In the not too distant past when America was mostly rural, farm families had their own cemeteries. On the huge farms that owned slaves they were buried there too. Some even had grave markers but many just had a simple stone to mark the grave.
The number of headstones can range from one to ten or more. The ones you see in the pic are actually better cared for than the majority of them. I believe the family cemetery at my mom’s home farm is now under a lake.
What happens to these cemeteries is that they are swallowed up by urban sprawl. Many times no one bothers to move them, other times crooked people will remove the headstones and leave the bodies behind.
So what do you do now?? That’s a really good question. You need to find out if it’s an actual grave. A local Funeral Home would have a far better idea how this is done. If it truly is a grave there’ll be certain laws you’ll need to follow in dealing with it. For example; in Missouri if someone shows up and wants to visit the grave site of a relative on your property, you’ll have to provide them access.
All states, cities, counties, and small towns will have different laws about this situation.