Cool post OP. I knew there were a lot of old stone monuments in New England, but I didn't know about the ones in the southeast.

You might enjoy reading at The New England Antiquities Research Association (NEARA)

[link to www.neara.org]

I think that's the right link. It's hard to find the article archive on the web site there, if I remember correctly. you have to poke around for it but there are cool articles about old stone walls, underground tunnels and tombs, standing stones, petroglyphs, etc.