The geology on which the present maps are based is from field work and petrology done from 1965-1967.
University of Minnesota Duluth, Natural Resources Research Institute, Duluth MN; University of Minnesota Duluth, Dept. of Earth and Environmental Sciences, Duluth MN
Grant, James A; Oreskovich, Julie A.
Archean Geology of the Minnesota River Valley Sacred Heart to Morton Geology.
University of Minnesota Duluth.
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