Colorado by Nature: Black Canyon of the Gunnison

Although it’s neither the deepest nor the longest gorge in the western U.S., Colorado’s Black Canyon of the Gunnison is arguably the most spectacular. “No other canyon in North America combines the depth, narrowness, sheerness, and somber countenance of the Black Canyon of the Gunnison,” geologist Wallace Hansen wrote back in 1965.

At its deepest point, the Black Canyon stretches 2,722 feet from rim to river—more than twice the depth of the Royal Gorge and 5 feet higher than Dubai’s towering Burj Khalifa, the world’s tallest building. But its depth is only half the story. The Black Canyon is also incredibly narrow—so narrow, in fact, that in certain places the 40-foot-wide river receives just minutes of sunlight each day. These deep shadows, plus the dark hue of the canyon walls, gave rise to its unusual name.

The canyon’s impressive dimensions are due to the extreme durability of the rocks, including 1.7-billion-year-old metamorphics through which the Gunnison River has sliced. Yet despite the Black Canyon’s seeming permanence, neither the abyss nor the rocks through which it’s carved have been here very long, geologically speaking.

Faulting that occurred as the Rockies were uplifted around 65 million years ago arched the hard, metamorphics upward, forming a subsurface dome beneath the river in the Black Canyon area. Then, tens of millions of years later, the Gunnison River began to flow through the area, setting its course by carving into a series of much softer layers that lay above the bullet-hard metamorphics. Once the river carved the initial channel, it became “stuck” in that rut, like a saw blade in a wooden groove. That was true even after it encountered the much harder rocks below, so it couldn’t switch to a new course.

During the past two or so million years, the river, which once had larger flows than it does today, gradually excavated this impressive abyss, which has walls so tough that, unlike the Grand Canyon, they have barely retreated from the river. The gorge’s 12 most spectacular miles are preserved within Colorado’s Black Canyon of the Gunnison National Park, where scenic drives as well as cross-country skiing, cycling, and hiking are all popular means to reach the rim—and peer into its dark depths.