Term Paper: Geology of California

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Geology-Wines

Particularly over the past quarter century, California wines have grown in prestige to become among the world's most celebrated, even challenging more historically established wines from the Bordeaux region of France (Marcus). California's Napa Valley region is considered a bit of a geographic wonder in the wine-making industry for its ability to produce a wide variety of high-quality red wines in a fairly limited space - just 40,000 acres of cultivated, planted land (Livingston). The wines from this California region, about 50 miles north of San Francisco (See Map 1), owe their quality and diversity to some unique geological features of the area. Throughout its rich geological history, Napa Valley has been affected by a wide variety of natural occurrences ranging from volcanic eruptions to plate tectonics. Over the course of millions of years, these occurrences formed a geological foundation that is extremely conducive to the growing of a diverse set of quality wine grapes. According to vintner and geologist Robert Livingston, soil, bedrock, topography and climate and are four critical, inter-related factors that help foster the development of quality wines (Livingston). These factors all have benefited from Napa Valley's unique geological features, resulting in some of the best grape-growing conditions in the world.

Geology and soil

Every wine grower knows that soil conditions are critical to routinely producing hearty grapes. The geological history of Napa Valley has contributed to making its soil ideal for growing a variety of grapes commonly used in the production of red wines. According to Livingston (1998), there are at least 60 different soil types in Napa Valley, which means more types of wine can be produced there than in any other area of comparable size in the world. This variety of soils is the result of the unique geological conditions that are inherent to California's global positioning. It is well-known that California represents the meeting place of the North American and Pacific global plates, which results in friction that causes California's frequent earthquakes (See Map 2). That friction, over the course of millions of years, also once caused a great deal of volcanic activity in California and the Napa Valley, in general. As a result, the soil in Napa Valley frequently contains large deposits of igneous rock and volcanic ash, which helps support the healthy growing of crops in many regions of the world (Napa Valley Vintners).

Of course, volcanic ash is just one common component of Napa Valley soils. Because of plate tectonics -- the constant moving of plates -- Napa Valley soil contains rocks and minerals that are not necessarily indigenous to the region, but were deposited there by the Pacific plate (Livingston). As the Pacific and North American plates scraped together, parts of the Pacific plate rose and formed mountains that contained nutrient-rich oceanic crust, elements of which are found in Napa Valley soil. The Napa River, which flows to the bottom of the valley, also plays a critical role in depositing clays, which hold and allow for the easy transport of water, into the soils at the valley's low points.

In essence, if one was to take a sample of Napa Valley soil, one would find fine clays and sands at the valley's lowest levels, and larger rocks deposited by swift stream currents at slightly higher altitudes (Livingston). Volcanic ash is commonly found in the next highest levels, while the peaks of the hills and mountains in western Napa Valley often feature soils with high levels of iron and magnesium, which are common in rocks found in oceanic crust (Livingston). As one might expect, these different soils support a wide variety of grapes used in several kinds of wine (typically reds). For example, the low-lands, with their rich clay deposits, are perfect for growing large, robust grapes, while the soil in highlands, with features significant levels of oceanic crust and volcanic ash, typically supports smaller grapes with more robust flavors, strong mineral content and good levels of acidity (Napa Valley Vintners and "Napa Valley: An ideal"). But the fact that such a range of grapes can be produced in such a limited space is a testament to Napa Valley's unique geological features and the soils that resulted.

Bedrock

Naturally, the effects of plate tectonics, volcanic eruptions and waterways, such as the Napa River, have contributed to a bedrock composition in Napa Valley that is not uniform. According to Napa Valley Vintners, a trade association representing the region's wine growers, the bedrock in Napa Valley ranges from coarse sandstones to marine conglomerates to volcanic basalts and tuff (Napa Valley Vintners). These various rock deposits tend to be located on top of a layer of limestone, although, in some cases, the limestone foundation is all that various regions of the valley have in common with each other geologically.

