Sinosauropteryx, a famous denizen of Yixian. From wikimedia commons.
It's too easy to dash down to the bakery when searching for a good geological metaphor. But I'll do it anyway. The perennially productive Yixian Formation in China can be thought of as a layer cake. Only instead of chocolate and vanilla, you get tasty alternating tiers of basalt and sandstone.
Sandstones are associated with places where rock is ground down to the coarse particles we call sand. Deserts do that, as does the erosive labor of water. The latter, in the form of lakes and streams, created the sandstones of Lower Cretaceous Yixian. Basalt, on the other hand, is a rock which comes in many forms with one shared source: volcanism. Combine the two, and you have a recipe for gorgeous fossils: adding to the day-to-day burial of bones handled by the bodies of water would be occasional volcanic eruptions which would bury the entire local environment. We have these natural cycles to thank for Sinosauropteryx, pictured above, and the other feathered dinosaurs. But feathered dinosaurs aren't the only animals the locale has to offer.
Zhenyuanopterus longirostris, a large pterosaur, is the latest beauty from Yixian. It is described by Chinese paleontologist Lu Jungchang in a new paper appearing in Acta Geologica Sinica. Bop on over to Archosaur Musings to get a nice look at one of the finest pterosaur fossils you'll ever see, remarkably complete, articulated, and sporting a set of teeth seemingly made to satisfy the universal human fascination with gnarly monsters.