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Show central Utah, the Pavant, Tushar, and Sevier are drained by westward- flowing streams; the Kaipar- owits is the source of streams that go directly to the Colorado River; and the Wasatch, Fish Lake, Awapa, Aquarius, Paunsaugunt, and Markagunt Plateaus, and Pine Valley Mountains contribute water to the Colorado River and at the same time to the Great Basin. The plateaus that face the Colorado River are huge rock masses; nearly level platforms 25 to more than 500 square miles in area and bordered by terraced escarpments 4,000 to 5,000 feet high. From heights of 10,000 to 11,000 feet they overlook the lower series of plateaus along the Colorado River. Though the plateaus are now individual topographic units, it is believed that they once formed a continuous surface and that their present detachment is the result of faulting that has broken their once continuous surface into longitudinal, tilted earth blocks. The Paunsaugunt fault separates the Aquarius from the Paunsaugunt Plateau; the Sevier fault, the Paunsaugunt from the Markagunt; and the Hurricane fault, the Markagunt from the plateau- like Pine Valley Mountains. These long faults deformed all the sedimentary rocks and also the sheets of lava that overlaid them, some of them nearly 3,000 feet thick. This large- scale faulting accompanied by regional uplift introduced the long cycle of erosion still in progress. The Triassic, Jurassic, Cretaceous, and Tertiary rocks that form the stream- scoured fronts of the plateaus are but remnants. Corresponding formations appear south and east of Glen Canyon and doubtless once extended to the foothills of the Rocky Mountains. North of Grand Canyon, Triassic strata have been stripped back 30 to 80 miles, and the rocks of younger age still farther. To an extent not equalled elsewhere, the major erosion has been accomplished by wearing back the faces of cliffs rather than by abrasion and dissection of the plateau tops; erosion is directed against, rather than upon, the exposed strata. Because the individual rock layers differ in thickness and hardness, the protruding edges retreat at different rates, thus developing a zigzag vertical profile in which the resistant rocks appear as escarpments and the softer rocks as flats or gentle slopes. In other words, the plateau fronts are neither continuous nor broken curves: they are successive terraces that follow the contour for nearly 200 miles, and in distant view suggest a stairway whose ascending risers are the Chocolate Cliffs, Vermilion Cliffs, White Cliffs, and Pink Cliffs. The high plateaus of Utah comprise a landscape famous alike for its esthetic appeal and its geological interest. Their crenelated skyline rims, their elaborately carved frontal escarpments, the canyon walls decorated with arches, bridges, and caves, and the picturesque towers and terraces in their foothill belts- all brightly colored- well merit the term " marvelous." Naturally, the unique landscape has attracted the attention of poets, prose writers, and artists, and its features have been reproduced in countless photographs in color. Each year thousands of persons go to Zion and Bryce Canyon National Parks and Cedar Breaks National Monument to view the spectacular scenery. To the scientist, the region is the most comprehensive textbook on Mesozoic history and on processes involved in erosion. Fortunately, the significant features of structure, stratigraphy, and volcanism are fully exposed, and the fascinating story of geological events needs no profound study for interpretation. Few places in the world afford better opportunity to realize the power and persistence of the forces that have shaped the surface of the earth, for though displayed on an enormous scale the rock units show a certain simplicity of mass composition, form, and arrangement that makes their relations clear. Navajo Country.- The Navajo country, about 25,000 square miles in area, extends from the Little Colorado River eastward across Arizona into New Mexico and from the Rio Puerco northward to the San Juan and Colorado Rivers. Within this large area the landscapes are notably diversified. At its center lies the extensive, little- dissected Black Mesa, from which most of the major drainage passes southward through canyons in the high bordering cliffs and continues across relatively flat lowlands as shallow washes 40 to 60 miles long. East of Black Mesa the dominant topographic features are the up- arched Defiance Plateau and the lofty, narrow, cliff- walled Chuska Mountains, and the isolated Carrizo Mountains, which rise abruptly above the surrounding lowlands. The western part of the Navajo country adjoining the famous Painted Desert is substantially the surface of a chain of low- lying plateaus deeply trenched by the Moenkopi 37 |