Napa Valley is a truly amazing place.  Aside from the natural beauty, tranquility and abundance here, there exists a geological environment which is truly unique: Thirty -three different types of soil series, a variety of microclimates, steep mountains and sloping foothills on the Eastern and Western flanks, and a network of pocket valleys that meander eastward off the valley floor creates an environment found nowhere else in the United States.  It is said that the Napa Valley is Eden to the wine grape. However, 150 million years ago most of what we now know as the Napa Valley, or California for that matter, did not exist. Over time, a series of geologic events, described as a continual dance of crustal plates, caused the shifting, sliding and lifting of land masses that plastered material on to the edge of north America and formed it into its present, temporary and ever changing configuration. This seemingly eternal process has created this garden of eden for the wine grape and has positioned the Napa Valley as the premiere grape-growing region in the United States.

It didn't happen overnight, though. 145 million years ago cataclysmic events occurred which began to shape the current California geology and landscape. The Pacific plate dove beneath the North American plate, melting rocks into magma that rose to the surface forming a chain of volcanoes. Over thousands of years erosion eventually deposited sediments forming what is now Napa Valley. It is this bedrock material that is a major contributor to the unique soils that comprise the Napa Valley and helps to define the quality of grapes grown here. As the land masses danced with one another, shifting and sliding, material from the ocean plate was slathered onto the edge of North America, this material is now known as the Franciscan Formation, a complex and diverse rock unit that underlies much of coastal California and which is one of the major bedrock components of the Napa Valley AVA.
Closer to the present day, but still in a time that seems unimaginable in today's amnesiac culture, another huge geologic process contributed to the creation of the Napa Valley. About 24 million years ago, the Farallon, Pacific and North American plates met at a triple junction in Southern California.  Pushing northward, they created the San Andreas fault. As this triple junction slowly moved north, it drug the San Andreas faultline along with it.  The tremendous compression of this created wrinkles in the earth's crust that created what is now the coastal ranges and here in Napa, the Mayacamas Mountains. 

 

 

California is a dynamic place. It is unique in the regard that it, like the Napa Valley has a stunning array of biodiversity; mountains, beaches, deserts, and one of the few places on Earth that one might find Redwood Forests. However, in regard to wine making, it is the bedrock that was produced as a result of the geologic processes mentioned that are one of the major factors leading to the success of the California Wine Industry. Bedrock is the main source of the chemical and mineral elements of soils in which grapes grow.  It provides the necessary structure, and chemical make-up that invariably will provide all the right factors for world-class wines. The Great Valley sequence is a huge trough piled high with sandstone, conglomerate and shale deposited over a period of 140 million to 60 million years ago. These sandstones and shales, derived from volcanic rocks, contain quartz and feldspar and are rich in potassium and sodium.  Exposures of the great valley sequence can be seen mainly on the west side of the valley roughly between Oakville and Carneros, as well as at Stags leap,and near Calistoga. 

 

Another geologic feature of the Napa Valley is the Franciscan Formation.  It is unique in the regard that it has geologists puzzled as to its origins, and to date are unable to find an environment on or in Earth that shares the same characteristics of high pressure, low temperature environments. It is believed to be comprised of materials derived from oceanic environments of the Pacific and Farallon crustal plates. It is important for viticultarists to understand that it is rich in calcium and sodium feldspar which is generally indicative of low amounts of available water and nutrients, especially nitrogen and potassium, which leads to slower ripening and potentially lower yields (1 to 2 tons per acre) there are sequences of the Franciscan that run along the middle Mayacamas from the Southern boundary of the Oakville fan, north to St. Helena and West over the mountains into Sonoma County. While their hasn't been a lot of attention paid to the mysterious origins of the Franciscan formation, I often wonder how in the heck the material got here and, what exactly it is?  Galactic material of an unknown origin? meteor shards? Perhaps its better just to accept the fact that it produces world class wines and be content with that.