Colorado Desert District 

When most visitors think of Anza-Borrego Desert State Park, located in southern California's Colorado Desert, they usually envision wild flowers, bighorn sheep, or vast arid landscapes framed by rugged mountains. Few realize that the eroded badlands of Anza-Borrego provide a contrasting view, a window into the region's vanished past. The Park was not always the arid desert we experience today.

The key to understanding this prehistoric scene is paleontology, the study of the fossilized remains of ancient life. And Anza-Borrego has an exceptional fossil record. Over 500 different types of organisms have been identified, ranging form microscopic plant pollen and spores to the largest of mammoth elephants. Not only are the bones and teeth of long extinct animals preserved, but in some places, also their tracks.

The Salton Trough, a geologically active rift valley, which bounds the eastern edge of the Park once held a northward extension of the Sea of Cortez. Sediments laid down 5 million years ago in these warm clear tropical waters, now yield the preserved shells of a variety of clams, snails, crabs, and corals. These organisms have ties with the Caribbean Sea, and record a time before the Isthmus of Panama had formed. The remains of fish, walrus, baleen whales and even sea cows help us to more fully picture this long extinct marine ecosystem.

About 4 million years ago, the ancestral Colorado River began cutting through the Colorado Plateau of Arizona and Utah. The sediments eroded during the formation of the Grand Canyon spilled into the Salton Trough, creating a vast delta. These brackish marine deposits are recognized in the Park today by their extensive fossil oyster shell reefs and fossilized wood. The types of tress represented now live along the Pacific coast of southern California suggesting that any mountains west of the Trough must have been low.

As the Salton Trough was filled with sediment carried by the ancestral Colorado River, what was to become Anza-Borrego gradually changed from a predominately marine environment to a system of interrelated terrestrial habitats. By about 3 million years ago, most of the area once covered by the Sea of Cortez held a large, inland lake. Here, the remains of fresh water clams, snails, and fish are not uncommon. Streams and rivers draining the new uplifted Peninsular Range mountains, which border the western side of Anza-Borrego today, spread an apron of alluvium and floodplain deposits eastward into the Salton Trough. It is these sediments that provide us an almost uninterrupted record of terrestrial habitats spanning a period form about 3 million to less than a half million years ago. During this time, Anza-Borrego supported a rich diversity of wild life. Herds of mammoth elephants, tapirs, zebra-like horses, several species of camels, and llamas ranged across a landscape of stream border woodlands and savannah-like grassy scrublands. And, had we been there, we may have glimpsed a foraging giant ground sloth, beaver, or even a saber-toothed cat or American cheetah on the hunt.

Stout Research Center Paleontology LabSince the 1930s, paleontologists have documented the extensive terrestrial and marine fossil record preserved in the sediments deposited along the western Salton Trough and the Gulf of California. These deposits span approximately the last twenty million years. Over 500 different organisms have been identified, ranging from microscopic marine plants and shell fish to the largest of Mammoths. Not only are the bones and teeth of animals preserved, but in some places also their tracks.

Anza Borrego Desert State Park is home to the world class Stout Research Center Paleontology Lab (pictured here) where fossilized remains of extinct animals like mammoths and saber toothed cats are prepared, documented and cared for to be used by scientists all over the world.

The Colorado Desert District and Anza-Borrego Desert State Park  paleontology  staff  are responsible for protecting and managing these internationally significant paleontological and geological resources. An annual Paleontology Certification Training Program, which consists of classroom instruction, curation and laboratory training, and field exercises is conducted each year from November through May. This program was developed to provide and maintain professional credentials for paleontology volunteers.


The paleontology volunteer program at Anza-Borrego Desert State Park has been active for over 20 years and in October 1993 the Anza-Borrego Desert State Park Paleontology Society was formed under the direction of George Miller, paleontologist.. This volunteer group assists the District and State Park staff conserve and manage the Park's vast paleontological resources and collection. Those interested in participating in the program may visit their website at: or call or write for further information at:


George T. Jefferson, District Staff Paleontologist
Colorado Desert District Stout Research Center
Anza-Borrego Desert State Park
200 Palm Canyon Drive
Borrego Springs, California 92004



Downs, T., and J.A. White, 1968.
A vertebrate faunal succession in superposed sediments from late Pliocene to middle Pleistocene in California.
23rd International Geologic Congress 10:47-47.

Kurten, B., and E. Anderson, 1980.
Pleistocene mammals of North America.
Columbia University Press, New York, NY, 442.

Remeika, P., and L. Lindsay, 1993.
Geology of Anza-Borrego: Edge of Creation.
Sunbelt Publications, Kendall/Hunt Publishing Company, Dubuque, IA, 208.

California State Parks

[BRCC San Diego Natural History Museum: Paleontology]

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