Driftless Area, c.13,000 sq mi (33,670 sq km), largely in SW Wis. but extending into SE Minn., NE Iowa, and NW Ill. The continental glacier which covered most surrounding regions did not touch this area, which abounds in caves and sinkholes and has residual, well-drained soil. Because it was an important lead-mining region, the federal government prohibited farming in the Driftless Area until the 1840s. It was then settled by European immigrants.
"Driftless Area." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (February 21, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/driftless-area
"Driftless Area." The Columbia Encyclopedia, 6th ed.. . Retrieved February 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/driftless-area