Colorado is the state of the United States of America that encompasses most of the Southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the high western edge of the Great Plains. Fifty-five of the 124 highest major mountain peaks of North America rise in Colorado. Admitted to the Union on August 1, 1876, Colorado became the 38th U.S. state. Colorado ranks first in mean elevation, eighth in total area, and 22nd in population among the 50 U.S. states. The United States Census Bureau estimates that the population of Colorado was 5,456,574 on July 1, 2015, an increase of +8.50% since the 2010 United States Census. Denver is the state capital, the most populous city, and the heart of the most populous metropolitan area of the Rocky Mountain Region. Colorado Springs is the state's second most populous city. While the population of the Front Range Urban Corridor now exceeds 4.5 million, many rugged portions of the state remain pristine wilderness.