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



termed the Sierran 21 period, and the larger detrital slopes of the Great 

 Basin is referable to this period. 



The older detrital materials have undergone uplift at many points. 

 The hills just north of the Cave Spring road and just east of Fish Lake 

 valley are largely Pleistocene conglomerates overlying the Esmeralda 

 formation. This conglomerate is somewhat consolidated and dips north- 

 erly at angles of 10 to 35 degrees. There may be observed in it a white 

 layer composed of carbonate of lime. This is seen in the east face of the 

 first hill north of the Cave Spring road, and also on the north face of the 

 hill 4 miles northeast of the Crossing. To the south of the Cave Spring 

 road there are heavy beds of gravels and detritus, possibly formed at the 

 same time as the Pleistocene conglomerate, north of the road. The beds 

 to the south of the road are not tilted, but have undergone elevation, 

 forming a striking terrace (plate 8) facing Fish Lake valley. The recent 

 "washes" in this terrace show a thickness at one point of 250 feet of 

 detritus and gravel containing some boulders six feet in diameter. 



There are many gravel patches mixed with angular detritus on the 

 north slope of the Palmetto mountains and of the Silver Peak range east 

 of the road from Silver Peak to Oasis. The altitude of these masses is 

 approximately 6,500 feet, but they have a vertical range of several hun- 

 dred feet, probably due to these loose materials creeping down the slopes. 

 There is not much doubt, however, of their Pleistocene age, as they in 

 part distinctly overlie Tertiary lavas. The pebbles in these masses are 

 composed of granite, slate, and lava. Mr J. E. Spurr has noted in other 

 ranges of mountains in western Nevada bodies of gravel, often at an 

 elevation of 6,000 feet, which may be of the same character as those here 

 referred to. The gravels seen by Mr Spurr are thought by him to be 

 shore gravels formed by lakes contemporaneous with the Pliocene Sho- 

 shone lake of the Fortieth Parallel region described by Clarence King. 

 The evidence as to the origin of these gravels in the Silver Peak region 

 is too meager to warrant any conclusion further than they are probably 

 Pleistocene. 



In general it may be said that the rocks of the Pleistocene detrital 

 masses are usually the same in kind as the rocks of the present drainage 

 above them, indicating a local origin. When the older detritus is fine 

 grained, and where it is largely volcanic, it is sometimes difficult to dis- 

 tinguish it from the ordinary sediments or volcanic sandstones of the 

 Esmeralda formation. Eesting on the lavas north and northeast of Piper 

 peak, at an elevation of about 8,000 feet, there are some remarkable 



21 Proceedings of California Academy of Science, third series, Geology, vol. 1, p. 269. 

 The term was introduced by O. H. Hershey. 



