Sonoma County comprises the Santa Rosa, CA Metropolitan Statistical Area, which is also included in the San Jose-San Francisco-Oakland, CA Combined Statistical Area. It is the northwestern county in the nine-county San Francisco Bay Area region.
Sonoma is the southwestern county and largest producer of California’s Wine Country region, which also includes Napa, Mendocino, and Lake counties. It has 13 approved American Viticultural Areas and over 250 wineries. In 2002, Sonoma County ranked as the 32nd county in the United States in agricultural production. As early as 1920, Sonoma County was ranked as the eighth most agriculturally productive U.S county and a leading producer of poultry products, hops, grapes, prunes, apples and dairy products, largely due to the extent of available, fertile agricultural land, in addition to the abundance of high quality irrigation water. More than 7.4 million tourists visit each year, spending more than $1 billion in 2006. Sonoma County is the home of Sonoma State University and Santa Rosa Junior College.
The county lies in the North Coast Ranges of northwestern California. Its ranges include the Mayacamas and the Sonoma Mountains, the southern peak of the latter being the prominent landform, Sears Point. The highest peak in the Mayacamas within the county is Hood Mountain. It has uncommon occurrences of pygmy forest, dominated by Mendocino Cypress. The highest peak of the Sonoma Mountains is Sonoma Mountain itself, which boasts two significant public access properties: Jack London State Historic Park and Fairfield Osborn Preserve.
The county includes the City of Sonoma and the Sonoma Valley, in which the City of Sonoma is located. However, these are not synonymous. The City of Sonoma is merely one of several incorporated cities in the county. The Sonoma Valley itself makes up only the southeastern portion of the county, which includes many other valleys and geographic zones. Moreover, the Sonoma Valley itself includes not only the City of Sonoma, but a portion of the City of Santa Rosa and the unincorporated communities of Kenwood, Agua Caliente, Boyes Hot Springs, and Fetters Hot Springs. Other regions of the county beyond the Sonoma Valley include, among others, the Petaluma Valley, the Santa Rosa Plains, the Russian River, the Alexander Valley, and the Dry Creek Valley.
Distinct habitat areas within the county include oak woodland, redwood forest, northern coastal scrub, grassland, marshland, oak savanna and riparian woodland. The California oak woodland in the upper Yulupa Creek and Spring Creek watersheds in Annadel State Park is a relatively undisturbed ecosystem with considerable biodiversity. These forested areas have been characterized as some of the best examples of such woodlands. An unusual characteristic of these forests is the high content of undisturbed prehistoric bunchgrass understory, testifying to the absence of historic grazing or other agriculture.
Sonoma County, as is often the case with coastal counties in California, has a great degree of climatic variation and numerous, often very different, microclimates. Key determining factors for local climate are proximity to the ocean, elevation, and the presence and elevation of hills or mountains to the east and west. This is in large part due to the fact that, as throughout California, the prevailing weather systems and wind come normally from the Pacific Ocean, blowing in from the west and southwest so that places closer to the ocean and on the windward side of higher elevations tend to receive more rain from autumn through spring and more summer wind and fog. This itself is partly a result of the presence of high and low pressures in inland California, with persistent high summer temperatures in the Central Valley, in particular, leading to low pressures, drawing in moist air from the Pacific, cooling into damp cool breezes and fog over the cold coastal water. Those places further inland and particularly in the lee of significant elevations tend to receive less rain and less, in some cases no, fog in the summer.
The coast itself is typically cool and moist throughout summer, often foggy, with fog generally blowing in during the late afternoon and evening until it clears in the later morning to be sunny, before repeating. Coastal summer highs are typically in the mid to high 60s, warming to the low 70s further from the ocean.
Certain inland areas, including the Petaluma area and the Santa Rosa Plain, are also prone to this normal fog pattern in general. However, they tend to receive the fog later in the evening, the fog tends to be more short-lived, and mid-day temperatures are significantly higher than they are on the coast, typically in the low 80s F. This is particularly true for Petaluma, Cotati and Rohnert Park, and, only slightly less so, Santa Rosa, Windsor, and Sebastopol. In large part this results from lower elevations and the prominent Petaluma Gap in the hills between the ocean to the west and the Petaluma Valley and Santa Rosa Plain to the east.
Due to the varied scenery in Sonoma County and proximity to the city of San Francisco, a large number of motion pictures have been filmed using venues within the county. Some of the earliest U.S. filmmaking occurred in Sonoma County such as Salomy Jane (1914) and one of Broncho Billy Anderson’s 1915 Westerns. Many of these films are classics in American cinematography such as the 1947 film The Farmer’s Daughter (starring Joseph Cotten and Loretta Young) and two Alfred Hitchcock films, Shadow of a Doubt of 1943, filmed and set in Santa Rosa and The Birds of 1963, filmed largely in Bodega Bay and Bodega. Many other modern classics have used Sonoma County as a filming venue, including American Graffiti, filmed largely in Petaluma.