According to this near-devoid-of-meaning article, muons remain (?) embedded (?) in materials and their “accretion” – the only verb I got from there relating to the damn things, are/will be used in chronology. I think. Or traces of them, if I know anything about muons, which is a truly mind-boggling amount. Unless statistics of particle size and exposure to them might reveal something about the construction of the barrier, i.e. the pyramid itself. I have no clue.