Roeser, C. (Charles),  and United States. Post Office Dept.  "Post route map of the states of North and South Dakota with adjacent parts of Montana, Wyoming, Nebraska, Iowa and Minnesota and portions of the Dominion of Canada."  Map.  1891.  Norman B. Leventhal Map & Education Center,  https://collections.leventhalmap.org/search/commonwealth:cj82kj943 (accessed March 28, 2020).