Bulletin of the Geological Society of America . salt flows hadceased, and in other places later and minor basalt flows occurring afterits accumulation had well begun. If the sedimentary formation, or itslower part, is Ellensburg, its presence indicates clearly that the plateauis determined by the original surface of the Miocene lavas, not by anylater erosional plans developed on the basalt. PHYSIOGRAPHIC FEATURES 577 Physiography The surface of the plateau bears two strikingly different physiographicaspects. Locally, one is known as Palouse Hills and the other asScabland. Not alone are these s
Bulletin of the Geological Society of America . salt flows hadceased, and in other places later and minor basalt flows occurring afterits accumulation had well begun. If the sedimentary formation, or itslower part, is Ellensburg, its presence indicates clearly that the plateauis determined by the original surface of the Miocene lavas, not by anylater erosional plans developed on the basalt. PHYSIOGRAPHIC FEATURES 577 Physiography The surface of the plateau bears two strikingly different physiographicaspects. Locally, one is known as Palouse Hills and the other asScabland. Not alone are these sharply contrasted areas in close juxta-position, but they are interfingered and interlocked. Every one of theseven counties of the plateau possesses areas of both types. The Palouse Hills topography is best shown in Whitman Countysouth of Spokane and in the eastern half of the Palouse River region is essentially all in slopes, a network of drainage lines coversit, 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 topographyis typically mature. It is developed in the super-basalt sedimentary inlarge part. Its relief averages about 250 feet. The main streams now^are in canyons in basalt below the floors of the mature valleys. Thistype of topography (figure 2), with the same soils and underlying fomia-tion, is widely distributed elsewhere on the plateau, but the drainagepattern is not so intricately detailed farther west, where rainfall sincethe 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 578 J. H. BRETZ GLACIAL DRAINAGE OX COLUMBIA PLATEAU commonly ana
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