The genus AsydatesCasey, 1895 is redefined and revised. ScelopristisMayor, 2004, new synonymy, is treated as a new junior subjective synonym. Asydates grandiceps (LeConte, 1866), new combination, Asydates irwini (Howell, 1979), new combination, and Asydates vandykei (Blaisdell, 1924), new combination, are treated as new combinations from Scelopristis, and Asydates ruficauda (Blaisdell, 1924), new combination, is transferred from Trichochrous Motschulsky. Pristoscelis schlingeriHowell, 1997, new synonymy, and Pristoscelis volkiHowell, 1979, new synonymy, are treated as junior subjective synonyms of A. ruficauda. Asydates chumash Mayor and Gimmel, new species, Asydates kumeyaay Mayor and Gimmel, new species, Asydates inexpectatus Mayor and Gimmel, new species, Asydates phantasma Mayor and Gimmel, new species, Asydates shoshone Mayor and Gimmel, new species, Asydates tongva Mayor and Gimmel, new species, and Asydates washoe Mayor and Gimmel, new species, are described. The genus PseudasydatesBlaisdell, 1938, status restored, is redefined as distinct from Asydates. Pseudasydates inyoensisBlaisdell, 1938, combination restored, is removed from Asydates and returned to Pseudasydates. Pseudasydates explanatus (Casey, 1895), new combination, is moved from Asydates, with Asydates puncticeps Blaisdell, 1924 treated as a junior subjective synonym. Members of Asydates occur primarily in California and the Great Basin Region of North America. Adult beetles are visitors to inflorescences of plants primarily of the genera Stephanomeria Nutt., Ericameria Nutt. (both Asteraceae) and Eriogonum Michx. (Polygonaceae), and adults show a pronounced seasonality skew towards mid-summer to fall. Adult males are characteristic for their enlarged heads and mandibles; we provide a hypothesis for the behavioral function of these structures.