For most of the twentieth century Lechuguilla Cave was a minor hole in the backcountry of Carlsbad Caverns National Park, named for the canyon it opens into. It had a 90-foot entrance pit, about 400 feet of dry, dead-end passage, and a little history of guano mining. But cavers going down in the 1950s heard wind roaring up out of the rubble on its floor, and wind meant there was more cave somewhere below.
The breakthrough
In the mid-1980s a group of cavers got permission to dig. On May 26, 1986, they broke through the rubble into large walking passages. Since then explorers have mapped more than 150 miles of cave and pushed it to a depth of 1,604 feet, the deepest limestone cave known in the United States.
Dissolved from below
Most limestone caves are carved from above, by rainwater that picks up carbon dioxide and slowly eats the rock. Lechuguilla, like Carlsbad Cavern, was hollowed out from below. Hydrogen sulfide rising from oil and gas deposits deep in the basin met groundwater carrying oxygen, made sulfuric acid, and dissolved the ancient reef. The acid left gypsum and lemon-yellow sulfur behind in quantity, and the cave is decorated with formations found almost nowhere else: gypsum chandeliers twenty feet long, gypsum hairs and beards, soda straws eighteen feet long, hydromagnesite balloons and pools of cave pearls. It is also deep enough that geologists can study five separate rock formations from the inside.
Life without light
Sealed from the surface for so long, the cave holds microbes that feed on sulfur, iron and manganese in the rock and may help shape it. In 2012 a team including the microbiologist Hazel Barton reported that bacteria from isolated parts of Lechuguilla were resistant to many antibiotics they could never have met. The finding supported the view that resistance is ancient, not only a product of medicine's misuse, and it suggested the microbes make compounds that could become new drugs. Barton's team spends days underground at a time to reach the most remote passages.
Closed to all
Lechuguilla is not open to the public; only approved researchers and survey and exploration teams go in. In the 1990s, proposals to drill for oil and gas in nearby Dark Canyon raised fears for passages that might run beneath it, until the last remaining drilling application there was withdrawn.
Visitors to Carlsbad Caverns walk through the same reef, a few miles away, in rooms made by the same chemistry.