It's Nevada's largest and best-known hole this side of the Yucca Mountain tunnel, and new evidence suggests that Lehman Caves may be at least twice as old as originally thought.
Researchers studying formations in the cave for evidence of climate change have determined that the limestone cavern at the heart of Great Basin National Park probably has been around for at least 1 million years.
Visitors have long been told that the cave network was probably formed about 500,000 years ago.
"That was the number that was sort of handed down over the years by cave specialists. I don't think we had any hard data to back that up," said Ben Roberts, chief of natural resources for the national park 300 miles northeast of Las Vegas.
The new age estimate now being given on tours of the cave was arrived at by measuring the radioactive decay of small amounts of uranium that have percolated through the cave and collected in its stalagmites, stalactites and other formations. The assumption is the cave must be at least as old as its oldest formations.
As far as Roberts is concerned, the discovery only adds to the splendor of Nevada's largest cave.
"The cave is beautiful and amazing, and now you know you have something that may have been there for more than a million years," he said.
A team of geochemists from Massachusetts Institute of Technology and the universities of Arizona and Minnesota came up with the new age for Lehman in the fall, but that's not what they set out to do.
Roberts said their research is focused on far more recent climate events -- wet and dry periods that are recorded in the cave formations and could provide clues about past conditions and what might be in store.
"They're really interested in the last 20,000 years and the links to climate change," he said.
The work is being done against the backdrop of a controversial plan by the Southern Nevada Water Authority to pump groundwater from two valleys bracketing the national park and pipe it to Las Vegas.
Park officials have expressed concern about how large-scale pumping could affect moisture levels in Lehman and other caves in the area. Studies are now underway to determine baseline water levels in the park as a sort of early warning system when -- or perhaps if -- the authority is allowed to start up its pumps.
The findings by climate researchers are based on samples taken from stalagmites and stalactites that were broken and removed from the cave in the early years of its development as a tourist site.
"We're not going out knocking formations off the ceiling or the floors to get these readings," Roberts said.
About 28,000 people toured Lehman Caves last year. The ornate series of caverns stretches for just over a mile, but most visitors see about half to three-quarters of it, depending on the length of the tour.
A rancher named Absalom Lehman is widely credited with discovering the cave in the 1880s.
President Warren G. Harding declared Lehman Caves a national monument in 1922, but the site was left in the hands of private operators who had meetings, dances and weddings underground for almost a decade.
The monument was absorbed into Great Basin National Park when the 77,000-acre preserve was created in 1986.
Roberts said Lehman is far smaller than Carlsbad Caverns in New Mexico or Mammoth Cave in Kentucky, but it ranks among the finest anywhere in terms of formations. "It's exceedingly well decorated," he said.
Ongoing research is expected to help narrow the new age estimate even further.
"Who knows?" Roberts said. "We might be pushing 2 million years old or two and a half."
We'll know as soon as the tour guides do.
Contact reporter Henry Brean at hbrean@reviewjournal .com or 702-383-0350.