The formative geological events for the Napa Valley bedrock started approximately 24 million years ago, when the friction between the Pacific and North American plates resulted in the formation of the Mayacamas Mountains ("Napa Valley: An ideal,"). More recently, about five million years ago, heavy eruptions from Napa Valley volcanoes deposited igneous rocks and volcanic ash across large sections of the valley ("Napa Valley: An ideal"). In the end, these events resulted in the formation of three rock bodies that collectively make up the bedrock of Napa Valley - the upper Mesozoic Franciscan Complex, the Great Valley Sequence and the Pliocene Sonoma Volcanics (Howell). The Mesozoic Franciscan Complex and the Great Valley Sequence, both close to the coast, feature large quantities of marine sandstone and shale, reflecting the previously discussed rising of the oceanic crust, and also may contain serpentinite and greenstone (Howell). The Pliocene Sonoma Volcanics, in the eastern part of Napa Valley, are defined by igneous rocks such as basalt and rhyolite (Howell). Alluvial fans comprised of sediment from bedrock layers also are found throughout the valley (Howell).

Geologically, Napa Valley also played an important role in the development of the California gold and precious metal rushes of the 19th century. Mercuric sulfide, also known as quicksilver, exists in abundant supply in Napa Valley, and this material is commonly used in the mining of silver and gold (Smith). For a brief time in the latter half of the 20th century, there was even a working gold mine in Napa Valley, near Knoxville (Smith). The rich diversity of Napa Valley bedrock and surface stones has facilitated the growing of different types of quality wines. On the Great Valley bedrock in Wooden, for example, vintners are able to grow more intense grapes used in blending for famous winemakers, such as Caymus and Mondavi (Smith). The craggy shale and sandstone help create soil conditions that a smaller, more strong-flavored grape. In particular, cabernet sauvignon and sangiovese grapes thrive in this environment (Smith).

A ography

The topography of Napa Valley is unique and helps foster a variety of different climactic and soil conditions that are conducive to grape growing. Napa Valley is bordered by mountain ranges that each have their own distinctive characteristics. The Mayacamas Mountains border the valley to the west, the result of previously discussed plate friction. These mountains divide the Napa and Sonoma valleys and many peaks fall between 2,000 and 3,000 feet, with the highest point being Cobb Mountain at more than 4,700 feet. The Mayacamas are high enough to maintain cooler temperatures year-round, and many peaks will feature snow during winter months. The Mayacamas Mountains often contain soils with volcanic ash from ancient volcanoes (Napa Vintners Association). To the northeast, in Calistoga, is Mt. St. Helena, which is the highest point in the San Francisco Bay Area watershed. Mt. St. Helena rises to a peak of more than 4,300 feet, allowing it to tower over many of the Mayacamas peaks. It was formed by the rising of volcanic material from the Clear Lake volcanic field, which still features a variety of geysers and geothermal springs (Napa Vintners Association). In fact, this volcanic material also created a series of small hills in other parts of the valley (Napa Vintners Association). The Napa River also originates near Mt. St. Helena and runs down the mountain's southern slope, carrying igneous material and a variety of river sediments, such as clay, to the valley below. Mt. St. Helena can be cold during the winter, often showing snow in its upper sections.

On the east side of the Napa Valley are the Vaca Mountains, which are geologically distinct from the Mayacamas and Mt. St. Helena. Because the Mayacamas block the cool, moist air blowing in from the Pacific, the Vaca Mountains tend to be dryer and hotter (Larson). Where plants that require significant levels of water, such as conifers, thrive in the Mayacamas, the Vaca Mountains are characterized by low-moisture oaks and grasses (Larson). At their highest point, the Vaca Mountains rise to more than 2,800 feet above sea level, although many of the range's peaks are at significantly lower altitudes. According to the Web site for Rudd Winery, located in the foothills of the… [END OF PREVIEW]

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