"Big Falls," the largest single drop on the Big Duck River, would have been of particular significance to the builders of the Old Stone Fort. While water was sacred to prehistoric Native Americans, by the 1800s it was the primary power source for industry. This was the location of one of the large paper mills in the industrial period. The mound wall would have begun again here, after the ending of the sheer cliffs and the rise of the riverbed above the falls. It is likely that it angled up from the last sheer cliff immediately below the falls and then turned back towards the eastern terminus. Some apparent stone construction debris strengthens this view. There are only slight traces of the mound between the two mill foundations however, once past the second large paper mill remains, the surviving ancient wall will be more obvious again.