Everybody wants the ruins of Chaco Canyon to be a mystery. Stuart, an anthropologist at New Mexico who’s spent his career there, knows it isn’t. Chaco was a boom town. There were great houses five stories high, dead-straight roads running for miles across seemingly nothing, macaws and turquoise brought up from Mesoamerica via trade, timber hauled in from mountains a hundred miles off. Somebody was running a doozy of an operation. He argues societies go one of two ways: Powerful ones grow fast and spend everything to do it, while efficient ones grow slow and hang on. Chaco went powerful. Then the rain quit in the 1130s and the whole thing collapsed inside a generation. What Stuart most cares about is who was left standing when the dust settled: Farmers who scattered into little villages, planted a bit of this and a bit of that, and shared what came in. Those are the Pueblo people of today, still there. Then he points the same framing at modern New Mexico and it doesn’t take much to see where that’s going.