470 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



Buffalo Fork Peak, wliicli reaches an altitude of 10,200 feet, approxi- 

 mately, above the sea, offers an extensive view of the surrounding 

 country, and the isolation of the great dome-shaped uplift of which it is 

 the culmination, is most clearly brought out. To the north, beyond the 

 deep gorge traversed by Buffalo Fork in its passage across this mountain 

 ijplift, the corresponding northern half of the mass shows as a great 

 half-dome, over the summit of which the Quebec Group limestones are 

 curved from west to east. In the central portion of the uplift the 

 Archaean nucleus forms a lofty bench, in whose rugged caiion-face the 

 gneissose rocks present precipitous exposures several hundred feet in 

 height. On either flank reclines tiie Carboniferous, the inferior red- 

 stained beds forming a marked and easily traced horizon. The latter 

 deposits slope quite regularly, with a moderate inclination on the eastern 

 side, where they are seen on either side of the broad mountain basin, 

 gradually descending, and forming with the Quebec limestones lines of 

 low mural exposures. These extend a considerable distance up the val- 

 ley of both the main stream to the eastward and that of Lava Creek to 

 the northeast, above which the slo^Des are broken and do not reveal sat- 

 isfactory exposures at this distance. 



But on the western flank of the mountain an interesting series of 

 strata appears, all inclining off the mountain slope, exhibiting as seen 

 from this point the following lithological appearances : First api)ears a 

 heavy mass of Carboniferous limestone, which forms a sort of abrupt 

 foreland reaching well up on the western flank of the mountain, and de- 

 scending into the narrow valley of a small tributary which gains the 

 north bank of Buffalo Fork a short distance below the great gorge. In 

 the opposite acch\dty of this little valley appears a set of strata, which 

 probably represent the siliceous beds in the upper part of the Carbon- 

 iferous. The upper i)ortion of this slope shows a heavy deposit of deep 

 red beds, interspersed with beautiful green herbage-clad slopes, the 

 stratigraphic position and lithological character of which refer them 

 with little doubt to the Triassic. In the gentler western slope appear 

 less distinct exposures of light-drab deposits, with interlaminated in- 

 durated, probably calcareous, layers, which may pertain to the Jurassic. 

 And in the undulating slopes intervening between this point and Station 

 XLYIII, the light and buff- gray arenaceous clays and sandstones of the 

 Tertiary succeed, as has already been noted in connection with the ob- 

 servations made at that locality. The Carboniferous and Mesozoic beds 

 incline at a rather steep angle to the westward, and apjDear to fold round 

 the northern flank of the mountain, in the slopes descending into the 

 vaUey of Pacific Creek. This feature was especially remarked from 

 Htation XL VIII, from which point of view a high crown of the mount- 

 ain to the north of the caflon slopes shows a series of buff, rusty buff', 

 and reddish streaked beds, probably representing the Silurian and lower 

 beds of the Carboniferous, dipping steeply to the northward. On the 

 opposite or southeast flank, which falls into a broad depression oi^ening 

 between the uj)per vaUey of Black Eock Creek and the Buffalo Fork, 

 the strata rise up on the mountain presenting escarped exposures facing 

 Buffalo Fork Peak and the canon. On the outer slopes the "red beds" 

 reach up several hundred feet, apparently curving round this side of 

 the mountain conformably with the Carboniferous and older sedimentary 

 formations. This feature is finely displayed from the heights just south 

 of Togwotee Pass, a few miles to the east-southeast; but the interven- 

 ing undulating surface seems to be covered with the debris of the vol- 

 canic deposits, so that the "red beds" may constitute the latest of the 

 sedimentary deposits visible. 



