BED-ROCK: SOUTH OF THE MOKELUMNE RIVER. 121 
the gravel deposits, although numerous and often rich, are on too small 
a scale and too “spotted” to be capable of being attacked with success by 
hydraulic mining operations on a large scale. ‘ 
In describing the geology of the region south of the Stanislaus we may 
follow an order somewhat similar to that already indicated for the region 
farther north. 
§ 1. The Bed-Rock in Calaveras, Tuolumne, and Mariposa. 
So much has already been stated in regard to the bed-rock in Tuolumne and 
Mariposa * that this branch of the subject may be passed over with rapidity. 
The most interesting orographical feature of this region in connection 
with the bed-rock series is, the existence of a subordinate range in the 
foot-hills, parallel with the Sierra, but having more of an isolated and inde- 
pendent character than any other of the more or less continuous foot-hill 
ranges which lie along the base of the great mass of the Sierra itself. The 
range in question is so distinctly marked as to have received a name, and 
the group is known as the “ Bear Mountains.” It is, in fact, a double range, 
having two quite well-marked divisions; the more southwesterly, which is 
parallel with the other but quite subordinate to it, is known as the “ Gopher 
Hills.” A glance at the map of Central California will show the position of 
these elevated ranges. They extend between the Calaveras and the Stanis- 
laus rivers, and govern the distribution of the drainage within that region, 
giving it a character quite unlike what it usually has in this part of the 
Sierra. The various streams which rise in the upper portion of Calaveras 
County flow with the usual southwesterly course, until they reach the north- 
east edge of the Bear Mountains, when they turn at right angles, and flow 
northwest and southeast to the Calaveras or the Stanislaus. The smaller 
creeks, which rise in the rather broad and regular valley between the Gopher 
Hills and the Bear Mountains, also have courses parallel to that of the 
ranges themselves. 
The rocks of the Bear and Gopher ranges are all of the bed-rock series, 
and highly metamorphic. The slates are well developed in the depression 
between the two ranges, and are there associated with irregular bands of 
serpentine which are sometimes of great length and width. This region 
was formerly the seat of the most active copper-mining operations in the 
State, Copperopolis being the principal mining centre. The only important 
* See ante, pp. 43 - 47. 
