For a comprehensive overview of DC-area trails: http://www.bikewashington.org
The Mount Vernon trail goes along the Potomac from Arlington (Rosslyn) to Mount Vernon. I think it's 18 miles long. In Alexandria, you can access the pedestrian/bike path over the Wilson Bridge to go to National Harbor.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles