Page 786 - calmining1890

734 REPORT OF THE STATE MINERALOGIST.

TUOLUMNE COUNTY.

By L. P. Goldstone, E.M., Assistant in the Field.

Tuolumne County is one of the principal mining counties of the Stat*
and covers an area of about two thousand square miles. Its easter
boundaries are the summits of the Sierra Nevada Mountains, fror
whence the decrease in altitude through the foothills of that range
the western boundary line is quite regular and gradual. The genera
topography of the county is necessarily quite rough and rugged, con
taining, as it does, between its eastern and western boundary lines littl
besides hills and mountains. The county is generally well watered b;
the Tuolumne and Stanislaus Rivers and their numerous tributaries
the latter stream forming a part of the northern and western boundary
of the county. From an altitude of three thousand feet, extending east
ward toward the Sierra Nevadas, is an immense acreage of commercia
timber, while in nearly all localities a sufficiency of timber for minin
purposes is found. The climate is unexcelled, and all kinds of fruit
are grown of an exceptionally fine quality. Cereals of all kinds ar
raised, and in fact almost anything that will thrive in any localit
thrives here; even tobacco, small quantities of which are raised in severs
places on the forks of the Stanislaus River, of excellent flavor.
The geological character is varied. In many places it is volcani(
the main feature of which is the extensive basaltic table land runnin
for many miles through the county near to and bordering on the Star
islaus River. The eastern portion of the county is granitic in characte
with occasional dikes of porphyry and here and there cappings of basal
The granite in many places gives evidence of its once plastic conditioi]
The western portion of the county is made up of slate rocks, argillaceous
siliceous, and talcose in character. Belts of serpentine cross north an|
south through the western slate formations, and for a long distance oni
of them runs parallel with and near to the west wall of the great gold*
bearing lode — the Mother Lode of California — which courses north abou
35 degrees west through this county.

THE VOLCANIC TABLE.

The volcanic table mountain of the county is one of the most peciu
iar geological features of the State. It is in the neighborhood of thirt
miles in length, having a general northeasterly course. The cappin
is basalt, columnar in structure, which overlies a volcanic ash, whic
itself overlies a deposit of auriferous gravel. That this volcanic mal| |
ter overlies the channel of a once swift stream, all conditions and ev
dences tend to prove. Numerous tunnels have been drifted into th
mountain, of lengths varied by the conditions of the surface ground
some at points where slate forms the bed of the table, and others I
points where limestone is the underlying rock. These changes are du| a
to the fact that the table crosses the formation's in a general northeas