CENOZOIC HISTORY OF WIND RIVER MOUNTAINS 155 
River. The slope A-B is not an original plain, but was cut after 
the deposition of the gravels, and antedates the plain D—E, which 
cuts it. 
The last terrace deposit of this kind studied is on the north side 
of Bull Lake Creek (Fig. 3, C), at an elevation of 7,400 feet. No 
section is shown here, but the deposit lies above and distinct from 
the moraine of the earlier glacier, which occupied Bull Lake Creek 
Valley. It is believed to be much earlier than either of the two 
glaciations of the region. 
The meaning of the gravels —These high level gravels are a 
largely unsolved problem to us, as are similar deposits to other 
workers in the Rocky Mountain region. If our correlation is 
Fic. 7.—Diagram to show the relation of gravels on No. 2 (A-B) to the later 
plain (D-E). 
correct, at some time after the up-arching of the summit peneplain 
which had been developed over the entire region, a peneplain was 
developed around the mountain on the Mesozoic and younger beds. 
This is plain No. 2. Low foothills of Paleozoic sandstone and 
limestone rose above this, and within this Paleozoic rim was the 
higher mass of the central crystalline area. At this time broad 
valleys ran back well to the crest of the range. Along Bull Lake 
Creek, six miles within the range, such flats were seen at 9,800 feet, 
and they can be seen fingering into the uplands and rising to them 
with not very steep slopes. This condition was followed by a 
period of piedmont aggradation, which resulted in the deposit of 
the gravels widely about the cafon mouths. This aggradation 
may have been the result of aridity, or of crustal movement. It 
was followed by the planation which produced the nearly level 
flats on Table Mountain, Little Wind River, and Bull Lake Creek, 
which have been described. Subsequent to this period of plana- 
tion came the long period of terracing which produced No. 1 and 
lower plains. 
