... it. Only thus can be explained the canyons east-to-est course across a south-facing slope and the presence of plateaus that stand across the rivers course ithout having deflected it.The most significant aspect of the environment that is responsible for the canyon is frequently overlooked or not recognized. ere it not for the arid climate in the surrounding area, there ould be no Grand Canyon. Slope ash from rainfall ould have removed the canyon alls, the stairstep topography ould long ago have been excavated, the distinctive sculpturing and the multicoloured rock structures could not exist, the Painted Desert ould be gone, and the picturesque Monument Valley ould have only a fe rounded hillocks.Biological past and presentPlant and animal fossils are not abundant in the Grand Canyons sedimentary rocks and are confined mostly to primitive algae and mollusks, corals, trilobites, and other invertebrates. Animal life in the Grand Canyon area today is varied and abundant, hoever. The common animals are the many varieties of squirrels, coyotes, foxes, deer, badgers, bobcats, rabbits, chipmunks, and kangaroo rats. Plant life is also varied. In the bottom of the canyons are illos and cottonoods, hich require abundant ater during the groing season. At the other end of the moisture scale are drought-resistant plants such as the yucca, agave, and numerous species of cactus. On the canyon rims, north and south, there is a ide assortment of plant life. Typical of the South Rim is a ell-developed ponderosa pine forest, ith scattered stands of pion pine and juniper. Bush vegetation consists mainly of scrub oak, mountain mahogany, and large sagebrush. On the North Rim are magnificent forest communities of ponderosa pine, hite and Douglas fir, blue spruce, and aspen. Under less optimum conditions the plant life reverts to the desert varieties.Grand Canyon SeriesMajor division of rocks in northern Arizona dating from Precambrian time about 3.8 billion to 540 million years ago. The rocks of the Grand Canyon Series consist of about 3,400 m about 10,600 feet of quartz sandstones, shales, and thick sequences of carbonate rocks. Spectacular exposures of these rocks occur in the Grand Canyon of the Colorado River in northestern Arizona, here they overlie the strongly deformed and contorted Vishnu Schist, the angularity of hich stands in bold contrast to the almost horizontal bedding of the Grand Canyon Series. The Grand Canyon Series actually dips slightly eastard and is separated from the overlying Cambrian sandstones by a major erosion surface unconformity. A conglomerate as deposited on the eroded surface of the Vishnu Schist. Limestones, shales, and sandstones occur over the conglomerate and are thought to represent shallo ater deposits. The area of deposition as probably a large deltaic region that as sloly subsiding, alloing great thicknesses of sediment to accumulate near sea level . The presence of Precambrian organisms is indicated by calcareous algaelike structures in the carbonate rocks, as ell as by tracks and trails of ormlike creatures in other rocks. Initially, in a generalized outline of the Precambrian history of the region, the Vishnu Schist as upraised, folded, and metamorphosed and then sloly eroded and orn don to a flat surface. The Grand Canyon Series as deposited perhaps as part of a sloly subsiding geosynclinal trough. The region as then subjected to uplift and tilting, and a Precambrian period of erosion for the Grand Canyon Series began. This action as later folloed by a long period of deposition during the Paleozoic Era 540 to 245 million years ago and then further erosion during the Cenozoic Era beginning 66.4 million years ago until the region assumed its modern configuration. ... Download