686 DESCRIPTIVE GEOLOGY. 



developing steep cliffs and precipices not unlike the outlines of many 

 granites. The same reddish tints observed characterizing the rhyolites to 

 the north may be seen here. The extreme southernmost end of the range 

 was not visited, and other forms of rhj^olite may exist there, with possibly 

 isolated patches of the older sedimentary strata. 



In crossing the range from west to east at Golconda Pass, a low 

 depression in the rhyolitic body, there is seen at the entrance of the canon 

 an outcrop of bluish-gray limestone, so obscured either by the overlying 

 rhyolite or by the coarse Quaternary gravel that its relations with other 

 sedimentary beds are entirely wanting; it has, however, from its proximity 

 to other beds in the range, been colored upon the map as belonging to the 

 Star Peak Triassic. The rhyolite extends up to the summit of the pass and 

 for some distance down the eastern slope, the entire mass having a gentle 

 inclination to the eastward. 



Directly superimposed upon the rhyolite occurs a long north and south 

 ridge of dark compact basalt, which form the eastern foot-hills. In places, 

 it rises above the rhyolite in bold, prominent masses, presenting unbroken 

 cliff-like faces several hundred feet in height, toward the line of contact, but 

 falling away with even slopes toward the valley. The entire basaltic 

 body, which is a massive eruption, inclines, like the rhyolite, to the 

 eastward. Along the base of the basaltic ridge, skirting the valley, are 

 some interesting stratified beds, which have been tilted up by the outbursts 

 of the volcanic rocks, and consequently are of earlier age than the massive 

 eruptions of basalt. They belong, undoubtedly, to the same geological 

 horizon as the upturned sedimentary beds bordering the Augusta Mountains 

 and Shoshone Range, and have therefore been referred to the Truckee 

 Miocene. Although they are well exposed here in many of the ravines and 

 basins, they offer no good sections across the beds, owing to their loose, 

 friable nature and irregular modes of weathering. The upper stratum, 

 which is about 4 feet thick, consists of light cream-colored beds of exceed- 

 ingly fine volcanic ash, more or less compacted together and splitting into 

 thin layers, below which is a bed, also 4 feet thick, of lavender-colored 

 sands, so very friable as to crumble at the least blow into a fine pumice-like 

 powder. This is in turn underlaid by strata of undetermined thickness, 



