Arizona is a state in the southwestern region of the United States. It is also part of the Western United States and of the Mountain West states. It is the sixth largest and the 15th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is one of the Four Corners states. It has borders with New Mexico, Utah, Nevada, California, and Mexico, and one point in common with the southwestern corner of Colorado. Arizona's border with Mexico is 389 miles long, on the northern border of the Mexican states of Sonora and Baja California.Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. It was previously part of the territory of Alta California in New Spain before being passed down to independent Mexico and later ceded to the United States after the Mexican-American War. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.