360 REPORT UNITED STATES GEOLOGICAL SURVEY. 



The rock may possibly be volcanic; but it is rather believed to belong 

 to the sandstone series which appears in the low hills to the southeast 

 of the lake, where they dip gently southwesterly, and pass into the ad- 

 jacent district. The latter hills and their imperfectly-exposed strati- 

 graphy will be briefly noticed in connection with the section across the 

 Caribou Bange, through Station XXVIII (Mount Caribou), in the follow- 

 ing section of this chapter. 



THE CARIBOU RANGE. 



The highland belt lying between the Willow Creek Basin andthedower 

 valley of the Snake and its southern continuation, the Salt Eiver Valley, 

 to which the general designation Caribou Eange has been given, com- 

 prises a rather regular area which extends from a point south of our 

 southern boundary northwesterly a distance of 40 to 45 miles within our 

 district, with an average width of about 14 miles. South of McCoy 

 Creek and the Caribou mining district, where it attains the latter breadth, 

 it gradually narrows, and where its crest shows a series of undulating, 

 wooded bills. To the north, again, it expands to 18 miles across, be- 

 tween Fall Creek and the next considerable stream to the south, Pyra- 

 mid Creek ; and thence northward it is continued in a lower and narrower 

 ridge, which finally expands into a plateau overlooking the grassy up- 

 land on the borders of the Snake plain. The culminating points along 

 the main crest, which lies well to the east of the geographical axis of 

 the range, attain altitudes ranging from 8,000 to 9,G00 feet above sea- 

 level ; but on the southwestern border in the southern portion of the 

 range, the somewhat isolated mountain mass in the Caribou mining dis- 

 trict reaches an altitude of 9,800 feet, and which dominates the whole 

 southwestern section of this district. This peak, which was variously 

 known by the names Caribou Mountain and Mount Pisgah, was re- 

 christened, by Mr. Bechler Mount Bainbridge, in honor of Captain Bain- 

 bridge, commandant at Fort Hall, from whom and Lieut. Joseph Hall, 

 of the same post, our party met with courteous and generous reception, 

 which contributed materially towards furthering the objects of our visit. 



A marked peculiarity of this range is the relation of the main or topo- 

 graphic crest to the hydrographic divide or watershed. As above re? 

 marked, the culminating crest lies to the east of the central longer axis, 

 which is thrown into a devious course by the drainage, with an intricate 

 system of supporting ridges due solely to erosion, and rugged inter- 

 mountain spurs, which were determined by the stratigraphic structure of 

 the range. This belt is boldly severed by the drainage channels, across 

 which their beds Me hi deep, rugged gorges, abounding in wild and pic- 

 turesque scenery, their sources originating in beautiful little mountain 

 basins situate within the southwestern half of the range. The water- 

 shed, which separates this main drainage from that flowing into the Wil- 

 low Creek basin, is alike irregular in its course and elevation, though 

 uniformly lower than the topographic crest, except a limited portion of 

 the divide, only a few miles in extent, formed by the dominating peak, 

 Mount Bainbridge. But to the north of the latter mountain, as also to 

 the south, the watershed is crowded nearly over to the southwest verge 

 of the range, the sources of Tin-cup and McCoy Creeks rising within 

 three or four miles of the basin plain of Day's Lake. Xear the middle, 

 and between the latter creek and Fall Creek, the East Fork of John Day's 

 Creek heads well up in the range at a point from which radiates the 

 drainage of the three principal water-courses which flow directly into 

 the Snake, viz, McCoy, Pyramid, and Fall Creeks. To the north, two 



