

?***< 



102 



THE AUKIFEROUS GRAVELS OF THE SIERRA NEVADA. 



i 





In the Sugar Loaf Hill, at the north end of a short ridge or spur between Clapboard and Indian 

 gulches, near Volcano, there has been considerable hydraulicking, exposing banks from seventy- 

 five to eighty feet in height. This hill is capped with a thickness of from fifteen to twenty feet of 

 black lava, which over the central portion of the hill lies nearly horizontal ; but, at the sides, bends 

 downwards, reaching thus sometimes thirty or forty feet lower. This bending, however, is not 

 smooth and regular, but of such a character as to prove that there has been considerable sliding of 

 the banks at some time in the past. So irregular is the surface of the limestone, that the thickness 

 of the travel cannot be made out ; and there are large masses of decomposed slates imbedded in it, 

 the whole having been crushed together by the slipping and sliding which lias here taken place. 



In the W. T. Jamison Mine, near Eiddletown, a tunnel was driven about 630 feet, in a south- 

 erly direction, under Loafer Hill. No well-defined channel seems to exist here, the broad, gcntly- 

 nndulating surface of the soft slate bed-rock being almost everywhere covered with from two to 

 fifteen feet of gravel which is immediately overlain by "white lava." The gravel varies a good 

 deal in color, is not very hard, and consists almost entirely of metamorphic material, though con- 

 taining occasional boulders of "white lava." It also contains a good deal of clayey matter and 



furnishes very smooth casts of its pebbles. This gravel has paid well for drifting. The general 

 surface of the bed-rock under it is said to have a gentle fall everywhere towards the southwest. 

 The whole mass of Loafer Hill is " white lava." 



At Michigan Bar the gravel is all metamorphic, and its pebbles are small. The gold also is 

 generally fine and smoothly worn. The area of gravel here is estimated at three eighths of a 

 square mile, with an average depth of 15 to 20 feet. 



At Forest Home the gravel is generally pretty well washed, and many of the hills are covered 

 with it, to depths ranging from ten to thirty feet ; it contains no large boulders. 



The 'gravel in the hills at Muletown ranges from a few feet to seventy-five, or possibly a hun- 

 dred, feet in maximum depth. It is a ferruginous quartz gravel, but little washed, and containing 

 very' few, if any, large boulders. Nine tenths of the pebbles it contains are of quartz, and there 

 are none 'of volcanic origin. These gravel beds form the southwestern termination of a series of 

 spurs of the chaparral hills, and rise two or three hundred feet above the general level of the 

 country immediately to the southwest. In the different spurs, immediately to the northeast of 

 the gravel, the crests of the hills continue on perfectly smooth, but at the edge of the gravel, the 

 bed-rock, consisting of hard clay-slates, rises abruptly to the surface and forms the crests continu- 

 ously in that direction. The whole structure of the banks here is full of evidence of the action of 

 shifting currents, on a small scale, and probably of no great force. None of the gravel is thor- 

 oughly water-worn ; it consists chiefly of small angular fragments of quartz. In the soft bed-rock 

 underlying this gravel just such quartz occurs in little crushed seams. At Irish Hill, two or three 

 miles northwest of Muletown, the gravel is quite different in character, consisting chiefly of meta- 

 morphic slaty rock, with a good deal of dark-colored quartzose material, and occasional volcanic 

 pebbles, but hardly any white quartz. The pebbles are more water-worn than those of the Mule- 

 town gravel. 



Near Irish Hill the greatest part of the work has been done in a mass of rolling, chamisal-covercd 



hills scattered over a quarter of a section of ground, in which some eight or ten acres have been 

 washed away, with an average depth of gravel of perhaps twenty feet. The surface is irregularly 

 cut up by gulches, and the pits are equally irregular in their distribution. The maximum depth 

 of the "ravel is perhaps forty or fifty feet. The whole character of the gravel at Irish Hill is so 

 different from that of Muletown, that it appears quite impossible that these deposits should have 

 been formed by the same stream. The gravel of Irish Hill would appear to bate been deposited 

 by a stream draining nearly the same area of country as that now drained by Dry Creek. 



At Tunnel Hill, near Jackson, an area has been washed off estimated at 1320' x 440' to an 

 average depth of ten or twelve feet. The gravel is red, with plenty of moderate-sized boulders, 

 but few large ones. The smaller pebbles are nearly all quartz, and but partially rounded ; some 

 of the quartz is jaspery. There are no volcanic pebbles. 



