NO. 4 GEOLOGY, WIND RIVER BASIN—TOURTELOT 19 
the northeastern part of the Wind River Basin. The Tepee Trail 
formation in the northeastern part of the Wind River Basin thus may 
include rocks of the same age as the upper part of the Aycross forma- 
tion in the northwestern part of the Wind River Basin. 
Van Houten (1950, 1954, 1955) has described a formation of both 
middle and late Eocene age, rich in volcanic material, along the south- 
ern margin of the Wind River Basin. This formation includes ma- 
terial from both the Absaroka volcanic center and the Rattlesnake 
Hills, a volcanic field of middle and late Eocene age in southern 
Natrona County. The middle Eocene part of this sequence is not 
separable from the late Eocene part of the sequence on a lithologic 
basis. 
STRUCTURE 
The Tepee Trail strata of the northeastern part of the Wind River 
Basin are moderately deformed. The most prominent structural fea- 
ture involving the Tepee Trail formation is the Cedar Ridge fault, 
which everywhere within the area of figure 2 forms the southern 
boundary of the Tepee Trail outcrop area. Most of the structural 
features within the outcrop area of the Tepee Trail are related to 
this fault, the displacement of which is indeterminable. A minimum 
displacement of about 1,000 feet, however, is indicated for that part 
of the fault in T. 39 N., R. 89 W. Here, a total of about 500 feet 
of Tepee Trail strata is exposed near the fault, and the top of these 
beds is about 500 feet below the top of Cedar Ridge which is made 
up of Wind River boulder beds. This is the largest displacement that 
can be demonstrated but the actual displacement on the fault may be 
much larger. 
In the Dry Creek drainage, the Cedar Ridge fault divides into 
several branches that enclose grabens in which Tepee Trail strata 
are found, and horsts made up of boulder beds assigned to the Wind 
River formation. Some parts of the faults in this area cut pre- 
Tertiary rocks. 
The Tepee Trail strata exposed along the north side of Cedar 
Ridge probably are cut by many normal faults of small displacement 
and extent. Only a few of these could be mapped and shown on 
figure 2. Most of the minor faults join the trace of the Cedar Ridge 
fault at large angles. Similar minor faults, essentially normal to the 
Cedar Ridge fault, probably cut Tepee Trail strata at other places 
along the Cedar Ridge fault but they could not be recognized. All 
are believed to be the result of adjustments in the relatively down- 
ward-moving block as the major faulting took place. 
