It's taken thirteen years, but paleontologists have now published a full description of the sprawling system of bonebeds discovered in 1997 near Hilda, Alberta. This new paper, published in New Perspectives on Horned Dinosaurs, puts forth the idea that sudden flooding brought on by a massive storm is the likely culprit, rather than the evergreen "river crossing" scenario. In the late Cretaceous, the area was a coastal floodplain, where lead author David Eberth of the Royal Tyrrell Museum says that Centrosaurus likely gathered in huge herds. When a storm hit, the flooding occurred too quickly over too large an area for them to escape.
Once the flood waters receded, the land would be littered with carcasses. After the scavengers had their way, the bones would be left to be covered by subsequent floods, fossilize, and eventually be exposed and discovered.
Drowning Centrosaurs by Michael Skrepnick, from the Royal Tyrrell Museum of Natural History
Scenes like this have always captured my imagination. It would have been an awesome sight to be sit on a low ridge and look out over hundreds of acres of Centrosaurus, the two species apertus and brinkmani differentiated by horn shape and perhaps coloration. But the imagination gets a little shaky when asked to picture those same dinosaurs desperately trying to find safety amid the chaos of a storm. Or to picture the reeking smorgasbord presented to local Albertasaurus, Gorgosaurus, and Troodon. Maybe some Hesperonychus would be hanging back, darting in for their share. Or maybe they wouldn't need to: there would be enough ceratopsian flesh to go around, and then some.
If I only had the money to commission that scene...