In 1955 the Bay Area Air Quality Management District (BAAQMD) was formed and was originally comprised of the urban counties of Alameda, Contra Costa, Marin, San Francisco, San Mateo and Santa Clara counties. Sonoma County was included as an “inactive” member at that time. In 1971 the southern portion of Sonoma County joined the BAAQMD as an active member and the northern portion of the county was established as its own Air District, The Northern Sonoma County Air Pollution Control District, primarily because of its rural nature.