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Geology and Hydrology of the USGS Site | US Geological Survey – United States Geological Survey (.gov)

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The USGS National Center site straddles the boundary of the eastern edge of the Triassic lowland and the margin of the Piedmont crystalline rock province. The Piedmont upland at the east side of the site is underlain by the Peters Creek Schist, a foliated metamorphic rock that is probably 550 to 650 million years old.
The schist is overlain at an erosion unconformity by a layered sequence of conglomerate, sandstone, siltstone, and shale. These sedimentary rocks of Late Triassic age are typically dark red. The sedimentary sequence was intruded by 195-million-year-old diabase, some of which lies 500 meters (1,640 feet) west of the site. The rocks in contact with the diabase intrusion were thermally meta-morphosed (changed by heat) into hornfels, a brittle gray and mauve rock containing abundant green epidote crystals. The layered rocks are locally cut by normal faults and tilted 10 to 30 degrees to the west. The rocks were eroded over time and are weathered near the surface. A veneer of Quaternary alluvial sand, gravel, silt, and clay occupies the two small stream valleys that drain most of the National Center site. 
USGS scientists continuously monitor the groundwater level at several observation wells on the National Center site. Between 1976 and 1980, the wells were drilled or cored to depths of 63 meters (205 feet) to 184 meters (605 feet). An observation well containing a continuous water-level recorder (hydrograph) is northeast of the main building in a small enclosed hut. Display panels explain the hydrograph’s operation and provide additional information on the local and regional hydrogeology. The observation well can be reached by taking the Woodland Walk.
Related News: Pokémon Go at the USGS National Center

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