South Mountain State Park: Appalachian Trail Shelters Professional Review and Guide
"The Appalachian Trail is blazed in white; blue blazes indicate trails to the Maryland shelters where you can pitch your tent. Prominent signage makes finding the shelters very easy. All shelters look pretty similar: a smallish, hewn-log structures sitting amid comparatively level ground (the areas around the shelters are invariably hilly).
There are six primitive shelters along the Maryland portion of the AT. From north to south, they are: Devils Racecourse (0. 2 miles from Pen Mar, near the Pennsylvania border), Ensign Cowall, Pine Knob, Rocky Run, Crampton Gap, and Ed Garvey, which is 3. 5 miles north of the C & O Canal and the Potomac River beyond."