Raymond A. Christopher David C. Prowell 2004 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. application/pdf 10.3133/ofr20041343 en Data collected from USGS drilling in Lafayette Park, Washington, D.C. in November-December, 1976 reports