Mary's Falls is a 15-foot waterfall found along Gilbert Creek on the property of the Fort Benning U.S. Army post in Columbus. There is little public information available about this waterfall, and its precise location is uncertain. An old newspaper article from the mid-1900s suggests that the waterfall was, at one point, seen on public guided tours of Fort Benning. However, no recent information or pictures exist. The vast property of Fort Benning is completely off-limits to any outside visitors, and trespassers would be stictly prosecuted. The only picture I've personally seen of Mary's Falls is the old postcard below, dated 1941. 

To learn about more waterfalls in South Georgia, see chapter 12 in Mark Ozboyd's "Waterfalls of Georgia" guidebook.