Local Terroir
The terroirs of most Lake County AVAs are variations on three themes: Mediterranean climate, high altitude, and red, volcanic soils. Even the lowest of the AVAs, Guenoc Valley, starts at 700 feet (213 m) and goes up from there. That’s a significant point of difference from nearby regions such Napa Valley and Sonoma Valley, both of which have significant vineyard acreage at sea level. Lake County is also further from the Pacific than those two regions.
Those factors mean that Lake County tends to experience less fog, less direct oceanic cooling, and more direct sun exposure on average. But that relatively simple picture quickly becomes complicated, because some vineyards are as high as 2,600 feet (702 m), some areas of the mountains run east-west (rather than north-south), and some growing areas are 20 miles (32 km) closer to the ocean than others.
Soils, and their ability to hold water, vary with the topography too, despite their generally volcanic origin. Some vineyards are on steep, mountain slopes and others lie on benches with gentler grades and deeper, but more gravelly, soils. There are others are on the valley floor, with fine soils and no slope to aid drainage.
There is variation within each AVA, of course. However, their boundaries are well-defined and the general terroir of each AVA is well-differentiated from all the others.
Sub-AVAs
Location/Geography
A high-mountain valley, well outside the Clear Lake AVA. West-by-southwest of the town of Lakeport, and almost immediately adjacent to the Mendocino County line.
Name Background
Benmore Valley takes its name from a notorious nineteenth-century cattle rustler.
Topography/Elevation/Water Sources/Geographic Features
A mountainous valley at 2,400-2,700 feet (732-823 m). Rainfall and groundwater are the water sources.
Geology/Soil Composition
Alluvial soils, principally Manzanita loam, similar to those of most Lake County vineyard areas. It is eroded/washed from the volcanic hills and is fairly well-drained.
Climate
High altitude, greater proximity to the Pacific Ocean, and fewer mountains blocking sea air make this the rainiest, foggiest, and coolest by far of Lake County AVAs.
Its cool, damp conditions and vulnerability to frost, and somewhat remote location, led grape growers to abandon the area.
Main Grape Varieties
Chardonnay (formerly, there are no active acres under vine now)
Location/Geography
On the western shore of central Clear Lake, directly across the lake from the High Valley AVA. It’s just west by northwest of Mt. Konocti.
Name Background
Written references to “Big Valley” go back to at least 1881. The area was the county’s largest and best-suited area for agriculture, including fruit trees, row crops, and grapes. It was home to the first modern vineyards in the county.
Topography/Elevation/Water Sources/Geographic Features
Lake County is high-altitude overall, thus Big Valley’s vineyards at 1,330-1,440 feet (405-439 m) are only slightly above the lake.
Geology/Soil Composition
Relatively fertile, lake-deposited clay and loam, streaked with gravel beds created by mountain streams. Hard clay beneath those soils can limit root depth. (Shallow root depth can make vines vulnerable in times of drought. It also limits the diversity of minerals and microbes to which the roots are exposed.)
Climate
Warm-summer Mediterranean, with long, daily sun exposure due to altitude. The high altitude allows for some cooling Pacific breezes, but more direct moderation and cooling breezes come off the adjacent lake.
The lake effect makes it considerably cooler than the Red Hills Lake County AVA, resulting in about 800°F (427°C) fewer degree days per vintage. Thus, it’s a high Region II or low Region III on the Winkler-Amerine scale.
Being in a rain shadow, rather than in the mountains, makes it drier as well. It averages 20 inches (51 cm) precipitation/year. Red Hills Lake County gets 50% more.
Main Grape Varieties
Sauvignon Blanc, Chardonnay, Viogner, Riesling, Cabernet Franc, Zinfandel and Merlot
Location/Geography
Completely encircles Clear Lake. All other Lake County AVAs, except Benmore Valley and Guenoc Valley, are nested within it.
Name Background
Named for the massive lake which it surrounds
Topography/Elevation/Water Sources/Geographic Features
Vineyard altitudes (outside of nested AVAs) run from 1,300 to 1,500 feet (396-457 m).
Most vineyards employ irrigation as needed. The majority draw upon groundwater. Some, close to the lake, pull water from that.
Geology/Soil Composition
Hills and terraces feature Manzanita loam, a red, volcanic soil, rich in gravel and thus well-draining.
The valley soils are alluvial and fluvial, derived from streams and run-off. They are generally well-drained and consist of loam, sand, and gravel.
Climate
Warm-summer Mediterranean, with long, daily sun exposure due to altitude. The high altitude allows for some cooling Pacific breezes, despite its distance from the ocean
Main Grape Varieties
Cabernet Sauvignon, Chardonnay, Muscat, Sauvignon Blanc, and Zinfandel
Location/Geography
A valley and hills just north of Mount St. Helena which sits on the Napa County line. Butts Canyon Road, which runs north out of Napa’s Pope Valley, runs through it on the way to Middletown.
