Together, these strata of vegetation enable the canyon to function as a nexus in which some seventy-five ecological communities are spread across four distinct biomes and two geological provinces. 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
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