“American explorers had considered the Rocky Mountains impenetrable, but native peoples of the Ute and Arapahoe tribes had long passed back and forth over the range; the two park roads now crossing the mountains follow their general routes. Trail Ridge Road was constructed between 1926 and 1932. The maximum grade on Trail Ridge does not exceed 7%, and eight miles of the road are above 11,000 feet in elevation. Reaching 12,183 feet on Trail Ridge, it is the highest continuous highway in the United States.”