The fossil reef holding Carlsbad Caverns dates from the Permian period, about 250 million years, with the caves less than a tenth as old. these caves formed and grew as the surrounding land rose well above sea level and mildly acidic rainwater percolated through natural faults and fissures, slowly dissolving and expanding the gaps. Around every turn a wonder of water works appears on scales from fractions of an inch to hundreds of feet. Here, a grotesquely alien face appears in the lit limestone, its mouth tempting forbidden entry.
4 W Whites City NM (9 Jun 14) Underground