Local Terroir
Geological Influences
Sonoma County lies about an hour’s drive north of San Francisco, situated between the Pacific Ocean and the Napa Valley, covering about 1 million acres/414,398 hectares in all, roughly 40 miles/64 km from north to south and 40 miles/64 km across. Mendocino and Lake counties are due north, while the Oregon border is another five hours’ drive north.
Thanks to tectonic plate collisions, volcanic eruptions and coastal erosion, elevations in Sonoma County range from sea level to 4,715 feet/1,437 meters, with valleys, benchlands and mountain slopes in between; average elevation is 620 feet/189 meters.
The region straddles the boundary between the North American plate and the Pacific plate. These plates created the California Coast Ranges some 30 million years ago. The San Andreas Fault, where earthquakes occur between the plates, extends along most of the California coast and through Sonoma County.
The Mayacamas Mountains, part of the California Coast Ranges created by tectonic upheavals that left volcanic ash and lava in the soil, form most of Sonoma County’s eastern boundary.
On the other side of the Mayacamas, to the east, lies Napa Valley. In northeastern-based Sonoma Knights Valley, 4,341-feet/1,323-meter high volcanic Mount St. Helena, among the highest peaks of the Mayacamas, is a dominant feature.
Mountains/River/Other Key Influences
Though planted to winegrapes and populated by 494,000 people (2019), half of Sonoma County remains covered by forest and woodland, while 36% is pasture. The Mayacamas Mountains form the eastern boundary of almost all of Sonoma County, separating it from both Napa Valley and Lake County to its east. The mountains act as a barrier, trapping cool temperatures and fog traveling in from the Pacific Ocean and eastward toward Napa.
Several of the area’s appellations are named for their mountainous peaks: Sonoma Mountain (2,400 feet/732 m), Moon Mountain (2,200 feet/671 m), Rockpile (1,900 feet/579 m) and Pine Mountain-Cloverdale Peak (3,000 feet/914 m).
The Russian River travels through Sonoma County from Mendocino County to the Pacific Ocean, exiting at the small coastal town of Jenner. At 100 miles/161 km long, it is an important lifeblood for the region’s wildlife, recreational and agricultural endeavors, and a significant influence on climate, pulling cool fog from the ocean to warmer inland areas. The Laguna de Santa Rosa is a seasonal wetland that also impacts the growing conditions of the Russian River Valley AVA.
The Russian River appellation is so vast and varied that winemakers and growers there teamed up in 2014 to launch the Neighborhoods Initiative, an attempt to systematize what they have formally and informally believed about individual microclimates and variations in soils in different “neighborhoods,” focusing specifically on how these factors impact Pinot Noir. These neighborhoods include, from north to south and generally warmer to cooler, Westside Road, Middle Reach, Laguna Ridge, Santa Rosa Plain, Green Valley (an appellation already in its own right) and Sebastopol Hills.
Within the Sonoma Coast appellation, many vineyards are high enough in elevation to rise above the fog line, which makes it possible to ripen winegrapes in such cold climes. In fact, higher elevation vineyards across Sonoma County typically receive more sunshine in the growing season, the fog burning off sooner than on the valley floor, resulting in strong UV light that contributes thicker skins to the grapes, adding structure as well as color and flavor. Still, the tannins often need more time to mature due to stressed soils than they do in more fertile areas.
Unique to Sonoma County, the Geysers is the largest steam-powered geothermal development in the world, containing a complex of 18 geothermal power plants, encompassing 45 square miles along the border between Sonoma and Lake Counties. Hot water, steam and heat in the Mayacamas Mountains supply a significant amount of electricity to the region.
Soil Diversity
Sonoma County soils are extremely varied, thanks to tectonic plate collisions, volcanic eruptions and coastal erosion over millions of years. Plate movements deposited younger volcanic and sedimentary rock, once part of an ancient seafloor, that remain rich in calcium, gravel, sand and clay, especially at higher elevations. At lower elevations, rich soils often show the signs of long-term erosion from higher up, deposited over millennia. In all, the region has 11 major formation types and 31 different soil series -- more than the entirety of France!
As Jancis Robinson MW has written in the Sonoma Chapter of the 7th edition of The World Atlas of Wine: “Local knowledge is everything in California; its terroirs are baffling to outsiders.”
