California Coastal National Monument

Abiotic Dimension

Currents, Tides, & Waves

Wind and wave action help determine the physical characteristics of the coastline. North of Point Conception, strong waves and wind have worked on the California Coast Ranges formations to form numerous offshore rocks and islands. The California Current is a cold water current that originates north of California and moves southward along the coast.    South of Point Conception, the coastline is more protected from the impact of storm waves by large offshore islands (i.e., the Channel Islands). The Davidson Current is a periodic, nearshore current that flows in a northerly direction, carrying warm waters from semitropical seas to Southern California. 

Inactions between offshore currents influence temperature, nutrients, and distribution of organisms and their offspring, and create three distinct marine biogeographical regions (or bioregions) along the coast of California. The southern region (known as the Southern California Bight), extending from the Mexican border to Point Conception near the City of Santa Barbara, is composed of warmer waters and primarily supports temperatures and warm water fish and invertebrate species. Point Conception is a transition zone where warmer Southern California waters mix with cold waters from the north. The second region is located offshore of the Central and Northern California coast, extending from Point Conception to Cape Mendocino where another transition zone occurs. A third region, extending from Cape Mendocino beyond the California/Oregon border (sometimes known as the Oregonian Province, contains colder waters and organisms adapted to such conditions (California Resources Agency 1997)

Productive oceanographic factors, such as major ocean currents, stimulate biological productivity and diversity in both nearshore and offshore ocean waters. Another factor is upwelling, the movement of deep ocean waters into shallower, nearshore areas. Upwelling provides essential nutrients needed to support plankton, a vital component of numerous food webs supporting fish, mammals, and bird populations.

Meteorology
Geology & Topography

The physical configuration of the California shoreline is dynamic and constantly changing due to coastal erosion and accretion. The rate of this shoreline change is determined by natural processes, such as rough seas, sea-level rise, high tides, nearshore currents, rainfall and runoff, landslides, and earthquakes, as well as by human developments that can restrict or accelerate the volume of sand available for beaches.

The CCNM comprises a wide variety of geologic and topographic features. The greater part of the monument, from approximately Point Conception in Santa Barbara County north to the Oregon border, is located within the Coast Ranges geomorphic province, which is characterized by sedimentary strata with a terraced, uplifted, and wave-cut coastline. A granitic core extending from the southern extremity of the Coast Ranges to north of the Farallon Islands is found in this region west of the San Andreas Fault. South of Point Conception, the coastline enters the Transverse Range geomorphic province, characterized by an east-west mountain structure that extends offshore. The majority of the coastal rocks in this province are of marine and non-marine sedimentary origin. South of this, the monument enters the Peninsular Range geomorphic province that is dominated by marine and non-marine sedimentary rocks along the coast and granitic rocks inland. Numerous faults are found offshore and nearshore in the vicinity of the CCNM. The San Andreas is the predominant fault system extending through most of California, and enters the Pacific Ocean south of the San Francisco Bay.

Geologic features found in the monument have either of two basic formative histories: (1) Tectonic and volcanic activity—generate uplifts that formed some of the larger islands off of the coast, including the Farallon and Channel Islands. Rocks and islands offshore of these islands, as well as some nearshore CCNM features, share this history. (2) Other nearshore rocks and islands are sedimentary in formation, the result of deposition of geologic material over time. In the case of (2), tectonic activity and faulting may have cleaved or uplifted these sedimentary rocks from the mainland and so tectonic activity plays a role in both formative histories.

Multiple physical factors lead to the formation and dissolution of the rocks and islands within the monument, including the erodibility of the geologic material and the extent of tectonic forces and wave, wind, and tidal action. As such, the rocks and islands off of the California coast are dynamic; certain rocks and islands will eventually be eroded below mean high tide, while other areas currently attached to the shoreline will become separated from the coast. Where wave forces are strong, offshore formations tend to be rocky, whereas in areas with lower wave energy, sandy areas and beaches may form. In general, north of Point Conception, strong waves and wind have caused numerous rocks and cliffs to form. To the south, the buffering effect of the Channel Islands and the Southern California Bight, an indentation and southeasterly shift in the coastline south of Point Conception, reduces the impact of storm waves, and rocks and islands tend to be fewer and more sandy.

