390 PROCEEDINGS OF THE CALIFORNIA 



than the three or four dollars per ton which I am told it yielded ; and in fact, 

 the general character of the float quartz of the region, when taken in connection 

 with the probable origin of the valley itself, and the fact that no important 

 placer " diggings " have been found here, does not seem to favor the probabil- 

 ity that these quartz veins will ever prove of much value. Between the pres- 

 ent mill and the site of the old one, as well as certain other localities in the val- 

 ley, are springs containing various alkaline salts, from which the name " Salt 

 Spring Valley " is derived. 



Accompanying the copper formation of Copperopolis, and just west of it, is 

 an immense body of serpentine, lying parallel with the general stratification of 

 the slates, and traceable for miles along the valley by the openings made in it 

 in the workings for copper. Opposite a point 1,000 or 1,200 feet northwest of 

 the upper shaft of the Keystone claim, but on the southwest flank of the out- 

 lier of Bear Mountain, already noticed, is another heavy mass of serpentine. 

 How far this extends in a northwest and a southeast direction I do not know, 

 as I have not followed its line of outcrop, but it is certainly not less than 1,000 

 feet in length. 



The lithological character of the Gopher Hills is entirely different from that 

 of Salt Spring Valley. They consist mainly of a pretty hard and tough, more 

 or less coarsely crystalline, and dark-colored hornblendic or pyroxenic rock, 

 which is evidently metamorphic, probably of a grit or sandstone. Epidote is 

 not uncommon in this rock, and calcite is occasionally found, though rare. 

 Through most of this region the original stratification has been largely ob- 

 scured, or nearly obliterated. Its general course, however, can still be traced 

 without difficulty in the more or less elongated and flattened form, and the gen- 

 eral trend which the rocky outcrops frequently assume when viewed from a little 

 distance. 



The texture of the rock varies considerably. In general it is rather coarsely 

 crystalline ; but not unfrequently it is much finer, or even compact ; sometimes 

 it is jointed. At one locality, in particular, (" Goodwin's," or " Sheep Ranch " 

 Gulch) I noticed this jointed structure so well developed that a compact and 

 very tough, almost imperishable rock could be quarried with facility, if desired, 

 in nearly rectangular blocks and slabs. 



It is not uncommon to find among these hills those peculiar holes in the rock 

 which were hollowed out and used by the Indians-as mortars in which to grind 

 their food. I observed a number of similar holes in the hard rock, precisely in 

 the bed of Rock Creek, in the ravine a short distance below the dam of the Salt 

 Spring Valley Reservoir. It may be a question here, whether they owe their 

 origin to the Indians or to the action of the stream, though from the peculiar 

 deep and narrow form, I am inclined to ascribe them to the former. Heavy 

 masses of flinty rock or hornstone also occur, particularly upon the southwest 

 flanks of the range. This rock usually exhibits a much more distinct bedding 

 than the ordinary mass of the hills. Its stratification is often perfectly regular, 

 and sometimes the layers are beautifully thin and delicate. There is a very 

 heavy outcrop of this finely banded rock in the ravine a short distance below 

 the dam at Rock Creek. Higher up the hill, upon the road known as " Black's 



