One fine afternoon last may, Jayne Belnap drove north out of Moab, Utah, in her beige Lexus SUV when the highway vanished. In an instant, a 100-foot-tall cloud of dust had swallowed up her vehicle. She wanted to brake, but she worried about another car slamming into her from behind. She tried to pull over, but she couldn’t see the shoulder. So Belnap split the difference: “I figured if I just crept slowly enough that I’d eventually get out of there or fall off the road.”