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Thrust Fault


Photo by Marli Miller, University of Oregon. Used by permission. (fair use policy)

The Keystone thrust near Las Vegas, Nevada, is a spectacular example of a thrust fault, a reverse fault with shallow dip. The dark-gray Cambrian limestone of the Bonanza King Formation is moved sideways and above the pink Aztec Sandstone, of Jurassic age. This area is preserved in the Red Rock Canyon National Conservation Area. In 1998 Clark Burchfiel argued, after detailed mapping of this area, that the Keystone fault is actually farther to the left and that this is the Wilson Cliffs thrust fault. But it is spectacular by any name.

The thrust fault was most active about 70 million years ago, during the long Sevier orogeny (mountain-building episode). Compressive forces caused by tectonic plate interactions to the west pushed the upper crust eastward. Movement on this thrust fault, which is part of the extensive Sevier fold-thrust belt, appears to have been nearly 100 kilometers.

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