Some tongue-in-cheek ideas: Stockpile of synthetic diamonds A few cemeteries could make for curious fossils Mines - some caves survived for 200+ million years

Some tongue-in-cheek ideas: Stockpile of synthetic diamonds A few cemeteries could make for curious fossils Mines - some caves survived for 200+ million years. Conceivably a part of a mine somewhere could survive, with concrete structural reinforcements and parts of non-corroding tools intact