Bedrock Geology of the Bull Run Mountain Natural Area
The Bedrock geology is the solid rock immediately underlying an unconsolidated material, such as soil.
The Bedrock units are:
Jwm - Millbrook Quarry Member of the Waterfall formation - Conglomerate, sandstone, and siltstone which intertongues with Jw; multicolored
Ch - Lower Cambrian Harpers formation - Phyllite and metasandstone (about 545 million years old); tan and gray
Cw - Lower Cambrian Weaverton formation - Metasandstone and phyllite; light gray
Zc- Late Proterozoic Catoctin formation - Greenstone metabasalt (about 571 million year old lava); greenish gray
Source: Data modified from the geological map of Washington West quadrangle by Peter Lyttle and others that is in production.