Schoolcraft, Henry Rowe, 1793-1864. Map of the Northwestern Territories of the United States, Showing the Track pursued by the Expedition under Gov. Cass in 1820, map, 1820; (https://digital.library.unt.edu/ark:/67531/metadc29427/m1/1/: accessed April 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .