Oh sure, I'm definitely familiar with those. The weird ones are in forests, a reminder that an area used to be clear and then was left to grow back.

The walls of stones were the result of collecting stones that were near the surface from what I understand (maybe plow depth). I was talking more like bigger stones that were buried several feet under the ground that could just stay where they are (when you fill in the hole), but for a compulsion to treat them as things.