I have found several hammer heads over the years and have given them all to a local museum. Several years ago, after a very dry summer with a couple bad wind storms, a couple asked me if I would allow them to walk across our farm and look for arrow heads. I was amazed when they came back into the yard a few hours later with several of them. My dad says he used to find lots of arrow heads when he was young but I haven't found any... but then I haven't looked real hard either.
I have a 1000 acre native pasture that has several teepee rings in it. They are still very visible and have never been disturbed except for cows walking over them. They are stones placed in a circle that were placed around the teepee to hold the teepee sides down. There are about 8 or 10 of these rings so it must have been a place where a tribe spent some time. I have always thought that there is a good chance there are lots of artifacts around them, but it would require disturbing the grass and doing some digging.