OK, thanks, you guys have put my mind to rest. It doesn't seem like it's the result of foul play. I thought if it had been, maybe it would really be my duty to report it, to maybe provide closure for someone.
I'm just going to leave it. But I may ask the neighbors. They all have really interesting stories about Frank, the guy who built the place. If it is a grave, it would have dated from his time or even earlier. It's pretty old looking.
"Saddle fit -- it's a no brainer!"" - random person