As Jean Muenchrath stood at the summit of Mount Whitney, a storm thundered in. It was May 1982, and here, at the highest point of the contiguous US, she and her boyfriend Ken were coming to the end of a month-long ski and hike, 359km along the John Muir Trail, through the Sierra Nevada mountain range in California.

The trip had been gruelling at times – equipment had broken and they had been threatened by bears and avalanches. But it had also been exhilarating. At 22, Muenchrath was fit, strong and an experienced hiker. She had skied since she was a child and worked as a ranger for the US national park service in Montana. She and Ken, who she had met at university, had been on many smaller adventures while preparing for this one.

To avoid the worst of the storm, they swapped their planned route for a different one down the mountain. It was steep and in order to descend they had to hang on to their ice axes, blades dug deep into the snow. Ken soon lost control and tumbled 800ft. But Muenchrath didn’t have the luxury of reacting. She had to focus on her own descent, trying to ignore her terror that she would find Ken’s broken body below.

Miraculously, when she reached him, he had survived virtually uninjured. His backpack had come off when he fell and he climbed down a rocky section to the ledge where it was resting, to retrieve their rope. Muenchrath remembers standing there, exhausted, the light waning, wondering whether she really needed to wait for the rope before continuing her descent. Ken had reached the ledge easily enough and she thought she could do the same. The skis tied to the sides of her backpack were a hazard, so she threw them down the mountain, then took off her mittens so she could grip the rock more easily.

It wasn’t long before she realised how difficult it was going to be. Ken had climbed down unhindered.