Northern Sonoma is one of California's largest AVAs, covering a total area of almost 350,000 acres (142,000ha). Measuring roughly 30 miles (50km) from north to south, it stretches from Sebastopol and Santa Rosa right up to the border with Mendocino County. Only marginally smaller from east to west, it falls just short of spanning the distance from Napa Valley to the Pacific coast.
Between Northern Sonoma and Sonoma County's two other big AVAs, Sonoma Coast and Sonoma Valley, every vineyard in the county is covered by one 'Sonoma' AVA or other. This jigsaw effect continues further down the tree within Northern Sonoma, which is itself composed of the Alexander, Dry Creek and Russian River valleys.
© Sonoma County Vintners
The Russian River, and the valley that traces its course, may be viewed as the main artery of Northern Sonoma. The river rises in the coastal mountains of Mendocino, and although it passes through Sonoma County for just one quarter of its length, the area it drains here constitutes the lion's share of Northern Sonoma's vineyards. The river plays a vital role in viticulture all over the region – its influence extends far beyond the AVA that bears its name.
The driving forces behind the creation of the Northern Sonoma AVA in 1986 were similar to those that gave rise to the Sonoma Coast AVA just one year later. In the mid-1980s, the Bureau of Alcohol, Tobacco and Firearms (the US government department that administers wine production and labeling laws) decreed that wines labeled as 'estate-bottled' had to be grown and vinified within the boundaries of a single AVA. Thus the creation of a large, over-arching AVA such as Northern Sonoma brought significant advantages to those Sonoma wineries with vineyards in multiple sub-regional AVAs. Without it, a wine vinified at a winery within the Russian River Valley AVA but made from grapes in the Knights Valley AVA would not qualify as 'estate-bottled'.
Thanks to cooling ocean breezes and the famous Bay Area fog that rolls in off San Pablo Bay and from the Pacific coast, the southern parts of Northern Sonoma have a cool climate, while further north and inland, the effects of this fog are greatly reduced and the climate is much warmer.
The inventory of grape varieties in Northern Sonoma's vineyards reflects that of California as a whole. Cabernet Sauvignon dominates the red-wine varieties, complemented by small quantities of its parent varieties Cabernet Franc and Sauvignon Blanc. The Cabernets' Bordeaux stablemate Merlot remains significant, even if plantings are far from what they were in the 1980s and 1990s. The United States' iconic red-wine grape Zinfandel is planted in warmer, drier spots, particularly in Dry Creek Valley, while Chardonnay and Pinot Noir are predominant in the area's cooler mesoclimates. Rhône Valley stalwarts Syrah and Viognier, although far from prolific, maintain a respectable representation here.