The Gadsden Purchase ( The Sale of La Mesilla), is a region of present-day southern Arizona and southwestern New Mexico that the United States acquired from Mexico by the Treaty of Mesilla, which took effect on June 8, 1854. The purchase included lands south of the Gila River and west of the Rio Grande where the U.S. wanted to build a transcontinental railroad along a deep southern route, which the Southern Pacific Railroad later completed in 1881-1883. The purchase also aimed to resolve other border issues.