Let me throw you a curve ball. I don't think it's Fort Donelson, Tennessee nor Fort Donelson, La. I don't put much stock in writing on cdvs unless it's a person's personal signature. In this case, we know the photographers were McPherson & Oliver. If you research them you'll see they were a well known, but short lived team, out of business in 1865. They were enamored of photographing forts, both union and confederate. Of the dozens of cdv photos they produced, most were taken in New Orleans area where they had their studio and up the Mississippi. They took an inordinate amount of photos documenting the seige of Port Hudson including Union camps and Confederate forts and defenses. For my dollar, your cdv shows a fortification at Port Hudson.