The coastal plains consist of marine and freshwater sediments forming flat mesas or terraces which are cut by west-flowing streams. The resultant canyons exhibit slopes with varying exposures to the sun, and a central channel often occupied by a woodland community.

Mesas and Exposed Slopes The mesas and canyon slopes are usually formed from marine and freshwater sandstones and shales. The soils may be loose and sandy, or cemented and hardened by precipitates of calcium carbonate called caliche. Layers of clay may be distributed randomly throughout these formations. Exposure to direct sunlight is the major climatic feature that determines soil moisture, atmospheric humidity, ground and air temperatures, and vegetation types. The vegetation is often called coastal sage scrub or "soft chaparral." The plants are generally herbaceous or semi-woody, aromatic, narrow leaved and summer deciduous.

Protected slopes are those shielded from direct sunlight exposure. Accordingly, the soil and air temperatures are cooler, the humidity is higher, and the vegetation assumes a shrub-like growth form. The plants are woody and have a deeply penetrating root system. The broad, leathery leaves which are dropped throughout the year form a thick litter and decompose to help form a rich organic layer in the soil

*Extracted Natural History of Southern California: Ancinec, Radford, Schwenkmeyer