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| This view from the Split Mountain Overlook provides amazing facts about the history of the Earth in northeastern Utah. The geologic history is fairly to interpret here. First came the deposition of the sandy sediments during of the Weber Sandstone during late Paleozoic time (about 300 million years ago). The sedimentological features in the Weber Sandstone suggest that the sand accumulated in shallow water, beach, or in coastal dune settings). These rocks were later covered by younger sediments as the land subsided slowly in a great sedimentary basin along the western continental margin of North America. Beginning about 70 million years ago, a great period of mountain building began, and slowly over time the sedimentary rocks in the basin were folded and broken by faults. Over perhaps millions of years the great folded anticlines and synclines of the early Rocky Mountains formed (during the Laramide Orogeny). Throughout Tertiary time (65 million to about 2 million years) the mountains wore down and new ones began to rise. Late in this period the entire Colorado Plateau region rose form about sea level to its current average elevation of about a mile. As the land rose, rivers and streams cut downward carving the great canyons. Periods of glaciation within the last 2 million years. Climate variations occurred in association with these glacial periods and the intervening warm periods. Large-scale variations in climate had a significant impact on the amount of water flowing in the rivers and the amount of sediment moving down the river channels. As a result there were periods when the rivers and streams expanded their flood plains and sediments accumulated, and then during other periods the rivers and streams eroded down into their flood plains. These down cutting episodes left behind elevated stream terraces, two of which are clearly visible in this image—one is about 40 feet above the current river level and probably represents down cutting since the end of the last major glaciation about 18,000 years ago, and the higher, well developed surface probably corresponds to an earlier major glaciation period, possibly between 100,000 to 300,000 years ago. River terraces have been dated in other regions of the American West with more precision. Elevated terraces can be seen along river and stream valley throughout the western states. |
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