From Cape Vizcaíno in Mendocino County south to San Diego, the California coast comprises a discontinuous series of narrow, flat-lying marine terraces. Gradual erosion has created a relatively shallow submerged continental shelf offshore. This shelf varies in width, but is often no more than four or five miles wide, and is often etched by submarine canyons. Many of the rocks and islands found on the continental shelf are remnants of mainland areas that were exposed by tectonic uplift.

A small number of the rocks and islands, mainly concentrated in the northern portion of the coast, have native soils that support vegetation. These soils were likely formed under three conditions: (1) soil formation may have occurred on the rocks in-situ, (2) for rocks and islands that were once a part of the mainland, soil formation may have occurred while the islands were still attached to the mainland, and (3) some combination of the above.

California’s coastal beaches, wetlands and watersheds have been significantly affected by extensive human alteration of the natural flow of sediment to and along the coast. Some watersheds no longer provide a sufficient supply of sediment to beaches; in other areas, wetlands are compromised due to too much sedimentation, and beaches can erode due to lack of sand. The extent to which this alteration of natural processes has affected geomorphology of the CCNM is unknown.

Seismicity

The CCNM is subject to seismic hazards because of its proximity to numerous faults. These faults are known to be historically active and are capable of generating earthquakes with sufficient magnitude to cause strong ground motion in the area of the CCNM. Seismic hazards refer to earthquake fault ground rupture, ground shaking, liquefaction and related hazards, and earthquake-induced slope failure.

Numerous active, potentially active, and pre-Quaternary faults are found offshore and nearshore in the vicinity (i.e., located in an approximately 20-mile radius) of the CCNM. Most of these faults are aligned parallel to the coastline (i.e., trending in a southeast-to-northwest alignment). The San Andreas is the predominant fault system extending through most of California and enters the Pacific Ocean south of San Francisco Bay, rejoining the mainland at Point Arena and again at Shelter Cove. 

From north to south, other active faults include the Trinidad Fault, the Mad River Fault Zone, the Little Salmon Fault, the Mendocino Fault, the Maacama Fault Zone, the Rodgers Creek Fault Zone, the Hayward Fault Zone, the Calaveras Fault, the San Gregorio Fault Zone, the Palo Colorado Fault, the San Simeon Fault, the Los Osos Fault Zone, the Los Alamos Fault, the Santa Ynez Fault, the San Cayento Fault, the San Gabriel Fault Zone, the Red Mountain Fault, the Ventura Fault, the San Fernando Fault, the Verdugo Fault, the Santa Cruz Island Fault, the Malibu Coast Fault, the Hollywood Fault, the Raymond Fault, the Newport Inglewood Fault, the Palo Verdes Fault Zone, the Cabrillo Fault, the Whittier Fault, the Elsinore Fault Zone, the Palo Verdes Hills-Coronado Bank Fault Zone, the Newport Inglewood-Rose Canyon Fault Zone, the San Diego Trough Fault Zone, and the Coronado Bank Fault Zone  ( Jennings 1994 ). All of these faults are within Alquist-Priolo Earthquake Fault Zones ( Hart and Bryant 1997 ). 

Many other potentially active and pre-Quaternary faults are also found offshore and nearshore in the vicinity of the CCNM. 

Finally, north of the Mendocino Fault is found the Cascadia Subduction Zone, which extends north into Canada. In this zone, the eastward-moving Juan de Fuca tectonic plate meets the westward-moving North American plate. Periodic large earthquakes can occur approximately once every 500 years when the Juan de Fuca plate successfully slips beneath the North American plate. In the period between the earthquakes, the Juan de Fuca plate continues to attempt to slide beneath the North American plate, resulting in compression and uplift of the rocks along all the edges of the plates.

Paleontology

Information on the paleontological resources of the California coast is available from the paleontological resources database at the Museum of Paleontology at U.C. Berkeley in Berkeley, California, the largest single repository of paleontological information in the state, and from the publication Assessment of Fossil Management on Federal & Indian Lands  ( U.S. Department of the Interior 2000 ).

Because of the sedimentary nature of many of the CCNM’s features, the monument likely contains paleontological resources. In addition, the CCNM offers excellent opportunities to identify such resources because of the large areas of exposed geologic material found in the rocks and islands of the monument. Nevertheless, the extent of information available on coastal California’s paleontological resources has not been evaluated (BLM is currently conducting a review of literature on coastal paleontology, but this effort has not yet been completed).