On a scouting expedition in 2007, Jason Ballensky spotted a cave entrance in a remote area of Grand Canyon National Park. It looked big.

An experienced caver, Ballensky was working under a research grant to help the park inventory and document caves. The Grand Canyon is known for many things: stunning scenery, mind-bending geology, challenging hikes and river trips. Caves don’t usually make the list. But the Canyon region contains one of the largest cave systems in North America, and the park has documented more than 660 caves. 

Some contain rare ice-age fossils, and each is a little treasure chest that is, in its way, unique. Many of the caves Ballensky had found were small and took only a few minutes to explore, but he was realizing the Canyon had the potential for large caves. And this was just the kind of thing he had hoped to find. 

The biggest challenge was getting to it. There were no trails anywhere nearby, which wasn’t unusual in the Canyon. But gaining access to this one was particularly challenging, requiring a long, difficult rappel. Then, on his way to the entrance he had spotted, Ballensky found an even larger cave entrance tucked beneath the rim.

He had explored a lot of caves, but this one made an impression. First, it had all these crazy gypsum formations. And then, there were the bats. Dead bats. An incredible number of them. Some still clinging to the walls.

At first, Ballensky was nervous about what might be going on. Was something in the cave causing mammals to die? But as he looked around, he could see that although they were well preserved, the bats were of varying ages. It was obvious this was a significant find, but it would be years before Ballensky would know just how significant. 

The cave Ballensky discovered contained something no one had seen anywhere else in the world: the eerily well-preserved remains of thousands of bats, some older than our ability to carbon-date them. From a scientific perspective, the discovery is so important that, to protect it, the cave’s location, as well as that of a second cave nearby, is a closely held secret. 

Finding bats in this state of preservation is not unheard-of, but it’s rare. “Maybe around the world, we may have documented approximately 100 mummified bat remains — from everywhere,” says National Park Service senior paleontologist Vincent Santucci. “Here, in one cave, we have thousands of mummified bat remains that [have] preserved soft tissues that aren’t commonly encountered in the fossil record.” That gives researchers an opportunity that’s never existed before, Santucci says: to look at an animal’s evolutionary changes at a genetic level over that long a period and with such a large data set. 

This month, the research team will publish its first article dedicated to the project in a special issue of Parks Stewardship Forum. In it, they’ll announce the discovery and where the team is going with the research, but not its findings. For those, Santucci is targeting a high-profile, peer-reviewed journal such as Science or Nature. Once the findings are published, Santucci believes the project will go viral, attracting scientists from around the world. 

“We now have the capability of understanding things we never would have known,” says Dr. Carol Chambers, of Northern Arizona University’s Bat Ecology and Genetics Lab. “Morphologically, when you look at skeletonized bats, you don’t know what fur color they had or how long their ears were. Can we look at its gut contents? Can we look for parasites? What else can we do? It seems like we’re just opening a door here into discovery about the presence of bats on this planet [and] in the Southwest: their evolution, diet, so many things.”

Illustration by Sam Ward

Chambers got involved in the project through a biologist she worked with while studying mummified bat remains on the Navajo Nation. A woman who was planning surveys of the cave told Chambers about the bats in the Canyon and asked if she wanted her to take samples. 

They developed protocols to collect hair samples for isotope analysis and tissue samples for carbon dating. That was in 2010. But carbon dating was expensive, and Chambers didn’t have the funding. Then, sometime around 2018, she ran into Elaine Leslie, a colleague she’d worked with while studying rare spotted bats in the Grand Canyon. 

“She said, ‘Well, I’ve got some money you can carbon-date samples with,’ ” Chambers recalls. “So, I carbon-dated 12 samples of the 24 that I had, and the youngest one was 3,500 years before present, and the oldest was 33,000. Given that 12 for 12 we had ancient bats … she connected me with Vince.”

At this point, the team has surveyed about 350 bats in the two caves and carbon-dated between 100 and 200.
The bats represent at least nine species. The youngest died within the past 100 years, the oldest more than 50,000 years ago. 

Illustration by Sam Ward

So far, Chambers has looked at the difference in bat populations between the two caves. The first cave is long, with narrow, twisting passages. The second is much shorter, but with much larger passages. This seems to make a difference in the types of bats that inhabited them. Townsend’s big-eared bats, which can navigate in tight, cluttered spaces, dominate the first cave. Silver-haired bats, which can’t turn on a dime, are more common in the second. 

When carbon dating is completed, Chambers will see if the sample size the team has collected is large enough to provide a perspective on what the bat communities looked like across time. The next step will be to analyze their DNA. 

“We’ve collected about 60 to 70 samples for attempts at working with ancient DNA,” Chambers says. “We can look at the two species that were dominant in those two caves and compare them to modern-day bats. Because these animals look the same as they did. They don’t look different.”

Beyond providing excellent habitat for bats and stable conditions to preserve their remains, the caves themselves are unique in other ways. Volunteer cave mapper Shawn Thomas was one of the first people to set foot in the first cave, in 2009, and has joined several expeditions to map it. He’d been inside hundreds of caves, but this cave was like nothing he’d ever seen. First, it was unusually orderly, with passages at right angles leading off a central corridor that connected to other parallel passages. “On top of that, there’s levels above you and below you, to some degree,” he says.

Then, there’s the mineralogy. Gypsum has extruded slowly from the cave walls, curling into elaborate, flower-like petals and spirals. Gypsum flowers, as they’re known, are “rare, and they’re a big deal,” Thomas says. “And in this cave, they’re just everywhere.”

Finally, there are the bats. “As you get farther and farther from the entrance … you find yourself in these more intimate surroundings, and the floors and the walls have hundreds, probably thousands, of these desiccated bats throughout the cave,” Thomas says. “And they’re so well preserved that you can identify them to the species.”

At annual expeditions, teams would meet at the end of the day and talk about the bats. “It’s been great to finally get some dates off the samples we took,” Thomas says. “And to start to understand that this is actually a museum of a cave that’s preserving these animals over 40,000-plus years. That’s pretty incredible.” 

These and other caves in the Canyon feature mineral deposits that formed as they dried out between 4 million and 5 million years ago. Those deposits are helping scientists better understand the age of the Canyon and when and how the Colorado River cut through it. “There’s a lot of leftover information from millions of years ago about what was going on, and that’s what we keep digging into,” Ballensky says. “Every little new passage we find, you can kind of put extra pieces together to fill in some of that information.”

The first cave has been mapped at more than 40 miles so far. Ballensky believes there may be another 20 miles left, but he’s not sure he’ll ever see it. Passages have filled in, and he doesn’t think researchers will find a way around them. He thinks there may be another 5 miles the team is capable of mapping.

But just as the Canyon’s ancient Indigenous inhabitants didn’t have the technology we have today to access the cave, it’s possible that people in the future will have tools and techniques that will allow further exploration. “So, I’m not saying that the caves are done,” Ballensky says. “I’m just saying we may be reaching the limits of our abilities at the moment.”

That’s exactly why Santucci thinks it’s so important to protect these rare and fragile resources so they’ll be available to future scientists. “We would have never dreamed of these things back in the 1970s and ’80s,” he says. “What will be available 100 years from now? A thousand years from now? We can’t even imagine.”