Not an expert by any means, but Federal troops, which occupied N. Alabama for most of the last 3 years of the war, attempted to protect their rail lines by construction of numerous forts and "blockhouses" along them. The fort at Athens was perhaps one of the largest, but others more knowledgable than I have discussed this fort on this board before. You might find in the archives. Someone more familiar with the area might address Elkmont.

Late in the war, when the enlistments of many white troops began to expire, the Federals began conscripting large numbers of blacks for USCT (United States Colored Troops)regiments. These regiments were mainly used in garrison duty behind the lines, such as guarding railroads, to allow the white troops to participate in the large campaigns into the deep south. It might be of interest to you that the largest battle in Alabama, at Ft. Blakely, involved Gen. Hawkins full division of USCT troops. I think this was the 3rd largest formation of USCT troops engaged in combat in the war.