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GEOLOGY OF THE COAST RANGES. 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 Iiez 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 Ifez 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 are, 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 well 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 Ifez 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 shales and slates, not 
much 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 
edge, 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 
Cajion lie unconformably on the older rocks, gold has been obtained by wash- 
