What could This Be?

I have no idea.

It was on the other side of a fence at the soccer complex. There was nothing to indicate what it could be. The signs on the fence were so severely bleached by sun that I could barely make out the words: "STATE PROPERTY."

There was no gate - no way - to get to the other side so that I could get a better look.

Guess this mound bunker, or whatever it is, will remain a mystery for the time being.