S., the river flows generally southwest across the Colorado Plateau and through the Grand Canyon before reaching Lake Mead on the Arizona–Nevada border, where it turns south toward the international border.The river and its tributaries are controlled by an extensive system of dams, reservoirs, and aqueducts, which in most years divert its entire flow for agricultural irrigation and domestic water supply.Beginning with small bands of nomadic hunter-gatherers, Native Americans have inhabited the Colorado River basin for at least 8,000 years.Between 2,000 and 1,000 years ago, the river and its tributaries fostered large agricultural civilizations – some of the most sophisticated indigenous cultures in North America – which eventually faded due to a combination of severe drought and poor land use practices.Most native peoples that inhabit the basin today are descended from other groups that settled in the region beginning about 1,000 years ago.Europeans first entered the Colorado Basin in the 16th century, when explorers from Spain began mapping and claiming the area, which later became part of Mexico upon its independence in 1821.Its large flow and steep gradient are used for generating hydroelectric power, and its major dams regulate peaking power demands in much of the Intermountain West.
Farther downstream it receives the Dolores River and defines the southern border of Arches National Park, before passing Moab and flowing through "The Portal", where it exits the Moab Valley between a pair of 1,000-foot (300 m) sandstone cliffs.
As demands for Colorado River water continue to rise, the level of human development and control of the river continues to generate controversy.
For the first 250 miles (400 km) of its course, the Colorado carves its way through the mountainous Western Slope, a sparsely populated region defined by the portion of the state west of the Continental Divide.
Large-scale settlement of the lower basin began in the mid- to late-19th century, with steamboats providing transportation from the Gulf of California to landings along the river that linked to wagon roads to the interior.
Lesser numbers settled in the upper basin, which was the scene of major gold strikes in the 1860s and 1870s. federal government was the main driving force behind the construction of dams and aqueducts, although many state and local water agencies were also involved.