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The Role of Soil and Terrain on Wild Horse Valley Grape Growing

The AVA is located a few miles east of the Town of Napa in the Vaca Hills. The terrain of the region is made of volcanic soils. Mount George is just north of the AVA. It erupted millions of years ago and spewed volcanic ash and lava throughout Wild Horse Valley.

The soils contain a lot of weathered pumice from these eruptions. This soil type is porous, aerated, and has a high mineral content. Heron Lake Winery makes about 400 cases of Pinot Noir from grapes grown in these soils.

The majority of Wild Horse Valley is located in the southeastern hills of Napa Valley. Part of the 3,300 acre AVA is in Solano County. The valley sits at about 1,400 feet above sea level.

In general the eastern hills of Napa Valley are much drier than the west. Whereas redwood trees are common in the west, oak trees dominate the landscape in the eastern hills. Lake Madigan and Lake Frey are the major bodies of water in the region.

Owned by the Murray Family, Wild Horse Valley Ranch is a very large piece of property in the region. Because much of the AVA’s land is part of this property, there are not a lot of small plots of land available for vineyard development. This has stymied viticultural growth in Wild Horse Valley.

Soils are gravelly from alluvial flows from the surrounding volcanic hills. Grape vines are very stressed in these thin, mountain soils, and yields are very low. Heron Lake Winery owns a Pinot Noir vineyard that produces less than one-half ton per acre. Wild Horse Valley Chardonnay has crisp varietal characteristics with pear, apple, and mineral flavors. Local growers attribute these crisp varietal characteristics to the mineral rich soils in the AVA.

Because they contain a lot of oxidized iron, soils are a distinctive red color. There is also quite a bit of basalt in the soil. The topsoil is very thin, and the subsoil retains water extremely poorly. Irrigation is necessary at certain times during the year, but growers try to keep this to a minimum to avoid diluting the fruit and causing excessive canopy on the vines. They accomplish this by avoiding irrigation in the weeks preceding harvest.

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