Cite
Schwartz, George M. (George Melvin), 1892-1980. (1936). Geology of the Minneapolis-St. Paul metropolitan area, Bulletin 27, Plate 7. Minnesota Geological Survey. https://reflections.mndigital.org/catalog/mgs:1020 (map)
Available from: https://geo.btaa.org/catalog/ee9c9e0c-6a2b-494a-9d89-12f09141275c