Eoten offering pedestal spawned on top of a harvestable rock.
It behaved normally other than looking odd, but you could see it had no underside and the whole sinking animation was visible from the side of the rock.
The screenshot shows the pedestal after it has sunk in the ground when given an offering (the whole animation was visible).
I dunno what happens if you smash the rock, I didn't want to get smacked by the eoten.