2l6 



ELIOT BLACKW ELDER 



In the Wind River uplift deep canyons have been carved out 

 of the granitic rocks, but extensive remnants of the old plateau 

 surface are still preserved upon the interstream divides (Fig. 12). 

 The relative resistance of the hard Archean outcrops is well shown 

 in the channels of many of the creeks that flow out from the Wind 

 River Range. Thus it is generally easy to ascend these valleys 

 as far as they have been cut through the sedimentary strata, but 

 from the base of the Cambrian inward to the axis of the anticline, 



Fig. 29. — A canyon in the Archean rocks south of Mount Moran, in the Teton 

 Range. 



the Archean outcrop is marked by a series of rapids, falls, and 

 narrow gorges which make even foot travel difficult if not imprac- 

 ticable. Along old faults, which have brought the Archean into 

 contact with some of the weaker members of the sedimentary 

 column — as for example south of the great bend of Green River — 

 the streams have cut merely a few notches in the pre-Cambrian 

 rocks during the time in which the softer sedimentary beds have 

 been completely stripped away to a much lower elevation. This 

 satisfactorily explains why the Wind River plateau has an abrupt 

 front in this locality but not elsewhere. 



