Thanks to sheer, 1,000-foot-high walls and difficult access, as well as the National Monument designation, the 53-mile-long gorge cut by the Gunnison River has been preserved in its wild state. The river drops an average of 95 feet per mile, one of the steepest fall rates for a North American river. The deepest and most spectacular 12 miles lie within the National Monument's dark gray walls of gneiss and schist with pinkish crystalline granite bands. Abraham Lincoln Fellows, in his diary from the 1901 survey of the gorge, wrote, “Our surroundings were of the wildest possible description. The roar of the waterfalls was constantly in our ears, and the walls of the canyon, towering a half mile in height above us, were seemingly vertical. Occasionally a rock would fall from one side or the other, with a roar and crash, exploding like a ton of dynamite when it struck bottom, making us think our last day had come.”