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southward. A small part of the Cabinet Range extends into Idaho, ly- 
ing between the Clark Fork and Kootenai rivers and bounded on the west 
by the Purcell trench. This western part, lying within our region, is 
characterized for the most part by rounded peaks similar in height to. 
those of the Priest River Mountains. 
By far the largest mountain mass lying wthin our region and 
most characteristic of it is the Coeur d'Alene Range, with elevations 
in general ranging from 6000 to 7000 feet, or infrequently to 7500 
feet. As usually defined, this range extends from the Clark Fork and 
Lake Pend Oreille southward to the divide which separates the St. Joe 
and North Fork of the Clearwater rivers. Although the northern boun- 
dary of the range is clearly defined, the southern one is scarcely 
perceptible. In passing from the Coeur d'Alene to the Clearwater 
Mountains, one is hardly aware of any topographic change. Asa whole, 
these mountains are not greatly diversified, the ridges and peaks be- 
ing nearly equal in height, usually rounded and well-wooded to the 
summits, with only an occasional peak of irregular outline and asso- 
ciated talus slopes. Viewed from a height, the entire region suggests 
a much dissected plateau. 
The rocks of the greater part of these mountains are Pro- 
terozoic sediments. In the region of Lake Coeur d'Alene, and the 
Spokane, Coeur J’Alene and St. Maries rivers, occur extrusions of 
Miocene basalts which suvpvort a characteristic and local flora. Al- 
though geologically different, since they are largely granitic in 
nature, the Clearwater Mountains, at least within our region, are 
