Yesterday I found the trail I was looking for. It was tucked away in a corner of the county that adjoins the Fairfax County Parkway and its monolithic soundproof walls. 

The path featured several fair-weather stream crossings, but nothing that could scoot below or hang above all that parkway asphalt, as impassable as a raging river. 

There was a tunnel under a lesser road, though, a dark enclosure that paralleled a stream. I took that — despite the warning.

Sometimes you have to walk on the wild side.  Even in the suburbs.