Arizona South Of Gila River

The region south of the Gila River was inhabited by Paleo-Indians some 10,000 to 12,000 years ago, and later by the Ancestral Puebloan, Hohokam, Mogollon, and Sinagua cultures, all of which disappeared by the 15th and 16th centuries. It became part of Mexico's state of Sonora in 1822 and remained under Mexican sovereignty until the Gadsden Purchase took effect on June 8, 1854—six years after the north was ceded. The 29,640-square-mile purchase was signed on December 31, 1853, by James Gadsden and Antonio López de Santa Anna, and was motivated by the United States' desire to build a transcontinental railroad along a southern route, later completed by the Southern Pacific Railroad in 1881–1883. The cities of Yuma, Tucson, Nogales, Sierra Vista, Tombstone, and Douglas all lie within this purchased territory. The region became part of the Territory of New Mexico until the Arizona Territory was created in 1863, and Arizona was admitted as a state in 1912.

Pre-contact era

About 10,000 to 12,000 years ago, Paleo-Indians settled in what is now Arizona. The Ancestral Puebloan, Hohokam, Mogollon, and Sinagua cultures inhabited the region but all disappeared in the 15th and 16th centuries.

Colonial history

Territorial period

In 1863, Arizona was split off from the Territory of New Mexico to form the Arizona Territory, existing from February 24, 1863, until February 14, 1912. It was created from the western half of the New Mexico Territory during the American Civil War.

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