“That story, of course, isn’t unique to California, or to beavers. Europeans began despoiling North American ecosystems the moment they set boots on the stony shore of the New World. You’re probably familiar with most of the colonists’ original environmental sins: They wielded an ax against every tree, lowered a net to catch every fish, turned livestock onto every pasture, churned the prairie to dust. In California’s Sierra Nevada, nineteenth-century gold miners displaced so much sediment that the sludge could have filled the Panama Canal eight times.14 We are not accustomed to discussing the fur trade in the same breath as those earth-changing industries, but perhaps we should. The disappearance of beavers dried up wetlands and meadows, hastened erosion, altered the course of countless streams, and imperiled water-loving fish, fowl, and amphibians—an aquatic Dust Bowl. Centuries before the Glen Canyon Dam plugged up the Colorado and the Cuyahoga burst into flame, fur trappers were razing stream ecosystems. “[Beavers’] systematic and widespread removal,” wrote Sharon Brown and Suzanne Fouty in 2011, “represents the first large-scale Euro-American alteration of watersheds.”