U.S. Dept. of the Interior, Geological Survey, Exploration and Settlement 1850–1890, in: The National Atlas of the United States of America (Arch C. Gerlach, Hg.). Washington, D.C.: U.S. Dept. of the Interior, Geological Survey, 1970. Bildquelle: Perry-Castañeda Library Map Collection. Mit freundlicher Genehmigung der University of Texas Libraries, The University of Texas at Austin, gemeinfrei.