High Quality Content by WIKIPEDIA articles! The Gadsden Purchase (known as Venta de La Mesilla, or Sale of La Mesilla, in Mexico) is a 29,670-square-mile (76,800 km2) region of present-day southern Arizona and southwestern New Mexico that was purchased by the United States in a treaty signed by James Gadsden, the American ambassador to Mexico at the time, on December 30, 1853. It was then ratified, with changes, by the U.S. Senate on April 25, 1854 and signed by President Franklin Pierce, with final approval action taken by Mexico on June 8, 1854. The purchase was the last major territorial acquisition in the contiguous United States, adding a large area to the United States.