Fossil Leaf from Mystery Wyoming Site

Description: This leaf fossil comes from a very old collection, some 50 to 60 years old, the plant fossil collection of a man and wife who combed more than 100 plant fossil sites, almost all west of the Mississippi River. No doubt, some of these sites have been subsumed by strip malls, and urban sprawl, or are otherwise no longer open to collecting. There was no Internet for these collectors to research their treasures, so most are unidentified by them. This one is marked as x214, meaning site 214, which their key says is Union Pass, Wyoming. I can find no fossil site information associated with this name. The fossil plants of the Paleocene Fort Union Formation in Wyoming are on distinctly red matrix, so this one if different. The site's age, sometime in the Cenozoic, is a mystery, but the natural beauty speaks for itself. The dark fossils on light matrix is quite striking.