The list contains the largest contiguous public parks-preserves within of either Baltimore, Maryland or Washington, D.C., which is within the Baltimore–Washington metropolitan area. Prince William Forest - Locust Shade, Virginia; — about one-third is closed to the public Patuxent Wildlife Research Refuge - Fran Uhler (Patuxent River Park), Maryland; — about one-third is closed to the public Seneca Creek - McKee-Beshers - C & O Canal - Germantown, Maryland / Algonkian, Virginia; Upper Patapsco, Maryland; Patuxent River Park - Merkle - Jug Bay Wetlands - House Creek, Maryland; Mason Neck - Accotink Bay - Pohick - Meadowwood - Gunston, Virginia; Patuxent River State Park, Maryland; Chapmans - Myrtle Grove - Mattawoman, Maryland; Sugarloaf Mountain - Monocacy River - C & O Canal, Maryland; Lower Gunpowder Falls, Maryland; Manassas Battlefield, Virginia; Little Bennett, Maryland; Great Falls, Virginia - C & O Canal, Maryland - Riverbend, Virginia - Scott's Run, Virginia - Carderock, Maryland; Lower Patapsco - Rockburn Branch, Maryland; Cedarville, Maryland; Smithsonian Environmental Research Center Maryland; - limited public access Upper Gunpowder Falls (Hereford), Maryland; Rock Creek Regional (Lake Needwood - North Branch); Susquehanna State Park, Maryland; Fountainhead, Virginia; Nanjemoy Creek, Maryland; - generally closed to the public Mid-Gunpowder Falls (Baldwin-Fork), Maryland; Eastern Neck, Maryland; Douglas Point - Mallows Bay - Purse State Park (Nanjemoy Wildlife Area), Maryland; Soldiers Delight, Maryland; Rock Creek Park, D.C.; Notes - only a portion of this park is publicly accessible - This list does not include interrupted, scattered parts of administrative units, but rather entire, contiguous park-preserve tracts. Strip park area (<1000 foot (300 m) width for more than 1/2 mile (800 m)) and public utility land (reservoirs) are excluded. Much of the Aberdeen Proving Grounds, Maryland. and Quantico Marine Base, Virginia are undeveloped, and constitute the largest such areas within of either Baltimore or Washington. Neither is generally open to the public. Quantico is contiguous with Prince William Forest Park. Washington and Baltimore are apart. References External links The Nature Conservancy - Maryland/DC Areas We Protect Prince William Forest Park Locust Shade Park Patuxent Wildlife Research Refuge Fran Uhler Natural Area Seneca Creek State Park McKee Beshers Wildlife Area Chesapeake and Ohio Canal South Germantown Park Algonkian Park Patapsco Valley State Park Patuxent River Park Merkle Wildlife Sanctuary Jug Bay Wetlands Sanctuary Mason Neck Pohick Bay Park Gunston Hall Meadowood Recreation Area Patuxent River State Park Sugarloaf Mountain Monocacy Wildlife Area Gunpowder Falls State