McGhee, in the map accompanying his Pleistocene History of Northeastern Iowa, makes the "Upper Till" overlap the "Lower Till." And the eastern boundary line of the "Upper Till" (Iowan), as shown by the same, and consequent western boundary line of the Driftless Area, in the counties of Winneshiek, Allamakee and Clayton, the three northeastern counties of Iowa, begins at the boundary line of Clayton County about six miles south of the mouth of the Turkey River, and runs thence northwesterly at about that distance south of the Turkey, to West Union in Fayette County, and from there runs nearly due north at about an average distance of six miles from the west boundary line of Winneshiek County, to the state line. Leaving all of Clayton but about half of the southwest township, all of Allamakee, and the eastern three-fourths of Winneshiek in the Driftless Area.
Proceedings of the Iowa Academy of Science
©1907 Iowa Academy of Science, Inc.
"Exposures of Iowan and Kansan (?) Drift, East of the Usually Accepted West Boundary Line of the Driftless Area,"
Proceedings of the Iowa Academy of Science, 14(1), 231-236.
Available at: https://scholarworks.uni.edu/pias/vol14/iss1/20