CENOZOIC HISTORY OF WIND RIVER MOUNTAINS m5 7 
Along the Beaver north from Hailey, No.1 has | 
been well dissected. During this later terracing & 
Little Popo and Willow Creek have cut back and 
captured the streams which during the cutting of 
No. 1 had flowed northwest to Lander. In some 
cases there has been a recent silting-up of valleys, 
into which filling the present streams are again 
cutting. This is the case along the lower Beaver, 
the Wind River, and Sage Creek. The Little Wind 
River and the Big Popo are flowing on broad flats, 
and if silting has been going on they have not com- 
menced to cut again. 
M2, later moraine 
WIND RIVER 
GLACIAL HISTORY 
The Wind River Mountains support a dozen or 
more small glaciers, and the summit region shows 
quite generally an Alpine topography, as a result 
of cirque growth (Fig. 1). In Pleistocene time 
glaciers occupied the main valleys, and in some 
cases extended a number of miles out onto the 
plains at the base of the range. Glacial features 
are considered in this paper only for the purpose 
of dating the terracing which has already been 
described, and for this purpose the conditions 
about Bull Lake Creek can best be used (Fig. 8). 
Moraines of an earlier and a later period occur; 
and in each case the ice advanced about ten miles 
from the foot of the range, almost to the Wind 
River. The moraines of the later glaciation make 
concentric ridges about the lower end of Bull Lake 
and connect with gravel outwash which floors the 
inner valley (Fig. 8, A—A) of Wind River. Since 
their deposition they have been cut somewhat 
where Bull Lake Creek passes through them, 
and along Wind River ten feet of silt has been 
deposited above the outwash gravels (the river 
is now cutting into silt and gravels); but in all 
8 lL ES 
Profile along Bull Lake Creek, showing position of the two moraines and of the valley terraces. 
---PALE OZO/C---- > 
Fic. 8: 
