\ st. sonn.] WIND RIVER BASIN—TERTIARY AND POST-TERTIARY. 263 
Mesozoic series, forming a gently sloping plane loaded with morainal 
deposits. The south-side blufis exhibit less perfect exposures of the 
same rocks, which extend but a short distance below the lake, whence 
the border slopes and uplands alike are covered with the loose drift 
materials all the way to Wind River. 
A high bench projects into the basin between Bull Lake Fork and 
Sage Creek, traversed by two or more narrow drainage channels, in the 
steep bluffs of which similar exhibitions of horizontal Tertiary strata are 
met with. In the borders of one of these ravine-like depressions about 
two miles south of Bull Lake Tork and as far again from Wind River, 
the exposures consist of soft yellowish sandstones containing vegetable 
remains like compressed stems, and which are weathered into curious 
monumental forms by atmospheric erosion. Higher beds apparently be- 
longing to the same series were observed in the divide between Wind 
River and Sage Creek, in the south slope of which to the west of the 
depression down which the road passes into the valley of the latter 
stream, the same soft yellow sandstones reappear, in horizontal position, 
on the west flank of the outer mountain fold in which the Mesozoics are 
brought to view. 
A few miles to the west-northwest of the last locality, in the high out- 
lying bench, pale red variegated deposits overlaid by drab and greenish 
arenaceous clay appear in the east side of a wide shallow drainage de- 
pression tributary to Sage Creek above the bend. These deposits, con- 
stituting here well-marked horizons gently inclined in the direction of 
Wind River, hold a position superior to the dark drab clays of the Creta- 
ceous Colorado Group, and to the northeast they pass beneath the above- 
mentioned soft yellow sandstones that occupy the interval extending over 
to Wind River. The geological relations of these horizons are obscured 
along the line of contact with the subjacent Colorado shales, where they 
have been eroded and overlaid by the uncontormable conglomerate of 
Pliocene, or possibly Post-Tertiary age. This interval may well embrace 
the horizon of the Fox Hills Cretaceous, which shows characteristic ex- 
posures in the bluffs above Bull Lake. Lithologically, the deposits here 
alluded to recall the exposures on Wind River in the vicinity of Dry 
Creek, where. as has been stated in a preceding page, similar reddish 
and drab horizons occur, resting upon a heavy ledge of buff sandstone, 
which is gently upraised to the southwest. The local appearance of the 
above-mentioned deposits is shown in the profile section representing the 
mountain flank in the vicinity of Sage Creek Caton. At the time of the 
examinations in this quarter it was the impression that the reddish varie- 
gated beds here alluded to were one and the same with the great forma- 
tion of similarly colored variegated deposits that constitute so important 
a geologic feature in the mid-basin area a little higher up Wind Miver. 
Post-Tertiary.—In the area of the basin region, even including the 
mountain border, it is probable that comparatively slight changes in the 
pre-glacial surface contours have been effected by the erosive agents 
that have wrought during and since the glacial epoch. Speaking in gen- 
eral terms, the conntry here alluded to has probably suffered to greater 
extent changes in its surface configuration due to fluviatile and those 
other potentatmospherical denuding agents than that produced by glacial 
action. The latter has evidently acted with greater effect as a degrad- 
ing force in the high mountain regions, while in the lower border region 
it was chiefly confined to a transporting function. In this latter respect 
the results are grouped about the debouching cafions, where they may be 
advantageously studied as so many local exhibitions of a part of the 
phenomena of glacial section. The great ice-flows naturally sought the 
