This subsection is on parts of the plain north and west of San Pablo Bay that are less than 10 feet above mean sea level.  The climate is temperate and subhumid. MLRA 14d.

Subsection 263Ac, Northwest of Vallejo (Charles B. Goudey)

Lithology and Stratigraphy

This subsection contains Quaternary bay-fill, largely silt and clay.

Geomorphology

This subsection is on a tidal flat.  The entire subsection is less than 10 feet above mean sea-level.  The main geomorphic processes are coastal marine, and, on the inner edges of the subsection, fluvial.

Soils

The soils are mostly Sulfic Fluvaquents and Endoaquepts, Typic Hydraquents, and Haplaquepts.  The soil temperature regimes are isomesic.  Soil moisture regimes are aquic.

Vegetation

The predominant natural plant community is Pickleweed series.  Saltgrass series is prevalent around the inland margin of the salt marsh.  Sedge meadow communities and Emergent aquatic communities are prevalent on the inner edges of the subsection, away from the bay.

Characteristic series by lifeform include:

• Grasslands: California annual grassland series, Introduced perennial grassland series.
• Saltmarsh vegetation: Cordgrass series, Ditch-grass series, Pickleweed series, Saltgrass series.
• Freshwater marshes: Bulrush series, Bulrush - cattail series, Cattail series, Duckweed series, Mosquito fern series, Sedge series.

Climate

The mean annual precipitation is about 20 to 30 inches.  There is some summer fog.  Mean annual temperature is about 56° to 58°F.  The mean freeze-free period is about 250 to 275 days.

Surface Water

High tides inundate most of the area.  During winter, fresh water flows onto the flats.  Deltas of the Napa River and Sonoma, Petaluma, and Novato Creeks are in this subsection.

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