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Rocks composed of large angular fragments of volcanic material are referred to as breccias (pronounced BRETCH-ee-ahs).  Breccias often show a picturesque mixture of rock chunks of different colors and textures, but the size of many of the chunks gives one a sense of the power of the erupting volcano.

The erosional towers on the far side of the reservoir are carved in the West Elk Breccia, which is exposed in numerous places around Gunnison on Highway 50.  The breccias are part of a large stratavolcano whose vent is about 15 miles north of Blue Mesa Reservoir in the West Elk Mountains.

  A closeup of the West Elk Breccia shows it to be composed of angular fragments of a variety of volcanic rock types. 
Large angular blocks in a volcanic breccia along the south flank of Rabbit Ears Peak in northern Colorado. 

 Colorado Geological Survey
Last Updated: 1/24/2013 2:15 PM 
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