“The mosaic is so rich and varied that a hiker who descends from the highest point on the North Rim to the lowest point inside the canyon will pass through a spectrum of life equivalent to moving from the cool boreal forests of subarctic Canada to the sunstruck deserts of Mexico that lie just above the Tropic of Cancer – thereby compressing a distribution of plants and animals that typically stretch over more than two thousand horizontal miles into a single vertical mile.”
