Ancient carvings of a helicopter, tank, submarine, and LANDSPEEDER.
There isn't a good explanation for this by the mainstream. The chances all 4 of those coincidentally appear in the exact same spot is impossible. The second carver they describe would have seen the previous grooves when applying his own.
Unless someone recently snuck in and carved these without anyone noticing the act, nor the freshness of the new carve, then these carvings are exactly what they look like.