The Western States ultramarathon, a yearly act of insanity in the northern Sierra Nevada, began in the 1950s as an endurance horse ride in which competitors had to traverse the equivalent of nearly four marathons along murderous terrain from Lake Tahoe to the foothills town of Auburn in less than 24 hours. Then in 1974, a shaggy-haired woodcutter from Gold Country named Gordy Ainsleigh showed up to the starting line in his sneakers — no horse.

At the time, running the course was considered by some to be beyond human ability, and Ainsleigh, 29, seemed hardly the sort to pull it off. He was big, standing 6’4″ and more than 200 pounds. He had run track in school, but was no great talent. His obsession with running, he told WBUR, had grown out of feeling like a misfit:

“I remember this one day — I think it was second grade. I came out on the playground with a bag lunch. Grandma had packed the lunch, and I just couldn’t see anybody I could go up to and say, ‘You want to have lunch?’ I panicked. And I just felt like I couldn’t breathe. And I just dropped my lunch, and I ran home for lunch.”

Ainsleigh found peace in running. But by around mile 55 of his Western States attempt, he thought he might die. The temperature rose to triple digits. “There’s a dead horse in the canyon, and that could be me,” he told a friend at a checkpoint, according to Runners World. “I’m going to quit.” Yet somehow he kept moving. Fueled by canned peaches and water from a creek, Ainsleigh eventually found himself in Auburn with only minutes to spare. He dove into a somersault as he crossed the finish line.

Ainsleigh had run nonstop for 23 hours and 42 minutes. The next year, another runner crashed the course, and by 1978, dozens of runners were attempting it. In time, the Western States 100 became the world’s premier ultramarathon trail race, drawing top runners from around the world. Ainsleigh, now 74 and still running 100-milers, has watched with satisfaction as the sport he helped popularize produces athletes of a caliber unimaginable to many in the 1970s.

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