PARK CITY, Utah — From my seat on the ski lift whisking me up a mountain at Deer Valley Resort, the trails below look like they could knock my teeth out. They snake down the mountain like unfurling ribbons, swooping around big banked corners and dipping in and out of thickets of pines and aspens. They bristle with bike-snaring roots, rocks that rise like incisors from the mountain’s jaws, and Volkswagen-sized humps that seem capable of sending cyclists skyward.