The Bull Run - Occoquan trail runs through Northern Virginia Regional Park land along Bull Run/Occoquan River.  It is maintained by the Potomac Appalachian Trail Club.  It starts from Bull Run Regional Park (not to be confused with Bull Run National Park opertional Park operated by the National Park Service).  Additional access from Route 28, Hemlock Overlook Park, Bull Run Marina, Wolf Run Shoals Rd, & Fountainhead Park.