Alexander Valley’s valley floor is typical of other valleys in the region, like Sonoma, Knights and Dry Creek, with fertile alluvial soils, while benchlands tend to have soils that are rocky, well-drained and less fertile. In an appellation like Chalk Hill, chalky white ash volcanic soils dominate, while foggy Green Valley and Russian River Valley brim with fine sandy soils like Goldridge that contribute good drainage, natural chemical balance and viticultural greatness to their Pinot Noirs. Franciscan soils, rockier than Goldridge, are also common.
The southernmost portion of the Los Carneros AVA, along San Pablo Bay, an extension of the San Francisco Bay, has less-fertile, shallow clay-loam soils that impact vigor.
The diversity of growing conditions is reflected in the fact that for every one acre of vineyards, Sonoma farmers grow two acres of diversified agriculture, including hay, poultry, dairy and apples.
Climate
Sonoma County enjoys cool nights and temperate days, thanks much to the moderating effects of the Pacific Ocean, extending along 76 miles/122 km of its border, and the San Pablo Bay on its southeastern flank, which contributes cooling winds, especially in Los Carneros. During the growing season of May through September, temperatures range from the low 70s to low 90 degrees F (21 to 32 degrees Celsius) during the day, while nighttime averages are in the 40s and low 50s F (4° to 10° C). This allows for ample acid retention as does the morning fog that is common, giving the grapes the most amount of heat typically midday and late afternoon.
Frost and rainfall are rare during the growing season. In fact, average rainfall per year is about 25 to 30 inches/64 to 76 cm, though the amount can vary widely depending on location. In Fort Ross-Seaview, a mile off the coast, Fort Ross Vineyard can get between 75 and 125 inches/191 to 318 cm per year, while in the warm, inland Alexander Valley, a year’s average is closer to 42 inches/107 cm.
The region’s newest AVA, Petaluma Gap, was singled out for the influence of cold air from the Pacific Ocean, which travels through a 15-mile/24-km-wide opening (or gap) in the coastal mountain range. This air ensures heavy morning fog during the growing season and wind in the afternoon. Daily temperatures can swing 40 to 50 degrees F/4 to 10 C, ideal for slow ripening. The wind also tends to keep botrytis and mildew pressures away.
Additionally, Sonoma continues to suffer consecutive years of drought, forcing those in agriculture to better manage available water resources and take steps to insulate themselves from future impacts. In the wine industry, this includes farming with less irrigation and even dry farming, as well as planting more drought-resistant varieties and rootstocks.
Location/Geography
In the northeastern section of Sonoma County, Alexander Valley is south of the Mendocino County line. The Russian River runs along the length of appellation north to south and the town of Healdsburg. To the east is Knights Valley and to the west is Dry Creek Valley. Geyserville and Cloverdale are among its towns, and Highway 128 is the main route through.
Name Background
Named for Cyrus Alexander who arrived in 1840, receiving a land grant from the Mexican government. He is credited for being the first to grow vines.
Topography/Elevation/Water Sources/Geographic Features
Elevations range from 100 to 2,572 feet/30 to 784 meters. High elevation sites receive more sunlight as coastal fog burns off earlier in the day. The valley rises on the east into benchland slopes where 80% of vineyards are located, clustered in the middle of the valley at the base of the Mayacamas Mountains. The mountains border the appellation to the east; the Russian River runs through it.
Geology/Soil Composition
Benchland soils are rocky and less fertile than the valley floor and well-drained, typically contributing lower yields. The soils are diverse, thanks to the area’s history of plate movements, featuring volcanic and sedimentary rock and rich in calcium, gravel, sand and clay content. Benchland soils are gravelly, sandy loam, primarily Yolo and Cortina, and well-drained due to slope and have calcium magnesium ratio for Cabernet Sauvignon.
Climate
Largely Mediterranean with wet, cool winters and warm, arid summers. Cooled from south to north by marine air that travels along the Russian River.
Main Grape Varieties
Cabernet Sauvignon, Chardonnay, Zinfandel
Location/Geography
The appellation is near the town of Santa Rosa north of Sonoma Mountain and Sonoma Valley and surrounded by three peaks. It sits within the Sonoma Valley appellation and overlaps with both Sonoma Mountain and Sonoma Coast.
