Geology

Several canyons in the American West are longer and some are deeper, but none combines the depth, sheerness, narrowness, darkness, and dread of the Black Canyon.
—Duane Vandenbusche, Western Colorado University professor

Deep, Steep, and Narrow

About 60 million years ago, a small area of land uplifted and brought 1.8 billion year old metamorphic rock to high elevations. This is called the Gunnison Uplift. About 30 million years ago, large volcanoes erupted on either side of this uplift, burying it in volcanic rock. Then, as early as two million years ago, the Gunnison River began flowing in force. The river and time eroded all of the volcanic rock and cut a deep canyon in the metamorphic rock below.

What you see today is a deep, steep, and narrow canyon: the Black Canyon of the Gunnison.