Page 180 - 1915, Springs of CA.

164 SPRINGS OF CALIFORNIA.
KESSLER SPRINGS (SAN LUIS OBISPO 10).
The other group of springs at which onyx marble has been formed
is at Kessler Springs better known as the Kessler Mexican onyx
quarries in San Luis Obispo County, about 20 miles northeast of
Arroyo Grande, among hills of sandstone and shale that are probably
of Tertiary age. The principal outcrop of the onyx marble forms a
ledge, several yards in height and extent, at the side of a small ravine;
a smaller exposure of veins of the material, several inches in thick-
ness, appears in a dark mud shale in a prospect trench a quarter of
a mile northward. Between these two places are several outcrops
of the stone, at three or four of which issue small amounts of
slightly carbonated saline water. During the dry season the run-off
channels are crusted with deposits that consist largely of common
salt.
The property was filed on as a mineral claim in the early seventies,
and a number of slabs of the stone were taken out by means of steel
blades and emery, but the material contains too many cavities to
enable it to compete as a merchantable stone with that from other
quarries, and development ceased about 1895. The material at the
prospect trench is almost pure white, but at the larger exposure,
where most of it was obtained, it is more translucent, and has a
mottled, cloudy appearance that is due to the inclusion of a small
amount of clay.
Although the amount of water that now issues is very small, the
fact that the onyx marble is essentially a spring deposit entitles the
locality to description in this paper.
Two minor onyx marble deposits, probably formed by mineral
springs, have been worked. One of these is near the western side of
Sacramento River, near Shasta Springs, and was known as the Griffin
quarry. Material large enough only for paper weights and similar
small articles was obtained at this quarry. The other locality is near
the Elgin quicksilver mine, about 30 miles west of Williams in Colusa
County.1
The two analyses of Californian onyx marbles that are available
are presented in the following table:
1 In the description of the deposits at the hot springs near Bridgeport, Mono County (p. 134), Merrill has
been quoted concerning the formation of onyx marble. He states that most of the onyx marbles are of
calcite, not aragonite. Microscopic examination of material from the Bridgeport, Tolenas, and Kessler
quarries, and determinations of the specific gravity of specimens show that nearly all of it is calcite, but
a small specimen from the Tolenas quarry consists of two nearly equal bands of aragonite and calcite.