The list contains the largest[b] contiguous public parks-preserves within 30 miles (48 km) of either Baltimore, Maryland or Washington, D.C., which is within the Baltimore–Washington metropolitan area.Prince William Forest[a] - Locust Shade, Virginia; 18,255 acres (74 km2) — about one-third is closed to the public Patuxent Wildlife Research Refuge[a] - Fran Uhler, Maryland; 13,300 acres (54 km2) — about one-third is closed to the public Seneca Creek - McKee-Beshers - C & O Canal - Germantown, Maryland / Algonkian, Virginia; 12,435 acres (50 km2) Upper Patapsco, Maryland; 9,575 acres (39 km2) Patuxent River Park - Merkle - Jug Bay Wetlands - House Creek, Maryland; 8,759 acres (35 km2) Mason Neck - Accotink Bay - Pohick - Meadowwood - Gunston[a], Virginia; 7,690 acres (31 km2) Patuxent River State Park, Maryland; 6,650 acres (27 km2) Chapmans - Myrtle Grove - Mattawoman, Maryland; 6,278 acres (25 km2) Sugarloaf Mountain[a] - Monocacy River - C & O Canal, Maryland; 5,790 acres (23 km2) Lower Gunpowder Falls, Maryland; 5,325 acres (22 km2) Manassas Battlefield, Virginia; 4,355 acres (18 km2) Little Bennett, Maryland; 3,700 acres (15 km2) Great Falls, Virginia - C & O Canal, Maryland - Riverbend, Virginia - Scott's Run, Virginia - Carderock, Maryland; 3,440 acres (14 km2) Lower Patapsco - Rockburn Branch, Maryland; 3,435 acres (14 km2) Cedarville, Maryland; 2,848 acres (12 km2) Smithsonian Environmental Research Center[a] Maryland; 2,800 acres (11 km2) - limited public access Upper Gunpowder Falls (Hereford), Maryland; 2,755 acres (11 km2) Rock Creek Regional ; 2,670 acres (11 km2) Susquehanna State Park, Maryland; 2,645 acres (11 km2) Fountainhead, Virginia; 2,450 acres (10 km2) Nanjemoy Creek[a], Maryland; 2,415 acres (10 km2) - generally closed to the public Mid-Gunpowder Falls (Baldwin-Fork), Maryland; 2,300 acres (9 km2) Eastern Neck, Maryland; 2,285 acres (9 km2) Douglas Point - Mallows Bay - Purse State Park, Maryland; 1,920 acres (8 km2) Soldiers Delight, Maryland; 1,920 acres (8 km2) Rock Creek Park, D.C.; 1,754 acres (7 km2)