THE SPOKANE GLACIATIOX 595 



river gravels. About the margin of the basin the gravel is thinner and 

 rests directly on the basalt. The aggradational plain noAV is dissected 

 by stream-cut valleys which lead southward to a group of very irregular 

 channels eroded in basalt around the eastern nose of the Frenchman 

 Hills anticline and thence west to the Columbia between this fold and 

 the parallel Saddle Mountains anticline. Though this drainage line is 

 named Crab Creek, no surface waters from Crab Creek above the Quincy 

 basin now reach it. Dunes of basaltic sand have closed the lower part 

 of these converging valle3^s and thus formed Moses Lake. 



The group of channels around the end of Frenchman Hills anticline 

 will here be termed the Drumheller channels (see figure 8) . The altitude 

 of the basalt floor at the head of these channels is 950 feet and the high- 

 est altitude over which the water clearly flowed is about 1,200 feet. The 

 group begins as three canyons of nearly equal dimensions, but for most 

 of its length only two dominant canyoned channels exist, one containing 

 a narrow elongated lake, the other containing Crab Creek. The depth 

 of these canyons averages 200 feet. The whole area, however, is scored 

 and gashed by hundreds of similar smaller channels. The two main 

 gorges separate on an accordant level and unite 4 miles downstream, 

 again accordantly, but 100 feet lower than their point of separation. 



South of the Frenchman Hills anticline, Crab Creek Valley turns 

 abruptly west and follows the syncline between this fold and Saddle 

 Mountains anticline to Columbia Eiver at Beverly. A capacious, unin- 

 terrupted old river course of low gradient exists along this syncline. It 

 is repeatedly referred to in the literature as the lower part of the Grand 

 Coulee route of the diverted Columbia; and certainly the stream which 

 eroded the two dominant channels of the Drumheller plexus took this 

 course; but at an earlier date, before the present Drumheller channels 

 had been eroded, glacial waters also continued directly southward to pass 

 the east end of Saddle Mountain anticline as well. Channeled scabland 

 and stream gravel with granitic material cover 150 square miles of the 

 region south of the end of this fold. As in the Palouse scabland, hills 

 of mature topography and deep soils, developed in a weak sedimentary 

 (presumably the Ellensburg formation) above the basalt, flank the scab- 

 land and are isolated in it. Some of the glacial waters entered Esquatzel 

 Coulee and some went by way of Koontz Coulee to the Columbia near 

 Ringgold. Indeed, Esquatzel Coulee below Council has been eroded in 

 the scabland subsequent to the maximum flooding. 



The waters around the tip of the Saddle Mountain anticlinal nose 

 never cut deeper than 900 feet above tide, while the head of the syn- 

 clinal course just below the Drumheller plexus is eroded in basalt to 700 



