Grand Natural History
Within the Canyon are located many ecological systems, as well as four of the seven major temperate zones of the North American continent. The difference in elevation from 2,400 feet above sea level at the bottom of the canyon to 12,670 feet at the top of Mount Humphreys in the San Francisco peaks is responsible for the wide variation. As the crow flies, only 90 horizontal miles separate those points, but at the Grandd Canyon, distance is vertical. A 1,000 foot increase in elevation up the canyon walls is equivalent to a 300 mile move northward across flat country. As a result, the contrast in vegetation and animal life between the lowest and the highest points in the park is like that between Sonora, Mexico, and British Columbia!
Inner Gorge
The life zone at the bottom of the canyon is designated Lower Sonoran. In summer, the weather is steamy, and the temperature is 20o warmer on the average than that at the South Rim. Less than 10 inches of rain falls annually, and the vegetation is sparse. Willows and cottonwoods grow along watercourses like Bright Angel Creek and around seeps that form natural springs. Warblers, grosbeaks, and vireos make use of the leafy cover these trees provide. Hummingbirds flit among the shrubs searching for nectar. Under the murky surface of the Colorado River, the native fish that once flourished have nearly been annihilated as a result of the frigid change in water temperature created by Glen Canyon Dam. Squawfish, chub, and razorback sucker have been replaced by carp and rainbow trout.
Along the riparian corridor and on the Tonto Plateau are found different varieties of cactus, agave, and yucca. Lower Sonoran forms like mesquite, ocotillo, and creosote bush are also present. The black throated sparrow, a popular desert bird, lives here. Blackbrush, found at similar elevations of the Mojave Desert, is a common shrub.
As in most arid environments, the mammals have adopted a nocturnal way of life. Western pipistrelle bats search the air at night for insects. The spotted skunk steals forth in the moonlight to look for deermice. At midday, when the heat is suffocating, chuckwallas and other lizards retreat to shadowy crevices. Located at this level, too, is the Grand Canyon rattlesnake. Over the millennia, this species has developed a protective adaptation its salmon colored skin blends in with the pink rocks.
Among larger animals, mule deer dip their delicate tongues into the cold river . Bighorn sheep move nimbly along the narrow ledges of the Inner Gorge. Colin Fletcher, in his book The Man Who Walked Through Time, tells of seeing beaver and wild burros. The burros, descendants of those used by miners to haul out ore from the canyon, are a controversial newcomer to the wildlife of the canyon. They feed on grasses that normally provide forage for the mule deer and the bighorn sheep. During the past decades, their numbers have increased. Recently, a few burros were rounded up and removed from the park.
Canyon South Rim
From the South Rim, the ground slants southward onto the broad slope of the Coconino Plateau, carrying most of the scant rain water and much of the soil with it. Due to the light rainfall approximately 16 inches a year trees do not grow very tall on the South Rim. Their abbreviated height has caused them to be termed a "pygmy forest." The ponderosa pine, which grows back from the rim, may reach 100 feet, but this is unusual. Common trees like the pinon pine and the Utah juniper are no more than 20 to 30 feet tall.
Wildflowers grow in abundance on the South Rim. Cliffrose a gnarled, shaggy evergreen with creamy, aromatic blossoms is everywhere. Fernbush, another member of the rose family, flowers in August and September, which is late considering the warm climate. Three varieties of pentstemon are found in the park. The most prevalent on the South Rim is the Eaton pentstemon. Down in the canyon it flowers in April; on the South Rim, in June and July. Eight species of thistle are present, including the carmine thistle, which blooms from May to October.
Smaller animals that make the South Rim their home are the porcupine, the striped skunk, and the Abert, or tassel-eared, squirrel. Cliff chipmunks and rock squirrels scamper fearlessly along the rim.
Turkey vultures wheel in wide circles looking for carrion. Ravens with glossy black wings glide over the canyon, making peculiar croaking sounds. Violet green swallows zoom overhead. In the trees and shrubs along the rim are chickadees, nuthatches, scrub jays, and Steller's jays.
Canyon North Rim
The North Rim is more than 1,000 feet higher than the South Rim, and ecologically it is a much different place. The South Rim belongs to the tipper Sonoran and Transition life zones, the North Rim to the Canadian. The average annual rainfall on the North Rim is 28 inches, compared with half that on the South Rim; the North Rim receives around 140 inches of snow a year, compared with only 61 inches on its counterpart. The North Rim's higher elevation and additional moisture support two distinct coniferous forests the spruce-fir-aspen and the yellow and ponderosa pines. The pinon pine and Utah juniper "pygmy forest" grows far below the rim, along the steep slopes of the canyon. Masses of warm air that rise out of the depths feed these growths. In the late summer months, the warm air, cooling as it rises, forms dark thunder-heads that keep the North Rim liberally doused with rain.
Back from the canyon, the landscape of the North Rim is characterized by pristine forests and flowing meadows. Although the growing season is shorter than that of the South Rim, the variety of wildflowers is greater. Pink phlox blooms in early spring. Goldenrod, sunflowers, and mountain dandelions add a splash of color to the green meadows. Asters bloom in late summer, after many other flowers have wilted.
The soil on the North Rim is richer and deeper than that on the South Rim, and it supports a diverse group of burrowing animals such as voles, weasels, and pocket gophers. The lush meadows provide a perfect habitat for them; above their tunnels they beat innumerable tiny paths through the high grass, out of reach of predatory birds. Shrews, skunks, wood rats, deermice, and horned toads add to the list of small animal life. Among the larger creatures are mule deer, coyote, porcupine, and an occasional mountain lion. Birds include wild turkeys, flickers, great horned owls, and red tailed hawks.
Perhaps the most distinctive animal on the North Rim is the Kaibab squirrel. A large squirrel, with tasseled ears and a bushy white tail, it is closely related to the Abert squirrel, which lives on the South Rim. The different coloration of the two squirrels evolved through speciation. As it cut down through the rock layers, the Colorado River gradually widened the gap between the rims. The squirrels, unable to cross the barrier, were isolated in different habitats and eventually developed different characteristics.
Extract from "The Sierra Club Guides To The National Parks Desert Southwest".
Published by Stewart, Tabori & Chang. Distributed by Random House. 1984.
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