From the back of a bush plane at Mission Field, the Crazy Mountains were only 20 miles in the distance, close enough for me to see late-afternoon shadows drift across their avalanche-scarred ridges. Here at the airport serving Livingston, Montana, at the northern gateway to Yellowstone National Park, the state’s decadelong economic boom was in full effect. Men in cowboy hats, carrying briefcases, crossed the tarmac. Horns blared in the distance. Then came the other sound I’d come to associate with a state once so empty that, until recently, it had only one representative in the U.S. House: hammering. Human activity was everywhere, yet those mountains on the horizon, the mystical Crazies, seemed frozen in time, artifacts of an unpeopled world placed under glass.