the inner valley, where they may merge with high-level terrace deposits (Johnson, 1958; Hodson and Wahl, 1960, p. 13). Cretaceous rocks crop out in bluffs that separate these terrace deposits and the inner valley, and also in areas where the outer valley slopes are not protected by flanking-pediment veneer. Exposures of the Smoky Hill Chalk Member are particularly susceptible to erosion by rain wash and streams and in a number of places this unit has been carved into badlands with steep-walled canyons, natural bridges, and slender pinnacles. Where dissection of the upper parts of valley slopes has exposed lithi- fied Ogallala beds that underlie the upland surface, that formation holds up steep cliffs that are picturesque in their own right. During the afternoon of the second day, we will cross the eastern edge of the High Plains in an area where the Ogallala Formation has been stripped by erosion from all but the highest divides, where the unit remains as thin discontinuous remnants nearly to the crest of the Fort Hays Escarpment. Most of the area is underlain by the Smoky Hill, which is thinly veneered by Pleistocene loess. Upland areas underlain by Ogallala deposits are generally flatter than those underlain by Cretaceous rocks. Along the Smoky Hill River in Trego and Ellis counties a conspicuous high terrace known as Pfeifer Terrace lies 25 to 60 feet above the present flood plain and 60 to 120 feet below the upland surface (Leonard and Berry, 1961, p. 14). Remnants of flanking pediments, like those in Gove and Logan counties, locally slope down from the Fort Hays Escarpment and merge with this high terrace. Pfeifer Terrace has been traced from Ellsworth County, in the Smoky Hills, to as far west as Logan County in the High Plains (Frye and Leonard, 1952, p. 97). Deposits underlying the Pfeifer Terrace are assigned to the Kansan, Yarmouthian, and Illi- oisanan Stages of the Pleistocene Series. Near the eastern edge of the High Plains a lower terrace, lying only a few feet above the present flood plain along the inner valley of Smoky Hill River and some of its tributaries, is assigned a late Wisconsinan age by Leonard and Berry (1961, p. 48), who have traced the terrace westward to Logan County. Development of Present Topography Following final retreat of the Western Interior Sea, Cretaceous rocks in western Kansas were truncated during an erosional interval that produced, just prior to inception of Plio- cene deposition, broad plains of low relief across which drainage was generally eastward in the area of our interest (Johnson, 1958, p. 28; Frye and Leonard, 1952, p. 185). Major up- lift in the Rocky Mountains region brought a flood of detritus that filled valleys and buried divides beneath a complex of coalescent alluvial plains; these deposits levelled the existent topography and formed the monotonous topography that remains little modified in undissected areas of the High Plains. 6