Geology of Pinnacles National Park Area - Modesto JC

San Luis Reservoir

The first stop of the day was at San Luis Reservoir (what was left of it) to observe exposures of the sedimentary Great Valley Sequence.

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The second stop of the day was in the City of Hollister to look at the creeping Calaveras Fault that is causing the city streets and houses to offest several cm per year.

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DeRose Winery

De Rose Winery was the third stop of the day. The San Andreas runs throught hte middle of the property causing some interesting offsets on the property.

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The last stop of the day was at the newest National Park in the US (as of this posting). The rhyolite tuff that makes the pinnacles actually fromed when a huge stratovolcano erupted about 22 million years ago near Lancaster, CA. It just happend to erupt on over the San Andreas Fault which has caused the rocks in Pinnacles to shift NW over 190 miles since its eruptions ended.

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