Geology

Geology. . , In northern Arizona, the history by the earth is revealed on a gigantic scale. Exposures of rock at the bottom of Grand Canyon reveal two episodes of mountain building, each separated by extensive erosion. These rocks, from two billion to 570 million years old, contain few fossils, mainly primitive one-celled organisms. , From the end of that era until 65 million years ago, this region was a low-lying plain, sometimes under the ocean, at other times a plain crossed by sluggish rivers and occasionally a desert with blowing sand. During this period, over 10,000 feet of sediment accumulated-rocks present today at Grand Canyon and on the Indian reservations to the east. , From 65 million years ago to the present, the region was uplifted over two miles, and the Grand Canyon and Oak Creek Canyon were formed. Later in this period, eruptions built a volcanic field, which includes the San Francisco Peaks and Sunset Crater. The peaks were later modified by glaciation. All of northern Arizona has been only slightly disturbed by faulting and folding and is mainly underlain by horizontal beds-in stark contrast to surrounding regions. In the layers of this age around Flagstaff, remains of primitive elephants, camels, horses, and even giant sloths have been found. , William J. Breed , Geologist