Name Background
Named for settler James Bennett, who served as a state senator in the 1850s and introduced a bill making Santa Rosa the county seat.
Topography/Elevation/Water Sources/Geographic Features
Gently sloped benchlands and high sloping ridges, hills and swales form beneath the valley’s three peaks: Sonoma Mountain, Taylor Mountain and Bennett Peak, all dormant volcanoes whose ash is found in the soils. The Matanzas Creek watershed is the water source and the valley actually more of an alluvial bench than valley. The topography is diverse, with a range of exposures and terrains. Most vineyards are planted on benchlands between 400 and 1,100 feet/122 to 335 meters, though the highest elevation is 1,887 feet/575 meters.
Geology/Soil Composition
The volcanic history defines the steep, rocky soils with good drainage. The volcanic-origin Goulding-Toomes-Guenoc Association soils include lava flow, tuff beds and sandstone, gravel and conglomerate. The lower slopes and valley floor soils are more diverse, including some alluvial and spreckels loam.
Climate
Considered cool climate, due to consistent marine influence through the Petaluma Gap, combined with early morning fog and marine breezes during the growing season. The mountains help protect it from extremes.
Main Grape Varieties
Chardonnay, Merlot, Syrah
Location/Geography
Set in the northeast corner of the Russian River Valley AVA, surrounded clockwise by Dry Creek Valley, Alexander Valley and Knights Valley, Chalk Hill lies east along Highway 101 from Windsor to Healdsburg.
Name Background
Named for chalky white volcanic ash, a distinctive feature of its soils.
Topography/Elevation/Water Sources/Geographic Features
A meandering region that travels through hills and valleys, it reaches as high as 1,600 feet/488 meters in elevation.
Geology/Soil Composition
Mildly fertile, chalky white volcanic ash.
Climate
Warmer than the rest of the Russian River Valley as it is farther from the ocean’s cooling influence and largely above the fog.
Main Grape Varieties
Chardonnay, Cabernet Sauvignon
Location/Geography
In the northwestern section of Sonoma County, Dry Creek Valley is 16 miles long and two miles wide, and lies west of Healdsburg and Geyserville, protected from the ocean by high coastal mountains. At its northern end it spills into the Rockpile AVA.
Name Background
Named for Dry Creek, a tributary of the Russian River.
Topography/Elevation/Water Sources/Geographic Features
Fairly flat, Dry Creek is also marked by benchlands and hillsides along both sides of its fertile valley floor. Lake Sonoma lies at the northern tip of the AVA. The Russian River travels to the west of the region and heads south below Healdsburg, where it meets the Dry Creek.
Geology/Soil Composition
Created by the uplift and subsidence along earthquake faults and the deposit of alluvial material, Dry Creek’s valley soils are gravelly and sandy loam, deep, well-drained and fertile. Soils on the benches and hills are gravelly clay loam, rocky and red in color, draining exceptionally well.
Climate
On the northern edge of fog intrusion from the ocean, both coastal and inland influences exist here, with the coastal range to the west keeping cool marine temperatures at bay during long, warm days while serving as a conduit for coastal cold air and fog at night.
Main Grape Varieties
Zinfandel, Cabernet Sauvignon, Sauvignon Blanc
Location/Geography
On the far coast of Sonoma County, the 27,500-acre/11,129-hectare appellation was the first successful carving out of the larger Sonoma Coast AVA. Remote, wooded and mountainous, it lies in the high ridges above Jenner, where the Russian River meets the Pacific Ocean, largely centered along Meyers Grade Road.
Name Background
Named for Fort Ross, the historic outpost of Russian settlers set along Highway 1, and the small community of Seaview along Seaview Road.
Topography/Elevation/Water Sources/Geographic Features
Buffeted by the ocean by Black Mountain to the west, this AVA is defined by steep elevation, lying largely above the fog line, from 920 to 1,800 feet/280 to 549 meters elevation. That height allows it to enjoy plenty of sunlight and heat during the growing season, despite its proximity to the coast. The area is rugged, widely sloped and forested.
