Principal components analysis of 24 morphological and color-pattern characters scored for 634 specimens reveals four distinct, geographic groups within Phrynosoma coronatum. The four groups can be diagnosed on the basis of color pattern characters, but there are nearly discrete differences in morphological characters as well. Morphological evidence of hybridization has been detected between two groups. The four morphological groups are likely genetic entities given the close correspondence between the morphological patterns in Phrynosoma and genetic units detected in Urosaurus. Therefore, the four groups of coast horned lizards are treated as separate species. Latinized names (blainvillii, cerroense, coronatum) are available for three of the four taxa. The subspecies frontale and schmidti cannot be adequately distinguished by the multivariate analysis and are placed in the synonymy of P. blainvillii. In addition, a new species, Phrynosoma wigginsi, is described from the eastern side of the Sierra de Guadalupe and Sierra de La Giganta in the central Gulf Coast region of the peninsula of Baja California. Diversification in Phrynosoma has occurred via allopatric speciation and the geographic juxtaposition of these morphological groups provides additional evidence for two ancient transpeninsular seaways.