Down into the blackness, they march one by one: cavers, covered in dirt-scuffed hard hats and waterproof suits of olive, purple, blue, and red. With only the quiet clank of metal foot traction, they pass a sleeping bat hanging at one of the entrances at the Oregon Caves National Monument. Soon, darkness closes around them and the rocky walls transform into a curving clay maze. Headlamps flash on. The image of sunny skies and three-foot snowbanks outside fades with the light. The cavers don’t mind spending most of their weekend underground in the cold, wet muck, though. They have a mission. And it’s not for off-season spelunking, but an early spring-cleaning.

Every winter, when Oregon Caves closes to tourists, a group of volunteers and staff gather to remove human debris left by its 48,000 annual visitors. They meet at the monument’s chalet, hidden in the pine-laden hills of the Siskiyou Mountains. But this is no ordinary cleanup — candy wrappers and stray batteries are not the main enemies. It’s the minuscule bits of skin, hair, and lint associated with human traffic that pose the greatest threats to the delicate ecology of the caves. With nearly 5,000 animals, 500 plants, 2,000 fungi, and more than 1,000,000 kinds of bacteria per acre, Oregon Caves Monument is rich in biodiversity. The caves also host valuable fossil remains, including the most complete jaguar fossil in the United States. So while picking bluish, muddy, lint globs from cracks and crevices can be tedious, the unique subsurface environment needs human help to counter human harm.

Armed with tweezers, spray bottles and sponges, paintbrushes, scrub brushes and toothbrushes, the cave cleaners enter the Ghost Room, a section of the cave roughly the size of a small two-story house. Dim lights illuminate a cement pathway. Bizarre, almost gothic shapes drip from the walls and ceiling like melting cinnamon and sugar. The crew will spend most of its time here in the largest room on the cave tour.

Up a thirty-five-step metal staircase, volunteer Aaron Stavens scrubs a rock jutting into the pathway. “There is some satisfaction in picking lint off the walls,” he says. “It’s a cause, and there are so many causes in life. It’s just one we choose to pursue.” Above Stavens, another volunteer washes down a hall of formations known as Paradise Lost. Water trickles, echoing into the Ghost Room, as it glistens down the face of stacked oatmeal-colored globs, some six feet tall. To clean the debris, he sprays and lightly brushes the cave wall where lint has built up. He then collects the hairy globs and drops them into a Ziploc bag. On the stairs, more workers collect lint with brick-sized yellow sponges. In 2007, the crew collected a total 4.2 pounds of dried lint.

In 2006, Oregon Caves began the Visitor Impact Mapping project using Geographic Information Systems to monitor how tourists affect the cave environment. They’ve since discovered that this fuzzy stuff is altering the fragile underground ecosystem. “There’s evidence that not cleaning caves increases the amount of impact,” says John Roth, chief of resource management. Whether it’s invasive surface insects coming in and crowding out native cave insects like mites, centipedes, and beetles, or rising cave temperatures caused in part by human body heat, “there are some weird things going on,” Roth says. Even exhaled carbon dioxide changes the chemical composition of some minerals. Also, filtration rates and the amount of water running through the caves have decreased, probably in part due to more than a century of fire suppression in the Siskiyous. Abundant trees and other surface organisms suck up water that should be dripping into the caves.

Back in the Ghost Room, a volunteer brushes up footprints planted in some off-trail dirt. Nearby, someone picks up a wad of gum. Elizabeth Hale, leader of the restoration crew and the monument’s physical science technician, remembers scraping graffiti from about ten different rock surfaces last year. The cleaning crew does whatever it can, in the time it has. “Anything we do makes a difference,” Hale says, “if we just do it thoroughly.”