Digging Into The Past

What spot is good for beachcombing, convenient to the Valley, and nearly 10 miles from the ocean? Any local paleontologist could solve the riddle: The “beach” is an ancient area of sedimentary rock layers in the Santa Monica Mountains that hold marine fossils dating back to when the area was underwater.

What is now Old Topanga Canyon was a shallow bay 16 million years ago. When the water receded, it left behind more than 100 species of marine fossils, including ancient clam and snail shells, barnacles, crabs, sand dollars, shark and ray teeth, fish scales and whale bones.

The same process occurred throughout the mountains of Southern California. THere are sedimentary areas of the Santa Susanas, Simi Hills and Mojave Desert that contain similar marine fossils.

Because of the various state and federal regulations concerning fossil collecting, fossil hunters should take part in classes or trips sponsored by local museums and universities. The Los Angeles County Museum of Natural history offers day and weekend fossil hunting trips. Fossil-hunting classes are offered at Learning Tree University in Chatsworth and Wilderness Institute in Agoura Hills. In addition, there are several rockhound clubs in the Valley, including the Woodland Hills Rock Chippers, (818) 347-2056, and the Del-Aires Rock Hound Club, (818) 347-2056.

Paleontologist John Alderson of Learning Tree University teaches his fossil-hunting class to preserve rather than to rad fossil-rich areas: “I recommend a class so someone can learn techniques on how to collect, prepare and clean fossils, as well as learn something about what it is they’ve got and what it means.”

Fossils You Might Find

Concretion: Calcium carbonate collects around shell, binding sand grains to encase the shell in rock.

Clam: A large number of these 1-to-3-inch bivalves dwelled on the ocean floor.

Turritella: This 2-to-3-inch-long corkscrew-shaped, spired shell once housed a snail.

Snail: Snails once dwelled in these lower-spired shells, still common along seashore.

How Fossils Got There

The Santa Monica Mountains have undergone dramatic faulting, twisting and uplifting over millions of years, resulting in a complex landscape of layered contours of rock.

Sedimentation:

After seas receded, sediment consisting of mud, silt and sand settled. Dead marine animals became preserved in this layer. Marine sediment hardened into shale.

Granitic Intrusion:

Volcanic eruptions forced molten granite into the shale, baking and then cooling it, changing it into slate. Uplifting from seismic activity has caused folding and cracking of rock layers, resulting in the area’s unique contours.

Erosion:

Weather and wind caused softer sedimentary layers to wear down, exposing fossils at the surface. Layers of rock are visible at road-cuts through the mountains.

On The Hunt

* Looking For Clues: Fossil hunting involves some detective work. One sign that marine fossils are present is a reddish/orange discoloration of rock, which indicates that water carrying iron and other minerals penetrated the rock.

* Extracting Fossils: Rock is chiseled away by starting a few inches from the fossil and directing the force of the chisel away from rather than toward the fossil to isolate it so it can be easily removed.

* Best Time: Immediately after a rain is best for fossil hunting. Water washes away dirt and dust, exposing fossils.

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Sources: California State Parks; Santa Monica Mountains National Recreation Area; Los Angeles County Museum of Natural History; paleontologist John Alderson; Eyewitness Books’ “Fossil”; Book of Dinorsaurs; Researched by JULIE SHEER / Los Angeles Times