It's rather easy from the images to follow the trail from the observation deck back to the parking area via the trial. There's also a telescope mounted on the observation deck for those who forget to bring a pair of binoculars... a great place to watch beavers, heron, assorted ducks and geese, and of course, bald eagles, which nest in the area along the marsh.
From
www.patc.net:
The Great Marsh Trail departs from Gunston Road, about one mile past the turnoff to Mason Neck State Park. Care must be taken not to miss the somewhat hidden parking area nestled back in the woods. The Great Marsh Trail follows an old road from the parking area and basically follows in a straight line through pretty woods to an ending point one mile away at a wildlife observation deck. This is an outstanding area to observe the bald eagles that frequent the marsh. Hikers can then retrace their steps back to the parking area.
Misc, Parks 
