602 J. H. BRETZ GLACIAL DRAINAGE OX COLUMBIA PLATEAU 



Columbia. Therefore, thougli no till or strite left by the Spokane ice are 

 known on the south side of the Columbia west of Grand Coulee, the oper- 

 ation of both Moses and Grand coulees proves that Cordilleran ice did 

 cross the Columbia, and the Spokane features of Moses Coulee prove that 

 it reached nearly as far south as it did in the later Wisconsin epoch. 



Figure 11. — Cliffs of lower Closes Coulee 



The cliffs are 800 feet high. There are shown the pre-Spoltane tributary valleys, the 

 main canyon of Spokane age, and the post-Spokane talus. 



The AViscoxsin" Glaciatiox 



The terminal moraine deposited by the Cordilleran ice-sheet in north- 

 eastern Washington during the Wisconsin glaciation has been traced in 

 part by Salisbury and student assistants.^- The ice reached the Colum- 

 bia Plateau in two places. One of these was south of the capacious 

 Okanogan Eiver Valley, and the lobe which spread out on the plateau 

 here reached 35 miles beyond the river and was nearly 50 miles wide. 

 The other place was on the lower Spokane Eiver and was of little conse- 

 quence. The only noteworthy Wisconsin drainage derangement of the 

 entire plateau was the reoccupation of Grand Coulee and lower Crab 

 Creek. Through this route was poured the water from the Cordilleran 

 ice-sheet along the entire front from the Rocky Mountains to the 

 Okanogan lobe. Though the Spokane ice yielded much greater volumes 

 of water, all told, than did the Wisconsin, it was carried by many valleys, 

 no one of which ever contained the quantity which went through Grand 

 Coulee during the later diversion. That flood was greater than the deep- 



^- R. D. Salisbury: Glacial work in the western mountains in lOoi. Jour Geol vol 

 9, 1901, pp. 721-723. 



George Garrey : Glaciation between the Rockies and the Cascades. Master's thesis, 

 in library of Department of Geology, University of Chicago. 



