The Black Canyon, which has been carved by the Gunnison River as it hurries to join the Colorado, is 53 miles long, but only the deepest, most spectacular 12 miles of the gorge lie within the Black Canyon of the Gunnison National Monument. Slanting rays of sunlight penetrate this deep and narrow canyon's dark grey walls of schist and gneiss that are shrouded in heavy shadows most of the day - hence, "Black Canyon." East of the park the Gunnison River has been impounded and tamed behind three dams. In the Black Canyon, however, it remains one of the few unspoiled wild rivers in the country.