82 SOUTHERN CALIFORNIA GEOLOGY 



The arching of the group of folded ranges, I believe, 

 was the result of horizontal pressures exerted 

 in east-west directions. It represents a portion of a 

 great bend or partial buckle whereby the normal north- 

 west trends were deflected more to the west. These 

 aspects are discussed more fully in the chapters on 

 structure. 



The dual structural history is also largely reflected 

 by the drainage. Several large streamways occur in 

 the region, among which may be mentioned the Santa 

 Clara River of the south, Piru and Castaic Creeks, 

 Some of these, like the latter, are the antecedent 

 streams of earlier epochs and cross the ranges at 

 right angles. Others, like the Santa Clara, are con- 

 sequent streams of a later epoch and flow in synclinal 

 troughs. 



The exposed materials of the Ventura Ranges are 

 nearly all sedimentary rocks of Cretaceous, Tertiary 

 and Quaternary ages. The latter predominate at the 

 surface, as has been shown in the excellent earlier 

 descriptions and maps by Eldridge and Arnold, and 

 later by W. S. Kew.i 



THE SANTA MONICA-ANACAPA CHAIN 

 A ribbon-like range extends from Glendale west- 

 ward for one hundred and thirty miles to the west 

 end of the Channel Islands, which I will term the 

 Anacapa - Santa Monica Range. Physiographically 

 speaking this is a long and narrow east-west moun- 

 tain range, the southernmost of the Transverse Belt. 

 It is partially drowned by the sea and dissected into 

 several individual summits of which San Miguel, 

 Santa Rosa, Santa Cruz and the Anacapa Islands are 



'Bulletins Nos. 309 and 753 respectively of the U. S. Geologrcal Survey. 



