December 30, 1853.
The treaty, known as the Gadsden Purchase, was signed in Mexico City.
Named after the U.S. Minister to Mexico, James Gadsden, the treaty settled the dispute over the location of the Mexican border west of El Paso, Texas.
For the price of $15 million — later reduced to $10 million — it established the final boundaries
of the southern United States.
30,000 square miles of what is now New Mexico and Arizona was included in the purchase.
The land was deemed to be a highly strategic location for the construction of the southern transcontinental railroad.
Eight years later, in 1861, the Southern Pacific branch of the Central Pacific Railroad was established.