A survey of the upper Eel River watershed in the high North Coast Ranges of California resulted in the identification of four species of Chaoboridae and 12 species of Culicidae. The boreal species Mochlonyx cinctipes (Coquillett), Eucorethra underwoodi Underwood and Aedes fitchii (Felt and Young) were collected south of previously known distributions within the Pacific Coast Ranges of North America. Biogeographical, physical, seasonal and water quality characteristics of the larval habitats are described. We also describe and discuss species associations and the taxonomic, distributional and ecological details of the new records both within the study area and in comparison to other localities in North America.