Looks a little like an early concept of millstones. Though not a more modern millstone as there is no center hole to drive it.
Lands and grooves and a place for crushed grain to flow if turned counter clockwise.
Very interesting find indeed!.
The context in which found may help.
Were early grains harvested in the area, or were hardwoods predominant thousands of years ago as they are suspected of being now? ,though unlikely.