GEOLOGY OF THE COAST EANGES. 



19 



Range has for a portion of its length an anticlinal structure, and a central 

 axis of granite, forming in this respect a marked contrast with most of the 

 ranges of the Coast Mountains. The Santa Inez Range, which is narrow and 

 very steep, has also an anticlinal structure, with the axis of the flexure irregu- 

 lar, and not everywhere coinciding with the crest of the range, so that the 

 latter appears sometimes to have a monoclinal dip ; and, in places, the whole 

 of the upper portion of the mountain has an inclination to the north, and in 

 other places, in the opposite direction. These rocks are overlain along the 

 coast, in places, with a slightly disturbed, nearly horizontal deposit of Pliocene 

 beds ; the underlying Miocene is here tilted up into a nearly vertical posi- 

 tion, and very much contorted. The internal forces which elevated the 

 Santa Inez Range seem to have exhausted themselves in the vicinity of San 

 Buenaventura, so that from the river of that name eastward to the head of 

 the Santa Clara Valley, while the mountains are still high, reaching an ele- 

 vation of 3,000 feet above the sea-level, the rocks composing them are, in 

 general, but little disturbed ; there arc, however, local contortions and some 

 marked changes of strike. The Sulphur Mountains, lying between the San 

 Buenaventura and Sespe Rivers, are made up of considerably contorted 

 strata of bituminous slates, and are w r ell known from the numerous attempts 

 which have been made here to strike, by boring, flowing wells of petroleum. 

 The great mass of the San Rafael Mountains, occupying the area between 

 the Santa Inez and Cuyama rivers, is chiefly composed of Miocene shales 

 and sandstones, considerably disturbed towards its northern edge, and per- 

 haps folded, the want of any maps of this region making it difficult to con- 

 nect the observations, so as to make out the structure. A section across the 

 ranges, from San Buenaventura to Tar Springs in Tulare Valley, shows the 

 great mass of the mountains to be made of bituminous si 1 ales and slates, not 

 ^uch disturbed, except locally, until towards the northern extremity of the 

 section, where there are two sharp folds, between which runs the Cuyama 

 River. At the north end of San Fernando Valley, and in various other 

 places in this region, there are small areas of Pliocene gravels lying nearly 

 horizontally on the upturned edges of the Miocene. Passing up the Santa 

 Clara River, when we have reached the San Francisco Pass, we find the 

 entire structure of the range changed. The Miocene rocks are turned up on 

 e( %e, and in places so much metamorphosed as to be converted into mica- 

 slate In the Pliocene gravels, which at the mouth of the San Francisco 

 Canon lie unconformable on the older rocks, gold has been obtained by wash- 



