New Mexico is a southwestern U.S. state whose diverse terrain encompasses the Chihuahuan Desert and the Sangre de Cristo Mountains. New Mexico was admitted to the union as the 47th state on January 6, 1912. It is usually considered one of the Mountain States. New Mexico is fifth by area, the 36th-most populous, and the sixth-least densely populated of the 50 United States. The capital, Santa Fe, was founded in 1610.