Colorado River

The Colorado River is the defining waterway of the American Southwest — 1,450 miles from the Rocky Mountain headwaters in Colorado to its historical terminus at the Gulf of California. The river carved the Grand Canyon, built the Canyonlands, and divided the Colorado Plateau into the architecture of high desert civilization. For boaters, it is a system of systems: the technical pool-drop of Westwater Canyon; the 40 miles of Cataract Canyon, where the whitewater concentrates in the first fourteen below the Confluence; the 226 miles of permit-controlled wilderness in the Grand Canyon; the quiet flatwater of Moab Daily and Meander Canyon between them. The Colorado is simultaneously one of the most over-allocated rivers in the world — every drop spoken for by compact law — and one of the most powerful wild experiences available to those who can access its permits. It flows through the ancient Precambrian basement of the Colorado Plateau, through a mile of exposed rock in the Grand Canyon, and through the heart of the most contested water politics in the Western United States.

The Colorado cuts through strata raised by the Laramide Orogeny, which lifted most of the Colorado Plateau between 70 and 40 million years ago, and by the Plateau's ongoing rise. In the Grand Canyon it exposes the Vishnu Schist and the granites of the Zoroaster complex — basement dated to about 1.75 billion years — beneath a rim of 270-million-year-old Kaibab Formation. The canyon is a mile deep, and the river cut it in roughly the last 5 to 6 million years. Through Cataract Canyon in Canyonlands, the river exposes Pennsylvanian and Permian strata: the Honaker Trail Formation at river level, Cutler red beds above. Westwater, farther upstream, cuts deeper in time than either — its inner gorge reaches the same Precambrian basement the river meets again in the Grand Canyon's Inner Gorge.

The Colorado River corridor supports four federally listed native fish — Colorado pikeminnow, razorback sucker, and bonytail, all endangered, and humpback chub, downlisted from endangered to threatened in 2021 — that evolved over millions of years in the warm, silt-laden, seasonally variable flows of the pre-dam river. Dams, diversions, and altered water temperatures have severely impacted native fish populations. Recovery programs operate throughout the system. Tamarisk, established throughout much of the riparian corridor since the mid-20th century, has displaced native cottonwood-willow communities across large reaches.