It’s hard to imagine that camels, lions, and mammoths once roamed the landscape around Las Vegas, Nevada. But such was the case during the latter part of the Pleistocene era, which spanned a period of time between 11,000 years and 2.5 million years ago. The area -- known as the Upper Las Vegas Wash –- is rich with the fossils of these and many more creatures as well as ancient plants and pollens.