POST-CRETACEOUS HISTORY OF WESTERN WYOMING 197 



trenching of the plateau by many canyons, and especially the 

 scouring of its surface by widespread alpine glaciers in a compara- 

 tively recent epoch, have generally effaced the original details of 

 its topography. The higher mountain peaks do not, however, 

 appear to have any relation to especially hard rocks, but rather 

 form a definite range or divide near the crest of the anticline. 

 In short, if the plain was largely fashioned by wind action, all 

 evidence of the fact seems to have disappeared. 



The competency of streams to reduce hard and soft rocks alike 

 to monotonous relief, without removing the last residual mountains, 

 is generally admitted. Upon such a plain there should be only 

 thin alluvial deposits and widespread residual soil. It is an 

 observed fact that on the southwest side of the Wind River Range 





Fig. 15. — Drawing (from a photograph) of Wind River peneplain and range as 

 seen from Triangle Peak in the Gros Ventre Range. 



deposits of soil, several feet deep, due to the decay of the granitic 

 rock in place, still exist upon the tops of mountains 11,300 feet 

 high, which constitute a part of this or a still younger plain (Fig. 

 16). Since the original drainage can no longer be seen, and since 

 in all but a few places topographic detail has been modified by 

 subsequent glaciation, the evidence directly in favor of river 

 erosion is but little more satisfactory than that for wind action. 

 The most significant fact is perhaps the continuous range of peaks, 

 forming a divide independent of rock structure. Such divides 

 are characteristic of stream-made topographies, but of no others. 

 As the problem now stands there is then only a measure of probabil- 

 ity, but not proof, that streams were the agents of planation; and 

 so, for convenience, the old plateau surface will be called in later 

 pages a "peneplain," implying thereby only that it was produced 

 by the long-continued action of degrading agencies. 



If reconstructed by filling the depressions cut out of it, the 

 summit peneplain would stand forth as a gently undulating 



