PINYOiSr PEAK CONGLOMERATE. 185 



near the base than it does higher up in the deposits. Mingled with the 

 quartzite are found rounded and polished pebbles of granite, gneiss, 

 argillite, and indurated slates, probably derived from Archean and pre- 

 Cambrian land surfaces. Occasional fragments of andesite have been 

 found, indicating a volcanic origin for some of the detrital material. Such 

 pebbles, however, are hard to find and play no part in the great mass of 

 the deposit. Possibly they may have been derived from the capping of the 

 breccia found on the top of Pinyon Peak, as described later. Pebbles of 

 sandstone, limestone, and other sedimentary rocks have been picked up in 

 the conglomerate, evidently derived from neighboring Paleozoic and Meso- 

 zoic sources. Neai the base of the conglomerate waterworn fragments of 

 coal have been observed associated with gray sandstone and resembling 

 that known to occur in the Laramie. 



Throughout the entire mass of the conglomerate the bowlders present 

 much the same general appearance from base to summit. The characteristic 

 forms of the long ridges radiating from the culminating mass of the peak 

 are due solely to the peculiar erosion of the indurated coarse conglomerate. 

 Erosion has worn deep recesses into the very core of the peak, with broad 

 amphitheaters encircled by nearly perpendicular walls for long distances, 

 absolutely impossible to scale. Along their tops many of these ridges are 

 mere knife edges, barely permitting one to walk in safety. In places the 

 vertical walls rise for over 300 feet without any perceptible change. 

 Enormous amounts of the conglomerate have been swept away by erosion, 

 the material when once disintegrated being easily transported. Every- 

 where the lower slopes of Pinyon Peak are covered by loose pebbles and 

 bowlders brought down from higher elevations. Coulter and Wolverine 

 creeks are literally clogged up with quartzite bowlders, and Gravel Creek, 

 draining the southwest slopes of Pinyon Peak, derives its name from the 

 huge piles of reassorted bowlders which line the valley for miles. 



For many years the gravels along Snake River and Pacific Creek in 

 the neighborhood of Jackson Lake have been known to yield a slight 

 amount of gold to mining prospectors, but not in remunerative quantities. 

 Evidences of gold may be found by washing with a pan almost anywhere 

 in the streams coming down from the conglomerate. It is quite likely that 

 this gold has in great part been derived from the conglomerates of the 

 Pinyon Peak formation. In many places the indurated conglomerate and 



