A chemical weapons plant outside Denver was fenced off for demolition until bald eagles were found roosting there in 1986, and the $2.1 billion cleanup that followed handed 15,988 acres to a bison herd, because an eagle reads an emptied, poisoned field as good hunting ground

An endangered species roosting on federal land triggered legal machinery of its own, and the eagles became the emblem for an idea that had been unthinkable: that the arsenal’s fate should be wildlife, not warehouses. Congress passed the Rocky Mountain Arsenal National Wildlife Refuge Act in 1992, and the Army, Shell and the EPA ground through one of the largest environmental cleanups in American history, roughly $2.1 billion over two decades, digging out and entombing the worst soil in engineered cells, capping the basins, and treating the groundwater in perpetuity.