The two major geologic units of the battlefield (siltstone and diabase) greatly influence soil development, texture, and chemistry. In general, soils weathered from diabase are loamy, rich in clay minerals, and tend to have well developed subsoil hardpans that limit permeability. They also have significantly higher pH, calcium, magnesium, and manganese concentrations, along with significantly lower iron concentrations, than soils weathered from siltstone. Although a few of the latter have moderate clay subsoils, most have silty upper horizons and loamy subsoils with good drainage. Most residual upland soils weathered from siltstone are strongly to extremely acidic, with relatively low base cation concentrations (except iron). However, below the limit of surface leaching, calcareous soil material may be abundant and is frequently exposed on steep slopes and bluffs undercut by streams. The soil survey for Prince William County (Elder 1989) indicates that approximately 79% of soils in the Park are derived from siltstone or metasiltstone, with the remainder weathered from diabase (19%) or from alluvium (2%). The most common soil types, covering more than 40% of the Park, belong to the Arcola and Nestoria series. These soils are moderately deep to shallow, well-drained silt loams with gravelly silt loam subsoils.
Fleming, G.P. and J.T. Weber. 2003. Inventory, classification, and map of forested ecological communities at Manassas National Battlefield Park, Virginia. Natural Heritage Tech. Rep. 03-7. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. Unpublished report submitted to the National Park Service. 101 pp. plus appendix.
Elder, J.H. 1989. Soil survey of Prince William County, Virginia. U.S.D.A. Soil Conservation Service in cooperation with Virginia Polytechnic Institute and State University. U.S. Government Printing Office, Washington, D.C. 245 pp. plus maps.