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La Jolla Falls Fossils EarthCache

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Hidden : 2/15/2008
Difficulty:
2.5 out of 5
Terrain:
2.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

Both fossil impressions of shells and individual shells can be found at La Jolla Falls in Point Mugu State Park The presence of these fossils provide evidence that this area was once under the sea.

There is both paid parking and unpaid parking available. The paid parking will get you about ¼ mile further up the canyon and off PCH. Unpaid parking is available along PCH and usually gets quite crowded.

The trail from the parking area is a wide path with a gentle but noticeable uphill for 0.8 mile. The final few hundred feet to the middle of the falls have steps. The crossing of the stream requires almost no rock hopping. A relatively steep switchback leads to the top of the falls and the primary coordinates. The fossils can also be found around and below the pond, but are primarily found on the sides of loose boulders. Besides the geology, the pool below the falls has many animals. Mosquitos are prevalent during the late spring through fall.

At first glance, the rocks near the falls appear to be a drab featureless gray rock. Even a close examination typically reveals a grey mass with a few areas that have some white specks. Usually no grains or layering are visible. There are some cracks that run through the rock that have filled with quartz. However, with a little searching (and direction) you can find some areas with abundant fossils and recognize the fossils that are actually relatively common around the falls.

This rock is the Topanga Canyon Formation and is one of the most fossiliferous rocks in the Santa Monica Mountains. It formed under water a near the shore of the sea during Early to Middle Miocene (16 to 26 million years ago). Evidence that these rocks formed in a shallow marine environment comes from the type of rocks in the Formation and the fossils that are found in it.

Mudstone, siltstone, sandstone, and shale can be found in the Topanga Canyon Formation, but in this area it is predominantly siltstone and mudstone with some areas of very fine sandstone. This combination of rocks are characteristic of shallow marine areas that have slow moving water (so we aren’t talking about the surf zone).

Now for the fossils... At the coordinates, look for a rust colored area just east of the stream. This area contains abundant marine shells. Most likely they are gastropods(aka snails), but could also include foraminifera(tiny shelled organisms usually less than 1 mm diameter), plant fragments, bivalves (double shelled organisms that are usually symmetrical), sand dollars, barnacles, and crab claws. Elsewhere invertebrate burrows, algae, fish scales, shark gill-rakers, whale bones, and sea lion bones have been found in the Topanga Canyon Formation. Similar species are found in monder-day near shore sub-marine environments. Mostly what you see are the fossils of shells that have been cut in half, so they look like circles and white lines. Now that you can recognize the fossils, you can go back to the gray areas and reexamine the white specks and recognize them as fossil shells.

A more rare find in this area is the imprint of a large pectin, a shell that looks like the Shell Oil Symbol. Go to the secondary coordinates (it requires some climbing and searching N34 5.559 W119 2.600). Look for its imprint on the side of a boulder.

Logging question:

  1. What size are the fossils at the primary coordinates?
  2. How many types of shells can you count?
  3. How big is the pectin imprint? Finding other cool fossils will also be accepted upon request and a good description, photo, and/or coordinates.
Please begin your e-mail with the name of the earthcache and make sure your log includes the number of people in your group.

The above information was compiled from the following sources:

  • Discovering the Beauty of Charmlee Park's Geological Formations GDEP Symposium Long Beach, 8 August 2003 Geoscience Diversity Enhancement Project A collaboration of the departments of: Geological Sciences, Geography, and Anthropology California State University Long Beach, CA 90840 http://www.csulb.edu/depts/geography/gdep/posters03/charmleegeology/
  • GEOLOGIC MAP OF THE POINT MUGU 7.5-MINUTE QUADRANGLE VENTURA COUNTY, CALIFORNIA: A DIGITAL DATABASE VERSION 1.0 By Siang S. Tan and Kevin B. Clahan California Department of Conservation California Geological Survey.
  • Santa Monica Mountains National Recreation Area Paleontological Survey Alison L. Koch, Vincent L. Santucci, and Ted R. Weasma Technical Report NPS/NRGRD/GRDTR-04/01 United States Department of the Interior - National Park Service - Geologic Resources Division 2004
  • Placement approved by Point Mugu State Park


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