Geology/Soil Composition
Defined by the San Andreas Fault and Pacific Ocean, the soils are diverse and derived from sedimentary rocks and deposits. Well-drained gravelly loam soils derived from sandstone and shale are common.
Climate
Heavy winter rainfall, moderate conditions during the growing season, with drier, warmer temperatures than many of the valley AVAs that sit in summertime fog.
Main Grape Varieties
Pinot Noir, Chardonnay
Location/Geography
In eastern Sonoma outside of Santa Rosa, this small AVA is surrounded by Sonoma Valley and Bennett Valley to the south, Knights Valley and Chalk Hill to the north and the Russian River Valley to the west. The Mayacamas Mountains border it to the east.
Name Background
Named for the historic Fountain Grove Winery founded in the 1870s, a one-time communal living cult formerly defined by a red round barn sadly destroyed in the 2017 Tubbs Fire.
Topography/Elevation/Water Sources/Geographic Features
The AVA is defined by its elevation, reaching as high as 2,000 feet/610 meters.
Geology/Soil Composition
Defined by volcanic soils that resulted from long-ago eruptions of Mount St. Helena on the northern edge of the Sonoma-Napa border, this volcanic ash is moderately rich and well-draining. Sedimentary Franciscan Complex soils are also found.
Climate
It enjoys a marine influence caused by gaps in mountains between the ocean and Santa Rosa, though being inland, it is warmer than many of its more western peers. Hillsides provide microclimates.
Main Grape Varieties
Cabernet Sauvignon, Merlot, Syrah
Location/Geography
Southwestern part of the Russian River Valley near Sebastopol, Freestone and Occidental.
Name Background
Named for a creek that originates in Camp Meeker, a tributary of the Russian River.
Topography/Elevation/Water Sources/Geographic Features
Fairly flat and heavily influenced by the Pacific Ocean, the Russian River travels just north of the town of Forestville on its way to meeting the ocean at Jenner.
Geology/Soil Composition
Once covered by shallow inland sea, Goldridge soils dominate here, a fine, sandy loam over fractured sandstone with excellent drainage and low fertility. Also, rocky Franciscan soils.
Climate
Exceptionally foggy, with lengthy cold temperatures. First place fog comes in and last place fog goes out. Coastal climate with narrow temperature swings. Lowest average summer temperature in Sonoma County.
Main Grape Varieties
Pinot Noir, Chardonnay
Location/Geography
On the far northeastern edge of Sonoma County, bordering Lake and Napa Counties to the east and Alexander Valley and Chalk Hill to the west, with the Mayacamas Mountains and 4,344-feet-/1324-meters-high Mount St. Helena looming to the east.
Name Background
Named for Thomas Knight, a member of the Bear Flag Revolt who purchased part of a land-grant ranch in the 1850s.
Topography/Elevation/Water Sources/Geographic Features
The Mayacamas Mountains to the east and high-elevation Mount St. Helena protect the area from coastal influence, keeping it warm and dry.
Geology/Soil Composition
Rich, well-drained soils influenced by volcanic activity. Shallow, alluvial and gravelly, with volcanic ash and rock.
Climate
Warm afternoon and cool evenings are the norm, with the daytime temperatures during the growing season among the highest in Sonoma County.
Main Grape Varieties
Cabernet Sauvignon
Location/Geography
The only appellation to straddle both the Napa Valley and Sonoma County, with 60% of Los Carneros located in Sonoma County. Los Carneros is also Sonoma County’s southernmost appellation, south of Sonoma Valley and bordering San Pablo Bay. Highway 12 and 121 are the main routes through, connecting to both Napa and Sonoma.
Name Background
Translated as “the rams,” Los Carneros is named for a Spanish land grant.
Topography/Elevation/Water Sources/Geographic Features
Defined by flatlands and rolling foothills. The Pacific Ocean, Coast Mountain Ranges and San Pablo Bay all influence its cool climate.
Geology/Soil Composition
Considered some of the youngest soils in Northern California: a mix of clay loam and marine sediment, with denser clay and fractured sandstone deeper down
Climate
Cool, with prevailing marine winds from the San Pablo Bay and through the Petaluma Gap to the west. Cooling fog moderates the heat of the growing season. High temperatures during summer rarely exceed 80°F (27°C) with less diurnal range variation.
