Stretching 15 miles from the village of Aldie in Loudoun County south to New Baltimore in Fauquier County, the Bull Run Mountains have stories to tell. The mountain range is home to 10 unique plant, forest and woodland ecosystems supporting uncommon and threatened plant and animal species. Its hills were the scene of the Battle at Thoroughfare Gap during the Civil War. The rocky ridges and quartzite cliffs on its western side, along with the shadow of its eastern toe and its hollows, are said to have once guided slaves fleeing bondage via the Underground Railroad.