st.johx.] GENERAL SURFACE FEATURES. 325 



Snake. In the southwest, the Blackfoot drains a considerable area in 

 its winding course, finally breaking through the low hill-ranges bordering 

 the Snake plain to the northeast of Fort Hall, and gains the Snake near 

 the southwest corner of the district. The Salt and John Day's Rivers, 

 two fine affluents which rise in the district to the south, reach the Snake 

 at a point just below its debouchure from the Grand Canon on the south- 

 ern central border. To the east of the Teton Range the Gros Ventre and 

 Buffalo Fork gather the main drainage on the west flank of the water- 

 shed, joining the Snake in the mountain basin of Jackson's Hole. The 

 ultimate sources of the main stream rise in the divide north of Buffalo 

 Fork, while Lake Fork drains a part of the lake plateau to the north of 

 our district. 



Mountain ranges. — In some measure conforming to the drainage system 

 of the region, the mountain belts may be distributed into well-defined 

 areas of greater or less regularity of courses and magnitude. Nearly 

 centrally located, and forming the dominating range whose axial peaks 

 rise 11,000 to near 14,000 feet altitude, the Teton Mountains constitute 

 one of the most conspicuous orographic groups in this northern region. 

 Its orographic relations may be likened to that of a wedge, separating 

 the Gros Ventre on the one hand from the Snake River Range on the 

 other, its longer axis lying nearly meridional a distance of about 40 miles 

 from north to south, and an average breadth of 15 miles. 



Along the eastern border, the water-shed north of Warm-Water Pass 

 forms a high wooded divide, which, in the region of Buffalo Fork Peak, 

 is broken down in the gap of Togwotee Pass, from which point it pur- 

 sues a course east of north, heading Buffalo Fork, and throughout its 

 extent within the district it is made up of a vast accumulation of volcanic 

 materials, which, to the north, rise above timber-line. Intermediate, or 

 between the continental divide and Jackson's Basin, the northeastern 

 quarter of the district is occupied by clusters of sedimentary and vol- 

 canic hills and ridges, which the drainage has fashioned into distinct 

 groups, to which belong the highlands between the Buffalo Fork and the 

 sources of the main Snake, and the Mount Leidy groups situated between 

 the former stream and the Gros Ventre River, the culminating points 

 of which attain altitudes of from 10,000 to 11,000 feet above the sea. 



To the south of the latter group, the Gros Ventre Range constitutes 

 a rather wide belt of upheaval, trending nearly at right angles to the 

 Teton Range, forming a sort of bridge, or great transverse highland, 

 connecting the latter with the Wind River Range, in the southeastern 

 quarter of the district. The geological relations of this highland belt 

 will be briefly discussed farther on. Its axial course lies a little south 

 of east and north of west, its heights rising 12,000 feet above the sea, 

 and offering great diversity in its geological and concomitant topograph- 

 ical features. 



The Snake River Range forms a rather wide and broken belt which 

 rises in the plateau dividing the Green and Bear River Basins to the 

 south of this district, and, pursuing a northwesterly direction, terminates 

 in the Snake Plain south of Pierre's River, after a course of about 60 

 miles within the present district. It intersects the southern terminus of 

 the Teton Range at an angle of about 45°, to the south of which it is 

 completely severed by the grand carion of the Snake River. Its eastern 

 limits south of Hoback's River have not been explored, but below the 

 Teton Pass it descends into the lower portion of Jackson's Basin, while 

 to the northwest it is separated from the Teton Range by Pierre's Basin. 

 Its southwestern flank is bounded by the lower valley courses of Salt 

 and Snake Rivers. 



