Subsection 263Ai
Point Arena

Lithology and Stratigraphy.   This subsection contains Eocene marine and nonmarine deposits and some Quaternary marine terrace deposits and Franciscan marine sedimentary rocks of the Coastal Belt.

Geomorphology.  This subsection is on an elevated coastal plain with thin Quaternary terrace deposits over Eocene sedimentary rocks that have been eroded to exposed Cretaceous sedimentary rocks.  The surface is gently sloping to moderately steep, with some steep-sided ravines crossing the plain.  The elevation range is from sea-level up to about 1400 feet.  Ocean currents, waves, and wind are active along the outer edges of the coastal plain.  Fluvial erosion is the main geomorphic processes on the coastal plain, although eolian erosion and deposition has been active in the past.  Mass wasting is another process that is active on steep ravine slopes.

Soils.  The soils on terraces are mostly Typic and Plinthic Tropohumults and Dystropepts.  Those on Cretaceous sedimentary rocks are mostly Ultic Hapudalfs.  There are very small areas of Albaqults.  The soil temperature regimes are isomesic.  Soil moisture regimes are mostly udic with some aquic.

Vegetation.   The predominant natural plant community is Redwood series.   There are minor occurrences of Bishop pine series and Pygmy cypress series.   Dune lupine - goldenbush series is common on coastal bluffs.

Characteristic series by lifeform include:
Dune vegetation: Native dunegrass series, European beachgrass series, Sand-verbena - beach bursage series.
Grasslands: Introduced perennial grassland series, Pacific reedgrass series.
Shrublands: Dune lupine - goldenbush series.
Forests and woodlands: Grand fir series, Pygmy cypress series, Red alder series.

Surface Water.  Water runs off of the coastal plain moderately slowly to moderately rapidly, with the exception of a few terraces that drain very slowly.