POST-CRETACEOUS HISTORY OF WESTERN WYOMING 311 



this cycle, although the correlation is not assured. At the south- 

 east end of the range, Westgate and Branson^ distinguish two 

 erosion cycles beneath the summit peneplain and higher than the 

 cycle represented by Table Mountain near Lander, which I have 

 tentatively correlated with the Blackrock cycle, farther east; 

 these do not appear to be as distinct in the region I have studied, 

 and were not recognized. 



Still farther westward, there are, at a comparable elevation, 

 broad, open, and well-graded valley heads both east and west of 

 Twogwotee Pass, but always deeply intrenched farther down- 

 stream. Aged forms of similar aspect and relations have been 

 observed between the valleys of Jack Pine and Conant creeks in 

 the northwest part of the Teton Range. This gently sloping sur- 

 face lies decidedly higher than the oldest deposits of glacial drift, 

 but is a thousand feet or more below the tabular remnant inter- 

 preted as possibly part of the Goat Flat peneplain. In fact, the 

 whole western slope of the Teton Range in the vicinity of the north 

 fork of Pierre's River is a gently inclined plain rising from the 

 general plateau level of about 6,000 feet to the bases of the more 

 rugged peaks at 9,000-9,500 feet. Although it has been incised 

 by deep canyons, there are still broad smooth remnants on the 

 divides. The fact that the canyons are much deeper near their 

 heads than farther west suggests that the surface has been tilted 

 by being raised on the east. Although it is underlain by rocks of 

 various types and structures, the plain is but Httle modified by 

 structure. 



At the west end of the Gros Ventre Range a few miles northeast 

 of Jackson, there are rather large remnants of an ancient gentle 

 valley slope cut across folded Paleozoic rocks. These remnants 

 stand nearly 2,000 feet above the channels of the present streams. 



No doubt the surface produced in the Union Pass cycle was 

 broadly planed on the weak Mesozoic and Tertiary clays, although 

 only late mature topography developed on the harder rocks near 

 the headwaters of the streams, and some remnants of the summit 

 peneplain were left untouched. In this cycle the latter was 



^L. G. Westgate and E. B. Branson, "Cenozoic Histon- of the Wind River 

 Mountains," Jour. GeoL, XXI (1913), 142-59. 



