Geologic Periods

The following is from Santa Barbara Day Hikes by Ray Ford

Continental drift begins about 250 million years ago. 135 million years ago: North American Plate begins to override the Pacific Plate. Subduction of Pacific Plate causes rise of the Sierras. Along coast and to the base of Sierras, land subsides to create a large basin. Sea moves inland to the base of the Sierras.


Paleocene 60 million
Santa Barbara is under a deep sea. Climate beyond the Sierras to the interior becomes warmer. Sediments deposited on the ocean floor as mountains are weathered get subducted under the North American Plate. These do not appear in the strata of the Santa Ynez Range.

Eocene 50 million
Subduction slows. Pacific Plate is now being pushed north as well as being subducted. Sediments deposited on the ocean floor at this time become the basic geological units of the Santa Ynez Mountains: Juncal, Matilija, Cozy Dell Shale, and Coldwater Sandstone formations. Climate has become subtropical. Large mammals evolve in the lush jungle vegetation. Marine life begins to evolve.

Oligocene 35 million
Pacific Plate has almost passed north of Santa Barbara. The Eocene and early Oligocene sediments begin to fill the large basin. The sea becomes shallow. Santa Barbara area rises above sea level for the first time. The purplish-red Sespe Formation is the first non-marine sediment to be laid down. Climate becomes cooler and drier. Subtropical vegetation is replaced by savanna and oak woodland environments. Large mammals such as the wooly mammoth become extinct. Several grazing animals and their predators evolve.

Miocene 30 million
Subduction ends when the Pacific Plate moves north of Santa Barbara and to its present position off the Washington coast. American and Pacific Plates come into direct contact along the San Andreas Fault. Northward moving Pacific Plate causes a shearing stress. Land mass moves north and into contact with the Sierra range, creating a lateral compression giving rise to the Santa Ynez Range. Climate is cooler and drier and sea life more abundant than at any other time.

Pliocene 13 million
Santa Barbara is above sea level for good and present topography develops. Santa Ynez crest is forced upward by the lateral compression, causing depression of the Santa Ynez Valley. Climate is warm and dry. Chaparral plant communities spread from the Southwest across Southern California. Many mammals reach their evolutionary peak of development.


Pleistocene 3 million
Santa Ynez Mountains are uplifted from 1,000 to 2,000 feet higher than at present and interior valleys subside further. Onset of a series of Ice Ages. Ocean level drops 350 feet, coastline retreats, and Channel Islands become one long island. Climate becomes cold and moist and forest plant and animal communities flourish. Crest of mountains slowly erode to present relief.

Recent 11,000 Years
Warming trend develops across continent and ice sheets melt. Sea level rises quickly. Canyons fill with creek sediments and valleys are covered with layers of alluvia. Evergreen plant communities retreat to canyons and mountain crests. Chaparral becomes the predominant plant community. Man migrates to the Santa Barbara area about 10,000 years ago and has become semi-sedentary by about 8,000 years ago.


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Thursday, July 23, 2015