Collection contains correspondence, photographs, newsletters, maps, meeting minutes, reports, and surveys. This material convers the years 1954-94 and documents the activities of the C & O Canal Association and relate specifically to the C & O Canal.

Collection contains materials related to Thomas Hahn's involvement in the C&O Canal Association, as well as other canals related to the C&O, and canals in general. A large part of the collection consists of photographic negatives, slides and prints of the C&O Canal. Most of these photographs, negatives, and slides relate to illustrations in publications that he authored or co-authored. Other items include reference material for his books, correspondence, and maps.