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Channel Islands of California

  • Vicinity: Off the coast of Southern California, Pacific Ocean
  • Type: Archipelago
  • Travel Genus: Sight
  • Sight Category: Terrestrial Feature

Most of the mountain ranges of California trend north-south, but the Transverse Ranges, including the Santa Monica Mountains and their extension into the ocean, the northern Channel Islands, trend east-west. Geologists believe that, 20 million years ago, the platform on which the islands are located was oriented north-south along the coast, with San Miguel lying just offshore of San Diego. Forces resulting from relative movements of the Pacific and North American plates have caused the western Transverse Ranges to rotate clockwise to their present position. It is as if one sliver of the continent - the Transverse Ranges - got caught up in the shear between the plates. It rotated 'much like a floating plank that has one end snagged on the river bank, while the other end is dragged along by the current'. Evidence for this rotation is found, in part, by magnetism in the rocks of the islands. When the rocks of the northern Channel islands were formed, magnetic particles in the rocks would have been in line with the magnetic poles of the Earth. Measurements now taken in the rocks of the northern Channel Islands show that the magnetic particles differing by about 100 degrees from a polar orientation, with the oldest rocks showing the greatest variance. This suggests that the islands have rotated clockwise about 100 degrees since the formation of the rocks. - NPS



Channel Islands National Park

Geography »

Physiographic feature Archipelago

Data »

Particulars for Channel Islands of California:
Historic Use Natural Feature
Sight Category Terrestrial Feature

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