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Scientists are still mapping Lechuguilla Cave, known to be at least 150 miles long, and they suspect it may extend outside the protection zone.

Krakauer regaled with a scientific trio’s exploration of Lechuguilla Cave in Carlsbad Caverns National Park, New Mexico - reading about the long, roped descent into the cave’s dark maw, its miles of narrow passageways and the objects of study, rock-eating microbes.

In 1991, the caving expert Emily Davis Mobley was exploring Lechuguilla Cave, in Carlsbad, N.M., when a falling 80-pound rock broke her leg.

Another group led by Hazel Barton, a microbiologist at the University of Akron, discovered microorganisms harboring antibiotic-resistance genes in the Lechuguilla Cave in New Mexico.

The shadeless limestone hills were stippled with vegetation — the shin daggers of lechuguilla, the star-burst of sotol, the lavender fuzz of plume tiquilia, ceramic-leafed tidestromia — spaced uniformly to make the most of what little moisture existed.