Also, one of my first photos of the canyon, these unusual spires caught my eye.  Below is more on the geological history illustrated in this photo:

Whatever the cause, the uplift allowed the early Gunnison River to easily cut its way down through the thick layers of Tertiary volcanics and Mesozoic sedimentary rocks. Then about two million years ago, the river began to expose the much harder Precambrian basement rocks of the Gunnison Uplift, a block of crust that had been forced upwards during the Laramide Orogeny. Trapped in its own canyon, the Gunnison had no other choice but to battle the rocks beneath it. At the rate of about one inch per every hundred years (or the width of a human hair each year), the Gunnison slowly worked its way through the resistant rock, forming the narrow, steep-sided Black Canyon of the Gunnison. Only a high volume, high-velocity river like the Gunnison could produce such a breath-taking canyon!