Columbia in the great Coeur d'Alene, St. Joe, and Clearwater Forests 
and adjacent lowlands, diminishing quickly and vanishing as one pas- 
ses the divide into Montana or into the Bitter Root Forest on the 
south. On the north and west, the boundaries are purely political 
and arbitrary and it is in the lowlands and valleys of this region 
that the greatest differencesin vegetation can be perceived. We are 
less concerned with the canyon of the Clearwater River below Orofino, 
inasmuch as the vegetation there passes quickly into the more xeric 
flora which characterizes the Snake River canyon. In the extreme 
southwest corner lies a portion of the Uniontown Plateau, a part of 
the rolling grassland of the wheat-growing Palouse region of south- 
eastern Washington. Along the valleys, this lowland flora penetrates 
irregularly eastward well into the forest proper. 
The region thus outlined lies wholly within the drainage of 
the Columbia River and is formed of the western spurs of the northern 
Rocky Mountain system, with a small portion of the Columbia plateau 
in the extreme southwest. The principal rivers are the Kootenai, Clark 
Fork, Spokane, and Clearwater rivers. Lesser but important streams are 
the Priest River, emptying into the Clark Fork, the Coeur d'Alene, St. 
Joe and St. Maries rivers, emptying ultimately into Lake Coeur d'Alene, 
from which flows the Spokane River, and the North Fork of the Clear- 
water. In addition, there are numerous smaller streams from which 
these derive their flow. 
Five mountain ranges are usually recognized within the area: 
the Priest River, the Purcell, the Cabinet, the Coeur d'Alene, and the 
