AFTER TESTING HIMSELF on the steepest lines in the Wasatch, the Tetons, the Cascades, and the Alaska Range, in 1999 McLean set out on one of his biggest projects to date.

The goal of the 1999 American Shishapangma Expedition was to reach the 26,289-foot summit, strap on skis, and become the first Americans to ski an 8,000-meter peak. The team was a mix of the old Black Diamond dawn patrollers—McLean, 40-year-old Alex Lowe, and Conrad Anker and Mark Holbrook, both in their thirties—and two up-and-comers, skier Hans Saari and climber and photographer Kristoffer Erickson, both in their twenties. On the well-funded expedition, team members posted regular dispatches via satellite phone on MountainZone.com. American Adventure Productions was also making a film of the trip, shot by Aspen-based cameraman David Bridges.

The approach to the Tibetan peak, which lies about 100 miles west of Everest, went almost too well. Led by the exuberant Lowe, the party marched up from 12,000 feet to 16,000 feet in a single push. That's a good way to save time but a bad way to acclimatize. During the night, McLean was struck with high-altitude pulmonary edema, an altitude-induced lung ailment that can be fatal if a climber doesn't immediately descend. Around midnight, McLean stumbled over to Lowe's tent.

"Andrew, typically self-effacing, apologized for waking me and, obviously shaken and frightened, said he was going to hike down and wanted me to know he was leaving camp," Lowe wrote in a MountainZone dispatch. McLean and Lowe, who insisted on helping his friend, labored downhill all night, stopping every few minutes so the wheezing McLean could catch his breath. McLean recovered, and a few days later rejoined the team to prepare for the summit climb.

It was during a routine reconnaissance for that climb that tragedy struck. On a warm, cloudless day, the team climbed above advance base camp for a closer look at the route. They split into two groups, with Lowe, Anker, and cameraman Bridges moving ahead of the rest across a flat section of glacier. The area was so far removed from any perceived avalanche threat that nobody carried beacons or poles.

Then, way up on the mountain, a little avalanche fell. It was at least 5,000 vertical feet away—a tiny, spindrifty thing. But as it came down, it triggered more slides. And bigger slides. "Holy shit," said Lowe. "Look at that avalanche." Nobody panicked. It still seemed unthinkable that the slide would reach them.

McLean stood on a low ridge a quarter-mile away, watching. At first he wasn't concerned either. Then the slide grew and he thought, They better do something. Moments later, he realized, Those guys are not going to make it out of this. He watched as Anker broke for the side of the glacier and Lowe and Bridges ran downhill, perhaps trying to hide in a crevasse.

By the time the avalanche reached Lowe and Bridges, it was a massive wall of ice and snow roaring down the mountain at more than 100 miles an hour. McLean, realizing that even he was in danger, jumped down the back side of the ridge and kept low while chunks of ice and pulverized rock flew overhead. When McLean stood and looked back, he saw that the glacier's crevasses had been erased. Filled in. One lone figure staggered across the snow. It was Anker, dazed, pieces of his scalp flapping from his ice-battered head. McLean ran to him.

"Alex is gone!" Anker kept repeating. "Alex is gone!"

At no time had McLean's steady, soft voice seemed more appropriate. "Yeah," McLean said. "I think he is."

The bodies of Bridges and Lowe were never recovered.