PINYON PEAK CONGLOMERATE. 187 



unturned Cretaceous sandstones. In all probability the breccia capping 

 the conglomerate is of the same age as that forming the great mass of Two 

 Ocean Plateau. 



It is quite impossible that this enormous mass of basic breccia should 

 have been poured out over so large an area of elevated country before the 

 deposition of the conglomerate and not have furnished a considerable 

 amount of material to the latter deposit. A discussion of the age of this 

 conglomerate will be found in Part I of this monograph. Evidence is 

 there adduced to show that the basic breccia of this region is in all prob- 

 ability of Miocene age and followed the conglomerate. The conglomerate 

 has been referred provisionally to the Eocene period, and has been regarded 

 as a distinct geological formation, to which the name "Piny on Peak con- 

 glomerate" has been given, after the locality where it is so characteristically 

 exposed. 



Southwest of Pinyon Peak and connected with it by a long ridge 8,500 

 feet above sea level, stands an east-west ridge whose culminating' point 

 attains an elevation at least 1,000 feet higher. This prominent ridge, which 

 has never received any distinctive appellation, measures over 2 miles in 

 length, standing out from the surrounding country like a broad rampart. 

 The underlying rocks of the ridge are apparently all Cretaceous sandstones 

 and have been referred to the Laramie formation, although it is quite pos- 

 sible that Montana strata may be represented, passing by insensible grada- 

 tions into higher horizons. The summit of this ridge is capped by a thick 

 deposit of Pinyon Peak conglomerate, which was evidently at one time 

 connected with the main body of Pinyon Peak. The north slopes of this 

 ridge are covered by dense vegetation and by soil, which completely 

 obscure the underlying rocks. On the south slopes the sandstones are 

 exposed for a long distance, but near their base the glacial drift comes 

 in and buries everything beneath it. 



From the divide at the head of Gravel Creek there is a descent of over 

 1,000 feet in 5 miles, the country south of Pinyon Peak falling away steadily 

 toward Pacific Creek, which lies just south of the limits of the mapped 

 area. Gravel Creek, characteristically named from the gravels which line 

 its banks, trends due south along the west base of Big Game Ridge. A 

 north-south fault probably runs along the west base of the ridge, although 

 its course has never been determined. The area of country lying between 



