Members of Fairfax County Fire and Rescue Battalion 407 responded to a 911 call at about 11:30 this morning.  A group was hiking in the woods surrounding Bull Run Marina on Old Yates Ford in Clifton when an elderly female slipped in mud and fell down a steep ravine, injuring her right shoulder.  She was transported to Fairfax Hospital by ambulance for what Battalion Chief Glenn Bydume described as "minor injuries."  A group member and witness reported the hikers had been walking for about five minutes when several members of the group slipped. Though the female hiker was the only injury, a rescue helicopter was called to the scene "as a precaution," according to Bynume.