Page 170 - 1915, Springs of CA.

154 SPRINGS OP CALIFORNIA.
In a general way the list shows the character of the rocks at the
various hot-spring localities, although, as in other groupings, the
springs can not be rigidly classified in this respect. The number of
localities is seen to be about the same in regions of granitic rocks, of
sediments (including the unaltered and the altered rocks), and of
lavas (including those issuing from alluvium near lava), being respec-
tively 36, 32, and 30. If any significance can be attached to this
fact, it indicates that the presence of thermal springs is due in most
places to structural conditions in which the character of the rocks is
not an important factor. It apparently emphasizes the evidence
shown by the faults on the map (PI. Ill, in pocket), that the ex-
istence of the thermal springs is due chiefly to crustal movements.
Exception must be made, however, of a few thermal springs whose
heat appears to be derived from lava that has not yet cooled to a
normal temperature.
There are notable deposits at 10 hot-spring localities. At 2 of
these, Morgan Hot Springs and Casa Diablo Hot Springs, the deposit
is in large part siliceous and the silica seems probably to be derived
from the lava; at the other 8 there are notable deposits of lime
carbonate, and 6 of these are closely associated with lava. At
1 of the 2 remaining localities Jordan Hot Springs lava on the
slopes to the north may possibly be in some way related to the
deposit at the springs. Buckeye Hot Spring, the last of the 8, is
only about 6 miles west of the springs near Bridgeport at which there
are extensive lime carbonate deposits in a lava area, and there may
be lava on the slopes near the Buckeye Spring, though it was not
observed. The springs at Sulphur Bank, in Lake County, and Ben-
ton Hot Spring, in Mono County, are the only hot, notably carbon-
ated springs observed that do not form deposits of considerable size.
The fact that most of the hot springs that issue in lava areas con-
tain an excess of carbon dioxide and considerable sodium and mag-
nesium with lesser amounts of calcium, suggests that the sodium
and magnesium tend to deprive the calcium of bicarbonate and cause
its deposition as lime carbonate. Thus the presence of notable
amounts of carbon dioxide, derived presumably from the lava, and of
the primary alkalies sodium and magnesium, apparently causes the
deposition of the calcium present in the form of carbonate. The
same fact seems also to be shown by the cool carbonated springs at
which there are notable deposits, as is indicated by the tabulated list
on pages 252-253. It is significant that relatively few of the car-
bonated springs that rise in sedimentary rocks form notable deposits,
though some of them contain more calcium than do some of the hot
springs that form extensive deposits. Most of the carbonated springs
that do issue from sedimentary rocks and form deposits are noticeably
thermal.