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In the days leading to a massive annual cleanup event in Yosemite Valley, climbing ranger Jesse McGahey was already thinking about one place he would probe for hidden deposits of trash: the top of El Capitan.

That’s where rangers recently retrieved hundreds of pounds of junk left by rock climbers, a cohort of seemingly unlikely culprits. Most of it was old gear — dirty nylon ropes, haul bags, climbing shoes — and lots of plastic water bottles. But in July, McGahey also found something he never had to clean up before: a used poop tube, the cylindrical waste-disposal apparatus that accompanies climbers who wrestle with big walls for days at a time.

McGahey is one of several climbing rangers participating in this year’s Yosemite Facelift, a six-day trash pick-up that draws about 2,000 volunteers each fall. The event, launched by climbers 16 years ago, started Tuesday and runs through Sunday, Sept. 29. In recent years, the annual trash tally has hit about 15,000 pounds. Much of it is run-of-the-mill litter like food packaging, cigarette butts and used toilet paper. But as climbing’s profile grows and more climbers visit the valley, rangers are finding more of the sport’s detritus hidden throughout the park.

El Capitan, the 3,000-foot granite monolith that greets visitors inside the valley’s West entrance, is not just one of the park’s most striking features, it’s a crucible for climbers around the world. It’s the site of Alex Honnold’s famous ropeless climb, captured in last year’s Oscar-winning documentary “Free Solo.” It’s home to the Dawn Wall, the object of a 19-day climbing project in 2015 that made headlines internationally.

No matter the route, scaling El Cap is highly technical. No one just marches up to the base with only cursory information and starts an ascent. Climbers routinely spend a week or longer living on the wall while attempting to climb it, meticulously scouting the route in advance. That often entails using fixed ropes to jumar up the face or rappel down to practice crux sections. During an ascent, climbers typically schlep along dozens of pounds of gear.

Often, climbers working on a project will stash gear in caves at the top of the mountain to save themselves the trouble of carrying heavy baggage up and down the 6-mile summit trail. In a perfect world, when they finish, they haul their gear and garbage out with them. However, in recent years, caves have been filling up with abandoned equipment, McGahey says.

“Sadly, it’s not like, surprise, surprise,” when rangers find junk up there, McGahey says. “It’s more like, let’s go check the regular spots.”

He understands storing ropes in caves for future climbing projects and even leaving behind half-empty water bottles — a thirsty climber might be grateful. But items like the poop tube, clearly months old, was inexcusable.

“I call it extreme janitorial services,” McGahey adds, only half joking.

Last year, atop El Capitan, rangers uncovered one cache of gear that contained water bottles that had green algae growing in them and ropes shredded by nesting rodents. They cleaned most of it out earlier this year. On a trash-collection trip in July, they stumbled on loads of new deposits from climbers. McGahey estimates they recovered 8,000 feet of old climbing rope on that trip alone.

“It’s unfortunate, because in general climbers are pretty good” about cleaning up after themselves, says Ken Yager, founder of the Yosemite Facelift and president of the Yosemite Climbing Association, a nonprofit that runs the event. Gear can get left behind if bad weather rolls in and climbers have to hightail it off the wall, Yager says. “We all get caught up in life sometimes. But it looks bad.”

Yosemite climbing rangers hold retrieved gear for two to three months, McGahey says. A person looking to reclaim it could face a $280 citation for abandoned property. Or, in egregious cases, McGahey might hit them with a mandatory court appearance. Usually, the gear goes unclaimed. (Climbers who don’t want their gear picked up by rangers should tag them with names, phone numbers and dates, McGahey says.)

The trash issue doesn’t end at the lip of El Capitan. On one of the peak’s more popular routes, called the Nose, there’s a ledge about 2,000 feet off the valley floor where climbers will stop to rest or sleep for the night. By that ledge is a deep, 6-inch crack that some climbers use as a trash bin. A group that cleaned out the crack in 2014, including McGahey, found more than 150 pounds of old tin food cans, soda bottles, underwear and other refuse.

“You get to this beautiful ledge and you’re sitting there looking out at the valley, then you notice it stinks and you look down and see all this trash,” says Jim Herson of Emerald Hills (San Diego County), who has climbed El Capitan for 30 years. “It really bums you out.”

In the past year alone, since the “Free Solo” and “The Dawn Wall” films, McGahey has seen a surge of interest in El Capitan from climbers and nonclimbers alike.

“People just want to touch the rock where the magic happened,” says McGahey, referring to Honnold’s incredible ascent.

Climbers may tend to be the type of outdoor enthusiasts who pick up after themselves. But the advent of the modern indoor climbing gym has catapulted climbing’s popularity among new demographics of participants who may not be as ethically inclined. It’s nudged the vibe at El Cap away from its early dirt-bag roots toward more of a gym atmosphere, McGahey says.

Even pros can be culpable. Herson and McGahey have spotted professional climbers and photographers leaving fixed lines and haul bags anchored to the rock face for extended periods when they’re not being used — an astounding display of entitlement.

“It’s disappointing that they’re showing that that’s their acceptable technique,” McGahey says.

Hauling out climbing gear won’t be the focus of this year’s Facelift event. Yager wants to plant over some social trails that have emerged in the nearby meadow. Evening programs feature talks from famous climbers like Tommy Caldwell and Emily Harrington.

But McGahey has already heard about new caches appearing atop El Capitan, and he’ll go look.

“It’s not just the eyesore, it’s the concept,” McGahey says. “The idea that you’re treating it like a gymnasium changes people’s attitudes toward this wilderness area.”

Gregory Thomas is The Chronicle’s Editor, Lifestyle & Outdoors. Email: gthomas@sfchronicle.com. Twitter: @GregRThomas.