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GRAPEGROWING (Cabernet Franc) and 803CS (Cabernet Sauvignon), which lie within the rhyolite flow unit and (to a lesser extent) the dacite unit. The dacite relationship is easy to accept, as it is the best vineyard plot unit at Shifflett and third best at Darms Lane; however, the rhyolite flow for second best was more difficult for me to fathom. There���s nothing like facts to mess up the story. Rhyolite lies on the other end of the chemical spectrum from basalt, the previously discussed star performer. The basaltbasaltic andesite contains an average calcium content of 9.87% CaO and iron content of 9.49% Fe2O3, while rhyolite flow contains an average calcium content of 0.53% CaO, an iron content of 2.60% Fe2O3, and it is also very low in magnesium. This rhyolite flow unit, with its lower calcium, iron and magnesium (but higher potassium) content, does not occur at Darms Lane or Shifflett, so the evidence is all at Trefethen. It stands as proof that the story is not all about rock chemistry and mineralogy. There are other important characteristics of rock that include fabric (or lack of fabric), fracturing, grain integrity, hydrothermal and weathering alteration���and even geophysical characteristics such as conductivity and magnetism, all of which can interact with the biosphere in ways that we are only (hopefully) beginning to understand. With all these variables, it is little wonder we lack a full understanding of why a grapevine of certain genetic makeup does better when growing upon a certain rock unit. Trefethen���s third best vineyard plot, a portion of 801CS, lies largely on alluvial fan, just as at Shifflett. Alluvial fans along the west side of Napa Valley are clearly good places to grow Cabernet Sauvignon���something Napa growers should note. The adjacent, southeastern-most part of the alluvial fan, a plot designated 897CS, is where the majority of grapes for the award-winning Trefethen 2005 Reserve Cabernet Sauvignon were sourced. Just to mess up the picture a little, however, Ruel says that since that spectacular vintage, the plot has not performed as well. Many diverse factors including geology must have converged in 2005 to create an excellent wine, and what happened once may happen again. A non-geological factor that is apparent at all three vineyards (Trefethen, Darms Lane and Shifflett) is that south-facing slopes do better for Cabernet Sauvignon than those facing in other directions, and here I must bow to microclimate as being nearly equal to geology as a factor. The proof of this is at Trefethen where, within the basalt-basaltic andesite, the largely southeast-facing slope behind the Trefethens��� house is a prime performer while in the same rock unit further south, on a northwest-facing slope, the vineyard does not perform as well. Conclusion Rock outcrop/sub-crop geology, not just soil, is of major importance in the determination of wine quality on the hillside vineyards of Napa. If mapped in detail, the geology can be used as a predictive tool in vineyard management. California professional geologist Dr. William Fuchs (PG 7695) obtained a master���s degree in geochemistry from Penn State University and a Ph.D. in structural geology from the University of Utah. A consulting geologist with an emphasis on mapping and prospect evaluation for the mining industry, Fuchs has mapped more than 200 square miles in his career and worked in the Napa, Calif., area for wine cave builder Magorian Mine Services. QUALITY STAINLESS TANKS QST offers its clients������. Professionally fabricated stainless tanks 35 years of tank fabrication experience Performance & reliability guarantees Custom designs & modern features Quick & competitive tank project pricing On site tank repairs & modifications Special application tanks of all sizes ���In stock tanks��� from 500 to 10,000 gallons 510 Caletti Ave. Windsor, Ca. 95492 Phone 707-837-2721 or Toll-Free 877-598-0672 www.qualitystainless.com Company Website winetanks@aol.com email contact/sales info Custom Fabricated Tanks for the perfect size & fit��� or Ready to Ship ���Stock Tanks��� Either way QST is ready to assist our clients! Call QST today for information or pricing! 94 W in e s & V i ne s JANUARY 20 13 SEE US AT UNIFIED, BOOTH #816