In Central Oregon, much emphasis is placed on the landscape’s most dramatic exteriors: the peaks of the Cascades, the contours of the Deschutes River. But below ground, a prehistoric labyrinth of lava tubes offers its own distinct — dark, cool, silent — allure.

Deschutes County — Oregon’s most cavernous area — is home to around 400 to 500 lava tubes, according to an official at Deschutes National Forest. The tubes are primarily basaltic lava tubes formed in the last 100,000 years.

The Forest Service has closed most of the readily accessible caves, such as Skeleton Cave and Lava River Cave, for the season (Oct. 15 to May 1) to protect bats in hibernation. Boyd Cave, however, located in the Deschutes National Forest, is open year-round and is — mostly — bat free. Visitors can explore its ribbed and spiky corridor in less than an hour with the help of a headlamp or flashlight. Crawling on their bellies to reach its final chamber might be necessary. (Don’t worry, there are no wrong turns to make.) Central Oregon spelunking, or cave exploring, is a fun outdoorsy alternative that is accessible to families and seniors alike. And, unlike skiing or mountain biking, it is not weather dependent.

“Every cave, whether you’re visiting it for the first time or the hundredth time, (offers) new wonder and uniqueness every time you walk through,” said Jeff Gartzke, a guide and chief operations officer at Bend-based Wanderlust Tours, which leads groups through several Central Oregon caves. More than 80,000 years old, Boyd Cave is part of the same lava flow as Skeleton Cave, which formed as a result of ancient eruptions in the Newberry volcanic system, according to Bart Wills, a forest geologist for the Deschutes National Forest. The cavern winds 1,800 feet, or about six football fields, beneath a blanket of sagebrush and cheatgrass near Coyote Butte, southeast of Bend. Before the Forest Service installed an aluminum staircase, visitors had to rappel from the cave’s “skylight,” or an area where its surface collapsed in on itself.

With each subsequent visit to a cave, Gartzke said, “You see something that you haven’t experienced or witnessed before.”

Into the abyss

Entering Boyd Cave is an exhilarating experience. It’s impossibly dark and the temperature hovers at a consistent 45 degrees — either invigoratingly cool or relatively warm, depending on the season above. At its entrance, Boyd Cave’s tubular walls are as wide as a subway tunnel. Walking is sometimes complicated by the knobby lava floor and ledges that rise and fall. Several hundred feet from the entrance, the cave tapers into the first of several near-ceiling-high mounds of collapsed material. A quick climb through the rubble leads to another chamber.

Throughout its length, Boyd Cave intermittently tapers to narrow spaces only passable by scrambling or shimmying. These bottlenecks, when not the result of collapse, are called lava plugs, said Gartzke, 35, who earned a degree in speleology — the study of caves — from the University of Wisconsin. During the tube’s formation, subsiding lava pressure caused the molten rock to collect and cool in low points of the tube. The Cave’s ceiling features pointy protrusions, but these aren’t stalactites, which are formed by the drips of mineral-rich water. Instead, they’re volcanic drips referred to as “lava-sicles” that cooled into place millennia ago, Gartzke said, .

“The volcanic history of Central Oregon goes back eons and eons,” he said. “I mean, under your feet there is a couple thousand feet of volcanic rock. Within that substrate there are countless more lava tubes that have just been covered up over the eons of more eruptions here in the Northwest. Volcanics have been the name of the game around here for millions of years.”

Lava tubes are the result of how molten rock flows. As the lava travels across a landscape, its outside layer is the first to cool. This forms a rock shell which keeps the inner flowing mass hot enough to keep going until the last round of lava is emptied, creating a hollow cavern. Patterns and textures on lava tube walls tell of various lava flow levels.

A cave is one of Gartzke’s favorite places to be. He estimates he’s explored hundreds of caves in his 16 years of guiding subterranean tours.

“What’s special about caves in general is it’s one of the few frontiers we still have on Earth in terms of exploration,” he said, adding that he has been in cave excavations where passages, untouched by humans, have been unearthed.

“It’s pretty epic. There are not many avenues that do that,” he said. “Pretty much anything the sun beats on, at some point a human being has looked upon it before you. But caverning still has that opportunity for exploration and discovery.”

The dark unknown

On a recent afternoon, Bend resident Kristin Edmark and some out-of-town friends took their flashlights through an unoccupied Boyd Cave. Wearing hiking boots and carrying requisite lights, they scrambled over boulders and ducked under low ceilings.

Exploring the lava tube was one of several outdoor activities the friends had enjoyed on that day, including a jaunt up Lava Butte and a bike ride in downtown Bend. Edmark said although this was her third visit, it’s the first time she’s ventured to any significant depth.

“I love the idea that lava was here. I love the history,” Edmark said. Barbara Dowe, partially illuminated by flashlight, added that it’s fun to brush up on geology before interacting with it hands-on. They intentionally didn’t research, however, how far Boyd Cave burrows because they wanted to heighten the sense of adventure.

“It’s an exploration of the unknown,” Edmark said. A narrowing space “increases the mystery: Can we go farther or is this the end? It’s a fun challenge.”

Cave etiquette

The old adage “Take only photos, leave only footprints,” is a good place to start with cave etiquette, said Gartzke, who has hauled garbage and beer cans out of a number of Central Oregon lava tubes, including Boyd Cave. A sense of stewardship goes a long way. Only bring water; sugary drinks, if spilled, can lead to massive mold growth and disrupt a delicate ecosystem that includes microorganisms like bacteria all the way to insects and bats — six of the microorganisms live in Boyd Cave, Gartzke said. Hibernating bats, if encountered, should not be disturbed. Waking a bat up twice during its hibernation can kill it; the disturbance causes it to burn through its fat reserve, inducing starvation before summer insects hatch, Gartzke said. To prevent the spreading of white nose syndrome, a fungal disease that is fatal to bats yet is harmless to humans, cave visitors should not wear the same shoes (closed-toe, please) and clothes — which can carry the fungus — from one cave to another.

As a matter of practicality, durable clothing should be worn, as squeezing through passages is a part of spelunking. Helmets are recommended — ones for cycling will do — due to the unpredictable rise and fall of the ceiling. A solid headlamp or flashlight with fresh batteries is integral to any cave visit.

Gartzke said spending time in caves is an opportunity to get away from the modern world.

“We’ve structured our lives around technology and concrete and steel, but the ecosystems and the geology that are happening in caves are, in those cases, places that are rather untouched from that human experience,” Gartzke said. “It’s really just going back to a more primordial existence that we don’t too often get in this world anymore.”

— Reporter: 541-617-7816,