After the Mexican-American War, under the terms of the Treaty of Guadalupe Hidalgo the United States acquired a large swath of land that was largely unexplored and unmapped. Between 1848 and 1855, the U.S. Army Corps of Topographical Engineers surveyed the land under the direction of U.S. Boundary Commissioner William H. Emory. Part of their mandate was to illustrate the border between the United States and Mexico. The red line in this sketch shows the U.S.-Mexico border before the land was purchased from Mexico. The area south of the Gila River is present-day Arizona.
The lengthy and extensive survey resulted in the Report on the United States and Mexican Boundary Survey, published in volumes from 1857 to 1859. The report was published as House Executive Document No. 135 during the 34th Congress. Richly illustrated with flora, fauna, and inhabitants of the region, it remains one of the foremost publications on exploration of the West.