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Soils, Geology and Faults of Napa County
The Physiography, relief, and drainage of Napa County
Napa County is part of the hilly to steep mountains of the California Coast Range. The county is characterized by a number of northwesterly parallel mountain ridges and intervening valleys of varying widths.
The soils in Napa Valley generally are very deep and have high potential productivity. They are used for vineyards, orchards, and pastures. The soils in the southern part of the valley have lower production potential because they are limited by a strongly developed subsoil. They are used mainly for dryland pasture and for oats and hay.
Maacama Mountain rises abruptly on the west side of Napa Valley. The soils in this area are moderately deep to very shallow over sandstone and shale, and they are used mainly for range, wildlife habitat, and watersheds. A few areas of moderately sloping soils are used for vineyards.
The mountain ridges on the west side of the valley extend as far south as Napa, where the landscape consists of rolling hills and dissected terraces. The soils in this area are moderately deep over sandstone and shale or are shallow to a claypan. They are used for range, pasture, and vineyards.
Howell Mountain borders Napa Valley on the east and rises abruptly from the valley floor. The soils in this area are moderately deep to shallow over rhyolitic tuff and basic igneous rock. They are used for timber, range, wildlife habitat, and watersheds. Where this ridge broadens to a plateau near Angwin, some areas of soils are used for vineyards and orchards.
The plateau drops off to the northeast into Pope Valley, and Vaca Mountain rises abruptly to the east. The soils in the northern and eastern part of the county are moderately deep to shallow over sandstone, shale, and serpentine. They are used for range, wildlife habitat, and watersheds.
The Napa River and its tributaries drain the western part of the county. The Napa River flows southward from north of Calistoga into San Pablo Bay. The northeastern part of the county drains into Lake Berryessa by way of Putah Creek and its tributaries. These tributaries drain Snell, Pope, and Cappel Valleys and part of Chiles Valley.
