Mysterious valleys

One of the interesting features of the preserve are the small dips in the middle of the the scrub. They appear to be manmade. Nothing or little grows in them, but they make interesting relief in the landscape. It seems a remote spot to remove so little dirt. The larger pit on the edge is less mysterious. It has all the appearance of small borrow pit. However, I have to consider that at one time the terrain may have been more open and it was easier to traverse. I recently found a pile of concrete fairly deep inside, telling me the place wasn't always quite so thickly vegetated.