It's the leftover base of an above-ground swimming pool that the previous home owners took when they left. My big plan for the summer was to remove the sand and underlying tarps/burlap, fill in the area with nice dirt and either sow seed or lay sod.
But then it got hot out. And I got lazy.
Okay, fine. I got lazier.
When the crew dug up the yard for the fence posts, I had them put the dirt on a sheet of plastic in the sand pit, so we'd at least have the dirt there when we got around to removing the sand.
Now, instead of having just a sand pit in my backyward, I now have a dirt pile on top of a sand pit. That's classy!
And to my dismay, the soil is really, really rocky. There are some decent size boulders in that pile. Here's an example:
This new dirt pile, on top of the sand pit, has really added something to my backyard.
I'm not quite sure what it's added, but my guess would be a lot more work.