Oak Knoll Soil, Terrain & Geology
The Diversity of Oak Knoll Terrain and Soil
In general, Oak Knoll soils are made of sand, gravel, and clay over a rock base layer. Most are porous and drain well. This forces vineyard roots to extend deep into the ground in search of water. While this stresses the vine, it also leads to long term health.
Geologic uplifts and volcanic activity that formed the surrounding hills has impacted the Oak Knoll’s geology. Over the years, soil and debris have eroded from these adjacent hills, forming alluvial fans in the region.
There are several major alluvial fans throughout the Napa Valley caused by this phenomenon. The Dry Creek Alluvial Fan dominates the soil composition of Oak Knoll. Northeastern Oak Knoll has an infusion of volcanic soils that have eroded from Stags Leap.
The San Pablo Bay once extended over part of the region. It left fossilized sea life in the soils as evidence. Sand, gravel and clay also remained as the bay receded. Oak Knoll was affected to a lesser extent than Carneros by this process.
Soil in the northern part of the AVA near the hills retains heat quite well and is capable of ripening full bodied red varietals. Budbreak occurs earlier on these warmer soils. The result is a longer growing season and more time for grapes to develop.
There is also a substantial amount of clay dominated soil that is usually closer to the river. These vineyard sites are naturally more productive and often need to be pruned. Nonetheless, an astute vineyard manager can grow very high quality grapes on these sites. Red wines typically are a little less tannic when made from grapes grown in this denser soil.
Soil on the valley floor has been shaped over the millennia by deposits from the meandering Napa River. Pinot Noir, Chardonnay, and other cool weather varietals are normally planted in this clay influenced soil. Crop yield is closely monitored to maximize the amount of energy going into each grape.
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