GRAVEL AND VOLCANIC FORMATIONS: CALAVERAS COUNTY. 129 
could be run through the sluices. That this could be done with profit, — 
as must have been the case from the length of time the operation was car- 
ried on, — shows that the gravel must have been quite rich in gold. The 
continuation of the Mokelumne Hill channel below Chili Gulch, towards 
Double Springs, has, apparently, not been found worth working to any 
considerable extent. 
In that portion of Calaveras County which lies to the southeast of the 
river of that name there are numerous localities where gravel deposits occur 
under the volcanic materials; but none of these are of great extent, or 
have been worked very continuously. The localities where these gravels 
occur are chiefly in the vicinity of San Andreas, Altaville, and Vallecito. 
The gravel deposits at San Andreas have been worked in former years to 
considerable extent. The formation appears to be from 100 to 150 feet 
in thickness. A section, as given by two of the miners at this place, will 
be found farther on, in the chapter devoted to the remains and works of 
man in the gravel under the volcanic beds. The eruptive masses here would 
appear from their position to be connected with the flow which has come 
down from the Sierra behind the Big Tree Grove, and which passes about 
two miles north of Cave City, and is there known as Table Mountain, a 
name very commonly given in California to lava flows, and especially to 
isolated patches of such flat-topped masses. 
In the vicinity of Douglass Flat and Altaville there is a large develop- 
ment of volcanic materials, and some gravels which have been worked from 
time to time. There is a nearly level tract of land extending north from 
Vallecito to Douglass Flat, known as Vallecito Flat, which is an area de- 
pressed below the surrounding region, and filled to a considerable depth by 
gravel, of which the exact limits seem to be not well known. The bottom 
of this depression is too deep to be drained, except by a long tunnel, and 
such a one was commenced many years ago, but never completed. A tunnel 
from the forks of Coyote Creek, about a mile in length, would, it is supposed, 
open this ground at a sufficient depth to permit its beimg worked by the 
hydraulic method. There is an elevated ridge of volcanic breccia extending 
along the northwest side of Vallecito Flat, which rises to a height of nearly 
600 feet above the lower portions of the surface of the Flat, and the Sonora 
Table Mountain extends, with a nearly equal elevation, along the east side, 
occupying most of the space enclosed between Murphy’s, Douglass Flat, and 
Vallecito Flat on the west, and the Stanislaus River on the east, as far as 
