Napa Valley has an amazing assortment of mi-
croclimates, soils, weather, and topography,
which allow a wide array of fine wine grapes
to grow extraordinarily well here, from Al-
bariño to Zinfandel. Between 2001 and 2003,
the NVV commissioned three major studies
to verify that the Napa Valley’s unique attri-
butes all work together to nurture the wine
grapes. The scientists and geologists who
conducted the studies were Jonathan Swin-
chatt of EarthVision, Paul W. Skinner, Ph.D. of
Terra Spase, and David G. Howell of the USGS.
What we now know is that about 150 million
years ago, a series of geologic events caused
the shifting, sliding, and lifting of land masses
in the area that we know of today as Califor-
nia. That plastered material onto the edge of
North America and formed it into its present,
yet ever-changing configuration. This is the
process that created the Napa Valley. Over
time the mountains eroded and reformed,
helping to create California.
Geologists call this the Great Valley Sequence,
the remains of which are generally found on
the east side of the Napa Valley along the
Vaca Range. As volcanoes were forming in-
land, the surface of the ocean floor was being
sheered-off as it met the coastline, literally
plastering all sorts of marine sediment on top
of the newly forming landmass, extending
California westward. Geologists call this the
Franciscan Formation, the remains of which
are generally found on the west side of pres-
ent-day Napa Valley.
About 24 million years ago the San Andreas
Fault system took shape with tremendous
compression forces that created the Coast
Range and Mayacamas Mountains. San Pablo
Bay – the northern arm of the San Francisco
Bay – engulfed the lower valley as far inland
as current day Yountville, only to retreat and
then engulf the lower valley floor again.
Napa Valley has some of the greatest soil
diversity found in any winegrowing region
in the world. Soils act as building blocks in
determining the quality of premium wine
grapes. Napa Valley contains more than 100
soil variations, 33 soil series, and half the soil
orders found in the world.
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