The Rocky Mountains, commonly known as the Rockies, pass through the states of New Mexico, Colorado, Utah, Wyoming, Montana and Idaho. Extending between the United States and northwestern Canada, the Rockies contain more than 40 separate mountain ranges. The width of the Rocky Mountain system varies between 70 and 300 miles.
The highest mountain peaks in North America are contained in the Rockies. Mount Elbert in Colorado rises 14,400 feet above sea level and is the highest peak in the Rocky Mountain system. Although the initial economic exploitation of the Rockies was driven by furs and minerals, the area never become densely populated. Few cities contain over 50,000 inhabitants. It is home to a number of indigenous peoples, such as the Cheyenne, Apache and Sioux. The first European to cross the Rocky Mountains was Sir Alexander MacKenzie in 1793. The first scientific exploration of the area was made between 1804 and 1806 by the Lewis and Clark expedition.