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Geologic Trips, San
Francisco Lands End The small islands and rocks seen along the
shoreline east of Ocean Lookout Park represent hard blocks of serpentine,
basalt, chert and sandstone that have been eroded from the soft clay matrix
of the City College mélange. The melange was formed along the zone of thrusting between the rocks of
the San Bruno Mountain terrane and the Marin Headlands terrane while the
rocks were in the Franciscan subduction zone. The fine clay matrix of the
melange was formed from rocks that were thoroughly ground up by the
thrusting. The blocks in the melange are pieces of hard rock that survived
the grinding. Wave erosion along the
bluff at Lands End has washed away much of the softer clay matrix and left
behind the hard rocks seen in the photo. Exterior Websites Golden Gate NPark Conservancy: Wikipedia:
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From Lands End looking northeast toward the
Golden Gate. |