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Bull Run Mountains

Three and a half years ago, I walked the mountain taking careful notes on the vegetation, topography, and geology as a naturalist trained to be a jack of all trades, but master of none. After a long hike, my notes read, in part: "a nice variety of landscape features, dominated by chestnut oak and mountain laurel, similar to the Sauratown Mountains of the North Carolina Piedmont but minus Carolina hemlock, rhododendron catawbiense, and cucumber trees among other things." In addition, I noted that given the natural area's proximity to Washington, D.C., it seemed remarkable that no one was out hiking on a beautiful Saturday in autumn.

Until I received more information about the Bull Run Mountains, that visit could have been my last. Then, I learned that these mountains were possibly the most scrutinized and studied landscape in Virginia. There was detailed vegetation work dating back to the 1930s, incredible history including the Civil War, and intensive work from conservationists and planners. For those that have just moved to the area and for those that have lived here all of their lives, there is much to learn about this unique Piedmont resource.

The Bull Run Mountains are the most easterly chain in the Piedmont, and they protect the headwaters of two major watersheds: Occoquan and Goose Creek. Seven perennial streams originate in the mountains and five are presently being monitored by BRMC. Approximately 45 miles from Washington, D.C., the mountains are part of an important greenbelt around the nation's capital and are vital because of their proximity to ever-increasing population and development.

The Bull Run Mountains are composed of rock masses of metamorphic sandstones called quartzite. They are remnants of an earlier erosion cycle that occurred when the whole Piedmont was level with their summits. The Piedmont presently is a series of rolling hills dissected by streams and rivers. A plain that is not yet worn entirely smooth by the agents of erosion is called a peneplain. Classified as monadnocks (isolated hills of resistant rock rising above the peneplain), the resistant metasedimentary rock at its highest point is 1,369 feet in elevation, with the peneplain on the western and eastern flanks at approximately 600 feet and 400 feet, respectively. The high, nearly vertical cliffs at Thoroughfare Gap, High Point, and White Rock are unique Piedmont features. In addition, many small quarry operations exploited the geologically younger, thinner bedded "flaggy" quartzite found on the eastern slopes for building stones and flagstones, making a sizeable contribution to the local economy.

The Bull Run Mountains' varied elevation, topography, soils, and hydrology contribute to a great diversity of habitats and species. These ridges provide an isolated, rugged highland terrain within the generally lowland piedmont. Based on its location, the mountains' landscape supports plants and animals at the eastern and western limits of their distribution in Virginia. Much of this flora is primarily associated with central Appalachian lower-elevation Blue Ridge sites, but there are also a number of coastal plain/lowland plants.

Species tend to vary morphologically, physiologically, and behaviorally across their geographic ranges. Disjunct populations that are at their peripheral limits, like we see in the Bull Run Mountains, are important to the conservation of a species' overall genetic diversity. In the 1930s, a botanist named H.A. Allard recognized the mountains' uniqueness and took advantage of its ease of access (via the region's railway service) to begin a long and intensive vegetation study. Allard made 55 trips a year, totaling more than 3,000 miles of walking and exploration and collecting close to 15,000 plant and lichen specimens. Each specimen was identified and species' habitats recorded, providing a vast amount of information on the plant life and ecological condition of the Bull Run Mountains in the 1930s and 1940s.

Recently, Gary Fleming, a Virginia Division of Natural Heritage (DNH) staff vegetation ecologist, documented baseline vegetation and floristic data for conservation planning and natural area stewardship. Allard's permanent collection at the Smithsonian's National Herbarium was invaluable when compiling an annotated list of both vascular plants and lichens along with vegetation changes over the past fifty years. After making the proper additions and deletions from the flora, 1,016 species of plants and 112 species of lichens have been formally documented. Of these, 25 populations of 17 state-rare plant species have been documented historically.

Historically the Bull Run Mountains served as hunting and sacred grounds for Native Americans, who valued the view afforded by the rock outcrops. In the 1700s, John Chapman saw Thoroughfare Gap as a strategic point between the farms of the Shenandoah Valley and the port in Alexandria. He used the 200-foot drop in elevation of Broad Run from the west to east side of the gap to power the mill he built in the 1750s. When the railroad came through in 1850, the second John Chapman raised the mill to five stories and began grinding limestone as well as grist. The gap and mountain proved to be important obstacles and points of defense leading up to Second Manassas. (See our annual commemoration of the Battle of Thoroughfare Gap in our program calendar.) Logging was a major economic incentive for big landowners in the mountains. In Hungry Hollow alone there were three saw mills in operation in the 1930s.

One must always look back to see ahead. Bull Run Mountains Conservancy continues to improve our education, research, and stewardship activities so that our members and the public at large can appreciate one of the Commonwealth's unique resources.