Clear Lake is an AVA surrounding the largest expanse of fresh water in California. Located just north of Napa and Sonoma counties and east of Mendocino, it is part of the larger Lake County AVA. It is one of California's cooler wine-growing areas and as such produces bright, aromatic white wines made of Sauvignon Blanc and elegant, concentrated red wines made from Cabernet Sauvignon and Zinfandel.
The land surrounding Clear Lake is rugged and mountainous, the result of ancient lava flows from the volcanoes that dot the region. Vineyards are planted to take advantage of the topography here: they line the ridges and slopes overlooking the lake, where they benefit from exposure to intense sunlight. The increased altitude on these ridges brings with it markedly colder nights, slowing ripening and allowing the grapes to develop rich aromatics while retaining precious acidity.
The lake, occupying nearly half of the acreage of the AVA, has a significant moderating effect on the surrounding area's climate. Cool breezes that come off the water provide relief for the vines in the late afternoons, particularly in the sub-regions of High Valley and Red Hills Lake County. Without the climate-moderating effects of the lake, the area would be too hot for viticulture.
Bright-red volcanic soils provide an excellent base for vines in Clear Lake as they are shallow, free-draining and rich in the magnesium that is vital to vine health. Vines are able to develop deep root systems, resulting in lower yields and more-concentrated berries. The tephra (small volcanic pebbles) and obsidian that are found in pockets here are also good at retaining heat throughout the day.
Prior to Prohibition in 1920, Clear Lake's viticultural area was significantly larger than it is today. Since being rediscovered by wine-growers in the 1980s and 1990s (led by the Kendall Jackson winery, among others), Clear Lake has become significantly more quality-oriented, although the total area of land under vine is smaller now.
