Deep inside the dark, damp caves of Kartchner Caverns State Park lies something that sounds more suited to a fairy tale than to a rock formation.
The so-called Big Room holds the world’s largest formation of brushite moonmilk — sometimes called “elf’s milk” — a sparkling white, creamy-looking substance that occurs when bat guano mixes with limestone.
The moonmilk might be nicer to look at, but it’s the bat poop that really makes the cave special, said Robert Casavant, natural resource and science manager for Arizona State Parks.
“The bat guano is the basis of the Big Room’s ecosystem,” he said.
For 10 years now, the Big Room has been open to visitors from mid-October through mid-April, when its resident bats migrate elsewhere, complementing the Throne Room that opened to visitors in 1999.
Arizona State Parks celebrated the Big Room’s anniversary earlier this month with special speakers and presentations, including the dedication of the Kartchner Caverns Underground Microbiology Exhibit.