Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912, coinciding with Valentine's Day. Historically part of the territory of Alta California in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.
About one-quarter of the state is made up of Indian reservations that serve as the home of 27 federally recognized Native American tribes, including the Navajo Nation, the largest in the state and the United States, with more than 300,000 citizens. Although federal law gave all Native Americans the right to vote in 1924, Arizona excluded those living on reservations in the state from voting until the state Supreme Court ruled in favor of Native American plaintiffs in Trujillo v. Garley (1948).
The state's name appears to originate from an earlier Spanish name, Arizonac, derived from the O'odham name alĭ ṣonak, meaning "small spring", which initially applied only to an area near the silver mining camp of Planchas de Plata, Sonora. To the European settlers, their pronunciation sounded like "Arissona". The area is still known as alĭ ṣonak in the O'odham language. Another possible origin is the Basque phrase haritz ona ("the good oak"), as there were numerous Basque sheepherders in the area.
There is a misconception that the state's name originated from the Spanish term Árida Zona ("Arid Zone").