Sandwiched between the coal layers of an open-pit coal mine in the Wuda basin in Inner Mongolia is the imprint of a lush forest from the Early Permian period. The forest, whose imprint spans an estimated 20 square kilometers, was preserved when a volcano erupted roughly 298 million years ago. Ash hardened into a 66-centimeter-thick band of chalklike tuff that entombed trunks, branches, and even whole trees. Around the world, just a few ancient forests are known to have been preserved under ash. The Wuda tuff flora—the first discovered in Asia—is remarkably accessible and thick and contains a puzzling group of extinct fernlike plants. Protecting the remaining tuff bed long enough to study it will be no small feat, however. The region's economy depends on coal. Mining has already claimed parts of the fossilized forest, while excavations to extinguish coal-seam fires have destroyed other swaths.