San Francisco Bay Region Geology and Geologic Hazards

Stories > Monterey - Plutonic Rock (Granite)

Monterey - Plutonic Rock (Granite)

Monterey peninsula, like most of the region west of the San Andreas Fault, is underlain by Late Cretaceous (100-65 million years old) granite (shown as unit Kgr on the geologic map). The granite near Monterey is mostly covered with sand dunes and marine terrace sediments, so the best place to see it is along the coast where waves have washed it clean.

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Granite outcrops along the coast in Monterey.

Granite is a plutonic rock, formed by slow cooling of a body of melted rock (magma) deep under the Earth's surface. You can tell a rock is plutonic because it is made of interlocking large (>1 mm) crystals.

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A close-up of granite from Monterey. Notice the interlocking large crystals. The largest crystal is over 2 cm in length.


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