Page 8 - 1915, Springs of CA.

8 SPRINGS OF CALIFORNIA.
tains. To the south, trending in general east and west and forming the
northern boundary of Trinity County, are the Scott Mountains. The
Trinity Mountains, and, farther southwest,the Bully Choop and Yolla
Bolly mountains, form the eastern boundary of the same county. In
the southwestern part of Trinity County, along the eastern side of
Mad River, are the South Fork Mountains. Farther south, in southern
Humboldt County, an area of sharply cut ridges and canyons, locally
known as the Wildcat region, forms part of the Mendocino Range.
A similar system of ridges continues southward through Mendocino
County, but the mountains forming this portion of the Coastal system
are not known by a distinctive name.
The name Klamath Mountains was suggested^ by Maj. Powell as
a general title for this group of ranges in the northwestern part of
the State, and this name has been adopted by Diller 1 in his publica-
tions on the region. These mountains, generally speaking, are less
than 5,000 feet in elevation, but the higher peaks of Scott and Yolla
Boliy mountains are more than 7,000 feet above sea level. They
are composed mainly of slates, schists, and granitic rocks of Triassic,
Carboniferous, or, perhaps, earlier geologic age,2 and of a younger
series of altered sandstones and shales associated with cherts and
schists that probably belongs to the Franciscan formation, which is
believed to be either Jurassic 3 or Lower Cretaceous in age.4 The
Franciscan sedimentary rocks generally contain intrusive masses of
serp'entine and of basaltic material that usually has the character
of a diabase. These intrusive rocks are so commonly present in
the Franciscan that they may be regarded as characteristically
associated with that formation, although they do not properly form a
part of it. Granitic rocks and gneisses are also exposed among the
altered sediments of the northern Coast Ranges and are thought to
be in part intruded in the sediments. The sedimentary rocks
throughout the Klamath Mountain region have been sharply folded,
and their structure is intricate and complex, but it is not known in
detail because only reconnaissance studies have been made, of these
rocks.
A few sulphur springs issue from the schists of this region, occa-
sional salt springs yield flows of slight amount from the slates and
shales, and a few small carbonated springs are scattered through the
areas of granitic rocks.
In Mendocino, Lake, and Sonoma counties, south of the region
that is considered to compose the Klamath Mountains, there are
1 Diller, J. S., Tertiary revolution in the topography of the Pacific coast: U. S. Geol. Survey Fourteenth
Ann. Report, pt. 2, pp. 404-405,1894.
« Diller, J. S., op. cit., PL XLV.
3 Branner, J. C., Newsom, J. F., and Arnold, Ralph: U. S. Geol. Survey Geol. Atlas, Santa Cruz folio
(No. 163), p. 2,1909.
4 Lawson, A. C., The California earthquake of Apr. 18,1906: Rept. State Earthquake Investigation
Comm., vol. 1, pt. 1, pp. 7-S, 1908.