Ultrarunning has never experienced a day like May 22, when 21 runners died as a storm descended on a high mountain pass during a 62-mile race in northwestern China.

Tragedy is hardly a foreign concept in ultrarunning, races longer than the standard marathon distance of 26.2 miles. But the scale of the loss of life in Gansu province was hard for even veterans of the growing sport to fathom.

Usually, tragedy strikes an ultrarace on a runner-by-runner basis. Last year, Kateryna Katiuscheva of Ukraine, known as the "Iron Lady” of ultrarunning, collapsed six miles from the finish of a 42-mile trail race. Organizers found her after an eight-hour search but she died in the hospital, at age 33, the following day. And last summer, the veteran ultrarunner Kim McCoy lost her leg when she was struck by a car while crossing a highway 70 miles from the finish line of a 340-mile race across the American South.