636 / HARLEN BRETZ 



A much larger volume of water spilled across the preglacial 

 divide south of Hooper. Before the great canyoned channel now 

 transecting this divide had been eroded, the stream was 10 to 15 

 miles wide. Several channels of canyon proportion were initiated, 

 but one outran the others in its deepening and finally secured all 

 the discharge. Many of the shallower canyons enter the southern 

 part of the main one over abandoned waterfalls. These channels 

 could have carried water only when the wide scabland of the divide 

 had no deep canyon completely across it. Their falls could have 

 developed only after a deep main canyon existed below their junc- 

 tion. It follows, therefore, that Palouse Canyon was cut by retreat- 

 ing waterfalls, though these were destroyed later in the epoch. 

 One only survived, now notched considerably by the post-glacial 

 work of the Palouse River. The falls today are 198 feet high. 

 Palouse Canyon is another Devils Canyon in all save its greater 

 width and the fact that the preglacial divide was cut entirely in two. 



Drumheller Channels and Othello Channels are two remark- 

 able cases where the glacial flood crossed anticlinal ranges.^ In 

 both, the anticline is asymmetrical and the waters flowed down 

 the gentle slope. In both, the flood at first was wide but became 

 concentrated later in the deepening canyons. The maximum depth 

 of erosion in Drumheller Channels was 400 feet, about 100 feet 

 of which was in a weak sedimentary formation (probably the 

 Ellensburg), and 300 feet in basalt (Fig. 11). The width of the 

 Drumheller denuded tract is about 10 miles. This particular 

 scabland area has a more striking and more complicated develop- 

 ment of channels and rock basins than any other on the plateau. 

 It. is the only area of this type now topographically mapped. 

 Below the Channels, along the northern flank of Saddle Mountains, 

 the ancient river eroded 300 feet into the broader scabland. 



But Drumheller Channels is not wholly the product of the 

 glacial flood whose history we have been following. It and the 

 main canyon of Grand Coulee carried drainage from a later ice 

 sheet, and it has carried Crab Creek since the later glacial epoch. 

 The amount of deepening during each Pleistocene epoch is diffi- 



' Drumheller Channels crosses the eastern nose of Frenchman Hills anticline, 

 Othello Channels crosses the eastern nose of Saddle Mountains anticline. 



