CHANNELED SCABLANDS OF THE COLUMBIA PLATEAU 637 



cult to determine. Othello Channels 

 carried less water than Drumheller 

 Channels, consequently is a smaller 

 tract. Furthermore, it received water 

 during only the earlier epoch. The 

 degree of development of its canyons 

 and rock basins is comparable to that 

 of the larger tract and makes it prob- 

 able that most of Drumheller Channels 

 were formed during the earlier epoch. 

 The features of Grand Coulee are 

 of such magnitude and its history so 

 complicated by local conditions that 

 an entire paper might well be devoted 

 to it. It affords the greatest example 

 of canyon-cutting by glacial streams, 

 not alone for the Columbia Plateau, 

 but for the world. The field evidence 

 indicates that no preglacial drainage 

 route ever existed here. Scabland 

 with shallow channels margins the 

 upper part of the Coulee, though i ,000 

 feet higher than the adjacent coulee 

 floor, and there are no tributaries in 

 the mature topography such as are 

 possessed by Lower Moses Coulee and 

 Washtucna Coulee. A glacial river, 

 3, miles in minimum width, spilled 

 southward here over, the divide and 

 down a steep monoclinal slope. Judg- 

 ing by present grades and altitudes 

 of this structural slope, the stream 

 descended nearly 1,000 feet on a 

 grade of approximately 10°, a few 

 miles north of Coulee City. Such a 

 situation is unparalleled, even in 

 this region of huge, suddenly initi- 



