NO. 4 GEOLOGY, WIND RIVER BASIN—TOURTELOT 5 
and late Eocene age, grades southward along the scarp into orange- 
red fine-grained rocks. These, in turn, grade southward into gray 
siltstone and claystone associated with thin carbonaceous beds and 
sandstone in channels. The boulder conglomerate and conglomeratic 
sandstone contain pieces of sandstone, limestone, and dolomite de- 
rived by erosion from Paleozoic rocks. Fragments of Mesozoic rocks 
are included in the Lysite member along Lysite Creek in T. 39 N., 
R. go W., and sec. 9, T. 39 N., R. 89 W. 
The Lost Cabin member of the Wind River formation consists 
chiefly of violet-red, purple, and gray variegated siltstone and clay- 
stone with beds of gray to brown fine-grained to conglomeratic sand- 
stone and boulder conglomerate. The boulder conglomerate makes 
up the main mass of Cedar Ridge in the southeastern part of T. 39 N., 
R. 89 W. The average size of the rock pieces in the conglomerate is 
about 1 foot, but pieces as large as 6 feet in diameter are locally 
present. The boulder conglomerate grades southward into finer 
grained rocks, and claystone and siltstone become prominent in the 
sequence as the conglomeratic beds disappear. Channels filled with 
sandstone are a conspicuous feature of the fine-grained facies of the 
member. The boulder conglomerate is made up almost entirely of 
granite, gneiss, and other igneous and metamorphic rocks eroded from 
the Big Horn Mountains. 
The two members of the Wind River formation could not be sepa- 
rated west of R. 91 W., but boulder conglomerate similar to that in 
Cedar Ridge forms prominent hills just south of the Cedar Ridge 
fault in T. 39 N., R. 92 W., and also grades southward into finer 
grained rocks. 
Together, the composition and other characteristics of the Lysite 
and Lost Cabin members of the Wind River formation indicate a 
tectonically active mountain front shedding debris into the adjacent 
basin. The coarseness of the boulder conglomerate suggests that 
depositional slopes may have been steep. The Paleozoic and Mesozoic 
materials in the Lysite member and the Pre-Cambrian material in the 
overlying Lost Cabin indicate the progressive nature of the deforma- 
tion undergone by the mountains and their contemporaneous erosion. 
THE TEPEE TRAIL FORMATION 
In the Absaroka Range, about 70 miles west-northwest of the 
northeastern part of the Wind River Basin, Love applied the forma- 
tion name “Tepee Trail” to a thick sequence of volcanic sedimentary 
rocks that also include volcanic breccias, tuffs, and some flows. The 
