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Natural Features of the Grand Canyon
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, but distinct habitats are located at different elevations along the 8,000 foot elevation gradient. Near the Colorado River, riparian vegetation and sandy beaches prevail. Just above the river corridor a desert scrub community exists complete with a wide variety of cacti and warm desert scrub species. A pinyon pine and juniper forest grows above the desert scrub up to 6,200 feet, while between 6,200 feet and 8,200 feet ponderosa pine is abundant. On the North Rim at elevations above 8,200 feet, a spruce-fir forest tops out the park.
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.
Hidden within the Grand Canyon are an estimated 1,000 caves. Of those, 335 have been recorded. Very few have been mapped or inventoried. Most have developed in the limestone of the Redwall and Muav formations, although some are known to exist in other formations. Some caves are well known and, over the years, have been frequented often by visitors, such as the Cave of the Domes on Horseshoe Mesa. Cave resources include unique cave formations or "speleothems," mummified remains of extinct Ice Age fauna, archeological remains (including split-twig figurines), and unique biological systems. Many caves also play a major role in regional hydrology, as evidenced by incredible waterfalls and substantial streams emerging from places like Vaseys Paradise, Cheyava Falls, and Roaring, Thunder, and Tapeats springs. Under the current park policy, all caves are closed to visitation except for research purposes.
Exposed in the walls of the Grand Canyon, are numerous faults that document the region’s earthquake – or tectonic – history. Since faults in the Grand Canyon are not only exposed on horizontal surfaces, but also in the walls of the canyon, geologists are provided with a rare opportunity to study what faults look like thousands of feet down into the earth’s crust. Faults are seen cutting through practically every geologic layer in the canyon, from the oldest, two-billion-year-old Precambrian rocks through some of the most recent lava flows less than 10,000 years old. The amount of movement measured on the faults varies from 15 feet to 16,000 feet. One of the most famous faults at the Grand Canyon is the Bright Angel Fault. Originating south of the canyon, it is oriented northeast and slices through Grand Canyon Village, down past Indian Gardens and Phantom Ranch, and northward up Bright Angel Canyon – which is a fault-oriented canyon – and terminates near the North Rim. The Bright Angel Trail descends steeply down the broken, shattered rocks along the fault line, which provides one of the few breaks in the massive cliff faces that generally prohibit descent into the canyon.
Monoclines seen in the Grand Canyon are another expression of the region’s faults. Monoclines are folds, or bends, in the otherwise horizontal rock layers that dominate the canyon. Folds form when a fault deep underground becomes active but doesn’t actually break the surface rocks. Instead, the surface layers bend to form a fold that is draped over the displacement along the underlying fault. The most visible example is from Desert View Watchtower, where the East Kaibab monocline traverses the canyon and has folded the rock layers seen on the north side of the canyon.
Grand Canyon National Park has three distinct forest communities. From 4,200 feet up to 6,200 feet there is a woodland consisting of pinyon pine and one seed and Utah junipers. Other species in this woodland include big sagebrush, snakeweed, Mormon tea, cliffrose, apache plume, Utah agave, narrowleaf and banana yucca, snakeweed, winterfat, Indian ricegrass, dropseed, and needlegrass. Above the woodland between elevations of 6,500 and 8,200 feet on both the North and South rims is a forest characterized by ponderosa pine. Other typical plants in this community are Gambel oak, New Mexico locust, mountain mahogany, elderberry, creeping mahonia, and fescue. Another forest type is found on the North Rim above 8,200 feet. This is a spruce-fir forest, characterized by Englemann spruce, blue spruce, Douglas fir, white fir, aspen, and mountain ash. Associated plants include several species of perennial grasses, groundsels, yarrow, cinquefoil, lupines, sedges, and asters.
Paleontological resources in Grand Canyon's sediments are diverse. The semi-arid climate and cold temperatures deep within canyon caves have combined to create a perfect environment for preservation of ancient materials. Pleistocene and Holocene remains have been unearthed within many of these caves. Some of the paleofauna and paleoflora that have been found include algal mats and bacterial spores over a billion years old, mummified dung and hair about 11,000 years old, and a multitude of additional body and trace fossils from the Paleozoic Era, 550-250 million years ago. Also, sedimentary units exposed throughout the Canyon, are rich with marine fossils such as chrinoids and brachiopods.
