The Treaty of 1816 officially extended the states' frontier northeast up the Chattooga River, where it remains the current boundary.
The first Georgia v. South Carolina case in 1922 was regarding the islands in the Tugaloo, which was not explicitly named in the treaty because that was prior to its discovery.
Although the treaty prescribes the northerly branch as the boundary, and the Chattooga flows in a perpendicular direction (putting Rabun County, Georgia on the north side and Oconee County, South Carolina on the south), Georgia was given the islands as in the lower rivers.
Although South Carolina was in adverse possession of the land, Georgia lost this case due to acquiescence, rather than as a matter of the treaty's wording.
An 1876 case, South Carolina v. Georgia, was about dredging for navigation around an island in the river at the port city of Savannah, and not about the boundary location.