Thursday, June 30, 2011

The Green River is very strange. Unlike most rivers, the Green goes straight though the Uinta Mountains instead of going around this enormous obstacle. The process that created this phenomenon began about thirty million years ago. At the time there was a Northern Green River that flowed east from the Uinta Mountains, and a Southern Green River that flowed south. Over the course of a few million years the Uinta Mountains were eroded creating what is called the Gilbert Peak Erosional Surface. On this erosional surface layers of sediment were deposited that are today called the Bishop Conglomerate and the Brown’s Park Formation. At the same time the southern Green River drainage was eroding faster than the northern Green River. The flat surface of the eroded and covered Uintas and the steeper gradient of the Southern Green river made it possible for the southern Green River to capture the northern Green River. The two rivers combined and began to flow over the eroded Uintas. Then about 10 million years ago a geological phenomenon called uplift raised the Uinta Mountains. This renewed uplift in the Rocky Mountains caused the Green River to cut right into the folds of the Uinta Mountains, thus creating the present landscape. This is called superimposed drainage. Without our knowledge of geological history it would have seemed impossible for the Green River to have its current course. The diagram below shows the changes in the Green River’s drainage north and south of the Uintas over this period of time:

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