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Boundary between the United States and Mexico, map by William H. Emory, 1855

Between 1849 and 1857, the Army Corps of Topographical Engineers marked and mapped the U.S.-Mexico boundary and published a report on natural features of the borderland. The vast new western territories immediately became a focus of congressional dispute regarding slavery in new states. This map shows the border between New Mexico and Chihuahua, Mexico.

Geography and Map Division, Library of Congress

Boundary between the United States and Mexico, map by William H. Emory, 1855

Surveying the Mexican Border

The Treaty of Guadalupe Hidalgo, approved for ratification by the U.S. Senate in 1848, set the terms for ending the Mexican War. Mexico agreed to cede more than half its territory to the United States for $15 million. A new, 2,000-mile border between the two countries was to run along the Rio Grande and Rio Gila to the Pacific Ocean with a boundary commission from each country surveying and marking its location. Congress authorized the Army Corps of Topographical Engineers to conduct the survey for the United States.