Giant Fossils Trove Found in California Declared One of the Most Significant in State History

A petrified forest discovered by a ranger for California's East Bay Municipal Utility District (EBMUD) has yielded what SFGate calls the "the largest and most diverse" collection of fossils in the state's history.

Geologists and paleontologists at California State University, Chico, which has partnered with the district to excavate, identify, preserve and store the fossils, anticipate that conducting a complete inventory could take years. But they're thrilled at the prospect of building on existing knowledge of prehistoric North America.

While walking last July through the Mokelumne River watershed, a drainage basin in the Sierra Nevada foothills that provides water to 1.4 million Bay Area residents, Greg Francek noticed a petrified tree protruding from the mud. Looking around, he noticed another, and then another, and then another.

"After finding dozens of trees, I realized that what I was looking at was the remains of a petrified forest," Francek said, according to an EBMUD statement released early last week.

His interest piqued, Francek returned to the site multiple times in the succeeding weeks. He soon realized that it harbored not only petrified wood but also vertebrate fossils. Hundreds of them.

"What I didn't comprehend at the time was the amazing fact that I was looking at the bones of great beasts that had roamed this landscape millions of years ago," he said, according to SFGate.

The fossils are believed to date to the Miocene epoch, a period spanning 23 million to 5.3 million years ago that saw an increase in the diversity of flora and fauna, according to the University of California Museum of Paleontology. They include the remains of contemporary plants, fish, birds, horses, camels, tapirs, tortoises, rhinoceroses and elephant-like mammals known as mastodons and gomphotheres, according to the statement.

However, the original creatures would have often borne only a passing resemblance to their modern-day counterparts. The camel had not yet evolved its distinctive hump; the horse had three toes; and the fish, a salmon, may have had spiked teeth and weighed as much as 400 pounds, according to the statement.

"The discovery is highly significant because of both the sheer number and diversity of specimens found. Few other fossil discoveries like this exist in California," Russell Shapiro, one of the California State University geologists, said in a statement, according to SFGate. "The bones paint a clearer picture of life 10 million years ago, when animals evolved from living in forests to grassland as the landscape changed."

The specimens recovered so far include horse teeth, camel foot bones, the jaw of a rhino, the plastron (bottom plate) of a tortoise, the skull of a mastodon and, most exciting of all, a nearly complete set of mastodon tusks. The latter find has Shapiro and his colleagues particularly excited. Mastodon remains have not been discovered in California since 1947, when a surveyor named Murray Kelley found vertebrae, a tusk and a jawbone while assisting with the construction of an EBMUD pipeline, according to the statement.

A paleontologist brushes the dust off fossil.
A paleontologist brushes the dust off of a dinosaur fossil. A California ranger recently stumbled upon an enormous trove of fossils in a valley near the Bay Area. CARL DE SOUZA/Getty Images