Page 12 - 1915, Springs of CA.

12 SPRINGS OP CALIFORNIA.

Sacramento Valley there is a considerable area of lava agglomerate
and tuff that has been described by Diller * as the Tuscan tuff. It is
considered to consist of volcanic material that was deposited in fresh
water and hence is shown on the geologic map (PL II, in pocket) as a
sediment, but in some places it closely resembles a lava.
There are very few springs in the Great Valley. Sulphur water
seeps out at a few places along stream channels, and salt water issues
in perhaps three or four localities, while a few springs that are not
noticeably mineralized issue along its eastern margin.
LAVA-COVEBED REGION.
The lava-covered region forms an extensive area in the northeastern
part of the State. Its western boundary is formed approximately by
Sacramento River and by Shasta River, a tributary of the Klamath.
The southern boundary extends nearly east and west past the southern
base of Lassen Peak; the northern and eastern limits are beyond the
boundaries of the State. The central and northern portions of the_
lava mass form a plateau that is between 4,000 and 5,000 feet in eleva-
tion. In the northeast the Warner Mountains reach an altitude of
8,000 feet; on the south Lassen Peak rises to a height of more than 10,000
feet; to the west Mount Shasta towers to an elevation of 14,380 feet.
Practically all of this region is covered with lava, which is probably of
Tertiary and later geologic age. In a few places there are lake-bed
deposits of partly consolidated sands and clays, and areas of alluvium
form occasional patches of meadow and valley land.
A number of hot springs issue in the eastern part of this lava region
and in the neighborhood of Lassen Peak; in the western portion there
are many carbonated springs; and in the western and central portions
are several large cold springs.

glEBBA NEVADA.
The Sierra Nevada, the dominating physical feature of the State
and one of the most imposing mountain groups of the United States,
extends east of south from the southern base of Lassen Peak to Tejon
Pass. In the main it forms a great single range which rises in a long
gentle slope eastward from the Great Central Valley to its crest, and
thence descends abruptly to the desert region at its eastern base.
Although as .a whole its western side forms a comparatively uniform
slope that is known to geologists as the Sierran peneplain, in detail it
departs far from the character of a plain. Numerous peaks form
prominent irregularities, though their summits conform approximately
to the mean slope of a peneplain. Deep canyons score this surface
in a westward direction and further add to the ruggedness of its
detailed character. In its northern section the crest of the range
i Diller, J. 8., Geology of the Lassen Peak district: U. 8. Geol. Survey Eighth Ann. Kept., pt. 1,
pp. 422-424,1889.