Soil

Napa Valley soils are generally are very deep and have high potential productivity. 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 soils 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. Southwest soils are moderately deep over sandstone and shale or are shallow to a claypan. They are used for range, pasture, and vineyards.

Howell Mountain soils 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 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.