Soils and Climate

Soils

The Napa Valley appellation is unique for the diversity of soils found in such a small geographic area. Soils of volcanic, maritime and alluvial origin exist, each created by geological events that have occurred over a 60-million-year history. The valley was formed by tectonic plate movement and volcanic activity, by alluvial waters and the flooding of San Pablo Bay, which once reached as far as the site of the present-day town of Yountville. Rocky knolls and alluvial fans interrupt the level expanses of the valley floor, each bearing testimony to geologic occurrences in the past.

The area's topography supports a wide variety of soils-more than 30 different types have been identified. Ranging from well-drained gravelly loams to moisture-retaining silty clays, these soils vary in depth and fertility. The structure and composition of the soil greatly affects the vegetation, including grapes, which it sustains.

In general, the soils found on the level flood plain of the Napa River and valley floor are deeper than the rocky soils covering the slopes and hills. Experience has shown, however, that a highly fertile and deep soil is neither necessary nor always desirable for the growing of premium wine grapes. While yields may suffer as a grapevine's roots struggle to penetrate the thin and rocky soils of hillside vineyards, the resulting stress often results in smaller grapes of highly concentrated color and flavors.

Napa Valley Rocks: The Napa Valley Appellation Education Program

Climate

Defined by mountain ranges and influenced by the proximity to the Pacific Ocean, the Napa Valley enjoys a temperate climate perfectly suited to the growing of fine wine grapes. The long growing season is marked by sunny, warm and dry days followed by cool evenings, an ideal combination for allowing grapes to ripen slowly and evenly. Within the Napa Valley Viticultural Area, the microclimates are distinctive and dramatic. The most moderate temperatures are found in the Carneros region to the through the Golden Gate and across San Pablo Bay. Farther up the valley, the Pacific Ocean exerts less influence: temperatures are warmer in the summer and cooler in the winter, and rainfall is greater than in the south. Configuration of hills, exposure and elevation all work to create distinct microclimates within the Napa Valley appellation.

Napa Valley Rocks: The Napa Valley Appellation Education Program

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