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Bryce Geology Bryce Geology is an exemplary result of three major geological forces deposition, uplift, and erosion. Deposition The foundations of Bryce Park were laid down by a shallow sea that existed about 150 million years ago. Although these sedimentary layers can be seen in Zion Park, they cannot be seen in Bryce. The depositions that form Bryce began to be laid down about 70 million years ago. Helping to delineate these sediments were a series of mountains. One group, the north south ranging Rockies, began rising to the east. They eventually were joined by unnamed east west ranging mountains that existed close to the present location of the Grand Canyon of the Colorado. Simultaneously, yet another mountain range began to rise along what is now the Idaho border. These three chains merged to form a bowl shaped series of mountains that trapped a huge body of water referred to by geologists as Lake Flagstaff. During the existence of Lake Flagstaff, waters ranged from one huge lake to a chain of large lakes. Siltstone, which is extremely soft, was the primary sediment in these lakes. Also brought in by the various rivers and streams that fed into Lake Flagstaff was the compound calcium carbonate, which acts as a binding agent and helps add strength and rigidity to the rocks with which it becomes associated. Alternating layers of hard and soft rock, which geologists call differential hardness, contribute directly to some of the unique formations in Bryce . Coloring these structures are minute amounts of iron and manganese, which were deposited in Lake Flagstaff. Iron creates the reds; manganese, the blues and lavenders. Uplift In some areas of the world, similar sediments undoubtedly were deposited, and they have lain undisturbed through the eons. But 25 million years ago, deep within the earth beneath southern Utah and northern Arizona, powerful forces were at work. Gradually, over millions of years, the Colorado Plateau was uplifted until parts of it were 2 miles above sea level. Lake Flagstaff disappeared at about the same time that the land was uplifted, but it left sediments that eventually contributed to the Wasatch Formation the portion of Bryce that is visible today. Because of its vivid coloration, this 30 mile long formation is also called the Pink Cliffs. The pressures exerted on the Colorado Plateau were so great that the uplifted land broke into huge chunks along fault lines breaks in the continuity of a body of rock. Southwestern Utah is dominated by seven of these masses. Bryce has eroded from one of them, the Paunsaugunt Plateau, while Cedar Breaks and Zion Park have been formed from another, the Markagunt Plateau. Concurrent with the pressures that created the Colorado Plateau and its subsequent fault lines was the creation of joints, or weak areas of fracture within an individual rock or a group of rocks. The existence of many such areas has contributed substantially to some of the park's major geological formations. Erosion This Canyon is the result of deterioration on a grand scale. While deposition and uplift occurred many millions of years ago, erosion maintains its relentless onslaught against the Colorado Plateau. In Bryce, it is water "time and raindrops, time and snow, time and ice," as naturalists frequently say that creates the spires and pinnacles. Wind plays a very insignificant part in forming these imposing hoodoos. A study of the weather records has indicated that a cycle of freeze and thaw occurs in Bryce more than 200 times a year. During the day, snowmelt drips into the cracks in rocks and is held fast. Then during the night, the water cools, freezes, and expands. The expanding ice exerts such a strong force that it widens the cracks and joints in the rocks. Over a period of a few years, massive rocks are pushed, shoved, and broken down by the action of ice; indeed, freeze thaw action is probably the most important way bedrock is broken down into successively finer fragments. Eventually, whole sections of wall may fall, windows may collapse, and the rim of canyon is pushed back. 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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