Local Terroir
Geological Influences
The growing regions of Solano County are fairly uniform with respect to geological origins and also soils. The county is in the northern part of the Great Valley, which began to form during the Jurassic period, starting 200 million years ago. The valley was an ocean basin that became enclosed by Franciscan Formation mountains, such as the Mayacamas and Coast Range in the west and a line of volcanoes in the east, where the Sierras are now. Over many millions of years, the Great Valley was filled by alluvial sediment resulting from the erosion of those mountains.
The chief exception in the county is parts of the Green Valley, including Wild Horse Valley AVA. This AVA has areas created by volcanic activity, including Sonoma Volcanics which are very common in Sonoma, Napa, and Lake Counties. The Vaca Range and Mt. George are volcanic in origin and those two AVAs are tucked in between them.
Mountains/River/Other Key Influences
On top of this Great Valley sediment in Solano County is alluvial sediment from a much more recent period, fluvial sediment deposited by flooding rivers, including today’s Sacramento and San Joaquin, and marine sediment that occurred when sea levels were higher and the greater San Francisco Bay extended well into the county.
The mountains to the west and bays to the south and south-west also affect climate. The bays’ water mass creates a moderating effect, along with afternoon breezes that cool the area. The mountains prevent any direct airflow from the ocean. They also protect nearby areas, such as the Solano side of Wild Horse Valley, from the coolest of the bay breezes.
Soil Diversity
The flat lands of Solano County feature various types of reasonably similar clay-loam soils. Green Valley and, especially, Wild Horse Valley are heavily volcanic and better draining.
Climate
The climate of Solano County overall is warm-summer Mediterranean, with heat accumulation placing it in the category of Winkler-Amerine Region III. The precise level of heat accumulation will vary in general, according to proximity to the bay. Climate change has brought about a warming trend overall and more variability between years than existed 50 years ago.
In keeping with the warm-summer Mediterranean climate type, rainfall during the growing season is extremely low. The region averages 20 inches (51 cm) of rain per year, which falls almost exclusively during the winter months. The area does not see any snow. Frost risk is minimized by the bay’s moderating effects.
Humidity is generally low to moderate. Fog is rare in most parts of the county. That, coupled with a lack of rainfall during the growing season, means disease pressure is minimal.
Sunlight is not, for the most part, blocked by mountains in Solano County. Nor is there much fog or cloud cover. Therefore, the area enjoys long, sunny days during the growing season.
Sub-AVA’s
Location/Geography
64,640 acres (26,159 ha) in Sacramento, Solano, and Yolo Counties, generally between the Sacramento and San Joaquin Rivers. Much of the AVA comprises islands within rivers and sloughs.
There is a proposal to expand the AVA. The comment period ended on January 11, 2021. Expansion will be in Sacramento and Solano Counties. The added acreage shares all key viticultural characteristics with the existing AVA.
Name Background
Named for the town of Clarksburg, which took its name for Judge Robert Clark, a pioneer who arrived there in 1849.
Topography/Elevation/Water Sources/Geographic Features
Flat, with altitudes ranging from 10 feet (3m) above to 10 feet (3m) below sea level. The water table is high. Drains and canals are required to lower the water table within vineyards. Highly water-tolerant rootstock is required. The landforms are alluvial fan-basin and flood plain-basin-blackswamp.
Geology/Soil Composition
Poorly drained clay and clay loam
Climate
Warm-summer Mediterranean. Winkler-Amerine Region III. Climate is moderated by the considerable amount of surrounding water. Mean temperature during growing season is 68°F (20°C) with a daily min/max of 52°/86°F (11°/30°C). Rainfall is 16 inches (41 cm) per year on average (in non-drought years).
Main Grape Varieties
Chenin Blanc, Chardonnay, Petite Sirah
Location/Geography
The AVA is in eastern Solano County, bordering Napa County and Wild Horse Valley AVA.
Name Background
Named for the town of Green Valley, a township since at least 1890, and Green Valley Creek
Note: This AVA is wholly different from the Green Valley of Russian River Valley AVA. The modifiers “Solano County” and “Russian River Valley” are included in the official TTB designations to avoid confusion.
Topography/Elevation/Water Sources/Geographic Features
The valley runs roughly north-south between the southern ends of Mt. George and Vaca Ranges.
Geology/Soil Composition
Volcanic, Conejo clay loam, alluvial
Climate
Warm-summer Mediterranean, Winkler-Amerine II-III, cooled by moist breezes off San Pablo and Suisun Bays. Frequently foggy.
Location/Geography
A rectangular AVA, about 3 miles by 8 miles (5-13 km), immediately south of Stags Leap District AVA and east of Solano County Green Valley. The southern boundary is just south of Interstate 80. 15,360 total acres (6,216 ha) and about 3,000 (1,214 ha) planted.
Name Background
The Suisun were a Native American tribe in the area. The name is said to mean “where the west wind blows.” Suisun Bay was the first geographical location to be given the name.
Geology/Soil Composition
Brentwood clay loam, Sycamore silty clay loam, San Ysidro sandy loam and Rincon clay loam
Climate
Warm-summer Mediterranean, Winkler-Amerine Region III-V, depending on the year. It averages 3,350 degree days (1,843 in degrees celsius). The area is cooled during the growing season by all-day breezes coming off Suisun Bay. It is rarely foggy.
Main Grape Varieties
At least 24 varieties are grown, notably Petite Sirah
Location/Geography
Located in the Vaca Mountains above the city of Napa. The AVA is one of the smallest in the United States, covering just 3,300 acres/ 1,350 hectares of land on the hills above Coombsville.
Name Background
The very first grapes were planted in the 1880s by Joseph Volpe and Contsantino Malandrino. Back then the area was home to many wild horses, hence the name.
Topography/Elevation/Water Sources/Geographic Features
Elevation: 850 to 2,130 feet (259 to 650 m).
Rainfall: 35 inches (94 cm) annually.
Geology/Soil Composition
Volcanic in origin, with basaltic red color; shallow with limited water retention, so irrigation often essential.
Climate
Due to elevation and proximity to San Pablo Bay, it is the coolest of all Napa Valley AVAs. The air mass that passes over Carneros cools another 10 degrees by the time it rises to the AVA.
However, the Solano County side is warmer, because the bay breezes are largely blocked by hills.
Main Grape Varieties
Pinot Noir and Chardonnay