Colorado is a landlocked state in the Mountain West subregion of the Western United States. Colorado borders Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, Utah to the west, and meets Arizona to the southwest at the Four Corners. Colorado is noted for its landscape of mountains, forests, high plains, mesas, canyons, plateaus, rivers, and desert lands. Colorado is one of the Mountain States and is often considered to be part of the southwestern United States. The high plains of Colorado may be considered a part of the midwestern United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. Colorado is the eighth most extensive and 21st most populous U.S. state. The United States Census Bureau estimated the population of Colorado at 5,877,610 as of July 1, 2023, a 1.80% increase since the 2020 United States census.

New Mexico is a landlocked state in the Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also borders Texas to the east and southeast, Oklahoma to the northeast, and the Mexican states of Chihuahua and Sonora to the south. New Mexico's largest city is Albuquerque, and its state capital is Santa Fe, the oldest state capital in the U.S., founded in 1610 as the government seat of Nuevo México in New Spain.