For more than a million years, the bones lay out of sight, buried under layers of sediment that had accumulated over the eons in San Timoteo Canyon in Riverside County.
It was only through a lucky twist of fate that they came to light in 2009 when Southern California Edison (SCE) began building the El Casco Substation.
The discovery ultimately became one of the largest collections of fossils found in Southern California for a geologic period that predates the finds at the La Brea Tar Pits by at least 1 million years.
Now, after about a year of preparation and nearly four years housed at the Western Science Center in Hemet, the first of the more than 15,000 El Casco fossils will go on display as part of the center’s “Stories from Bones” exhibit opening on Halloween.
“The fossils tell the story about the life of the animals,” said Alton Dooley, the center’s executive director. “The condition of these bones tell us if an animal was eaten by a predator or was injured or lived to be old and had arthritis.”
Among the fossils on display will be a replica of a horse skeleton that was found 70 percent complete at El Casco.
“It is really exciting for me,” said Dave Hanna Jr., the SCE archaeologist who oversaw the El Casco project.
Hanna is one of seven SCE archaeologists. The team ensures compliance with state and federal environmental law. The archaeologists identify and manage important archaeological and paleontological resources potentially affected by both new construction and maintenance of existing facilities.
Over the years, SCE archaeologists discovered or preserved geoglyphs up to 170 feet long carved into the desert near Blythe and important Native American rock wall paintings in the Burro Flats area of Topanga Canyon.
When the company built an electrical generating station at Pebbly Beach on Catalina Island, archaeologists identified and protected the historical architecture of the old Catalina Tile and Pottery Co., which dates back to 1919.
Part of Hanna’s job on El Casco was to research the geology of San Timoteo Canyon. He found that they would likely encounter important fossils during construction of the substation, but no one expected to find the amount of fossils or their importance in understanding California’s dynamic history.
“The first really big thing we found was on the first day,” Hanna said. “It was bones.”
As paleontologists washed and screened some of the first samples of the sedentary rock, they realized they had unearthed not just a few bones, but an entire bed of bones.
The Western Science Center’s Dooley said the El Casco fossils reveal much about a period in Southern California that hasn’t been very well known until now.
“The work at El Casco tells a pretty rich story,” he said.