Arizona Navajo: Hoozdo Hahoodzo O'odham: Alĭ ṣonak is a U.S. state in the southwestern region of the United States. It is also part of the Western and the Mountain states. It is the sixth largest and the 14th 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 626 km long, on the northern border of the Mexican states of Sonora and Baja California.