PHYSIOGRAPHIC FEATURES 



577 



Physiography 



The surface of the plateau bears two strikingly different physiographic 

 aspects. Locally, one is known as "Palouse Hills" and the other as 

 "Scabland." Not alone are these sharply contrasted areas in close juxta- 

 position, but they are interfingered and interlocked. Every one of the 

 seven counties of the plateau possesses areas of both types. 



The "Palouse Hills" topography is best shown in Whitman County 

 south of Spokane and in the eastern half of the Palouse River system. 

 The region is essentially all in slopes, a network of drainage lines covers 

 it, the soils are fine and deep, and ledges of basalt are exposed only on 



Figure 2. — Steptoe Butte and the maturely dissected Palouse Begion east of the 



"Scal)lands" 



lower slopes and rarely on these. Profiles are coilVex only on hilltops; 

 all valley slopes are strikingly concave. The "Palouse Hills" topography 

 is typically mature. It is developed in the super-basalt sedimentary in 

 large part. Its relief averages about 250 feet. The main streams now^ 

 are in canyons in basalt below the floors of the mature valleys. This 

 type of topography (figure 2), with the same soils and underlying fomia- 

 tion, is widely distributed elsewhere on the plateau, but the drainage 

 pattern is not so intricately detailed farther west, where rainfall since 

 the uplift of the Cascade Range has been less. 



The "Scablands" are lowlands among the groups of "Palouse Hills," 

 plane in a general way, but diversified by a multiplicity of irregular and 



XXXVIII — Bull. Geol. Soc. Am., Vol. 34, 1922 



