134 ABSABOKA DIVISION OF YELLOWSTONE POBEST KESEKVE. 



tions of long and broken spurs. The canyon system consists of narrow, short 

 troughs with rapid descents. The mean elevation of the range, including its 

 immediate slopes, is 8,200 feet, approximately; isolated knobs on a few of the 

 higher ridges attaining altitudes of 10,000 feet. 



The Absaroka Range consists of a huge uplift of granite flanked by limestones 

 and outflows of Tertiary lavas. It is a very rough and rugged region, deeply and 

 extensively sculptured by the erosive power of the vast glacier field, which in 

 times past covered its entire area. The tract is a succession of deep, cliff-lined 

 canyons and tortuous ridges, the larger with a generally north-south trend. The 

 crests of the ridges are mostly narrow and sharp, presenting vast masses of cracked 

 and crumbling overhang. Occasionally they widen and are studded with peaks'and 

 pinnacles, or become broader and expand into plateau-like tracts. Their slopes, as 

 they front on the valleys and canyons, are remarkably steep, frequently rising 

 in scarps and precipices 1,000 to 2,000 feet in height. Vast quantities of talus 

 extend up the slopes and deep deposits of bowlder and gravel drift litter the canyon 

 bottoms. The mean elevation of the tract outside the immediate canyon floors is 

 estimated at 8,500 feet. Here and there peaks reach altitudes of 11,000 to 12,000 

 feet; but none of the tracts reach the line of perpetual snow on all slopes. 



The high relief of the north half of the quadrangle is formed by a section of the 

 Bridger Range and the southern terrriination of the Crazy Mountains. The Bridger 

 Range, a northward continuation of the Gallatin Range, con^sts of a narrow, ser- 

 rated, extremely rocky ridge, rising sharply from the levels of the surrounding table- 

 land, buttressed by numerous short and steep spurs and indented by a multitude of 

 rifts, ravines, and gorge-like canyons. The average elevation is about 7,800 feet, 

 while points along the crest attain altitudes of 9,100 feet. The section of Gi-azy 

 Mountains in the north-central regions of the district covers a tract of approximately 

 47,000 acres, and consists of steep slopes rising directly and continuously from the 

 plains level to altitudes of ip,400 feet. 



The low areas of the quadrangle consist of a rolling, timberless plain, rising in 

 more or less broken and continuous terraces to intersecting broad swells and ridges, 

 falling away in long, gentle slopes to the valleys of Yellowstone and Shields rivers, 

 which border and bisect the district, or knobbed with lines of rocky buttes and 

 furrowed by shallow canyons and depressions. 



The lowest depressions in the quadrangle are along Shields and Yellowstone 

 rivers. The former bisects the quadi'angle from north to south; the latter forms in 

 part a dividing line between the mountainous southern areas and the plains districts 

 of the northern part of the quadrangle. Both streams flow in broad valleys lined 

 with low blufls, which alternately approach and recede from the stream banks. The 

 mean elevation of the plains regions is 5,200 feet; that of the Yellowstone flood 

 valley, 4,200 feet. 



