Subsection 263Ac
San Pablo Bay Flats

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.

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.