Last February, on a warm day with few clouds, thousands of people gathered on an icy lot in Big Sky, Montana, to watch a skijoring competition—a race contested by awkward hybrids of human and horse. A saddled rider pulls a skier or snowboarder who is attached to a thirty-three-foot rope tied to the saddle horn, through a gauntlet of snowy jumps, walls, and poles. Riders drifted past the crowd, grinning and clutching beer cans, and a team of freestyle snowmobilers launched backflips off a jump, interspersed with jets of flame. Pop-country blared while…