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Distribution of 4 Late Quaternary volcanic tephra layers
(ash, cinders, pumice) over the western United States

Map of 4 tephra layers in the western U.S.
Map prepared by Andrei Sarna-Wojcicki, USGS.
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URL: http://education.usgs.gov/california/maps/tephra.htm
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Page Last Modified: Tuesday, 28-Aug-2007 17:49:45 EDT