Name Background
Guenoc was the first formal settlement in southern Lake County and took its name from the Guenoc Rancho. Guenoc only existed as a “town” from 1865 to 1880. Rancho Guenoc had been established in 1845 by a Mexican land grant. The name “Guenoc” was the settlers’ adaptation of Wennok, the local Native American name for a nearby lake.
Topography/Elevation/Water Sources/Geographic Features
Vineyards lie at 700-1,500 feet (213-457 m). The altitude provides considerable sun exposure. Groundwater feeds irrigation.
Geology/Soil Composition
Hillside soils are largely shallow, well-drained loam with substantial sandstone and shale content.
Valley floor soils are primarily clay loams, the best of which are also well-drained.
Climate
Warm-summer Mediterranean, but with less oceanic impact than other Lake County AVAs and more influence from the surrounding Mayacamas mountains. Very hot days and cold air sliding down from the mountains at night mean frequent 50°F (10°C) diurnal shifts. It’s a Winkler-Amerine Region III zone.
Isolated from fog and seeing very little growing-season rain, disease pressure is low.
Main Grape Varieties
Cabernet Sauvignon, Cabernet Franc, Merlot, Syrah, Zinfandel, Petite Sirah, Petite Verdot, Malbec, Grenache, Mourvedre, Tempranillo, Pinot Noir. Petite Sirah does especially well.
Location/Geography
Immediately east of the midpoint of Clear Lake. The AVA comprises a 9- by 3-mile, east-west running valley and the mountains which enclose it.
Name Background
The AVA is literally a high valley.
Topography/Elevation/Water Sources/Geographic Features
The AVA ranges from 1,700 to 3,000 feet (518-914 m). Most vineyards are below 2,400 feet (732 m).
Geology/Soil Composition
All soils are either the direct result of volcanic activity or eroded from the ring of volcanic hills. The soils tend to be red, gravelly, and well-drained.
Climate
Warm-summer Mediterranean, with long daily sun exposure due to altitude. The high altitude allows for some cooling Pacific breezes, stronger than in most other Lake County AVAs, due to the east-west orientation. The lake also moderates temperatures. Diurnal shift can reach 50°F (10°C).
Main Grape Varieties
Cabernet Sauvignon, Cabernet Franc, Merlot, Syrah, Zinfandel, Petite Sirah, Petite Verdot, Malbec, Grenache, Mourvedre, Tempranillo, Pinot Noir
Location/Geography
Located immediately south of Big Valley District AVA. Kelsey Bench is separated from Clear Lake by Big Valley District on the north and Mt. Konocti on the east.
Name Background
Named for Andrew Kelsey, the first white settler in the area. The town of Kelseyville straddles the Big Valley District-Kelsey Bench boundary.
“Bench” is a reference to the topographical nature of the AVA.
Topography/Elevation/Water Sources/Geographic Features
Foothills and alluvial plateau sloping down to the northeast from the higher mountains. Vineyards go up to 1,600 feet, about 10% higher than in Big Valley District.
Geology/Soil Composition
Red, volcanic soil, streaked with gravel beds created by mountain streams, lie atop hard clay which is in turn on a bed of pyroclastic lava flow. These subsoils limit vine depth.
Climate
Essentially identical to Big Valley: Warm-summer Mediterranean, with long daily sun exposure due to altitude. The high altitude allows for some cooling Pacific breezes, but more direct moderation and cooling breezes come off the adjacent lake.
The lake effect makes it considerably cooler than the Red Hills Lake County AVA, resulting in about 800°F (427°C) fewer degree days per vintage. Thus, it’s a high Region II or low Region III on the Winkler-Amerine scale.
Being in a rain shadow, rather than in the mountains, makes it drier as well. It averages 20 inches (51 cm) precipitation/year. Red Hills Lake County gets 50% more.
Main Grape Varieties
Sauvignon Blanc, Chardonnay, Viogner, Riesling, Cabernet Franc, Zinfandel and Merlot
Location/Geography
Immediately southwest of Clear Lake. Nested within the Clear Lake AVA
Name Background
Named for its red, volcanic soils
Topography/Elevation/Water Sources/Geographic Features
Numerous hills, which are part of the Mayacamas range. Altitudes rise from 1,350 to 2,600 feet (411-792 m). Most vineyards lie above 2,000 feet (610 m).
Geology/Soil Composition
Well-drained, red, hillside volcanic soils, principally Glenview-Bottlerock- Arrowhead, Konocti-Benridge, and Collayomi-Aiken. Quartz crystals and obsidian (volcanic glass) stud the softer soils.
Climate
Warm-summer Mediterranean, with long daily sun exposure due to altitude. The high altitude allows for some cooling Pacific breezes, despite being more than miles from the ocean. Still it’s Winkler-Amerine Region IV in degree days.
Main Grape Varieties
Cabernet Franc, Cabernet Sauvignon, Petite Sirah, Sauvignon Blanc, Syrah, Zinfandel