Rivnuts from Homestead. PA on 4/25/2019 7:21:19 PM:
Literally speaking there is virtually no paving on the GAP Trail and C&O Canal Towpath Trail in Maryland between the Mason Dixon Line and Washington, DC. There is perhaps a couple of miles of pavement approaching Cumberland from the north.
That said there are two sections of trails that parallel the Towpath itself that are paved. These are the Western Maryland Rail Trail and the Capital Crescent Trail. The former is about 22 miles long (approximately 11 miles on either side of Hancock, MD) and the latter is about the last 3 miles into DC.
There is a, maybe, a couple of miles of paving near Big Pool where the original Towpath was washed out and a causeway constructed as a permanent repair.
All the remainder is crushed stone or compacted earth with roots and small gravel/rocks in route.