The Knoxville group 

 (Comanche) is believed to be absent. The Chico (Cretaceous) is 

 represented by the Panoche and Moreno formations, marine shales and 

 sandstones that reach the enormous thickness of 24,000 feet. The 

 Moreno, composed largely of organic remains such as diatoms and 

 foraminifers, has been referred by some authors to the Tertiary, but it 

 is now found to contain Cretaceous fossils. Hitherto strata of this type 

 have been known in California only in the Tertiary. 



The Martinez (lower Eocene) is present only in the southern part of 

 the area, where it is represented by 5,000 feet of marine beds. The 

 Tejon (upper Eocene) is present throughout the region, varying in 

 thickness from 50 to 2,200 feet. The Oligocene is represented by the 

 Kreyenhagen diatomaceous shale, with unconformities above and below. 

 In the southern part of this belt the Miocene is represented, as in the 

 Coalinga district, by the Vaqueros, Santa Margarita, and Etchegoin- 

 Jacolitos formations, with a maximum thickness of 5,000 feet, each 

 separated from the next adjoining by an unconformity. The Big Blue 

 serpentine, formerly considered to represent the lower part of the 

 Santa Margarita, contains typical Vaqueros fossils. Farther north the 

 lower and middle Miocene were not differentiated. The San Pablo is 

 equivalent in part at least to the Etchegoin-Jacolitos. Post-Miocene 

 beds up to 2,200 feet thick are tentatively correlated with the Tulare 

 formation. 



The local factors influencing the accumulation of oil, evidences of 

 oil in the region, and the future possibilities of development are dis- 



