Colorado River as 2 billion years. The of the river that flow through the Grand Canyon are largely encompassed by Grand Canyon National Park and are known for their difficult whitewater, separated by pools that reach up to in depth. At the lower end of Grand Canyon, the Colorado widens into Lake Mead, the largest reservoir in the continental United States, formed by Hoover Dam on the border of Arizona and Nevada. Situated southeast of metropolitan Las Vegas, the dam is an integral component for management of the Colorado River, controlling floods and storing water for farms and cities in the lower
Colorado River basin. Phoenix in Arizona and Las Vegas in Nevada are the largest metropolitan areas in the watershed. Population densities are also high along the lower Colorado River below Davis Dam, which includes Bullhead City, Lake Havasu City, and Yuma. Other significant population centers in the basin include Tucson, Arizona; St. George, Utah; and Grand Junction, Colorado. Colorado River basin states are among the fastest-growing in the U.S.; the population of Nevada alone increased by about 66 percent between 1990 and 2000 as Arizona grew by some 40 percent. The Colorado River basin shares drainage boundaries with many other major watersheds