392 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



enormous exposures of red and gray strata appear. To the nortlieast 

 opens the grand canon, a narrow defile bounded by steep slopes and 

 mountain escarpments composed of the magnificent exposure of Carbon- 

 iferous rocks described by Bradley. Far away a line of snowy peaks 

 l^oints out the course of the Wind Eiver Eange ; but grandest of aU are 

 the Tetons, whose great bare peaks rise like gigantic monoliths from a 

 broad mountain summit which even at this late season, July, had not 

 yet put off its winter raiment. 



We had been so long employed in breaking our own trails that it was 

 with a curious mixture of relief and positive pleasure we entered the 

 trail leading up the valley of McCoy Creek, crossing and recrossing the 

 rapid stream, now passing over pretty intervals, then along the face of 

 some jutting spur, until it finally emerges into the upper basin in which 

 this di'ainage is gathered. This little valley has a general course a little 

 north of east and south of west, with but one sharp curve near the mid- 

 dle, where it passes the lower narrow antichnal fold descending from 

 Station XXYII. It can hardly with prop;i?iety be termed a canon, al- 

 though at a few i3oints it is confined within narrow bounds by the near 

 approach of the bordering hills ; but it generally possesses a narrow in- 

 tervale, and at few places are the hills precipitous, though the country 

 is very rough and broken on either side. The stream is bordered by 

 willows, and in places ponded by beaver-dams, and would be beautiful 

 were its waters uncontaminated with the sediments from the placer mines 

 at its head. The fall of the stream in the ten miles between the moun- 

 tain basin and its mouth is about 630 feet. The basin in which the wa- 

 ters from numerous sources are collected is the largest of the mountain 

 basins in the range, and is separated from the basin of John Gray's Lake 

 by a narrow ridge of hills ; the surface is undulating and broken by spurs, 

 and though its altitude may be too great for successful agriculture, it is 

 a valuable grazing region. 



The sources of McCoy Creek rise in the two principal mountain ele- 

 vations of the range, that to the north being the same as the massive 

 mountain whose crest lies on the axis of the Station XXYII anticlinal, 

 and which is only two or three hundred feet lower than Mount Cari- 

 bou on the south, which attains an altitude of 9,800 feet above the 

 sea. This mountain, which was chosen for Station XXVIII and which 

 was also made a station of the primary triangulation by Mr. Wilson, 

 presents an.imijosing appearance from whatever direction it is viewed, 

 and it proved to be a most interesting locality geologically. Its summit 

 forms an irregular, shelving, flattened space, from which radiate three 

 principal spurs, of which the southern is the largest and at one point 

 rises into a dome but little inferior in elevation to the main simimit. 

 The two other spurs project respectively westward and north, inclosing 

 the depression or recess which bears so striking resemblance to a huge 

 crater whose northwest waU has been demolished, as seen from that 

 direction. Besides these, there are several large secondary spurs, the 

 disposition of which is an interesting topographic feature of the moun- 

 tain. They form rugged ridges in the easterly face of the mountain, en- 

 vironing at their heads little Alpine amphitheatres in some of which 

 aiestle tiny lakelets, dammed by accumulations of debris through which 

 their waters percolate and form the spring sources of Iowa Gulch, one 

 of the main tributaries of McCoy Creek. The slopes on the west are 

 much more uniform, a broad gulch penetrating this side between the 

 main crest and that of the south spur. To the southwestward the moun- 

 tain descends to a lower ridge, which extends in that dn-ection into the 

 ;adjacent district, defining the wide drainage belt flowing eastward into 



