Long before climate change severely parched California, priming it to burn at a record scale, federal foresters made an inventory of trees in the southern Sierra Nevada. The year was 1911, and the goal of the fledgling U.S. Forest Service was to document the amount of timber in the area. More than a century later, however, the historical data set proved invaluable to researchers with a far different purpose: assessing how much the forest, and the inherent threat of fires within it, had evolved.