THE RUT 50K, which takes place each August in Big Sky, Montana, may be the toughest race in the country. Runners ascend more than 10,000 vertical feet, skitter along an exposed ridge, and hurl themselves down a 40-degree scree field. Unlike most ultras in the U.S., where the main attraction is distance, this one was modeled on the European tradition of mountain racing—brutal competitions on serious, sometimes dangerous high-altitude terrain. Despite the difficulty, the Rut sold out all 600 spots last year. “People really respond to this type of steep, exposed, mountainstyle race,” says cofounder Mike Foote.
As of June, they no longer have to fly to Montana to find them. That’s when Skyrunning, a series that draws a total of 30,000 runners each year to 15 events in Europe,…