I found these tracks on ADVrider.
Not all of the files in the zip were in GPX format so I used :
to convert that Garmin GDB file format into GPX. The resolution of the tracks isn't great, but at least it gives us some areas to explore.
In looking for more off pavement opportunities in and around DC, I found these tracks on ADVRider. The best off-road sections are reported to be around GreenRidge National Forest.
According to the thread, the best roads are around Green Ridge State Forest:
There are supposed to be good unpaved roads around in this area.
Know of any unpaved roads in Maryland?