44 LEWIS G. WESTGATE AND E. B. BRANSON 
Verde (Montana), 2,000 feet. At the close of the Cretaceous came 
the uplift by which the present anticlinal structure of the range was 
produced. Parallel to the main uplift, and about six to eight miles 
east from the base of the range, is an anticlinal uplift which brings 
the Triassic, Jurassic, and Dakota Cretaceous out from under the 
Mancos shale, producing an interrupted line of hills (especially 
south of Lander), and forming a longitudinal valley southeast from 
Lander. This valley is now drained by a number of transverse 
streams, but this has apparently not always been the case. 
Extensive erosion followed the uplift of the region, even before 
the time of its earliest Tertiary rocks, for we find the Wind River 
Tertiaries lying on the upturned and eroded edges of the Mesozoic 
rocks. In early Eocene times, this erosion was replaced, about the 
base of the mountains, by deposition. The best section of the Ter- 
tiary rocks" shows along the north face of the Beaver Divide, where 
the early Eocene (Wind River beds) are overlaid by the Bridger( ?) 
and Uinta, and above an unconformity, by the Oligocene. These 
Tertiary rocks, largely shales and sandstones, are alluvial deposits 
laid down by streams from the higher central mountain area. The 
occurrence in the Beaver Divide Oligocene of a t1oo-foot gravel 
layer with bowlders of granite and other crystalline rocks up to a 
foot in diameter shows not only that there was considerable relief 
in the mountain region, but that any cover of sedimentaries had 
been cut through into the crystallines. How long after this the 
Oligocene deposit continued in the Wind River basin is not known, 
for the present top of the Oligocene cannot be shown to be the 
summit of the Tertiary series. Subsequent to Oligocene time came 
the erosion which ended in the production of the summit peneplain 
described below. From this point on, the history of the Wind 
River Mountains is to be read from the land forms and not from 
the sedimentary rocks. 
THE SUMMIT PENEPLAIN 
An accordance of summit levels in the central and northern part 
of the range is believed to be an inheritance from a peneplain which 
formerly extended throughout the range, and which in its highest 
t Sinclair and Granger, Eocene and Oligocene of ihe Wind River and Big Horn 
Basins, Bull. Am. Mus. Nat. Hist., Vol. XXX, Fig. 2 A. 
