page_title: San Rafael Swell
section_title: Geology
hierarchical_section_title: San Rafael Swell / Geology
context_page_description: The San Rafael Swell is a large geologic feature located in south-central Utah about 16 miles west of Green River, Utah. The San Rafael Swell, measuring approximately 75 by 40 miles, consists of a giant dome-shaped anticline of sandstone, shale, and limestone that was pushed up during the Paleocene Laramide Orogeny 60–40 million years ago. Since that time, infrequent but powerful flash floods have eroded the sedimentary rocks into numerous valleys, canyons, gorges, mesas, buttes and badlands.
  The swell is part of the Colorado Plateau physiographic region.
context_section_description: The San Rafael Swell was formed when deeply buried Precambrian dike swarm rocks faulted, or broke, during the Laramide orogeny, about 60 million years ago. These "basement" rocks below the present-day Swell moved upwards relative to the surrounding areas and caused the overlying sedimentary rocks to fold into a dome-like shape called an anticline. The resulting structure is analogous to a series of blankets draped over a box.
  Since that time, the relentless force of running water has eroded the geologic layers, resulting in older rocks becoming exposed in the middle of the Swell, and younger rocks exposed around the edges. Many of the most impressive landforms are composed of more resistant rocks, including the Jurassic Navajo Sandstone, Jurassic Wingate Sandstone, and Permian Coconino Sandstone. The folding is much steeper on the eastern edge of the Swell than in the west, and this eastern edge is referred to as the San Rafael Reef.
  Both the San Rafael River and Muddy Creek drain out of the high Wasatch Plateau and the cut directly across the uplift of the Reef, which marks them as superimposed streams, pre-dating the time of the uplift. Part of the Swell has geographic features that resemble Mars. The Mars Society decided to set up the Mars Desert Research Station in the area as a Mars analog for such reasons.
caption: The Little Grand Canyon on the San Rafael River
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