Bedrock map of Fairfax County, Virginia

The generalized rock-type of lithologic map separates the firm consolidated bedrock that underlies most of Fairfax County into thirteen (13) major rock types; each type groups rock units with grossly similar physical characteristics.  Although crystalline bedrock underlies the Coastal Plain deposits of Eastern Fairfax County, it was not subdivided on this map.  The only available information is based on interpretations from a few widely scattered deep drill holes and aeromagnetic and gravity surveys. Three sedimentary and ten (10) crystalline rocks on the Explanation are arranged in order from softest, best bedded, most foliated and readily splittable - to hardest, most massive, and least readily splittable.