12 ABSAEOKA DIVISION OV YELLOWSTONE FOREST RESERVE. 



considerable altitudes, far above timber line, there is not a single snow peak in the 

 reserve. Permanent snowfields occur in many localities in the high areas, but they 

 are simply the result of heavy winds piling up great banks of snow in gullies, 

 ravines, and on the lee side of the higher peaks, too deep to melt during the 

 short summer season, but yearly waxing and waning according to the severity of the 

 winter's downfall of snow. 



DRAINAGE. 



Primarily the area discussed is situated wholly within the Yellowstone Eiver 

 drainage. The run-off from its areas is carried into this river by a large number of 

 creeks and streams, which head mostly in the alpine and subalpine tracts. Some of 

 the streams form the heads of rivers of considerable size, others are mere alpine 

 rivulets. The larger and more important of the drainage basins and streams are as 

 follows: (1) The Boulder Eiver drainage, composed of (a) the heads and central areas 

 of West Boulder Eiver; (5) the head and central areas of Boulder River; (c) the head, 

 middle, and most of the lower portions of East Boulder River. (2) The upper 

 half, including all the heads, of Stillwater River. (3) The Rosebud drainage, 

 composed of (a) the head and central areas of West Rosebud Creek; (5) the head and 

 central areas of East Rosebud Creek. (4) The head of Red Lodge Creek Basin. 

 (5) The Rocky Fork drainage, composed of (a) all of West Rocky Fork, and (5) the 

 head and upper central areas of East Rocky Fork. (6) The northern heads of 

 Clark Fork drainage. (7) The head and central areas of Slough Creek drainage. 

 (8) The head and central areas of Hell Roaring Creek Basin. (9) The head and 

 central areas of Mill Creek. 



With the exception of Clark Fork, more than 99 per cent of the water which 

 these streams carry represents run-off originating, within the reserve. The tract 

 is thus a huge reservoir, furnishing a very large part of the annual flow in 

 Yellowstone River, and is therefore of very great importance to the irrigation 

 interests dependent on the waters of that stream. Excepting Slough and Hell 

 Roaring creeks, all the streams noted above are more or less utilized for irrigation 

 purposes above their confluences with Yellowstone River. 



The volume of water discharged by these streams during the summer season can 

 be greatly augmented by the construction of reservoirs in the alpine and subalpine 

 areas at their heads. 



BOCK FORMATIONS AND SOIXi. f j - 



Three-fourths of the area discussed consists of a great Archean uplift, cut and 

 seamed by dikes of various kinds of igneous rocks. The remainder consists of lavas 

 of various composition, limestones, and sandstones of Paleozoic age. The limestones 

 occur chiefly in the northern areas, flanking the first rises of the mountains along 



