In 1976, the U.S. Geological Survey drilled four holes in Lafayette Park in Washington, D.C. These holes encountered two Coastal Plain units (Quaternary (undifferentiated) and the Lower Cretaceous Potomac Group), and then bottomed in Paleozoic metamorphic bedrock. The stratigraphic relations of the Coastal Plain formations indicate that the Potomac Group strata become abruptly thicker from west to east across the park.
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USGS Numbered Series
Data collected from USGS drilling in Lafayette Park, Washington, D.C. in November-December, 1976