It was described in 2001 by Kenneth Carpenter and colleagues, who took the name for its location in the western United States. A nearly complete skull and much of the skeleton was found. The only species known is Hesperosaurus mjos. It is present in stratigraphic zone 1 of the Morrison Formation.[1] Susannah Maidment and colleagues proposed in 2008 that Hesperosaurus should be considered a synonym of Stegosaurus, with H. mjosi becoming Stegosaurus mjosi.