It has been determined recently that Aedes communis (De Geer) represents a complex of cryptic species, at least three of which are found in the western United States. Because members of this group have been implicated as vectors of Jamestown Canyon virus, it is important to delimit the distribution of individual species in order to clarify their viral associations. Specimens of Ae. communis s. l. collected in California and neighboring states were identified electrophoretically using allozyme markers. Populations from the Sierra Nevada, southern Cascades, and Trinity Alps in California were determined to be Ae. tahoensis Dyar. Specimens from Oregon, Washington, Nevada, and Utah were identified as Ae. nevadensis Chapman and Barr. Based on our collections and on previous literature, it appears these two species are allopatric, with Ae. tahoensis restricted to the high mountains of California.