When it came to climbing, Jason Wells and Tim Klein were in a league of their own. The duo, friends and climbing partners since their early 20s, would often scale Yosemite National Park’s famous El Capitan twice in the same weekend - a climb that takes even skilled climbers several days to complete.

So when they set out to climb the 3,000-foot granite rock formation in California on Saturday, Wells, 46, and Klein, 42, were well within their comfort zone. “They were not pushing the envelope,” a fellow climber and close friend of Wells’s, Brady Robinson, said in an interview with The Washington Post. “They weren’t going as fast as they could.”

In fact, the pair let a friend come along for Saturday’s climb, despite the fact that a third person would likely slow down their ascent. It was just another morning on El Cap, as climbers call it.

Attached to the same rope, Wells and Klein scaled the Freeblast Route of the Salathé Wall. Their friend, identified by Robinson as Kevin Prince, made his ascent while clipped to a separate rope and anchor. Then, Robinson said, “something weird happened.”

For unknown reasons, Wells and Klein fell, the National Park Service said. Tethered together, the duo dropped about 1,000 feet to their deaths.

A crowd of spectators had been gathered in a field below El Cap, known as The Meadow, to watch a different team of climbers attempt a possible record, Robinson said. So there were likely several people “poised with binoculars, just watching” around the time that Wells and Klein fell, he said. The Yosemite National Park Rangers received several 911 calls at about 8:15 alerting to the fallen climbers.

Since Prince was not attached to the same system, he survived. He was in an alcove of rock when Klein and Wells fell, and couldn’t see what happened in the moment.

The cause of the fall is still under investigation, but the deaths have shocked the elite climbing community, who considered Klein and Wells masters of the sport.

The incident baffled Robinson, who is the executive director of the Access Fund, an organization that works to protect climbing access in the U.S. The section of the Freeblast Route where the climbing duo fell was a relatively easy part of the ascent, Robinson said. But it’s known for its chunks of rocks that can occasionally become loose. Additionally, the technique the pair was employing, a type of speed-climbing called “simul-climbing” is an advanced one that becomes “inherently riskier” when a third person is added, Robinson said.

Their deaths underscored the dangers that even skilled climbers face while scaling the rocks of Yosemite, where more than 100 climbing accidents take place every year, according to data from the National Park Service. According to Climbing magazine, the pair’s fall marked the 25th accident this year that resulted in a death on El Capitan, a popular destination for elite climbers.

Just a couple weeks earlier, on May 21, a man slipped and fell to his death during a thunderstorm while climbing the park’s Half Dome. The man and a companion were climbing a trail where rangers had recently installed cables to help hikers get to the top of the rock face.

Robinson said he could not remember a fatal incident in recent years that involved climbers at the caliber of Wells and Klein.

“There might be some people in the climbing community who are seeing we need to be a little bit more mindful of the risks we’re taking with speed climbing,” Robinson said.

“I know that people in Yosemite are taking it really hard,” he said. One climber, Alex Honnold, who recently broke the speed record for an ascent of El Capitan’s Nose route, told Robinson that he and his team “were going to take a moment to reevaluate their safety margins,” Robinson recounted.

The two men had been climbing together since their college years, when they lived in San Diego, Klein’s friend Wayne Willoughby told Climbing magazine.

“This would have been Tim’s 107th [in a day] El Cap ascent,” Willoughby said.

The pair just scaled the Nose of El Capitan two weeks ago, in a typical whirlwind climbing weekend, Willoughby said. Wells would frequently fly to California from his home in Boulder, Colorado, on a Friday, and alongside Klein would climb one route of El Capitan at about 4 a.m. on Saturday. The next day the duo would wake up and climb another route before Wells had to fly back to Boulder, Robinson said.

“It was a routine,” Robinson said, calling it “something that I don’t know anyone else does.”

Wells and Klein were not necessarily famous outside of their inner circle of elite climbers. They were not professional or sponsored. “They didn’t do it for fame, they weren’t climbing to break records,” Robinson said.

“They were able to do these sorts of climbs just as a matter of course on a regular basis, just because they loved it,” he said. “They were not thrill seekers or trying to defy death. They were just world class athletes who just had an ability that’s unfathomable to even just the majority of the people in the climbing community, let alone to the general public.”

Wells worked as an investment manager at Granite View Asset Management. He was married in June 2016, and has a daughter from a previous marriage, according to Climbing magazine.

Klein, a father of two, was a longtime and beloved teacher at Antelope Valley Union High School District, where he just last week won teacher of the year for the second time.

“We are all heartbroken and mourn the loss of Tim Klein, our colleague and friend,” Betsy Sanchez, the Antelope Valley Union High School District’s director of communications, said in a statement to the Los Angeles NBC affiliate on Sunday. “He was an extraordinary human being, and all those who knew him have been touched in many ways.”

At Palmdale High School, he helped direct a program that taught students to become Emergency Medical Technicians. As part of a fundraiser for a student that was injured in a drive-by shooting, Klein scaled an indoor climbing wall in Santa Clara for 9 hours, 26 minutes and 15 seconds, reaching a total of 29,065 feet. He broke a Guinness World Record for the fastest time to climb the height of Mount Everest on an indoor climbing gym.

“Ultimately his goal was to elevate her,” Klein’s wife, JJ Tamura Klein, told CBSLA. Last week, Klein attended the graduation for the student.

Tamura Klein posted news of her husband’s death on Facebook.

“I know this is incredibly shocking and sad to so many of you who knew them, and it is still very surreal to the boys and I and our entire family and circle of friends,” Tamura Klein wrote. “He has left a void that no man can fill.”

Speaking to KTLA, she described Klein and Wells like “brothers.”

“When you climb together you really do develop that trust and that love for each other,” Tamura Klein said. But safety was always paramount to the climbers during their weekends scaling the rocks together.

“I thought the last place that he would die would be in Yosemite,” she said.