Sonoma is a patchwork quilt of wine appellations, several of which overlap. Visually, the lines formed by Sonoma’s AVA boundaries push down from the northwest to the southeast. We need to draw another important line that challenges this up/down statement, penciling in the Petaluma Gap. The gap shoves cooling Pacific goodness laterally across Sonoma, in a band ranging from 20 to 30 miles wide. The western edge of the Gap is the coastal lowlands around Bodega Bay. The eastern edge is the mouth of the Petaluma River as it flows into San Pablo Bay, the northern reach of the San Francisco Bay system (which in turn connects to the Sacramento-San Joaquin River Delta). The gap cuts across the capacious Sonoma Coast AVA and is responsible for the cool climate of the Russian River Valley AVA and its nested sub-AVA, the Green Valley of Russian River Valley AVA, both known for Pinot Noir and Chardonnay. In 2015 the Petaluma Gap Winegrowers Association submitted a petition to the TTB to declare the gap an AVA. The jury is still out. Until the Petaluma people get their own AVA, the overarching Sonoma Coast AVA will have to do. Up the coast from Petaluma, the high elevation Fort Ross-Seaview AVA is completely surrounded by Sonoma Coast. Approved by the TTB in 2011, the AVA specializes in Pinot Noir and Chardonnay, but expects significant new planting of a wide variety of grapes. Fort Ross-Seaview is a good example of Sonoma’s potential to develop new cool-climate growing regions.
Directly north of the Russian River Valley is the Dry Creek Valley AVA. Dry Creek is a tributary of the Russian River. Dry Creek is warmer and dryer than the Russian River Valley, but also benefits from ocean influence that leapfrogs the ridges between Dry Creek and the ocean. Before Prohibition, it was a Zinfandel specialist. Prohibition hit Dry Creek badly, and the region did not start to recover until the 1970s. Zinfandel once again reigns here, with much Cabernet Sauvignon (and Sauvignon Blanc for the white side of things). The Rockpile AVA juts into the northern edge of Dry Creek, producing Zinfandel, Cabernet Sauvignon and Petite Sirah.
To the east of Dry Creek lies the Alexander Valley AVA, a warm climate region known for its Cabernet Sauvignon. Alexander Valley is Sonoma’s largest and most widely planted AVA. The Russian River, flanked by vineyards, flows down the Alexander Valley before it lurches west to form the Russian River Valley AVA and make its way to the Pacific. The Russian River provides early morning fogs that burn off as the day advances. During the day, the Alexander Valley is decidedly warm, but nights turn favorably cool, allowing grapes to ripen slowly for voluptuous Cabernet Sauvignon and Merlot and richly tropical Chardonnay. Grapes as diverse as Tempranillo, Barbera, Sangiovese, Syrah, Viognier, and Zinfandel inhabit this large region.
Southwest of Alexander Valley hard by the Napa County line is Sonoma’s warmest region, the Knights Valley AVA, known for its Cabernet and Meritage (Bordeaux-style) blends. Directly south of Alexander is the Chalk Hill AVA, which overlaps a corner of the Russian River Valley (Sonoma is complicated). The name refers to the chalky soil of volcanic ash. Chalk Hill is warmer than the Russian River Valley but still benefits from some Petaluma Gap cooling. The cooling in fact continues its eastward path beyond Chalk Hill, relieving some of inland Napa’s heat. Chalk Hill is known for white varietals like Chardonnay and Sauvignon Blanc. South of Chalk Hill is the new (2015) Fountaingrove District AVA, producing Cabernet Sauvignon, Chardonnay, Sauvignon Blanc, Merlot, Cabernet Franc, Zinfandel, Syrah, and Viognier. Fountaingrove is characterized by rolling hills with volcanic soils (Sonoma shows a great deal of past volcanic activity).
In the southeast corner of the county lies the Sonoma Valley AVA. It is important here to differentiate the Sonoma Valley AVA from the Napa Valley AVA. Sonoma Valley is only a small portion of Sonoma County, but the Napa Valley AVA, filled with sub-AVAs, is an overarching AVA that encompasses most of Napa County. Sonoma Mountain (a sub-AVA) in the west of Sonoma Valley blocks Petaluma Gap Pacific cooling influence, but the two appellations are close enough to San Pablo Bay to benefit from its air conditioner. The Bennett Valley AVA straddles areas of Sonoma Valley, Sonoma Mountain and Sonoma Coast, and does reflect cooling ocean influence. Barbera, Cabernet Sauvignon, Cabernet Franc, Chardonnay, Grenache, Merlot, Pinot Noir, Sauvignon Blanc and Syrah thrive here.
Another, fairly new, sub-AVA of Sonoma Valley is the Moon Mountain District Sonoma County AVA. As the name implies, this is high elevation land, ranging up to 2000 feet above sea level. Soil is once again volcanic. Up here, we find the legendary Monte Rosso vineyard. Or we could call it a zin-yard. The warm climate twins, Cabernet Sauvignon and Zinfandel, rule here, but further south the slopes feeding on San Pablo Bay produce some fine breezy Pinot Noir.
In the extreme south of Sonoma County hard by San Pablo Bay, Sonoma shares the Los Carneros AVA with southern Napa. The Sonoma portion of Los Carneros (often called just “Carneros,”) can contribute grapes to Sonoma Valley labeled wines. The name Los Carneros means “the rams” in Spanish, a reference to its early function of these rolling hills as sheep grazing land. Because of the San Pablo Bay influence, Los Carneros is the coolest and most windy AVA in either Sonoma or Napa. The Pinot Noir and Chardonnay one would expect in such an environment have attracted a number of international Champagne producers, including Moët et Chandon (which runs Domaine Chandon California), and Taittinger (running Domaine Carneros).