18 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
the north face of Lysite Mountain, Tepee Trail strata lie with ap- 
parent conformity on lake beds of Green River type about 220 feet 
thick (Tourtelot, 1946). These lake beds are identical in type to those 
in the Tatman formation in the central part of the Big Horn Basin 
to the north. The relations between the Tatman formation and the 
lake beds and the overlying strata of the Tepee Trail formation of 
Lysite Mountain actually are indeterminable, but the available data 
suggest that middle Eocene time may well be represented in the lower 
part of the Tepee Trail. 
The top of the lake beds at Lysite Mountain is at an altitude of 
about 6,400 feet. On Tatman Mountain, 70 miles northwest of Lysite 
Mountain, the Tatman formation is about 700 feet thick (Van 
Houten, 1944, p. 194) and the uppermost beds preserved are at an 
altitude of about 6,200 feet. At Squaw Buttes, 55 miles northwest of 
Lysite Mountain, the Tatman formation is about 800 feet thick (Van 
Houten, 1944, p. 192), and the uppermost beds preserved are at an 
altitude of about 5,900 feet. Although the present altitude of the Tat- 
man formation is in part the result of post-Tatman structural move- 
ments (Van Houten, 1944), the essential uniformity of altitude of 
the youngest lake beds in the three areas mentioned makes it possible 
to interpret them as parts of a single episode of lake deposition. The 
Tatman formation is considered to be early Eocene in age in the 
central part of the Big Horn Basin (R. L. Hay, personal communica- 
tion, 1956), but the lake beds on Lysite Mountain could be either 
early or middle Eocene in age, or both. Even if the lake beds on 
Lysite Mountain should be considered to be middle Eocene in age, 
there is no line of evidence to suggest that all of middle Eocene time 
is represented there. The continuation of lake deposition from early 
to middle Eocene time in southwestern Wyoming and Utah is well 
known. Dane (1954) has shown that parts of the ancient Green 
River Lake persisted even into late Eocene time. 
Somewhat similar age relations of the lower part of the Tepee 
Trail formation can be deduced from the sequence in the Boysen 
area (Tourtelot and Thompson, 1948), just west of the area shown 
in figure 2. In the Boysen area, near Wind River Canyon, the Tepee 
Trail formation rests with apparent conformity on a brightly col- 
ored sequence continuous with the lower part of the Wind River 
formation. The brightly colored sequence was considered by Tour- 
telot and Thompson to be a part of the Wind River formation that 
might be of early middle Eocene age. This leaves most of the middle 
Eocene to be accounted for, and, provisionally, it is here considered 
to be represented in the lower part of the Tepee Trail formation of 
