Most of my specimens I generally purchase, since I specialize in vertebrates, are there are not many open private land sites with those in colorado, and are from locations such as the Hell Creek Fm. of SD, WY, and MT. When I do field hunt, I have a few sites I like to go to. One really neat one I have been to was a Lower (Early) Ordovician site near Pikes Peak, CO, where there are small to medium sized trilobites in pinkish orange dolomite rock. I generally collect all the trilobites since they are somewhat rare, but most of the brachiopods and cystoid echinoderm stems, I left.