Terroir of Sonoma County

In wine terms, terroir has to do with the growing area for the grapes; the climate, soil, and topography. The whole natural environment that "raised" the grapes will affect the taste of the wine. Sonoma County is full of variations in all of these. The diversity is amazing.

Morning fog stretching inland
A common sight in much of the county

Climate
The county has three main microclimates: coastal marine, coastal cool, and coastal warm. The micro zones within each of these is large, probably a number no one has tried to determine. The growing season climate is largely defined by the cold waters of the Pacific. Its interaction with the warm, sunny days gives cool nights, warm days, with a marine layer moving inland from the ocean and burning off in the morning.

Soil
There are 31 recognized soil types, or as they like to say, "That's more than all of France!" They range from sandy to volcanic rock. Put another way, you can drive to a different microclimate in a few minutes. You can often walk to a different soil type in a few minutes.

Topography
The elevation ranges from a few feet below sea level to over 4,000 feet. Vineyards range from sea level to 2,600 feet. Hills and mountain ranges are numerous, with many valleys. The valleys have a distinct climate vs. the hillsides/benchland vs. the higher elevations. Each of these will have different soils. The sunlight will be different depending on what direction the hillside faces.

Topography of Sonoma County
Click on map to enlarge

Following is a brief description of the terroir of Sonoma County's major appellations (grape growing areas) that you might see on a wine's label. There are numerous microclimates within each.

Alexander Valley
Summer days are quite warm. Nights cool off, especially to the south along the Russian River, where the cooler marine air filters in. This area is known for Cabernet Sauvignon.

Bennett Valley
This moderately cool area sits between three mountain peaks that were created by an ancient volcano. Most vineyards are on the alluvial plain, sitting from a few hundred feet above sea level to over 1,000 feet. It's known for Sauvignon Blanc, Chardonnay, and more recently, Pinot Noir.

Carneros
This area at the southern end of both Napa and Sonoma Counties sits on the bay. Cool summer temps with afternoon breezes are the norm. Soils are clay. Chardonnay and Pinot Noir are the main grapes.

Dry Creek Valley
A long, narrow valley with vineyards on the rocky valley floor and on the east- and west-facing bench land. Dry Creek is the home of Zinfandel. Sauvignon Blanc also does well along with Cabernet Sauvignon on the benchlands.

Moon Mountain
This growing area is situated between Sonoma and Napa Valleys vineyards ranging from 200 ft to 2,200 ft above sea level. Vineyards are largely southerly facing, with winds off the nearby San Pablo Bay. Many soil types, but best known is the iron rich volcanic rock of the historic Monte Rosso Vineyard. The area is most known for Zinfandel and Cabernet Sauvignon.

Petaluma Gap
Wind and fog from the coast get pulled through a gap in the coastal mountain range. Growing season is cool with foggy nights and mornings, then windy afternoons. It's all about Pinot Noir.

Rockpile
In a remote mountainous area north of Dry Creek Valley. Vineyards sit between 800 and 2,000 feet. There's lots of sun and afternoon winds. Cabernet Sauvignon and Zinfandel are the main grapes from this small appellation.

Russian River Valley
The area is defined by the significant influence of ocean cooling breezes and fog during the growing season. Soils are primarily sandy loam, including the famous(!) Goldridge soils. This is perhaps the most well-know appellation in the county because Pinot Noir is the star. Chardonnay and Syrah also do well.

Sonoma Coast
As the name implies, it's all about marine influences, with Chardonnay and Pinot Noir being the main grapes.

Sonoma Valley
A north-south valley in the southern part of the county. Cool air comes in from the south off the bay and from the north off the Santa Rosa plain. Valley soils are fertile, the hills on both sides are volcanic. Chardonnay is 25% of the grape crop, with the rest split between several other varietals.

Goldridge soil of west Sonoma County
image from pressdemocrat.com

Some of this information is from SonomaWineGrape.org