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A geologist examples a basaltic lava flow along the Madison River

By Yellowstone Volcano Observatory June 2017 (approx.)
A geologist examples a basaltic lava flow along the Madison River
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Detailed Description

A geologist examples a basaltic lava flow along the Madison River, looking for an area that can yield samples suitable for 40Ar/39Ar geochronology.  USGS photo by Jorge Vazquez, June 2017.

Sources/Usage

Public Domain.