(b SOUTHWESTERN NEVADA AND EASTERN (AETFORNTA. 
Mountain hills to the west, and in consequence the rocks are almost 
certainly Cambrian. 
Siebert lake beds. — The intensely dissected gap between the two 
groups of hills is composed of white or yellow, well-bedded tufa- 
ceous sandstones, conglomerates, and clays, slightly consolidated. 
About 400 feet of this formation is exposed. Thin sheets of rhyo- 
lite appear to be interbedded with the sediments at the south end of 
the exposures. These soft horizontal beds are eroded into number- 
less low rounded hills ami gullies. Veins of white calcite from one- 
fourth inch to 1 font thick cut the sediments and stand in relief on 
weathering. These beds are similar lithologicalry to the Siebert 
lake beds of Tonopah." and like them have thin sheets of the Tono- 
pah rhyolite near their top. 
Older alluvium. — North of the large isolated latite cone on the west 
side of the hills occur small exposures of white sandstones and con- 
glomerates. The pebbles and bowlders consist of latite and biotite- 
hornblende andesite. These beds are perhaps to be correlated with 
the older alluvium, probably of late Pliocene or early Pleistocene age. 
IGNEOUS ROCKS, 
Post-Jurassic <jr<in'<t>. — Three small areas of granitoid rocks lie 
near Southern Klondike. Three-fourths of a mile northwesl of the 
village a granite sheel 250 feel thick, which courses northeast, injects 
the Cambrian rock- parallel to their bedding. This is a line-grained 
rock, although minor portions are of medium to coarse grain. Undec 
the microscope it shows a- a rather fresh muscovite granite in which 
some oligoclase occurs with orthoclase. The quartz shows gentle 
undulose extinction, but the deformation indicated i^ not great. A 
little sericite and less kaolinitic materia] has been developed in the 
feldspars. This granite weathers into small rounded bowlders, and 
exposures are scarce. It is complexly cut by joints 6 inches apart, 
and in those parallel to the bedding of the surrounding sediments 
quartz veins occur. A -mall area of a similar muscovite granite of 
medium grain is exposed one-fourth mile west of Southern Klondike. 
An aplitic sheet of the game rock injects the limestone in a mining 
tunnel at the village. The sedimentary rocks are more or less meta- 
morphosed in the vicinity of the granite, the shale in particular being 
altered to a knotted silvery schist. Granite cuts the Cambrian rocks 
and occurs a- pebbles in the Siebert lake beds. It is believed to be 
of post-Jurassic age. 
Earlier rhyolite.— Trior to the eruption of the earlier rhyolite 
which occurs near Southern Klondike the Cambrian rocks and the 
granite were eroded into a group of hills of slightly greater relief 
"Spurr, J. E., Prof. Paper V. S. Geol. Survey X... 42, 1905, pp. 51 55. 
