The barbed wire fence traced a rusty meridian through the sagebrush, dividing the arid plain into rival kingdoms of dust and dirt. High above, the burning sun held its station while cirrus clouds assembled in the atmosphere.

Near a gate in the fence, a raven perched on a post, panting in the midday heat. The bird cocked its head and cawed at something in the distance. Then it flew away.

On the shimmering horizon, there appeared a vehicle, a white passenger van barreling down a dirt road toward the open gate. The van rumbled over the cattle guard and skidded to a stop at a fork in the road, brake lights flaring in the dust, tailpipe ruminating. Then it lurched forward, veering left.

At the top of a low mesa, the van pulled over and its driver shut off the engine. The side door slid open, and out stumbled eight or nine college students all blinking in the sudden light. They wore T-shirts, jeans, and hiking boots. Yawning and stretching, they gravitated toward a nearby vista overlooking a shallow canyon bordered by umber cliffs.

Their instructor stepped out of the driver's door and moved to the rear of the van. She was Black, maybe thirty, short and stocky. Despite the hot weather, she wore cargo pants and a fleece jacket.

She opened the van's rear doors to a little avalanche of orange construction helmets. Picking one up, she bellowed over her shoulder, "Let's go, people! We're on a schedule here."

The students shambled over, and each took a helmet. The instructor fitted hers with a headlamp. Then she clasped a first aid pack around her waist. "Everyone brings two sources of light. And wear something warm."

After locking the van, she led them through the dense sagebrush to a rocky depression in the ground. At the bottom was a rusty iron hatch bolted to the underlying rock.

A lanky white kid wearing a Nirvana T-shirt put on his helmet. "Let's do this!"

Everyone moaned. Someone pelted the back of his helmet with a pebble.

The instructor knelt and inserted a key into the weathered brass padlock, saying to no one in particular, "We have to get the key back to the BLM office in Burns by five p.m."

"Why is at all locked up?" asked Nirvana Boy. Two more pebbles ricocheted off his helmet, one after the other, and he whipped around. "What's your fucking problem?"

A female student sneered at him. "Dude, she explained it on the way out here."

"Yeah, well I was tired."

She raised an imaginary joint to her pursed lips. Everyone snickered and began putting on their helmets.

It took three of them to lift the hatch. When they had laid it open, everyone gathered around the jagged hole beneath.

The instructor sat at the edge and dangled her legs. Then she switched on her headlamp and gestured for a particular student to approach.

A pale girl stepped forward, her tiny, bird-like frame swimming beneath an oversized sweatshirt and baggy jeans. The orange helmet listed on her dainty head. A heavy black flashlight hung from her belt, something a security guard might carry. She approached the hole but stopped short.

The instructor patted the bare rock beside her. "Come on, now. Have a seat."

Bird Girl inched closer and peeped over the edge.

"See? It's only a few feet down."

She sat, cross-legged.

The instructor pushed off and lowered herself waist-deep to an unseen ledge below the surface. Turning around, she looked at Bird Girl and spread her arms wide. "Ready?"

Bird Girl shook her head stiffly, and someone behind her sighed.

The instructor laid her hand on her boot. "It's okay. Let's start with your feet." Gently, she unfolded the girl's legs and let her boots dangle over the edge. "How's that?"

When Bird Girl nodded, the instructor reached back and braced herself against the lip of rock behind her. Then she wrapped her free arm around the girl's slender waist. "Come on, now. Lean forward and put your hands on my shoulders. That's it."

She eased her off the edge, and Bird Girl latched on with all fours.

"I got you, girl," she whispered into her ear. "I got you." Then she began to climb down, Bird Girl clinging to her body.

A moment later, the instructor's muffled voice floated up from the darkness. "Now the rest of you! One at a time!"

Below was a natural cave, a tube-like tunnel big enough to drive a bus through. The walls were smooth and black. In one direction, the cave was blocked by rubble. But in the other, it ran straight, descending at a gentle angle. A cool, odorless moisture hung in the air. The floor was packed sand, pale and damp, pocked here and there by water dripping from the ceiling. If there were any footprints, they could not see them.

"We're the first group down here in eighteen months," the instructor said. She led them forward, the beam her headlamp slashing the ever-thickening darkness. After fifty yards, maybe a hundred, she stopped, her breath steaming as she spoke. "We're moving in the same direction the lava would have been flowing when this cave was formed, about seventy-five thousand years ago. The lava was probably following the path of a gully or a canyon. Up above us, exposed to the air, the lava would have cooled fast. But down here, it would have kept moving like a river."

"Was it pāhoehoe lava?" one of the students asked.

The instructor's headlamp dipped and rose through a languid nod. "Low viscosity, low silica basaltic magma from deep in the mantle. Just like the lava tubes on the Big Island of Hawai'i." She tilted back her head to illuminate the smooth, glistening ceiling. "See those drops of stone hanging down? Those are lavacicles. It means the heat of the flowing lava where we're standing now was sufficient to remelt the ceiling all the way up there."

"Well, it's effing cold now," someone quipped.

"And it's going to get colder." She led them a little farther to a sudden bend in the cave. Rounding it, they all stopped and gaped. From floor to ceiling, a wall of solid ice blocked the way. The ice was smooth and dirty, stained with horizontal stripes of green and brown. And it gave off an earthy smell, like moldering leaves. A shallow moat of meltwater surrounded its undercut base.

"We're actually two hundred feet lower than where we started," said the instructor. "The surrounding rock keeps it cold down here, right around the freezing point. The ice was formed by groundwater trickling down each spring, refreezing in the winter. Depending on the overall climate, the ice either advances or recedes, like a glacier above ground. According to records, the ice in this cave has been receding for several consecutive decades now."

Bird Girl hugged the instructor's arm and nodded her wobbly helmet at the ice. "What are those stripes?"

"Organic material carried in with the groundwater. The bottom layers are thousands of years old. Actually, paleobotanists have extracted frozen algae and pollen from it to make inferences about climate during the late Pleistocene."

Nirvana Boy stepped away from the group and aimed his flashlight at the bottom of the ice wall. "Hey! There's something in there. Look!"

Everyone turned.

"I don't see anything," said the instructor.

"It's right there. Can't you see it? It's huge."

There were no pebbles to throw this time, but several students took long hits off imaginary joints and exhaled their steamy breath.

The instructor shook Bird Girl from her arm and stood at Nirvana Boy's side. She added her light to his, peering into the ice, her orange helmet tilting by degrees. Then she froze.

"What is it?" said Bird Girl.

The instructor spun around, ripped off her fleece jacket, and handed it to her.

"What's this for?"

"Go to the far edge of the ice wall."

Frowning, Bird Girl slipped past the instructor to the wall. "Okay?"

"Now put your flashlight right up against the ice."

She leaned over the puddle of meltwater, braced herself against the rock, and pressed the powerful light to the glistening ice.

"Good. Now cover it all up with the jacket so no light reflects off the surface." When Bird Girl had done so, the instructor faced the rest of the group. "Okay, turn off your lights, all of you."

They murmured in protest.

"Just do it!"

With each reluctant click, the cave grew darker and darker until all that remained was the glowing ice, suffused with ghostly green light. Now, all could see what Nirvana Boy had seen. Breathlessly, they stared at it. Something big was trapped in the ice. It was wrapped in blue, curled into the fetal position—a human body.

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Image credit: Dave Bunnell