CompuServe Messages

One of my favorite fossil hunting sites (Simi Valley, CA) consists of an arroyo with Quaternary alluvium, which is surrounded by three formations contributing the majority of the fossils. The formations are of Late Cretaceous, Paleocene, and Eocene. I know how to recognize which formations the fossils are from when I find them because I've collected them at their sources. However, in the arroyo, they often occur together where they've washed down. What I want to know is, if the alluvium were to become a fossil site in the distant future, and all these different aged fossils became part of the same deposition layer, how easy is it to identify them as being of different origin? Also, assuming the future paleontologist is on the ball and recognizes the difference between them, how difficult is it to determine their respective ages at this point? This must be a very common phenomenon. Is this relevant to the purported "Cenozoic" dinosaurs from Canada that I've heard about? Anyone?? -Rande