The tar pits and oil seeps in Carpinteria are part of a series of oil producing areas along the Ventura and Santa Barbara Coast. Oil has naturally migrated to the surface in this area creating oil seeps, asphaltium, and at one time tar pits.
This earthcache is at the city of Carpinteria’s Tar Pits Park. From Carpinteria Avenue, take Concha Loma Avenue to Calle Ocho; park at the end of Calle Ocho and walk across the railroad tracks to the lookout point. This is an unsigned crossing, so carefully check the tracks before crossing. A signed crossing is available to the west on Palm Avenue near the entrance to the State Beach.
The rocks beneath this area are the Miocene Monterey Formation. The Monterey Formation is common along the coast of California. In fact, similar rocks were deposited throughout the Pacific Rim during the Miocene (17.5 to 6 million years ago). All of these rocks share similar characteristics. They are Diatomaceous (made up of the shells of microscopic plankton called diatoms) Phosphatic (containing phosphate) Dolomitic (containing dolomine); and Rich in organic matter (oil and gas)
This last characteristic, being rich in organic matter, makes these rocks economically important because they often are reservoirs for oil and gas. Most of the off-shore oil rigs along the California coast pump oil from this formation. Across the Pacific, Japan has similar rocks and oil reserves.
In this area, the oil has found natural paths to the surface. In the Pleistocene, tar pits similar to the La Brea Tar Pits existed in the area. Scientific excavations have recovered a collection of fossils that rivals the Rancho La Brea (earthcache hyperlink) collection. The collection includes mammal, bird, insect, and marine invertebrate remains. Birds are the most common animal found with over 57 different species including the California Condor and Golden Eagle
Unlike the collection from La Brea, a large number of fossil plants have been collected from Carpinteria. Ferns, redwoods, pines, and oaks are among the plant fossils. Some of these species require a cooler and moister climate than what is currently found in Southern California indicating that at some time during the Pleistocene, the climate of Southern California was not as hot and was wetter.
Today you specimens are continuing to be trapped in the tar. Sea shells and rocks are being covered in the seeping tar. In other areas where the oil continues to seep from cliffs, wave rounded rocks, seaweed, and shells continue to be trapped in the sticky tar.
These tar deposits were used by the Native Americans for waterproofing. In the 1920s, these pits were mined for road building. Then the open pits were used as a dump.
The above information was compiled from the following sources:
Richard J. Behl California State University, Long Beach, Monterey Formation, (
visit link)
HARTMAN MULTIMEDIA Carpinteria Asphalt Deposits (
visit link)
Ventura Basin: Geologic Introduction and Field Trip Guidebook, Martin H. Link Editor, The Pacific Section American Association of Petroleum Geologists, Los Angeles, California and Los Angels Basin Geologic Society, April 16, 1988 .