Page 9 - 1915, Springs of CA.

PHYSICAL FEATURES OF CALIFOBNIA. 9
other irregular but lower ranges. Perhaps the most distinctive of
these is the St. Helena Range, which forms the boundary between
Lake and Sonoma counties. The northern and western ranges in
these counties are composed largely of altered sedimentary rocks
that probably belong to the Franciscan formation. Glaucophane
schists and serpentine are associated with them. The age of other
altered sedimentary rocks in this area has not been determined.
Some geologists believe that they belong to the Franciscan forma-
tion, others believe that they are of Lower Cretaceous age and are a
part of the formation known as the Knoxville from the type locality
near Knoxville in Napa County, where they are well exposed. As
both series of sediments are more or less altered they are not differ-
entiated on the geologic map (PL II, in pocket).
In Napa County and the southern part of Lake County several
peaks and ridges are formed of lava that is probably of Tertiary age.
This lava overlies the altered sediments, and tuffaceous phases of it
form prominent cliffs at a number of localities. Numerous carbon-
ated springs of slight flow issue in this region north of the bay, both
from the sedimentary rocks antl from the lavas, and hot springs exist
at several places. A few springs of noticeably sulphureted water
have also been examined but are less numerous and less important
than those of the carbonated type.
The Coast Ranges between San Francisco and Los Angeles in gen-
eral trend nearly parallel with the coast. Among them are the ^anta
Cruz Mountains, which lie along the boundary between Santa Clara
and Santa Cruz counties; the Diablo Range, which separates San
Joaquin, and San Benito valleys; and the Gabilan Range, which lies
between San Benito and Monterey counties. The Santa Lucia Range
forms a mountainous region in southern Monterey and northern San
Luis Obispo counties, and the Temblor Range is in eastern San Luis
Obispo and western Kern counties. The San Rafael and Santa
Ynez mountains are in Santa Barbara County and trend in a general
northwest direction. In Ventura County, Pine Mountain and, east
of it, the Topatopa Mountains, extend in general from east to west, as
do the Santa Susana Mountains, in western Los Angeles County. The
Tehachapi Mountains trend northeastward through southern Kern
County, and although bridging the gap between the Coast Ranges
and the Sierra are, because of their rock types and structure, properly
regarded as belonging to the latter rather than to the former. Most
of the Coast Ranges south of San Francisco Bay are only 2,000 to
3,000 feet in elevation, but the highest parts of the Tehachapi Moun-
tains attain heights between 5,000 and 6,000 feet. For the m6st part
these Coas"t Ranges south of San Francisco Bay are composed of un-
altered sedimentary rocks of Cretaceous and Tertiary age, but con-
siderable masses of the Franciscan formation persist southward from