I have similar memories of building shanties and lean-tos and things with my brother behind our house in the woods. I had always assumed it was my grandfather's

I have similar memories of building shanties and lean-tos and things with my brother behind our house in the woods. I had always assumed it was my grandfather's land, but I only discovered recently that the logging company owns it. Not that they would care - they can't use it because it's protected due to the riparian habitat. It sounds like our productions were a lot less involved than your "log cabin" though. Mostly just switches and young hollies tied together with briar vines to form a roof, occasionally with walls (built of the same materials).