Northwestern Baja California, Mexico, shares a unique mediterranean biota with adjacent California, USA, as a result of the climatic conditions that dominate the area. Many of the vertebrates in it are restricted to this ecosystem, including most amphibians (Linsdale 1932; Mellink 2002). This ecosystem faces severe conservation problems, mostly derived from the extensive urbanization of California and northernmost Baja California. The resulting habitat modification has impacted some of the species of amphibians in southern California so strongly that the arroyo toad (Bufo californicus; sensu Gergus 1998) is officially considered endangered, and the red-legged frog (Rana aurora), threatened. In contrast with their diminished populations in southern California, these species, as well as other frogs and toads, fare much better in Baja California (Grismer 2002).