Hi,
Although information was sketchy, The Helen-Robertstwon (1 mile) section of the Gainesville and North Western (1916-1931) was probably dual gauge. The G&NW was SG. The logging roads in the area were 42" gauge. A 1918 document between the G&NW and the Morse Brothers Lumber Company (of Helen) for the permission to lay a 42" 3rd rail from Helen South to Asbestos, GA and leave in in place for up to 25 years. The sawmill was in Robertstown - 1 mile north of Helen in a small valley (probably had a river rapids or water fall for water power) while Helen was in a wider point in the valley for the depot and workers I would guess. Two miles south of Helen was Nacoochee where the railroad traveled south through the foothills.
Doug vV