392 BITTER ROOT FOREST RESERVE 



Salmon rivers. On the eastern slope is the Bitter Root river, 

 one fork of which heads in the southeast corner of the Reserve 

 and flows northward through the fertile valley of the same name. 

 This valley separates the Rocky mountains from the Bitter Root 

 range for a distance of about 100 miles and at present has a good 

 agricultural development. The main valley has a width of about 

 8 or 10 miles, its floor being comparatively level, composed of 

 lacustrine deposits and very fertile under irrigation. When the 

 drainage of the ancient lake occurred there was left a heavy 

 deposit of gravel and other sediment, through which the Bitter 

 Root river is still cutting, and this process has shifted the flood- 

 plain back and forth, the result being that in some portions of 

 the valley well defined terraces have been carved out correspond- 

 ing to the 'older floodplains. 



The Bitter Root river joins the Missoula near the town of the 

 same name and ultimately finds an outlet in the Columbia river 

 through Clarke's Fork and Lake Pend d'Oreille. The streams con- 

 stituting this drainage are remarkably straight and of a very steep 

 gradient. Their tangent-like course is due primarily to glacial 

 agencies, and they have not become modified on account of the 

 extreme hardness of the rocks. They seek the straight and direct 

 course and do not loiter amid the inhospitable granite to carve 

 out for themselves gentle curves. In their haste to reach the 

 valley they leap and jump and are tossed from boulder to boulder, 

 now lashing themselves into fleecy whiteness and now circling 

 in emerald eddies as they plunge into some quiet pool, where 

 they find a moment's rest and gather strength for their ever- 

 downward course. The beds are filled with boulders, and the 

 sides of the canyons are precipitous and almost entirely bare of 

 vegetation. These streams in their incessant activity are not only 

 continually deepening their own beds in the attempt to reach 

 baselevel, but are gradually working their wa} 7 westward and 

 capturing the tributaries of the less active affluents of the Clear- 

 water, causing what is termed a migration of the divide. The 

 shifting or migration of a divide is due to the weathering or wast- 

 ing away of the crest line, and may result from various causes. 

 It seems probable that the main crest of the Bjtter Roots has 

 moved to the westward, owing to the fact that the highest points 

 at present are all east of the crest line. Ward peak is 8 miles 

 to the east and about 800 feet higher than the general elevation 

 of the divide, and St Mary's and El Capitan peaks each attain 

 an elevation considerably higher than the divide. 



