In the comments someone says: "That is COOl, but it is a fence, hand made it has lasted well, No mortar and the round rocks in the middle are the giveaways that it is a fence. Where do you live?"
Bushcraft412 says: "I live in NY and I found this on public land in the Southern Tier. Not sure about it being a fence. It's a 30x30 foot square. The farm equipment being right next to it makes me think it was the foundation of a small barn or storage building. I'm going back to do some more exploring this weekend to see if I can find any more remnants or clues about what exactly it is. I know the land was abandoned farm that the state bought and reforested in the 1930s."