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Show SUMMARY The Colorado River Basin is one of the outstanding recreational regions in the United States because of its great variety of natural scenery, climatic conditions, areas and objects of scientific interest, abundant evidence of prehistoric occupation, and present Indian, Spanish, and Anglo cultures. Here one may enjoy a large amount of sunshine and find perfect climates and settings for various types of outdoor recreation the year around. The basin embraces latitudes from Mexico almost to Yellowstone National Park and altitudes ranging from 248 feet below sea level to 14,431 feet above sea level. All of the life zones of the United States are present except the Tropical Life Zone of southern Florida. Geologic features.- An unusual feature of the basin is the peculiar alinement and local setting of the drainage channels, glaringly out of accord with the topography, exemplified by the mile- deep Grand Canyon through the Kaibab Plateau and Split Mountain Canyon. The central part of the Colorado Basin is unique in geologic history, topographic form, and scenic grandeur. Within it are displayed the oldest and youngest rocks exposed on the North American Continent. Major subdivisions of the geologic time scale are represented in orderly succession. The Uinta Mountains and Uinta Basin are unique in the United States in that they trend east- west in contrast with the general north- south alinement of similar features elsewhere. The Uinta Basin is a famous source of fossils, and derives additional interest from its scattered outcrops of solid hydrocarbons, including rare forms, some of them unique and little understood. The outstanding features of the Colorado Plateau are the widespread Triassic, Jurassic, and Cretaceous strata in approximately horizontal position; the gigantic cliffs of different geological ages and marked by distinctive colors; and the multitude of canyons that carry the perennial, intermittent, and ephemeral run- off. In places, the surface has been roughened by folding, faulting, the building of volcanoes, and the intrusion of igneous rocks. 818271s 50- 2 Bordering the Colorado Plateau on the east is a belt of tangled topography developed on rocks complex in structure, composition and relationships. The landscape is characteristic of the Rocky Mountains rather than the plateau country. The Prescott, Ariz., area is significant in that great ore bodies have been brought up by faulting. Many mines have been developed in this region. The asbestos deposits that appear as conspicuous white lines from a distance are an outstanding geologic feature of the Sierra Ancha Mountains in central Arizona. Similar asbestos deposits are found in the Salt River Canyon. The Verde Hot Springs, Soda Springs, fossil trackways of prehistoric mammals, salt deposits, prehistoric salt mines, and lake deposits with mol- lusks are important features of the Verde Valley. The San Francisco Mountains, the White Mountains, and, to a lesser extent, the Mount Trumbull region are areas of geologically recent volcanic activity which have so modified both the appearance and character of the country as to merit special attention. The lower portion of the basin, below the great plateau region, is totally different from that to the north. Rugged mountain ranges rise out of broad, flat valleys like islands in the sea. The mountains contain rocks of many geologic ages and their structural histories are complex. The delta of the Colorado River is formed in, and is controlled by, one of the most remarkable and unique structural troughs in the earth's surface. It is a depression comparable to the trough of the Dead Sea and Jordan Valley in Palestine. Events representing the history of the earth undoubtedly are more closely and simply illustrated by the record of the rocks in the Colorado Plateau than anywhere else in the world. In order that this history may be skillfully presented to visitors, emphasis must be placed on original materials. Facts must be dealt with and presented in a way that will guide people's thoughts toward a realization of the principles. The task is to lead people to the best xix |
