The precipitous cliffs, steep-walled bluffs, and rocky headlands that characterize much of California's coastline are evidence of the ongoing geologic processes that shaped the western margin of the North American continent. Unlike the Atlantic and Gulf coasts of North America, whose gently sloping seashores are the result of gradual submergence of the continent's edges, the sheer walls and elevated terraces of the California coast were created by abrupt faulting and uplift. Bluffs and sea cliffs are a testament to the erosive power of waves, winter rainstorms, and wind, while headlands remain where coastal rock has withstood weathering by these elements.
Coastal bluffs are actually the seaward edges of marine terraces, shaped by ocean waves and currents, and uplifted from the ocean floor. Characteristic of the California coast from Mendocino County to San Diego, coastal bluffs are less evident along the Northern California coast where the coastal mountains plunge abruptly into the ocean. Rocky headlands are more prevalent along the Northern and Central California coast but may occur anywhere erosion-resistant rocks are found along the shore.
Coastal bluffs are composed mainly of sedimentary rocks such as sandstones and shales that are particularly prone to erosion. Grains of quartz, feldspar, and mica compressed into layers of sandstone crumble easily; when wet, shales and siltstones disintegrate, and clays and mudstones, soften and liquefy. Lying on top of the sedimentary deposits of many bluffs is alluvial soil, loosely consolidated sand and gravel deposited by ancient rivers and streams. Examples of sedimentary coastal bluffs are the sandstone bluffs of Santa Cruz, the alluvial cliffs at La Jolla, and the shale cliffs of Point Loma in San Diego County.
Rocky headlands are composed of igneous rocks--granites and basalts--that are resistant to wave erosion. Granitic formations include the Point Reyes Headlands in Marin County. Morro Rock in San Luis Obispo County, Point Dume in Los Angeles County, and Point Sur in Monterey County are outcroppings of basaltic lava.
Sea caves, sea stacks, and arches, are created by erosion of less resistant components of coastal landforms. Sea caves are formed by wave erosion where fractures occur in the bluff face. Sea stacks and arches, numerous along the wave-battered Mendocino coast, mark the last stand of more resistant rocks. Erosion of the sandstone cliffs at Natural Bridges State Beach in Santa Cruz created a number of arches; today only one remains, and eventually it too will collapse into the surf.
Landslides and cliff retreat are part of the natural process of coastal erosion along the California shore. Waves that undercut bluffs often initiate landslides. Burin winter storms heavy surf drags sand off-shore, denuding many beaches and exposing the cliff base to direct wave attack. Most cliff retreat occurs at this time; powerful breakers crash into the cliffs, splintering the softer rocks into fragments that fall into the retreating surf. Incessant winter rains beating down on coastal bluffs slowly penetrate rock fractures, lubricating the joints between the rock layers. Fractured shales, sandstones, and siltstones are most likely to slip and cause landslides, especially at locations where the land slants toward the beach. A coastal landslide of mud and rock can scrape a clean path, sweeping away roads and structures as it plunges seaward. Areas well known for landlsides are Devil's Slide in San Mateo County and Pacific Palisades in Los Angeles County.
Development of coastal sites has increased the rate of coastal erosion by the introduction of drain pipes and septic tanks that saturate soils with runoff; the irrigation of lawns and gardens can cause even the most stable sedimentary bluffs to collapse and slide into the sea.
Tough California's coastal cliffs are inhospitable environments for much plant and animal life--windy and dry, with shallow, salty soils--a specialized community of plants and animals has adapted to them. Ledges, gullies, slopes, and cracks provide spaces where soil can collect and seeds germinate. Sea figs, ice plants, and coyote brush grow on steep bluffs. Wildflowers such as poppies, irises, and lupines bloom in colorful profusion on the bluffs in spring; introduced annual grasses and native fescues produce a carpet of bright green after winter rains, turning honey-colored in the dry season. Buffered from the driving wind on protected ledges, seabirds such as the common murres rest and build nests.
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