6T.J0HX.] CARIBOU RANGE. 361 



considerable tributaries which rise iii the main crest gain the main Wil- 

 low Creek on its right bank, while Grouse Creek and several smaller 

 streams rise in the opi)osite side of the crest and How into the Snake. 



The bulk of the range is fashioned out of sedimentary formations, and 

 these belong chiefly to the Mesozoic and the earlier epoch of the Ceno- 

 zoic age. Along the middle portion of the northeastern border, rocks 

 of Palteozoic age are encountered, which, like the later-formed strata, 

 have been tilted and folded in a remarkable manner. The distui'bing 

 forces which resulted in the plication of these sedimentary deposits acted 

 pretty luiiformly along northwesterly and southeasterly lines, with, how- 

 ever, local deviations in both the direction and intensity of their mani- 

 festation, to which is attributable the variety of the phenomena here ob- 

 served. These may be briefly summed up as sharp anticlinal folds, and 

 corresponding synclinal troughs, great flexures marked on the one hand 

 by the vertical and even overturned position of the displaced beds, while 

 on the other they appear to have formed broad-topped folds with gentler 

 inclination on the opposite border; and it seems almost certain that, with 

 these more extraordinary displacements, are associated other attendant 

 phenomena, such as the faulting of the strata, by which formations of 

 remote periods of origin are brought into immediate juxtaposition in 

 the opposite walls of the severed beds. Besides the deposits of sedimen- 

 tary origin, there are limited areas in the higher mountain region where 

 rocks of volcanic origin are met with. These are supi)osed to represent 

 two distinct epochs of volcanic activity, the one and earlier occurring as 

 dike-like and intruded masses, the effusion of which not only fractured 

 the sedimentaries vertically, but forced apart the strata between which 

 they are intruded as gTeat wedges. The later effusion, consisting of 

 trachytic and other lavas, ajjpear simply to have overflowed pre-exist- 

 ing elevations, but which have since been subjected to extensive erosion, 

 from which the unconformably superimposed volcanics have suffered 

 almost to annihilation, only mere remnants remaining to show their prob- 

 able former extent. These latter volcanic flows pitch off towards the 

 basiu depressions, in the borders of which they are succeeded by the still 

 later basaltic lavas which fill the basin areas to the north and west. The 

 local aspects of the geological components of the range will be noticed 

 more at length in the following pages, devoted to the detail account of 

 the observations prosecuted in this quarter. These will be taken up in 

 nearly the order of their original observance. 



Our route penetrated the range at its widest part, following up the 

 East Fork of John Gray's Creek, or near the middle in its southwest 

 border. This stream, whose sources are gathered in a little hilly mount- 

 ain basin, cuts a short canon across a rather high outlying ridge, which 

 here forms the foot-hills along the southwest flank of the range. This 

 ridge rises rather abruptly from the basin plain, 800 to 1,400 feet in 

 height, its direction W. N. W. and E. S. E. It terminates abruptly on 

 Mosquito Creek five miles west of the deboucliure of East Fork, to the 

 east of which it merges into the watershed at the head of McCoy Creek, 

 ■where it reaches its greatest elevation. This is the appearance as seen 

 from the basin plaiu ; but it really forms part of a block of the western 

 flank of the range, from which erosion of the drainage channels has al- 

 most dissevered it, a series of extremely rugged saddles and combs 

 alone maintaining its connection with the parent mass. Like so many 

 of the streams in this range the East Fork divides in its mountain basin, 

 the two branches uniting fi'om opposite directions, which are found to 

 coincide with the general direction of the strike of the rocks in which 

 their beds are eroded. So, also, the courses of the i^ruicipal lateral tribu- 



