206 University of California Publications in Geology [Vol. 10 



has also been greatly complicated by numerous faults, probably due to 

 the same compressional forces. Many of these are extensive, causing 

 long belts of the older rocks to appear in the midst of later formations. 

 A large number of minor faults also are present, which are too local or 

 too unimportant to be shown on the usual geologic map. Besides the 

 faults in a general northwest-southeast direction there are numerous 

 cross-faults. An interesting instance of this is found in the formation 

 of Priest A 7 alley by the damming of the headwaters of Lewis Creek 

 and the consequent filling with alluvium to considerable depth. The 

 net result of the faulting has been to give the effect of a block of 

 Pliocene having dropped down between the older formations. In the 

 northwestern end, a few miles northeast of Lonoak, this fault zone 

 unites with the San Andreas fault zone, of which it appears to be a 

 branch. At the other end it disappears in the Jacalitos syncline a 

 few miles beyond Jacalitos Creek. In other areas of the region studied 

 faulting since the Pliocene has been insignificant. 



LlTHOLOGY OP THE EtCHEGOIN 



SANDSTONE, CLAY, AND CONGLOMERATE 



Due largely to the complicated distribution of the older rocks in 

 this region, from which the Pliocene is mostly a derivative, the lith- 

 ology of the Etchegoin varies considerably in going from one locality 

 to another, having in the various areas a great resemblance to the kind 

 of rock from which the sediments were derived. Also, since the 

 formation is largely a shallow-water deposit in more or less local 

 basins, possibly near frequently disturbed fault zones, the lithologic 

 character has been still further localized. In nearly all instances the 

 beds are not clearly marked off from those adjoining, but grade into 

 each other. Few beds can be traced on the basis of lithology for more 

 than a short distance. In the Jacalitos Hills and Priest Valley the 

 region has been greatly complicated by faulting. 



South of Coalinga in the Kreyenhagen Hills the lower portion of 

 the Etchegoin is composed of coarse, dark brown unfossiliferous 

 sandstone. Interstratified with this is usually a minor proportion of 

 yellowish-brown clay. Above this rests a great thickness of massive 

 sandstone with prominent, highly indurated fossiliferous beds. At 

 numerous horizons conglomerates occur or the beds may show their 

 conglomeratic character only by occasional pebbles in the coarse sand- 

 stone. Higher up in the formation the sandstone becomes of finer 



