184 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



REGION OF PINYON PEAK. 



Pinyon Peak, from whatever point of view it is looked at, stands out 

 prominently above the surrounding country. It rises boldly above Wol- 

 verine Creek for over 2,000 feet, and for more than 1,500 feet above the 

 connecting saddles which relate the peak to the mountains both east and 

 west. To the south the country falls away rapidly, and the peak presents 

 a still more isolated appearance when seen from that direction. In outline it 

 resembles a truncated pyramid rising from an elevated base. Dense timber 

 covers the peak on all sides except where the abrupt cliffs which form so 

 conspicuous a feature of the mountain are too precipitous to permit growth 

 of vegetation. 



Pinyon Peak attains an altitude of 9,600 feet above sea level. The 

 summit is flat topped, and the long ridges putting out in all directions from 

 the central mass resemble a very slightly inclined plane, with occasional 

 points rising above the general level. It is this peculiar feature of the 

 peak which, from a distance, gives it the form of a truncated pyramid. 



Resting upon the Laramie rocks, which everywhere form the base of 

 Pinyon Peak, comes a remarkable deposit of coarse conglomerate, measur- 

 ing nearly 600 feet in thickness. This conglomerate forms the greater 

 part of the summit of the peak and the many long ridges radiating from 

 the central bod}'. Nine-tenths of the conglomerate consists of smooth, 

 highly polished, waterworn material of various-colored quartzites. The 

 prevailing colors are red, white, and yellowish brown, but all so mingled 

 together as to give a general tone of reddish gray to the abrupt walls 

 and escarpments which form so prominent a feature of the deposit. This 

 siliceous material varies from gravel to coarse pebbles and quartzite bowl- 

 ders measuring 10 and 12 inches in diameter, although the largest are 

 by no means common. Much of the conglomerate is indurated and held 

 together by fine sands and ferruginous material. Occasionally thin beds of 

 friable sandstone are encountered throughout the conglomerate, but they 

 are insignificant in amount and do not appear to be very persistent over 

 any great distance, occurring as lenticular bodies in the coarse conglom- 

 erate, then as well-defined strata. Everywhere on the slopes of Pinyon 

 Peak the beds vary greatly in thickness and in continuity. In general 

 it may be said that the conglomerate formation carries more sandstone 



