Catoctin Mountain is the easternmost ridge of the Blue Ridge in Maryland and northern Virginia, stretching about 50 miles and shaping the eastern wall of the Loudoun and Middletown valleys. Formed largely of ancient greenstone, it supports diverse forests, wildlife, and hundreds of plant species, including threatened purple-fringed orchid. Its name is probably linked to the Kittoctons, and its history includes European settlement, iron furnaces, timber cutting, and later farming. Today it is known for protected lands such as Catoctin Mountain Park and Cunningham Falls State Park, as well as for Camp David, the presidential retreat established there in the 20th century.