"Right now they are forming in Washington a commission to come out here and draw up the boundary lines between our country and Mexico."
1856 Mitchell Map including the territory acquired following the Mexican American War and by the 1854 Gadsden Purchase
Public Domain1856 Mitchell Map including the territory acquired following the Mexican American War and by the 1854 Gadsden Purchase - Credit: Geographicus Rare Antique Maps

Followng the Mexican-American War, the Treaty of Guadalupe Hidalgo set the boundary between Mexico and the United States and provided for the establishment of a Mexican-United States Boundary Commission to survey and mark that boundary. On July 6, 1849, the United States commission met formally for the first time with the Mexican commission. Six years later, on October 15, 1855, the commission finished its surveying work, establishing a United States-Mexico borderline that remains virtually unchanged to this day.

The new boundary line placed on the American side the lands already ceded by Mexico in the Treaty of Guadalupe Hidalgo (modern Texas, California, Utah, Colorado, and most of New Mexico and Arizona) as well as the remaining bits of New Mexico and Arizona which the Santa Anna government had sold to the U.S. in the Gadsen Purchase of 1853.