600 J. H. BRETZ GLACIAL DRAIXAGE OX COLUMBIA PLATEAU 



Crab Creek and Grand Coulee. As in the Hartline structural basin, the 

 Spokane floods found the depression only partialh^ filled, but left it 

 l^rimming over with waste. 



The Frenchman Springs cataract, 8 miles south of 'The Potholes," 

 functioned at the same time and developed a double fall also, but carried 

 a smaller quantity of water. The northern of the two falls here outran 

 the southern in its recession and at the close of the history of the cataract 

 was carrying all of the discharge. 



AVhy did not Wisconsin waters use the Frenchman Springs and Pot- 

 holes cataracts? There are two possible answers: (1) Spokane dis- 

 charge through Drumheller Channels eroded this spillway more than it 

 did the rapids above either of the two cataracts, and (2) post-Spokane 

 but pre-Wisconsin warping depressed the Drumheller tract relative to 

 the channels above the two cataracts enough to cause complete Wisconsin 

 diversion to the southern route; and, of course, it is possible that some 

 combination of both occurred. 



MOSES COULEE 



This coulee (not to be confused with the valley which contains Moses 

 Lake) ranks second in spectacular proportions only to Grand Coulee. 

 It lies a few miles west of Grand Coulee and leads southwestward directly 

 to the Columbia, 10 miles above "The Potholes." Its length of 40 miles 

 is divisible into three portions, an upper and a lower canyon separated 

 by a ])road, shallow tract in a synclinal valley. The upper canyon is 

 eroded in the gentle southward dip slope of this part of the plateau. Its 

 depth averages about 200 feet. DijD of the basalt is greater than descent 

 of coulee floor. The inclosing walls thus become lower until they vir- 

 tually disappear and the floor of the canyon becomes the floor of the 

 synclinal valley. Here the coulee turns abruptly to the west and follows 

 the axis of the syncline for 6 miles. At Palisades it turns southward 

 again and leaves the syncline to cross a broad uplifted area, or flat- topped 

 anticline, the Badger Mountain fold. The lower canyon across this fold 

 is 900 feet deep. 



The lower canyon has been extended upstream by headward erosion 

 about half the length of the synclinal portion. Here it abruptly ends at 

 the foot of a cliff across the coulee. Two great castellated buttresses face 

 down tlie coulee, with lesser walls connecting them. This notched cliff 

 clearly was a waterfall, and before the deep notching it was comparable 

 in height to Grand Falls at Coulee City. 



From this transcoulee cliff to the lower end of the upper canyon is a 

 tract, 5 or 6 miles long and nearly as wide, where the basalt floor of the 

 syncline was widely overrun by a great stream which formed a com]) lex 



