a 
NO. 4 GEOLOGY, WIND RIVER BASIN—TOURTELOT 25 
Although the white clastic facies and scattered fragments of pre- 
Tertiary rocks in the Tepee Trail formation, such as those at the 
mouth of Sagebrush Draw, indicate some erosion of the uplands of 
pre-Tertiary rocks, the amount of such materials seems anomalously 
small. This is particularly evident where the Tepee Trail formation 
was deposited at the foot of relatively steep canyons such as shown 
in figures 6 and 7. Whatever may have been the actual amount of 
material eroded from the pre-Tertiary rocks of the mountains in 
Tepee Trail time, it seems obvious that such locally derived material 
was considerably diluted and may have been masked by the larger 
amount of volcanic material. 
A further possible explanation related to the mode of transport 
of the volcanic material also seems attractive. Hypothetical mud- 
flows, of which possibly Squaw Buttes is the only remnant, have been 
suggested as an agent in the transport of cobbles of volcanic rock to 
the northeastern part of the Wind River Basin in addition to possible 
stream transport of such materials from the Absaroka source. Mud- 
flows of such magnitude seemingly would be most likely to occur 
during long-continued volcanic activity in the Absaroka-Yellowstone 
region. It is easy to believe that large amounts of relatively fine- 
grained ejecta would have been carried aerially to the east. The 
presence of glass shards in most rocks and abundant euhedral crystals 
of feldspar in some of the resedimented crystal tuffs point to such 
a condition. If this truly pyroclastic material was transported aerially 
to the northeastern part of the Wind River Basin and deposited on 
the slopes in large enough amounts, the streams would have been 
choked with such debris and incapable of eroding the pre-Tertiary 
rocks. The pyroclastic material would have moved down the slopes 
either by rill wash or various kinds of mass movement. The streams 
at the bottoms of the slopes were short, draining only the south sides 
of the Big Horn and Owl Creek Moutains, and their capacities would 
be overloaded by relatively small amounts of pyroclastic debris. 
Hence, except for canyons that may have been delivering material 
from the Big Horn Basin into the Wind River Basin, little pre- 
Tertiary material could be expected to be incorporated in the Tepee 
Trail formation even though it was deposited at the foot of well- 
developed highlands. 
The upper unit of the Hendry Ranch member reflects a rather 
large change in depositional conditions. Vitreous volcanic ash became 
really conspicuous for the first time in strata assigned to the Tepee 
Trail. In addition, erosion of the pre-Tertiary rocks seems to have 
become more effective, judging from the conglomerate made up of 
