1956. Prokopovich, N. P. (Nikola P.) and Schwartz, George M. (George Melvin), 1892-1980. Mineral resources map of Minnesota, scale 1:1,000,000. Minnesota Geological Survey.
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1966. Prokopovich, N. P. (Nikola P.) and Schwartz, George M. (George Melvin), 1892-1980. Mineral resources map of Minnesota, scale 1:1,000,000. Minnesota Geological Survey.