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Most people, when they think about the geology of California, focus first on earthquakes. Indeed, as the mountains and valleys of California have been shaped, earthquakes have been the pounding of the carpenter’s hammer, a resounding echo from Earth-forming processes. Thus, even though most of us are horrified by the prospect of another devastating earthquake, the great beauty and abundant resources in California are a direct consequence of the very events that trigger these periodic Earth-shaking temblors.

Geology plays an important role in controlling the quality and nuances of California’s wine. It affects the soils—their chemistry and texture, the topography—mountain slopes versus valley floors, and the climate—humidity, sun angle, and temperature. The three S’s—soil, slope, and sun, helps us understand the principle factors that control wine quality. How the vintner manipulates these controls determines the specific attributes of each bottle of wine.

Understanding the geology of different California regions, and how it relates to wine growing, can be broken down into three basic categories: how the bedrock formed, evolution of the landscape, and relating these two factors to soil development and microclimatic conditions (Fig. 1).

Starting points in descriptions of Earth history are generally arbitrary owing to the age of the planet. This history is read from rocks; in North America we have identified rocks that are nearly 4000 m.y. old. Fortunately for you, and those of us who are trying to reconstruct the geologic history of California, it is not necessary to reach that far back in

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