Under California: An ancient tectonic plate

(Phys.org) —The Isabella anomaly—indications of a large mass of cool, dehydrated material about 100 kilometers beneath central California—is in fact a surviving slab of the Farallon oceanic plate. Most of the Farallon plate was driven deep into the Earth's mantle as the Pacific and North American plates began converging about 100 million years ago, eventually coming together to form the San Andreas fault.

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