This area south of the Rio Gila, sketched by U.S. Boundary Commissioner William H. Emory, is now part of Arizona. The red line shows the U.S.-Mexico border before the United States purchased the adjacent land from Mexico in 1853. Secretary of War Jefferson Davis gave Army engineers this map to explore a southern railroad route to the Pacific.
Records of the U.S. House of Representatives, National Archives and Records Administration
Sketch from the Office of the Mexican Boundary Survey, n.d.
Documenting the Discoveries
The Treaty of Guadalupe Hidalgo that ended the war with Mexico in 1848 added more than 525,000 square miles of western territory to the United States—an area that now encompasses all or parts of eight states. Members of Congress, recognizing the potential of this territory for settlement, fiercely debated whether or not to allow slavery there and which route a transcontinental railroad should follow through it. To inform future legislation, Congress funded a full report on the region as part of the boundary survey.
This area south of the Rio Gila, sketched by U.S. Boundary Commissioner William H. Emory, is now part of Arizona. The red line shows the U.S.-Mexico border before the United States purchased the adjacent land from Mexico in 1853. Secretary of War Jefferson Davis gave Army engineers this map to explore a southern railroad route to the Pacific.
Records of the U.S. House of Representatives, National Archives and Records Administration
