1918. Harder, E.C. and Johnston, A. W. (A. Walfred). Map of East Central Minnesota showing location of rock outcrops (location of rocks exposed at the land surface), scale 1 inch = 10 miles. Minnesota Geological Survey.
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1918. Harder, E.C. and Johnston, A. W. (A. Walfred). Map of the principal part of the Cuyuna Iron-ore District, showing the distribution of known iron-bearing rocks and lines of maximum magnetic attra... Minnesota Geological Survey.
1918. Harder, E.C. and Johnston, A. W. (A. Walfred). Map and sections showing the geology and workings of the Rowe Mine, Cuyuna Iron-ore District, surveyed in July, 1915, scale 1 inch = about 130 feet. Minnesota Geological Survey.
1918. Harder, E.C. and Johnston, A. W. (A. Walfred). Map and sections showing the geology and workings of the Pennington, Armour No. 1, and Armour No. 2 Mines, Cuyuna Iron-ore District, Minnesota, sur... Minnesota Geological Survey.
1918. Harder, E.C. and Johnston, A. W. (A. Walfred). Map and sections showing the geology and workings of the Thompson Mine, Cuyuna Iron-ore District, surveyed July, 1915, scale 1 inch = 130 miles. Minnesota Geological Survey.