topographically similar to the Coeur d'Alenes and Support essential-_ 
ly the same flora; indeed, they form with that range a floristic unit 
which extends in some degree as far south as the Locksa River. 
The lowlands within our region fall into two principal cat- 
egories. In the north, the valleys of the Clark Fork, Kootenai River 
and the Lakes Coeur d"Alene and Pend Oreille lie within the Purcell 
Trench; a comparatively broad structural valley, once strongly glaci- 
ated and now filled with silts and gravels of glacial origin. Both 
Lakes Pend Oreille and Coeur d'Alene are drowned valleys believed to 
have been formed by the damming action of a glacier retreating north- 
ward through the Purcell Trench. In addition to these larger lakes, 
numerous smaller ones are scattered throughout the region. 
In the southwest, south of Lake Coeur d'Alene and stretching 
in an irregular bowed line to the Clearwater canyon above Ororvino, is 
& portion of the Falouse region of southeastern Washington, known ag 
the Uniontown Plateau. This ig underlain by thick sheets of Columbia 
River basalt, through which the Clearwater has carved its canyon, now 
covered with fine-grained soils deposited by wind and water. The re- 
gion is rolling with rounded, even hills. Along the eastern border, 
outlying spurs of the Clearwater and Coeur d'Alene mountains rise to 
low elevations. Such spurs are uniformly forested. The lowlands are 
6rass-covered. Occasional outcrops occur which modify the local flora, 
Climatically, our region iso intermediate between the Pa- 
cific Coast climate of western Washington and the Rocky Mountain cli- 
mate, lying in that rainfall regime which has been designated as the 
antes enon 
