246 H. W. TURNER GEOLOGY OF THE SILVER PEAK QUADRANGLE 



Conglomerate beds. — The extensive conglomerate beds 4 miles north- 

 east of the Monocline show the action of moving water, and hence are 

 possibly of fluviatile origin. 



The Tertiary period in this region being a time of extensive volcanic 

 activity, the outlines of the lake must have undergone frequent changes, 

 and undoubtedly there were local upheavals and subsidences during the 

 lake period. The coarseness of the volcanic sediments are, however, no 

 evidence as to a shallow-water origin, since the ashes would be thrown out 

 from volcanoes all over the lake and form coarse deposits even in deep 

 water, where under normal conditions only fine sediments would be 

 deposited. 



Thickness of the beds. — ISTo continuous section of the entire formation 

 was found, but an attempt was made to estimate the approximate thick- 

 ness of the beds. They dip nearly everywhere at angles varying from 5 

 to 60 degrees from the horizontal and are broken by numerous small 

 faults, so that often a layer followed along the strike is found to offset 

 from 10 to 100 feet or more every few hundred feet. 



However, the lake sediments are finely exposed in the large area east 

 of the north end of the Silver Peak range and in a northwest-southeast 

 section constructed here across the strike of the beds. Xo evidence was 

 noted of a repetition by faulting or folding, and if there is no repetition 

 the series must have a total thickness of over 10,000 feet. Detailed 

 evidence as to this section and other information concerning the Esme- 

 ralda formation will be found in the paper before referred to in the 

 Twenty-first Annual Eeport of the U. S. Geological Survey. 



NEOCENE RIVER GRAVELS 



Outside of the gravels of the Esmeralda formation, there are in the 

 southern part of the quadrangle masses of well rounded gravel which 

 have no established connection with the lake beds. They presumably are 

 river deposits from streams that existed at the same time as lake Esme- 

 ralda. 



One of the masses lies 4i / o miles south of Cow Camp spring, east of the 

 road to Oasis; it is capped by basalt. The pebbles are well water-worn 

 and are of granite, slate, and lava. Another lies 4^ miles southwest 

 of Piper peak. The pebbles of this area are many of them several inches 

 in diameter. The deposit rests on supposed Ordovician rocks, next to an 

 area of rhyolite. Scattered pebbles are also found on the crest of the 

 Palmetto mountains about little patches of basalt, suggesting that they 

 are remnants of a river deposit once covered by basalt. A large area 

 of gravel and sand lies about 5 miles north of west from Piper peak and 



