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The Grand Canyon is considered one of the natural wonders of the world largely because of its natural features. The exposed geologic strata - layer upon layer from the basement Vishnu schist to the capping Kaibab limestone - rise over a mile above the river, representing one of the most complete records of geological history that can be seen anywhere in the world.
Geologic formations such as gneiss and schist found at the bottom of the Canyon date back 1,800 million years. This geologic incline creates a diversity of biotic communities, and five of the seven life zones are present in the park.
The entire park area is considered to be semi-arid desert, however, distinct habitats are located at different elevations along the 8,000 foot elevation gradient. Starting at the lowest elevation, at river level:
Along the Colorado River and its perennial tributaries, a riparian community exists. Coyote willow, arrowweed, seep willow, western honey mesquite, catclaw acacia, and exotic tamarisk (saltcedar) are the predominant species. Hanging gardens, seeps and springs often contain rare plants such as the white-flowering redbud tree, stream orchid, and McDougall's flaveria.
Above the river corridor a desert scrub community, composed of North American desert flora, thrives. Typical warm desert species such as creosote bush, white bursage, brittle brush, catclaw acacia, ocotillo, mariola, western honey mesquite, four-wing saltbush, big sagebrush, blackbrush and rubber rabbitbrush grow in this zone.
Above the desert scrub and up to 6,200 feet is a pinyon pine, Utah and one seed juniper woodland. Within this woodland one can find big sagebrush, snakeweed, Mormon tea, Utah agave, banana and narrowleaf yucca, snakeweed, winterfat, Indian ricegrass, dropseed, and needlegrass.
Ponderosa pine forests grow at elevations between 6,500 feet and 8,200 feet, on both North and South rims. Additional species such as Gambel oak, New Mexico locust, mountain mahogany, elderberry, creeping mahonia, and fescue have been identified in these forests. Above 8,200 feet, spruce-fir forests characterized by Englemann spruce, blue spruce, Douglas fir, white fir, aspen, and mountain ash, along with several species of perennial grasses, groundsels, yarrow, cinquefoil, lupines, sedges, and asters, brave the sub-alpine climate.
On the North Rim at elevations above 8,200 feet, a spruce-fir forest tops out the park. Montane meadows and subalpine grassland communities are rare and located only on the North Rim. Both are typified by many grass species. Some of these grasses include blue and black grama, big galleta, Indian ricegrass and three-awns. The wettest areas support sedges and forbs.
As in all natural habitats, the type and abundance of organisms is directly related to the presence or absence of water. The Colorado River and its tributaries, as well as springs, seeps, stock tanks and ephemeral pools provide oases to flora and fauna in this semi-arid southwest desert area.
The arid climate has been a benefit to the Paleontological resources of the park. The dry climate has been instrumental in preserving many prehistoric fossils deep within caves in Grand Canyon's geologic formations.
