The following materials are exerpts from the California Coastal Commission's California Coastal Resource Guide, which can be ordered from University of California Press by calling 1-800-822-6657.
From Cape Vizcaino in Mendocino County south to San Diego, the California coast comprises a discontinuous series of narrow, flat-lying marine terraces, or wave-cut benches, located between the sea cliffs and coastal mountain foothills.
These terraces are characteristic of exposed, windward coast where waves pound against the shore, cutting a vertical cliff face over time. The surging ocean then planes smooth the sea floor at the base of the cliff, forming the flat step of the submerged terrace. The existence of several terrace levels at one coastal site is evidence of the long-term geologic processes affecting the California coast. Between one and two million years ago the oldest and highest terraces were uplifted by the same mountain-building process that created the Coast Ranges. In addition to the incremental rise of the coast, the subsequent advance and retreat of Ice Age glaciers caused sea level to alternately drop and rise, and sequences of terraces were cut by waves and currents in the intervening periods of sea level stability.
The most extensive marine terraces along the California coast are exposed along the sides of the Palos Verdes Hills in Los Angeles County, where a series of thirteen terraces rises to 1,300 feet above sea level. More than twenty stepped terraces are visible along the coast of San Clemente Island. Well-developed terraces along the Mendocino coast near Jug Handle Creek feature five wave cut platforms--the highest, at 600 feet, is 500,000 years old, and the youngest terrace, presently at 100 feet above sea level, emerged 100,000 years age. Other terraces are visible at Fort Bragg in Mendocino County, at Duxbury Reef in Marin County, along the Santa Cruz coast, at Point Buchon in San Luis Obispo County and at Dana Point in Orange County. Submerged terraces to depths of 500 feet lie just offshore of the coast from Santa Barbara to San Diego. Less than 25,000 years old, these terraces are in the process of forming.
Terrace soils are generally thin, commonly composed of rock debris, marine fossils fragments, and shells that were deposited on the once-submerged terrace. These marine sediments are often buried under thick alluvial deposits of sand and gravel from streams and rivers crossing the terraces after they emerged form the sea. Grasses grow on many terraces. In Northern California the terraces are covered by redwood and pine forests. On the Mendocino coast, a unique forest of pygmy cypress and pine trees has adapted to the sandy, nutrient-deficient soils on the upper marine terraces.
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