Clear
Lake, although the great bituminous slate formation has been traced
from Cape Mendocino through the country south to Los Angeles.
South
of the bay of San Francisco the strata of this slate formation are
everywhere turned up at a high angle, while north of the bay they are
less disturbed. The tertiary, which is so limited north of San
Francisco Bay, increases in importance going south. It flanks the
cretaceous on both sides of the Mount Diablo range, and gradually
limits it. The western and larger portion of the Santa Cruz range (the
geology of which is somewhat complicated by the presence of intrusive
granite rocks in various places) is said to be miocene. In the Gavilan
and Santa Lucia system of ranges the tertiary is continued, and granite
and highly metamorphosed rocks occur in considerable quantity; but the
region is dry and very rough, and has been but little explored.
Asphaltum Deposits.—
The different ranges in Santa Barbara and Ventura counties are made up
chiefly of miocene rocks, consisting principally of a coarse-grained
sandstone below, and over this a fine-grained slate or shale, often
highly bituminous and generally very much contorted and tilted nearly
vertical. In Santa Barbara, Ventura, and Los Angeles counties, where
the tertiary bituminous slate predominates, the principal deposits of
superficial asphaltum have been found, and here attempts have been made
to strike flowing petroleum wells.
As
one approaches the Sierra Nevada to the east of this region, and also
in going south, granite becomes more frequent and the sedimentary rocks
get harder and more crystalline. There is a granitic belt forming a
continuation of the San Gabriel range, and connecting at Tejon Pass
with the metamorphic and granitic masses of the Sierra, the crystalline
rocks being apparently continuous, but the disturbance of the tertiary
and cretaceous formations not being visible cast of Tejon Pass. The
granite forming the divide between the branches of the
