 A large portion of the territory uses the Potomac ZIP code, but the northern portion uses the Rockville and Gaithersburg codes.As examples, Greenbrier Park, the Glenstone Museum, and Pennyfield Lock all have Potomac ZIP Codes of 20854 and are in the Travilah CDP.Because the state of Maryland controls the Potomac River, the Travilah CDP includes portions of the Potomac River in addition to the C&O Canal.