'2i'2 The American Geologist. April, 1894 
been deposited in the waters of the gulf that formerly occu- 
pied the basin of the great valley. Where studied by the 
writer in Amador and Calaveras counties, these gravels merge 
into the Pliocene river gravels. This is particularly notice- 
able to the east of Valley Springs. They may, therefore, be 
said to represent, in part, a delta formation, but the main 
mass of them, occurring as a capping to the ridges, is more 
properly designated as shore gravel. 
The unconformity of these gravels on the [one formation is plainly 
seen at the sandstone quarry, three miles south easl of Buena Vista, 
where they rest (in the undulating and smooth water-worn surface of the 
lone sandstone. Water-worn boulders of the sandstone occur in the 
gravel. In a cut of the San Joaquin and Sierra Nevada railroad, one 
mile southwest of Valley Springs, the gravels are well exposed and at- 
tain a thickness of two hundred feet. At the bottom of the cut may be 
seen irregular blocks of the gray clay-rock or tuff of the lone formation 
included in the gravel beds. The unconformity of the Pliocene shore 
gravels on the rhyolitic series may be seen at Valley Springs peak and 
at Buena Vista peak. At both places the gravels contain abundant peb- 
bles of the rhyolite that forms these two peaks. These heavy bodies of 
coarse gravel suggest the Pliocene to have been a period of rapid erosion. 
These gravels attain at Valley Springs peak a maximum elevation of 
1,000 feet. The greal bulk of them are from .~>00 to 700 feet above sea 
level. 
Early Pleistocene Shore and Rivek Gravels and Moraines. 
The early Pleistocene shore gravels consist almost entirely 
of quartzite and other highly siliceous pebbles. They appear 
to have been formed largely from Neocene (Miocene and Pli- 
ocene) gravels, from which the softer pebbles of igneous rocks 
were eliminated by long continued washing by the gulf 
waters. There are extensive areas of these gravels on the 
east side of the San Joaquin and Sacramento valleys. On 
the Jackson sheet they occur as low, broad plateaus, and in 
the depressions between the Neocene and older hills up to an 
elevation of 450 feet. They attain a maximum elevation of 
.")(»() feet at the Irish Hill gravel mine, four miles northwest of 
lone, in Amador county. The soil of the Pleistocene shore 
gravels is red in color. Since these gravels rest on the lone 
formation or on andesitic tuff, it is plain that the quartzite 
pebbles could not have been derived directly from quartzite 
croppings, which, moreover, do not occur along the west edge 
of the foot-hills, but only at a greater elevation than was at- 
