Directly north of San Francisco and bordering the Pacific Ocean, Sonoma County has 1 million acres (404,700 hectares) of land, making it more than twice as big as its next-door neighbour Napa Valley.
That size makes the county a geographical patchwork quilt of valleys, mountains, riverbeds, plains and benchlands, and within this shifting landscape lie sixteen viticultural areas that can be quite different in their nuances of climate and soil.
Historically and culturally Sonoma is rather different from Napa: vineyards were planted here as the nineteenth century dawned, well before Napa, and many vintners belong to old, established farming families.
A kicked-back country style pervades much of the region — people drive dusty pickups and the talk is as likely to be about tractors as about wine sales in Tokyo — yet among the top producers there is as much cutting-edge winemaking as anywhere in California.
The county is beautifully pastoral and is often called California's Provence, with vineyards alternating with apple orchards, vegetable farms, redwood forests, dairies, sheep ranches and aquaculture fisheries along the rugged coast.
Climatically, what makes Sonoma Sonoma is its pendulum-like rhythm: soft white fog rises in massive banks off the coast and drifts inland, wrapping around mountains and filling the valleys with cool vapour, giving a daily ebb and flow — almost a yin and yang — of fog and sunshine.
Areas closer to the coast (especially the Sonoma Coast AVA and parts of the Russian River Valley) are cooler and those farther inland warmer, but overall the warm days and cool nights are the classic scenario for grapes with the potential to mature evenly and fully.