CHANNELED SCABLANDS OF THE COLUMBIA PLATEAU 627 



accordant grades where they unite or diverge, the bottoms of the 

 shallower ones hanging above the floors of the deeper ones. Many 

 canyoned channels have abandoned cataracts and cascades in them 

 or at their heads. ^ Most canyoned channels have elongated rock 

 basins (see Fig. 6). Even in the shallow channels, basins or 

 pockets in the rock are common. Some of these rock basins 

 clearly were produced by recession of a cataract whose scarp still 



Fig. 5. — Devils Canyon near mid-length, looking north. Note the scrubbed 

 basalt ledges above the canyon rim, and the profile of the loessial bluffs, still higher and 

 farther back. 



exists.^ Others were produced by plucking of the columnar basalt 

 .in the canyon floors where the gradient was high.^ 



These features of the channeled scablands on the Columbia 

 basalt plateau do not closely resemble any other type of topography. 



' ' Dry Falls (400 feet high) in Grand Coulee, The Potholes (350 feet high) south 

 of Trinidad, Frenchman Springs (400 feet high) south of The Potholes, and The Three 

 Devils (600 feet total descent) in Moses Coulee are especially noteworthy. 



2 Deep Lake, below one of the Grand Coulee abandoned falls, has many associated 

 huge potholes, drilled into the basalt at the foot of the falls as they retreated. Each 

 of the two cataracts of "The Potholes," south of Trinidad, has a single elongated rock 

 basin at the foot (Fig. 7). 



3 Rock Lake in Whitman County, Goose Lake in Grant County, Washtucna Lake 

 and Eagle Lake in Franklin County, Pacific Lake and Tule Lake in Lincoln County, 

 Goose Lake in Grant County, Medical Lake, Silver Lake, and Farrington (Fish) Lake 

 in Spokane County, and Big Swamp Lake and Cow Lake in Adams County are examples 

 of hundreds of such basins. 



