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374 REPORT OF STATE MINERALOGIST.

LOS ANGELES FIELD DIVISION.
W. Burlixg Tucker, Mining Engineer.

MONO COUNTY.

Mono County was created April 24, 1861, and consists of 3030 square
miles. It is bounded on the north and east bv the state of Nevada,
on the south by Inyo County and on the west by Madera, Tuolumne
and Alpine counties. The county is extremely mountainous, the
western portion lying among- the Sierra Nevada Mountains, whose
principal peaks rise to elevations of over 13,000 feet. The greater
portion of the county, in its larger features, is a broad table land at an
altitude of from 5000 to 7000 feet above sea level, traversed by a

series of approximately parallel ranges running northerly and south-
erly, which rise several thousand feet above the plateau. The other
prominent mountain ranges are the Sweetwater Mountains, along the
eastern border of the county in its northern portion, and the White
Mountains crossing its extreme southeast corner.
Mono Lake is the only large body of water in the county. It lies
ten miles south of Bodie at an elevation of 6426 feet above sea level,

with an approximate area of 1100 square miles. The water of this
lake contains carbonate and sulphate of soda, sodium chloride, borax

and other salts. A detailed description of this lake, by I. C. Russell,
is contained in U. S. Geol. Survey Monograph XI, p. 267, 1885, The
principal streams are Owens River, in the south, which rises in a
high peak of the Sierras and flows southward, formerly emptying into
Owens Lake, but at present whose waters are conveyed by an aqueduct
as a supply for the city of Los Angeles; and the Walker River, which
flows northward into Nevada. Alining and stock raising are the
principal industries in the county.

The period of greatest activity in mining was from 1876 until 1888.
The most productive gold districts have been Bodie, Masonic and Mono

Lake. The principal production of silver has come from the Blind
Springs Hill District, near Benton. The lack of railroad transporta-
tion has retarded the development of the highly mineralized belt that
runs through the county. The only railroad in the county is the
Nevada-California Railroad, which runs through the southeast corner
of the county for a distance of 68 miles. In recent years the increase

in travel during the summer months of the general public to the
large number of pleasure resorts located in the high Sierra has led
to the improvement of the main travel routes throughout the county.

General Geology.
The west boundary of the county, extending in a northwest direction
from San Joaquin Peak to Topaz, is made up with deep-seated granitic
rocks, including granites, diorites. granodiorites and gabbros, also
metamorphic gneisses and schists. Included in this mass of granitic
rocks, there is a belt of Cambrian limestones that extends from June
Lake in a northerly direction to Virginia Creek. The central part of

this bell of limestone is located west of Mono Lake, being about
three miles in width on its southerly extremity, while at its northern
limits it is about six miles wide. In the Mono Lake and Lundy dis-
tricts, the belt is made up of metamorphic limestones, slates, green-
stones and quartzites.