236 REPORT UNITED STATES GEOLOGICAL SURVEY. 
Creek. The way thus far has passed successively over the hidden ledges 
of the Lower Carboniferous limestones and Silurian formations, the latter 
appearing as low ledges of rusty weathered limestone in the high ridge 
crests off to the eastward either side of the Warm Spring Cafion. In 
the south-side slopes rising from the Warm Spring Basin we encountered 
along the trail much débris of coarse buffand red sandstone, probably Pots- 
dam, which extends some 2 or 3 miles, reaching an altitude of near 9,400 
feet. Here we first met with Archean exposures, occurring in lowcombs 
on the eastern edge of the elevated grassy plateau that stretches across 
the summit in the vicinity of the pass. To the west of this point the 
surface is deeply buried beneath the Quaternary gravels; meager ex- 
posures of yellow and drab sandy clays, possibly referable to the Tertiary, 
occasionally appear in shallow valleys occupied by the southern sources 
of Warm Spring Creek. 
Above Warm Spring Creek the course of Wind River for 8 to 10 
miles is east-westerly. About midway it is joined by a small affluent 
heading in the watershed a few miles to the northwest of Union Pass 
summit, and which, itis believed, defines the limits of the Paleozoic belt 
around the northern extremity of the Wind River uplift. Vestiges of 
“red beds” holding thestratigraphical position of the Trias were observed 
in the slopes descending to Wind River between the confluence of this 
stream and Warm Spring Creek, but the surface configuration of the 
valley slopes, after the stream enters the hills, shows them to be wrought 
out of the comparatively soft deposits of Tertiary age. This is indicated 
by the benched and densely wooded slopes, contrasting with the long 
declivities characteristic of the Paleozoic mountain flank, as seen in the 
vicinity of Warm Spring Creek, and thence extending south nearly the 
entire length of the range along its eastern front. 
Warm Spring Creek, as before mentioned, rises in the elevated water- 
shed to the northwest of Union Pass, flowing in a general direction 
about east-northeast, ina direct course about 12 miles. The sources lie 
within the Tertiary area, its middle course occupying a rather wide 
mountain basin excavated out of the Paleozoic belt. Four or five miles 
above its mouth the stream enters a narrow defile which it has exca- 
vated across the upraised Paleozoic belt, its bed at the upper entrance 
to the cation being eroded several hundred feet into the Archean basis 
rocks. Lower down the sedimentary formations close in upon the stream, 
forming cliffs on either hand several hundred feet in height. In a dis- 
tance of 4 miles the stream descends about 600 feet, the course being 
nearly in the direction of the inclination of the strata across which it 
flows, the cafion becoming shal lower and finally emerging in the Triassic 
‘red beds” as the stream leaves the mountain and crosses the narrow 
terrace bordering the right bank of Wind River. The geological section 
exposed in the cafion walls is roughly reproduced in one of the accom- 
panying plates of section diagrams, a description of which follows: 
Section in Warm Spring Creek Canon. 
No. 1. Archean basis rocks, belong to the principal core-mass of the 
range. 
No. 2. Dark, rusty weathered outcrop, probably representing the Pots- 
dam sandstone, and forming the lowest member of the Paleozoic series. 
This ledge rises high up on the wooded Archean ridges that sweep 
round on either hand, and plates the declivity on the south side of the 
moutain basin above the canon. 
No. 3. Position of the Quebec formation, not clearly distinguishable 
