POST -CRETACEOUS HISTORY OF WESTERN WYOMING 199 



may well belong to the same stage, but they are less significant 

 because they lie upon horizontal strata. The more or less level 

 crest of the Hoback Range, at 9,000-10,000 feet, is somewhat more 

 suggestive of planation. This range consists of highly folded hard 

 and soft rocks, which if planated and then dissected would cause 

 the sculpturing of level- topped ridges. This type of topography 

 prevails southward along the Wyoming Range and is conspicuous 

 near Labarge Mountain northeast of Kemmerer. Along the crest 

 of the Gros Ventre Range and especially in the western half there 

 are some flats of considerable area at elevations of 10,300-10,800 

 feet. These have been cut across strata of varying hardness 

 tilted at angles of 10-50° on both flanks of an anticline. However, 

 it should be noted that they lie 1,000-2,000 feet lower than the 

 Wind River plateau. As the mountain ridges to the southwest are 

 considerably lower (8,000-9,500 feet) , they may belong to later pene- 

 plains, unless the Wind River surface has been notably warped. 



From the canvass of the district it appears that the peneplain 

 is preserved best on the very massive hard rocks of the broad 

 x\rchean outcrop in the Wind River Mountains. Somewhat 

 doubtfully I correlate with this the smaller flats along the crests 

 of ranges where hard folds in Paleozoic rocks have been trunkated. 

 Over the intervening territory the weakness of the Mesozoic and 

 Tertiary rocks has enabled the streams to destroy the peneplain. 



In the Teton Range there is a broad expanse of the massive 

 Archean formations, and hence the preservation of another large 

 peneplain remnant might be anticipated. Instead we find an 

 extremely rugged surface with but few small elevated flats. The 

 east base of the range is marked by a fault of more than 10,000 feet 

 displacement, along which the soft Cretaceous shales and Tertiary 

 clays have been brought down to the level of the massive Archean 

 gneiss. There is good evidence that this fault is not younger than 

 the mid-Tertiary epoch of diastrophism. Urged by such condi- 

 tions, the rejuvenated streams are believed to have rapidly exca- 

 vated Jackson Hole from the Cretaceous and Eocene beds, thus 

 leaving the Archean mass of the Tetons to form a wall of imposing 

 height along the west (Fig. 17). Consequent streams on the face 

 of the wall were able to cut only short steep gorges in the block, 