The Grand Canyon of the Colorado River is a world-renowned showplace of geology. Geologic studies in the park began with the work of Newberry in 1858, and continue today. The Grand Canyon’s excellent display of layered rock is invaluable in unraveling the region’s geologic history. Extensive carving of the plateaus allows for the detailed study of the Earth's movements. Processes of stream erosion and vulcanism are also easily seen and studied.
The Colorado River has carved the Grand Canyon into four plateaus of the Colorado Plateau Province. The Province is a large area in the Southwest characterized by nearly-horizontal sedimentary rocks lifted 5,000 to 13,000 feet above sea level. The Plateau’s arid climate produced many striking erosional forms, culminating in the Grand Canyon. The Canyon’s mile-high walls display a largely undisturbed cross section of the Earth’s crust extending back some two billion years. Three “Granite Gorges” expose crystalline rocks formed during the early-to-middle Proterozoic Era (late Precambrian). Originally deposited as sediments and lava flows, these rocks were intensely metamorphosed about 1,750 million years ago. Magma rose into the rocks, cooling and crystallizing into granite, and welding the region to the North American continent.
Beginning about 1,200 million years ago (late Proterozoic), 13,000 feet of sediment and lava were deposited in coastal and shallow marine environments. Mountain building about 725 million years ago lifted and tilted these rocks. Subsequent erosion removed these tilted layers from most areas leaving only the wedge-shaped remnants seen in the eastern Canyon.
Rock layers formed during the Paleozoic Era are the most conspicuous in the Grand Canyon’s walls. Coastal environments and several marine incursions from the west between 550 and 250 million years ago deposited sandstone, shale and limestone layers totaling 2,400 to 5,000 feet thick. Layers from the Cambrian, Devonian, Mississippian, Pennsylvanian and Permian periods are present. Erosion has removed most Mesozoic Era evidence from the Park, although small remnants can be found, particularly in the western Grand Canyon.
Nearby rock outcrops suggest 4,000 to 8,000 feet of sedimentary layers from the “Age of Dinosaurs” once covered the Grand Canyon area. Cenozoic Era (the “Age of Mammals”) layers are limited to the western Grand Canyon and terraces near the river itself. A few sedimentary deposits formed in lake beds, but the most spectacular recent deposits are the lava flows and cinder cones on the Shivwits and Uinkaret plateaus. Volcanic activity began about six million years ago and has continued to within the last several thousand years. Spectacular lava cascades down the Canyon walls have helped date the Grand Canyon’s carving.
The Grand Canyon itself is a late Cenozoic feature, characteristic of renewed erosion during this time. Vigorous cutting by the snow-fed Colorado River carved the Canyon’s depth. Canyon widening is held in check by the region’s dry climate. The asymmetry between rapid downcutting and slow widening results in the Grand Canyon rather than a more typical broad (and nondescript) river valley. Although violent storms may send flash floods gouging down narrow side canyons, the lack of steady moisture has created a stark landscape of mostly naked rock. Harder, erosion-resistant rocks such as the Coconino Sandstone and the Redwall Limestone have eroded into bold cliffs. Softer layers melt into slopes like the Tonto Platform (Bright Angel Shale) and the Esplanade (Hermit Shale). The oldest, crystalline rocks are chiseled into the craggy cliffs of the Granite Gorges.
Nearly 40 identified rock layers form the Grand Canyon’s walls. They have attracted students of earth history since 1858. Because most layers are exposed through the Canyon’s 277-mile length, they afford the opportunity for detailed studies of environmental changes from place to place (within a layer) in the geologic past. Geologic evolution through time can be studied through the changes between different layers. It was the work of geologists that began changing the public’s opinion of the Grand Canyon region from that of “a worthless locale” to “the most sublime of earthly spectacles.” After nearly 150 years, geologists are still not finished studying the Grand Canyon. In the mid-1970s, a new rock layer was identified in the Canyon walls. Scientists continue investigating how environment affects rock formation. Perhaps the biggest question of all, how the Colorado River chose this course and began carving the Canyon, still awaits a clear answer.
Prairies and Grasslands
Grassland communities in Grand Canyon are rare and few. Mountain meadows on the North Rim are of two types: montane meadows and upland subalpine grasslands. Both are typified by many grass species, with sedges in the wettest areas and forbs and grasses along the dry margins. Semi-desert shrub-grasslands occur at Toroweap Valley and above the Grand Wash Cliffs. These areas are characterized by big galleta, blue and black grama, Indian ricegrass, and three-awns.
Rivers and Streams
Water is a vital natural resource, particularly in the arid southwest. Most of the flow of the Colorado River through Grand Canyon originates in the Rocky Mountain region. From its origin to its mouth in the Gulf of California, many hands have claimed the Colorado waters for such purposes as irrigation and water supply.
