Los Carneros crosses the county line between Napa and Sonoma just north of San Pablo Bay, an extension of the larger San Francisco Bay. The larger portion of the roughly 90-square-mile (230-square-kilometer) region lies on the western, Sonoma County side of the line, sharing a border with Sonoma Valley along the spine of hills dividing Cotati Valley (and the Petaluma Gap area) from the Sonoma Creek watershed. Roughly 9,000 acres (3,642 hectares) of vineyards are planted around the region’s many low hills, ranging from 0 to 700 feet (213 meters) in elevation, taking advantage of diverse aspects. The water table at the lowest levels, and in the lowlands skirting San Pablo Bay, is high, with accompanying moisture and salinity rendering those areas unsuitable for grape growing (they’ve long been left to the sheep celebrated by the region’s name).
Surrounded by (clockwise): to the north, Napa Road on the outskirts of the town of Sonoma; to the east, the low southern hills of the Mayacamas Range and the Napa River, flowing into wetlands that drain into the bay; to the south, the wetlands and hayfields skirting San Pablo Bay; to the west, the border is shared with Sonoma Valley, along the spine of hills dividing Cotati Valley (and the Petaluma Gap area) from the Sonoma Creek watershed.
In the 1830s, under Mexican rule, the generals began awarding large land grants to prominent military personnel and citizens, making way for the shift from sacramental wine to commercial vineyards. The name “Los Carneros” itself is connected to one of the original land grants —Rincon de los Carneros (“corner of the rams”), but that land lies in what today is Monterey County.
Topography/Elevation/Water Sources/Geographic Features
San Pablo Bay itself is the overarching influence in Los Carneros, dictating temperatures, diurnal swings (or lack of), and the potential duration of the growing season across the board. The Pacific Ocean is close enough on the west to influence the vineyards to a lesser extent on the Sonoma side of the AVA.
Some 10,000 to 15,000 years ago, San Pablo Bay stretched much farther north than it does today, and Los Carneros was under water. This primarily accounts for the thin clay soils that dominate across the region. In many of the vineyards near the bay, soils run to a depth of only 30 inches, contributing to the stress on the vines.
Along with the sub-marine clay, topsoils here were carried downstream by the Napa River—erosion from the hills—joining accumulations from the bay. The most prominent soil series is Haire-Coombs. On the slopes, the soils are well-draining, and with rainfall in Los Carneros only 18 to 27 inches (46 to 69 centimeters) in non-drought years, primarily in the spring, the vineyards are generally irrigated.
Although Los Carneros, like much of coastal California, enjoys a water-moderated Mediterranean climate, the Pacific Ocean is much cooler than the Mediterranean and generates fog that is a significant cooling factor, moving in from San Pablo Bay, blanketing vineyards every morning during the growing season. Not only is the fog a major cooling factor, it blocks morning light, slowing ripening. Temperatures rarely exceed 80° Fahrenheit (27° Celsius) before frequently stiff afternoon breezes blow in off the cool water, further slowing sugar development.
The same patterns apply to the Pacific Ocean, and the western reaches of Carneros are cooled (albeit less dramatically, given the greater distance) by the morning fog and afternoon breezes funneling in from the coast through Sonoma’s Templeton Gap (which now boasts an AVA of its own).
The cool temperatures stretch out the growing season, and the vines struggle in the wind. Sugars rise very slowly and evenly, and acidity levels persist, giving winemakers the luxury during harvest of choosing when to pick based on the style nuances they’re looking for. And the extra time on the vine allows tannins to mature and fruit flavors to develop layers of complexity.
Main Grape Varieties
Carneros is one of the coolest and windiest AVAs in Napa and Sonoma Counties, conditions ideal for fine quality Pinot Noir and Chardonnay. And increasingly, attention is focused on Syrah and Merlot here, produced in cooler-climate styles that are gaining appreciation in the country today.