6T.J0HX] SNAKE RIVER RANGE — PIERRE's MOUNTAINS. 425 



tude renders tliem conspicnous laudmarks, notably so in the instance of 

 the ahnost perfect cone of Mount Baird, Avhich rises in the heart of the 

 broken region in the great bend of the Snake. 



That i)ortion of the range to the north of the Grand Canon closely 

 follows the valley course of Snake Eiver, where, as seen ironi the west 

 bank of the river, it presents an exceedingly rugged and imposing mount- 

 ain wall, cleft by the narrow valleys which give exit to the interior 

 drainage. To the south of the Graud Canon, as far as could be seen, it 

 is continued in an almost equally formidable barrier, which is traversed 

 by the defile of John Day's Eiver in nearly the direction of the trend of 

 the range. Between the latter stream and Salt Eiver, farther south, 

 lower ridges intervene, which Dr. Peale found to be made up in part of 

 Mesozoic strata. The main barrier fronting the lower valley of the Snake, 

 according to Professor Bradley, is mainly if not entirely composed of 

 Carboniferous deposits, and, judging from the resemblance of the harder 

 ledges in the lower or northern extension of this western front, the same 

 formation would appear to constitute the bulk of the mountain wall 

 throughout. Even ii'om the distant view with which we were compelled 

 to content ourselves, it was evident that this front ridge partakes in 

 some measai'c of the excessive disturbance which was found to charac- 

 terize the eastern portion in the regions of the Pierre's and Teton Pass 

 Mountains, the strata in i)laces rising in the steep slopes like a rocky 

 mail, elsewhere showing their edges dii)piug away from the valley or 

 northeast ; their foot, from a point about half way between the debou- 

 chure of the Snake and the lower entrance of the Grand CaDon, being 

 enveloped in the volcanic dei)osits which reach ui) the vallej' from the 

 plain. 



PIERRE'S MOUNTAINS. 



Such opi)ortunities as I possessed allowed only a partial examination 

 of this most interesting region, and this was mostly confined to the 

 Pierre's Mountains on the western border of the basin of the same name. 

 Viewed from the basin-plain, the eastern front of these moimtains pre- 

 sents a series of more or less regular spur-ridges, which gradually rise 

 up into the eastern mountain-crest, and which are much complicated by 

 secondary spurs due entirely to the erosive action of the short drainage 

 channels which flow out into Pierre's Basin. The princiiDal spurs, how- 

 ever, conform to the strike of the strata, and hence have a general north- 

 west and southeast direction.' One of these ridges forms the water-shed 

 of the drainage which flows into Pierre's Basin on the one hand, and on 

 the other is drained into the lower valley of the Snake through the stream 

 which gives exit to the waters collected in the mountain-basin west of 

 Low Pass. Pursuing a northwesterly course, it culminates in a high 

 point, on which Station XL was established, at an altitude of 10,100 feet 

 above the sea, or a relative elevation above the level of Pierre's Basin of 

 about 3,800 feet. It forms a monoclinal ridge of Jurassic beds, dipping 

 to the southwest at varying angles of inclination, and much broken by 

 the drainage channels which intersect it from either side. For a large 

 part of the way the ridge is capped by a heavy ledge of quartzite, be- 

 neath Avhich occur more or less distinct exhibitions of sandstones, drab 

 limestones, and shaly deposits. On approaching Station XL, the latter 

 are seen to rest upon a heavj' accumulation of deep red arenaceous shales 

 and sandstones, which form a wide belt of brilliant color in the northeast 

 face of the ridge. These are succeeded below by bufl-red siliceous beds 

 and intercalated limestones, which finally pass into the usual drab and 

 gray cherty limestones everywhere making up the lower measures of the 