The Colorado River within the boundaries of Grand Canyon National Park drains an area of approximately 41,070 square miles. The major perennial streams feeding into the Colorado (such as Kanab and Havasu creeks, the Little Colorado River and the Paria River) are related to large perennial spring systems on both the north and south sides of the Canyon. However, the majority of water sources are intermittent or ephemeral in nature. The availability of water in these individual systems is closely related to geologic structure, seasonality and annual precipitation. Knowledge of all water sources within Grand Canyon is incomplete. A partial inventory was done in 1979 over a 1,881 square mile area of the park which found 57 perennial water sources, 21 of which are streams and 36 which are seeps. Specific geologic layers, such as the Muav limestone, are the most common sources for these perennial waters.
Grand Canyon National Park scrublands are more precisely called desert scrub communities. A Mohavean desert scrub community extends from the Grand Wash Cliffs in extreme western Grand Canyon to near the Colorado River’s confluence with the Little Colorado River. It is typified by warm desert species such as creosote bush and white bursage. Frost-sensitive species more characteristic of the Sonoran Desert such as brittle brush, catclaw acacia, and ocotillo can also be found along this stretch of the river. Species such as mariola, western honey mesquite, and four-wing saltbush, considered typical of Chihuahuan Desert species, also grow here. Upstream of the Little Colorado River, in Marble Canyon and on the Tonto Platform, species more characteristic of the Great Basin Desert predominate, such as big sagebrush, blackbrush, and rubber rabbitbrush.
Geology and slope strongly influence most Grand Canyon soils. Currently, soils throughout the Canyon are categorized as poorly developed. Soils are highly variable, ranging from moist forest soils of the North Rim to shallow, dry mineral soils and bedrock exposures of the inner canyon. Inner canyon soil textures are sandy loam, sands, or loamy sands. It is likely that there are a few silt loams or clay loams in the Hermit and Bright Angel shales and in the Toroweap Valley.
Most soil types in Grand Canyon erode very easily and regenerate slowly. Their sandy nature allows water to be absorbed immediately, leaving the ground dry shortly after rain showers. The soils are typically fragile and require little disturbance to create erosional problems. Large park areas show essentially no human impacts to soils. Other areas, which were used for farming, grazing and mineral extraction, as well as developed areas, have heavily impacted soils. Biological soil (“cryptogamic”) crusts are very sensitive soil systems, specific to arid lands. These crusts cover a significant portion of inner canyon soil. Cyanobacteria form the crust, while other bacteria, algae, fungi, lichens, and mosses are often present. These crusts play important roles in reducing soil erosion, increasing water conservation and in promoting nitrogen fixation. They create a more favorable environment for vascular plants to germinate under arid conditions. These crusts are highly susceptible to trampling and air pollution.
Soil surveys exist for about 23% of the park (188,000 acres on the Sanup Plateau and 93,500 acres on the Havasupai Traditional Use Lands). These areas were surveyed as part of grazing allotment analyses. However, extensive soil surveys have not been conducted for much of the Canyon. The soils along the Colorado River are known in more detail. Land areas along the river are characterized by fine-grained beaches, coarse-grained cobble bars, and tributary fan deposits. The fine-grained deposits found on river terraces may be classified according their age (pre- or post-Glen Canyon Dam), how they were deposited (floods, wind action, or underwater reworking below present high water) and soil grain size (cohesive silts, and sands with negligible silt).
Springs and Seeps
Spring flow from the South Rim of the Grand Canyon is a significant resource of Grand Canyon National Park. Springs offer refuge to endemic and exotic terrestrial wildlife species of Grand Canyon and maintain the riparian areas that are associated with this resource. Recent development on the southern part of the Colorado Plateau has raised the awareness of environmentalists, commercial developers, and resource managers to the value of spring resources. Springs issue from regional and local water-bearing sedimentary rocks of the Colorado Plateau. The impact of regional pumping on the water quantity and quality of these delicate and rare ecosystems is unknown and current hydrologic models show that some flow reduction will occur to some springs.
Although springs make up less than 0.01% of Grand Canyon's landscape, 500 times more species concentrate in them than in the surrounding desert. Researchers have discovered that each spring is far more unique than expected: many contain rare species found nowhere else in the world. When visiting seeps, springs, and streams, please be at least 100 feet away from the water before using soaps or urinating. Human feces must be buried at least 100 feet away from any water resource.