That part of eastern Washington which lies between the Cascade Range, on the west, and the high Rockies, on the east, carries an extensive record of Pleistocene glaciation. The belt drained by the west-flowing segment of the Columbia River is of special significance because in it was localized the southern margin of glacier ice during at least two successive glaciations. The great terraces of stratified drift and the striking channels, dominated by the Grand Coulee, that are associated with these ice borders, have attracted interest since the first scientific exploration of the region. The present paper, in discussing the chief glacial features in the lower Okanogan trench and in the district extending east up the Columbia River from the mouth of the Okanogan, aims at a rational explanation of the relations between these features.
Northeastern Washington consists of a rugged highland, underlain chiefly by pre-Tertiary resistant rocks, . . .