Referring to the question of piles of rocks from the amature, In my experience it was very common for piles of rock to be a result of historic field clearing. It is common in Kentucky, I am sure. I am not sure about other areas. There is the possibility that these rock piles may be prehistoric stone mounds, however, I do not have much experience in that department. The description sounds more like land clearing to me. Hope I have helped. M. Jay Stottman University of Kentucky