The Geology of the Upper Mississippi Valley Zinc-Lead District

The upper Mississippi Valley zinc-lead district includes the southwest part of Wisconsin, the northwest corner of Illinois, and a narrow fringe of Iowa extending from Bellevue to McGregor, just west of the Mississippi River. The total area of the district is 4,000 square miles. The entire district is drained by the Mississippi River and its tributaries. The central part is a rolling plain dissected to a depth of about 300 feet by the larger stream valleys. Marginal parts of the district are relatively hilly. Most of the district lies within the so-called "Driftless Area", but glacial deposits occur in the eastern, southeastern, and western fringes of the district.