File:Lock 71 on C and O Canal from NPS.jpg

English: Lock 71. NPS site says: Lock 71 is the 13th of the 13 composite locks. These locks differ from the other locks on the canal. Between the upper end of the lower gate pockets to the lower end of the upper gate pockets the stone walls were moved 9 ¼° on each side, resulting in a clear dimension between lock walls of 16’-16 ½” rather that the 15’ previously adhered to. The normal clear dimension was resumed both up and down from these points. The walls were of rough-cut and rough-coursed limestone, principally dry-laid where the walls were timbers. This wooden section of the lock was “water-proofed” at first by being “kyanized” and later with creosote. Lock 71 is 1/4 miles above Lock 70 and 7½ miles below Lock 72 at the western edge of Oldtown, Maryland. This is a typical cut stone lift lock, though much of the stone and wood has since been replaced with concrete. The upper lock pockets received a thin coat of concrete. 15½' of wood lining was replaced with concrete on the lock walls from the lower end of the lock pockets. The next 59' remains wood lined. After that concrete continues for another 16' up from the upper edge of the lower lock gate pockets. The lower lock gate pockets are 20" deep on the upper end, and increase to a 27" depth at the lower end, as done in no other pocket. The towpath wall wood coping was replaced with 12" deep coping stones. Below the lower gate pockets, all wood copings were replaced with concrete. The dam at the upper end of Lock 70 backs up water to the top of the brest wall in the intervening canal and this lock. Piled stone above the upper berm wingwall indicates a stone-filled wood cribbage about 15' wide. It extends up the canal for 21' and divides the water entering the lock and the bypass flume. The pair of upper gates remain in a closed position. The hardware remains, and iron pins for the guard boards are still visible. Stone caps on the riverside cantilever 6" to shelter the guardboards. Stone caps on the bermside are missing.