Upper Las Vegas Wash is used for different purposes by various people. But I was there to hunt fossils. Many late Pleistocene land mammals are found there, like mammoths, horses, camels and prehistoric bison. I didn't see any of those, but I did find traces of large human-related objects.
See my real geologic photo gallery at
http://geology.about.com/od/geology_nv/ig/lasvegaswash/