Abstract

The east-flowing White River enters the Missouri River about 12 miles below Chamberlain, South Dakota. In the east wall of the 300- to 600-foot trench through which the Missouri flows is exposed a cross-section of a valley now filled with till, cut by the former continuation of the White River eastward to the James River Valley. The floor of this filled valley hangs about 115 feet above the present Missouri. Near by, also east of the Missouri and capping a bluff 550 feet above it, is gravel containing vertebrate fossils stated to be of late Kansan or younger age. This high, fossiliferous gravel was deposited by the White River prior to the cutting of the Missouri trench, and the vertical relations indicate that it antedates the cutting of the till-filled valley. Thus, if the age of the fossils is correct, the glacier that created the Missouri must have been younger than the Kansan. Several lines of evidence indicate that the ice that caused the White River and other streams to divert and form the Missouri was probably Illinoian rather than Wisconsin.

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