New Mexico is a state in the Southwestern United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region of the western U.S. with Utah, Colorado, and Arizona, and bordering Texas to the east and southeast, Oklahoma to the northeast, and the Mexican states of Chihuahua and Sonora to the south. The state capital is Santa Fe, which is the oldest capital in the U.S., founded in 1610 as the government seat of Nuevo México in New Spain; the largest city is Albuquerque. New Mexico is the fifth-largest of the fifty states, but with just over 2.1 million residents, ranks 36th in population and 46th in population density. Its climate and geography are highly varied, ranging from forested mountains to sparse deserts; the northern and eastern regions exhibit a colder alpine climate, while the west and south are warmer and more arid.