TOEFL Reading Practice 1

    Red Rock Canyon, part of the Red Rock Recreation Lands in Nevada, is an escarpment of Crimson Aztec sandstone cliffs and canyon walls that reveal the geologic history of the area. Bands of sediment layers tell of a deep sea bed that 400 million years ago rose eastward to shoreline in present-western Utah. As the ancient sea grew progressively more shallow, about 225 million years ago, marine limestone and shales were overlaid by sediments washed in from emerging land areas. As water in the shallow inland seas evaporated, salts and minerals were deposited in thick beds and fluctuating shorelines created intermixed beds of limestone. Shales, and minerals. Sediments from this period gave the canyon its name. Their red color was created from the weathering of iron compounds within. About 180 million years ago the area became arid and was covered in sand dunes more than 2,000 feet deep, which became cemented into the Aztec sandstone that is prominent in the canyon today. Its alternating hues of red, yellow and white are believed to have resulted from ground water percolating through the sand and leaching out the oxidized iron.

    The most significant geologic feature of the area is the Keystone Thrust fault, a fracture in the earth’s crust. Sixty-five million years ago, intense pressure thrust one rock plate over another, a phenomenon that can clearly be seen in the contrasting bands of gray limestone and red sandstone, where the gray limestone cap is actually older than the sandstone beneath it. The Keystone is one of the most easily identifiable thrust faults to be found anywhere.