They are located approximately 20 miles (32 km) east of the main chain, across the Loudoun Valley.

The Preserve at Bull Run Mountains has over seven miles of trails that are open to the public on Fridays, Saturdays, and Sundays year round.

In the north, from Aldie to the headwaters of Bull Run Creek, the range serves as the eastern border of the southern Loudoun Valley.

This formation consist mainly of Catoctin greenstone interspersed with white quartz and Precambrian metamorphosed basalt flows.

These rocks were transported westward to their current location and uplifted during the Alleghenian Orogeny.