The region which surrounds Sioux Palls, South Dakota, particularly that part lying south and east on both sides of the Big Sioux River and extending south to Fairview, South Dakota, has received much attention from students of Pleistocene geology. This is due to the fact that it displays two drifts and was supposed to lie partly in the sinus of a marginal lobe of the Wisconsin drift border, including ridges which were thought to be portions of the Altamont moraine. It also contains fossiliferous interglacial silt and gravel beds which have attracted attention.
The region was first carefully studied by Todd, whose preliminary report on the geology of South Dakota2 contains a description of four moraines, of which the first or outer moraine3 is described (page 116) as extending “to a high point south of Canton. It is then feebly developed, or entirely . . .