San Pablo Bay itself is the overarching influence in Los Carneros, dictating temperatures, diurnal swings (or lack of), and the potential length 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.
Main Grape Varieties
Chardonnay and Pinot Noir dominate, followed by Merlot and Syrah.
Location/Geography
Above Sonoma Valley to the east in the Mayacamas Mountains, bordering Napa Valley’s Mount Veeder. Glen Ellen and Kenwood are the closest towns. It also looms above the town of Sonoma.
Name Background
Named for a peak within the Mayacamas Mountains.
Topography/Elevation/Water Sources/Geographic Features
Vineyards are from 400 to 2,200 feet/122 to 671 meters/ elevation and mostly face southwest receiving afternoon sun and cooling winds from the Pacific Ocean to the west and San Pablo Bay to the south.
Geology/Soil Composition
Red volcanic and ash.
Climate
Above the fog line; enjoys long, warm days and cool, dry nights during the growing season, benefitting from cooling coastal winds.
Main Grape Varieties
Cabernet Sauvignon, Zinfandel, Pinot Noir, Chardonnay
Location/Geography
The Petaluma Gap wrangled 202,476 acres/81,939 hectares out of the larger Sonoma Coast appellation and is centered around the town of Petaluma, the southernmost city in Sonoma County, 25 miles/40 km north of San Francisco. The AVA extends southward into Marin County.
Name Background
Named for a 15-mile/24-km-wide opening in the coastal mountain range that brings in cold air from the Pacific Ocean, pulling it east over land to San Pablo Bay.
Topography/Elevation/Water Sources/Geographic Features
Mostly flat, there are a few high-elevation sites of note, including 1,400 feet/2,253 meters’ elevation Sun Chase and Gap’s Crown vineyards. Most sites are western-facing and sloped. The Sonoma Mountains buffer it to the east. The Petaluma River travels along Lakeville Highway to San Pablo Bay.
Geology/Soil Composition
Ashy tufa-like volcanic soils. Mineral-rich clay loam and sandy loam soils have gravelly river cobbles.
Climate
Heavy morning fog during the growing season and cooling wind in the afternoon. Temperatures consistently swing 40 to 50 degrees F (4 to 10 degrees C) in a day, with fog returning at night.
Main Grape Varieties
Pinot Noir, Chardonnay, Syrah
Location/Geography
On a remote ridge northeast of Cloverdale on the way to the Geysers, this is a high-elevation region bordering the northern tip of the Alexander Valley. The AVA overlaps both Sonoma and Mendocino counties.
Name Background
Named for the mountain on which it resides and its highest peak, 3,000 feet/914 meters above Alexander Valley.
Topography/Elevation/Water Sources/Geographic Features
Vineyards are 1,600 feet/488 meters elevation and above and typically steep, well above the fog line.
Geology/Soil Composition
Thin, shallow volcanic and rocky soils, plenty of water due to rainfall, and numerous natural springs.
Climate
Cool days and warm nights during the growing season. Marked by high winds and heavy rains in the wintertime, from 45 to 90 inches/114 to 229 cm a year.
Main Grape Varieties
Cabernet Sauvignon, Malbec
Location/Geography
Among the highest and most northern of Sonoma County’s appellations, Rockpile is just below the Mendocino County line and above Dry Creek Valley to the northwest. Rockpile straddles a ridge between two arms of Lake Sonoma.
Name Background
Rockpile is an historic name given to a rocky peak 15 miles/24 km from the Pacific Ocean, and the large ranch established around it that was named for the peak.
Topography/Elevation/Water Sources/Geographic Features
Elevations from 800 to 2,000 feet/244 to 610 meters above the fog line and above Lake Sonoma. The hillsides are steep and the terrain rocky. Lake Sonoma provides an inversion layer keeping it warm, sunny and well above the fog, though the AVA is only 13 miles/4 km from the ocean. A dominant earthquake fault runs through it.
Geology/Soil Composition
Thin gravelly loam, sedimentary rock, serpentine, shale; much of the soils are deep red.
Climate
Warm and windy, with coastal breezes howling throughout.
