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Hawk Hill |
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Looking east from Point Bonita
across the Marin Headlands. |
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Geologic Trips, Marin
Headlands Marin Headlands
Terrane The Marin Headlands are
made up of some unusual Franciscan rocks called the Marin Headlands
terrane. These rocks
are mainly pillow basalt, red chert and sandstone and were once the ocean
floor of the Farallon plate. When these rocks were formed, the Farallon plate
was very large, and underlay most of the eastern Pacific Ocean. During the
subduction process, almost all of the Farallon plate was devoured as it crept
eastward into the Franciscan subduction zone. As these rocks were crammed
into the subduction zone, they were
broken into numerous thin fault slices, so they now lay scattered around the
Marin Headlands like pieces of cucumbers, tomatoes, and cauliflower in a
giant salad. Exterior Websites Golden Gate NP Conservancy: National Park Service: _____ |