CHANNELED SCABLANDS OF THE COLUMBIA PLATEAU 649 



scabland tract except Grand Coulee in its later stages. It seems 

 necessary, therefore, to assume a prominent suhglacial drainage 

 line, across the area covered by the Spangle lobe. This is best 

 located along the preglacial valley of Lake (Marshall) Creek and the 

 rock basin of Farrington (Fish) Lake. Out of this rock basin, just 

 beneath the edge of the ice, the waters from the east emerged and 

 joined those coming directly from the ice. 



If the battle between the diluvialists and the glaciahsts, out of 

 which has emerged our conception of Pleistocene continental glacia- 

 tion, had been staged in the Pacific Northwest instead of the Atlantic 

 Northeast, it seems likely that the surrender of the idea of a debacle 

 might have been delayed a decade or so. Fully 3,000 square miles 

 of the Columbia plateau were swept by the glacial flood, and the 

 loess and silt cover removed.' More than 2,000 square miles of 

 this area were left as bare, eroded, rock-cut channel floors, now the 

 scablands, and nearly 1,000 square miles carry gravel deposits 

 derived from the eroded basalt. It was a debacle which swept the 

 Columbia Plateau. 



I Except in the Hartline and Quincy structural depressions. 



