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 47 miles of consequential Class IV–V whitewater through Cataract Canyon; 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 the deepest canyon on the continent, and through the heart of the most contested water politics in the Western United States.

The Colorado River is the most geologically exposed river on Earth for a major drainage. It carved through sedimentary strata uplifted by the Laramide Orogeny (65–50 Ma) and the ongoing uplift of the Colorado Plateau. In the Grand Canyon, it exposes the Vishnu Schist and Zoroaster Granite — basement rocks dating to 1.7 billion years. The river carved roughly a mile (~5,000–6,000 feet) of canyon in approximately 5–6 million years. Through Cataract Canyon in Canyonlands, the river exposes Pennsylvanian and Permian strata — the same units that built the walls of Westwater Canyon farther upstream.

The Colorado River corridor supports four federally listed endangered native fish — Colorado pikeminnow, razorback sucker, humpback chub, and bonytail chub — 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.