PHONE
800-231-3236 (toll free)
707-285-2200 (office)
707-285-2210 (fax)

ADDRESS
595 Helman Lane
Cotati, California
94931-9736

HOURS
Monday through Friday
7:00AM to 3:30PM

Marin and Sonoma Counties lie nestled between the marsh-lined northern shores of San Pablo Bay, the forested mountains of Mendocino, and the cool waters of the Pacific Ocean. This is the pastoral and agricultural region where northern California's wine industry was born more than a century ago. Its gentle, Mediterranian-type climate with warm summer days and cool nights, rainfall concentrated in the winter and early spring, sloping hillsides and abundant waterways make for great wines - and ideal conditions for breeding mosquitoes.

Winter weather is dominated by masses of cool air carried down from the Pacific Northwest, meeting warmer rain-bearing winds from the south. Temperatures range from 28 to 60 degrees, with only occasional, usually brief periods below freezing. Three quarters or more of the average annual rainfall of around 40 inches occurs between November and March.

Summer weather reflects regular 4 to 6 day cycles alternately governed by cool ocean breezes moving inland from the Pacific and masses of hot air expanding out from the sun-baked Great Central Valley. In most areas the warmer daytime temperatures range from 75 to 95, cooling to an average of about 50 degrees at night. Ocean fogs, hills and valleys create microclimates that can differ widely even on the same day.

The lower Sonoma Valley, San Pablo Bay and Marin's Mt. Tamalpais in the distance.
Watercolor by Virgil Williams, 1864.

Population is growing in both counties, but pasture, grasslands and forested woodlands still predominate. Ranching and dairying, orchards and vineyards are principal occupations, with annual agricultural sales topping $200 million. Growth brings challenges, and sometimes the responses cause unwanted results.

A sanitation district that encompasses four Sonoma county cities produces 23 million gallons per day of one of the cleanest reclaimed wastewaters in the state. Soon, decisions will be made on proposals to irrigate tens of thousands of acres with tertiary treated wastewater, rather than discharge it into the Russian River or the ocean. Properly applied irrigation has little impact on mosquito breeding, but on unprepared ground with natural depressions or pastured livestock, the new water could create extensive new mosquito habitat.

Another example deals with the concerted efforts to restore and create regions of tidal marshlands. More than 90 percent of the wetlands and tidal marshes of the San Francisco Bay have been lost to development and agriculture. The green pastures of the Santa Rosa plain were part of a large, shallow freshwater lake (the Laguna de Santa Rosa), until it was drained and diked off in the early 1900s. Many of the hay producing areas in Marin and Sonoma counties were tidal saltmarsh, leveed off in the late 1800s and early 1900s.

Intelligent design of reconstructed marshes, and provision for long-term maintenance will be needed to prevent mosquito and other pest insect populations from exploiting these areas. Historic tidal marshes provide unsuitable mosquito breeding habitat, and wherever possible the Marin / Sonoma Mosquito & Vector Control District favors the return of reclaimed areas to this state. At present, whenever the diked off lands are flooded with heavy rains or by breaks in the levees, mosquito populations bloom many times more than before.

Wildlife of all kinds is still common in both counties. For example, Sonoma County hosts at least 159 different species of resident, nesting birds, and many more pass through on annual migrations. Wild and domestic birds and mammals, and even reptiles and amphibians provide food for hungry blood-feeding arthropods, and sometimes a source of infectious agents that are carried to man.

Would you like to learn more about Marin and Sonoma Counties?

Marin County

• Marin County Internet Resource Directory MIDAS

Sonoma County

• Santa Rosa's Press Democrat Online
• Petaluma's Petaluma Electronic Network
• Sebastopol Community Directory SEBWEB
• Sonoma County Internet Directory Sterba
• Sonoma County Online SoCoOL