Subsection 263Aa
Crescent City Plain

Lithology and Stratigraphy.  This subsection contains predominantly Quaternary nonmarine and marine sand and clay coastal plain deposits of the Battery formation.  Also, there are substantial areas of beach and dune deposits along the ocean shoreline and recent alluvium and Quaternary fluvial terraces along the Smith River.

Geomorphology.  This subsection is on a nearly level coastal plain adjacent to the ocean.  Beaches line the outer edge of the plain and dunes of sand spread inland from the beaches.  Water is ponded on the plain behind the dunes and a large lake occupies much of the plain.  The entire plain is less than 200 feet above mean sea-level.  Ocean currents, waves, and wind (coastal marine and eolian processes) are active in forming the beaches and dunes.  Fluvial and erosion is the main geomorphic processes on the plain behind the beaches and on terraces along the Smith River.

Soils.  The soils are mostly Typic Tropohumults and Typic Humitropepts.  Udifluvents and Fluvaquents are common soils on recent alluvium.  Tropopsamments occur on dunes. The soil temperature regimes are isomesic.  Soil moisture regimes are mostly udic, and some aquic.

Vegetation.   The predominant natural plant communities on the plain are Sitka spruce series on the outer edge and Redwood series inland.  Red alder series is common in riparian areas.  The dunes support a succession of plant communities, from bare dune through Native dunegrass series, Sand - verbena - beach bursage series, and Beach pine series to Sitka spruce series.  Pickleweed series predominates in saltmarsh.

Characteristic series by lifeform include:
Dune vegetation: Native dunegrass series, European beachgrass series, Sand - verbena - beach bursage series.
Saltmarsh vegetation: Pickleweed series, Saltgrass series.
Grasslands: Introduced perennial grassland series.
Shrublands: Coyote brush series, Salal - California huckleberry series.
Forests and woodlands: Beach pine series, Red alder series, Redwood series, Sitka spruce series.

Surface Water.  Water is ponded on the coastal plain to form lakes, with the largest being Lake Earl.  The Smith River, a large distributary from the Klamath Mountains, has an outlet on the Plain.  Tidal water enters the mouth of the Smith River and may spill over into some of the lakes.