SO WHAT HAPPENED? How could two extremely experienced alpinists vanish on Mount Foraker?

Reconstructing a mountaineering accident is much like reexamining the evidence in a criminal investigation: You try to piece together all the clues to create potential scenarios.

"Three things are certain," says Miller. "Sue and Karen started the route on the 14th of May, lost the pack several days later, and continued climbing, reaching at least 16,600 feet."

Was it a mistake to keep climbing without the radio (their best shot at summoning help should they need it), sleeping bag, and pad? Probably not. According to Miller, McNeill and Nott had initially considered going to Foraker with just one sleeping bag, to save weight, a common practice among serious alpinists. Depending on where the pack was actually blown off, it might well have been safer and easier to finish the route, rather than retreat and rappel down dozens of pitches. At that stage, somewhere between May 15 and 20, the weather was still good and the two women were climbing in the sun and on pace.

Studying photographs of the tracks above 15,000 feet, it's clear they climbed this section of the route before the windstorm—the footprints are raised pedestals of compacted snow, indicating that they were made when the snow was still deep, before it was blown off the ridge. Which means that despite the loss of a pack, pad, and sleeping bag, McNeill and Nott probably finished the Infinite Spur on schedule in eight to ten days and were on their way up the lower-angle, mile-long snow slope to the summit when the wind started to maul Mount Foraker.

What happened then is pure speculation, but there are really only two realistic scenarios: They were blown off or they tried to burrow into the snow and froze to death in 50-below windchill.

"When you're that high on a difficult and committing line like the Infinite Spur," concludes Miller, "you cannot descend back down the route you just completed. Your only escape is up, and you just hope that when you reach the top to exit, the weather window will allow you safe passage. Sue and Karen were hit by winds so strong it would have been impossible to go up. They had no exit."

On June 18, a thousand people—climbers, friends, family—packed Vail's Ford Amphitheater for a service celebrating the life of Sue Nott; two days later a memorial was held in Canmore for Karen McNeill.

"Sue and Karen were in the right place at the wrong time," John Varco told me afterwards, in a voice barely more than a whisper. "There was nothing they could do about it. It would have been like trying to climb in a tornado. Anyone up there—you, me, the best alpinist in the world—would have met the same fate.

"But don't call it a tragedy. Yes, it's tragic for those of us left behind, but Sue and Karen were living big. Huge! They were celebrating life. We should do the same."