This started a fossil gold rush. Both locals and scientists have now dug so much, their work can be seen from space―perhaps the most extensive paleontological excavations anywhere.

By the 1990s, it was clear that the so-called Yixian Formation contained uniquely well preserved remains of dinosaurs, birds, mammals, insects, frogs, turtles and other creatures.

Unlike the skeletal and often fragmentary fossils unearthed in most other places, many animals came complete with internal organs, feathers, scales, fur and stomach contents. It suggested some kind of sudden, unusual preservation process at work. The finds even included a cat-size mammal and a small dinosaur locked in mortal combat, stopped in mid-action when they died.

The world's first known non-avian feathered dinosaurs showed up—some so intact that scientists worked out the feathers' colors. The discoveries revolutionized paleontology, clarifying the evolution of feathered dinosaurs, and proving without a doubt that modern birds are descended from them.

How did these fossils come to be so perfect? The leading hypothesis up to now has been sudden burial by volcanism, perhaps like the waves of hot ash from Mt. Vesuvius that entombed many citizens of Pompeii in A.D. 79. The Yixian deposits have been popularly dubbed the "Chinese Pompeii."