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:
Jw - Lower Jurassic Waterfall formation - Sandstone, siltstone, shale, and conglomerate (about 200 million years old); multicolored

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.
USGS