Main Grape Varieties
Zinfandel, Cabernet Sauvignon
Location/Geography
Smack dab in the middle of Sonoma County and defined and impacted by the Russian River that travels through it. Fairly flat. A large AVA, it touches Sonoma Coast, Dry Creek Valley, Chalk Hill and the Petaluma Gap, and envelops the entire Green Valley AVA.
Name Background
Named for the Russian colonists who planted grapes at Fort Ross and the river also named in their honor. The Russian River runs 100 miles/161 km, flowing into Sonoma north of Cloverdale and running west all the way to the ocean at Jenner.
Topography/Elevation/Water Sources/Geographic Features
The Russian River brings in fog and coastal breezes, as does the Petaluma Gap in the coastal mountains. Most of the area is a low-lying plain with benchlands and hillsides scattered throughout.
Geology/Soil Composition
Goldridge loam predominantly, with volcanic, alluvial and sedimentary.
Climate
Huge diurnal swings of 30 to 40-degree F (4 to 10 degrees C) are not unusual during the growing season, marked by warm afternoons with cooler mornings and evening temperatures. The ocean plays a big role, cooling with morning and evening fog that in some parts of the AVA can sit all day long.
Main Grape Varieties
Pinot Noir, Chardonnay, Zinfandel
Location/Geography
Encompassing 70-plus miles/113 km of coastline from the Mendocino border to the Petaluma Gap appellation, the AVA also includes several ridges and overlaps with several other appellations, including Fort-Ross Seaview, Green Valley, Russian River Valley and Los Carneros.
Name Background
Named for the county of Sonoma, which in itself was named for the Mission San Francisco Solano de Sonoma in the 1800s.
Topography/Elevation/Water Sources/Geographic Features
Largely flat and near the Pacific Ocean, it is hugely influenced by the cooling winds and temperatures of the fog and wind that result. Some rolling hillsides and high elevations in inland ridges above the fog, where warmer temperatures and ample sunlight are more typical. The San Andreas Fault runs through much of the appellation.
Geology/Soil Composition
Highly diverse, from marine deposits to Goldridge.
Climate
Cold and windy with extended periods of fog during the growing season. Higher-elevation sites enjoy more sun exposure within a still cool-climate environment. Twice the annual rainfall of interior Sonoma.
Main Grape Varieties
Pinot Noir, Chardonnay
Location/Geography
In the Sonoma Mountains above the town of Glen Ellen to the east and Petaluma to the west, with west-facing hillsides that look out to the Pacific Ocean.
Name Background
Named for the town of Sonoma, which in itself was named for the Mission San Francisco Solano de Sonoma in the 1800s.
Topography/Elevation/Water Sources/Geographic Features
The appellation is between 400 and 1,200 feet/122 to 366 meters, though the mountain itself reaches as high as 2,300 ft/701 meters. From the western side, it receives cooling ocean winds via the Petaluma Gap. Vineyards are on steep slopes with mostly eastern exposures.
Geology/Soil Composition
Ancient marine sediment over Franciscan complex, with volcanic and sedimentary origin. Some clay loam with rocky shale and basalt. Well-draining.
Climate
Vineyards are above the fog line, meaning more sun exposure during the day, including mornings. The altitude ensures cooler nights.
Main Grape Varieties
Chardonnay, Cabernet Sauvignon, Pinot Noir
Location/Geography
Running south to north from Los Carneros to the outskirts of Santa Rosa, this valley is nestled between the Mayacamas Mountains to the east and Sonoma Mountain to the west. Highway 12 is the main road through.
Name Background
Named for the town of Sonoma, which in itself was named for the Mission San Francisco Solano de Sonoma in the 1800s, this area is also often called Valley of the Moon.
Topography/Elevation/Water Sources/Geographic Features
Until the delineation of Sonoma Mountain and Moon Mountain AVAs, the valley included both sides of its mountains, but is now more of a true valley, running north to south and encompassing mostly low-elevation sites along with benchlands.
Geology/Soil Composition
Fifteen different soil series.
Climate
An open valley, cool air circulates from the Pacific Ocean north of the valley and from San Pablo Bay to the south.
Main Grape Varieties
Chardonnay, Cabernet Sauvignon, Merlot, Zinfandel