Unusual Plants & Rocks of the Presidio EarthCache
Hidden : 11/4/2009
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This EarthCache is located in the Presidio area of San Francisco and it is part of the Golden Gate National Recreation Area. This EarthCache is in a US National Park and therefore visitors should stay on designated trails and should not collect any materials or leave any physical markers.

Unusual Plants surviving on a Serpentinite Island:

Because serpentinite is altered rock from the Earth’s mantle, its chemistry is unlike most other continental rocks. Serpentinite is low in potassium and calcium, which are important plant nutrients. It also contains high levels of magnesium, nickel and chromium that are potentially toxic to plants. Plants living on serpentine soils have adapted to survive these chemical conditions. Eight of the thirteen rare plants found at the Presidio grow on serpentinite and the relative rarity of serpentinite outcrops contributes to the extreme rarity of these plants.

Unusual Rock:

This unique rock type is called serpentinite and is made from oceanic crust and mantle rocks that have been altered by the intense pressure and chemical-rich water present in areas known as subduction zones, places where one tectonic plate moves under another. The serpentinite visible below formed in a subduction zone that ran along the coast here about 100 million years ago. Faulting and uplift have subsequently moved the serpentinite to the earth’s surface. A plate underlying the Pacific Ocean slid under the North American Plate, rocks scraped from the base of the ocean crust underlying the Great Valley sequence were transformed into serpentinite.

To log this EarthCache:

1) Look at the cliff’s below at this site and E-mail us the COLOR of the Serpentinite Rock that you see.

2) Post a photo of yourself or group taken at this site. If you do it just right, you will have the Golden Gate Bridge in the background of your picture.

Parking is available.

For additional information, go to the GGNRA website http://www.nps.gov/goga

Enjoy the fantastic view of the Golden Gate Bridge!

Additional Hints (No hints available.)



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