Good eye; I didn't think about looking at the trees. It looks pre-Fall, but this is the South; I wouldn't be surprised if there were still leaves on the trees into late September.

This looks like a farm to me. That bunker is almost certainly a converted ice-house, but could also be slave housing. I'd guess ice-house, as that's what they look like in the mid-Atlantic. Also, I'd have expected fortifications to be built outside the city, given the nature of warfare in the mid-1800's. Surely they wouldn't have built those barriers in a more suburban area? The barriers looking fairly intact is what makes me suspect a "before" photo.