County Emerges as Fertile Field for Rare Fossils

If dirt and rocks were pages of a book, the soil of San Diego County would read like an epic novel, stretching across tens of millions of years.

Two million years ago, mastodons, huge saber-tooth cats, bears, horses, deer and antelope contended for supremacy on rolling, grassy plains that are now the Anza Borrego Desert.

Twenty-six to 27 million years ago, at the site of what is now a planned community going up in eastern Chula Vista, quail, short-legged cranes, tortoises and a diverse array of rodents shared an arid coastal flood plain with rhinos and camels.

A discovery this spring revealed that armored dinosaurs--previously unknown west of the Rockies--roamed a steep coastal mountain range 70 million years ago in the vicinity of the present-day Carlsbad Raceway.

Increasingly, San Diego County is proving to be one of the richest lodes of animal fossils on the West Coast, say paleontologists, who study prehistoric life forms and who do read rocks like a novel.

“You can’t help but collect fossils in San Diego,” said Thomas Demere, acting curator of paleontology at the San Diego Natural History Museum. Fossils are easier to find than most people would believe, he said.

Demere likes to use the analogy of rock layers as the pages of a book. To be certain, San Diego is not a complete book--entire chapters are missing. For dinosaur fossils, it doesn’t compare with the Midwest and southern Canada.

“If you’re looking for Miocene marine mammals, San Diego is not the place to look,” Demere said. “Bakersfield is the place to go.”

But the specific geologic epochs found here are widely recognized for their excellent skeletal treasures.

Evidence of exotic primates, bats, shrews, some of the first camels, and marine life forms that lived 45 million years ago, during the Eocene Epoch, has been found in the Oceanside-Carlsbad-Vista-San Marcos area. Mission Valley is also a fertile field for the Eocene Epoch (35 million to 55 million years ago).

In Anza Borrego Desert State Park, a curious formation offers a rare record of the interface between the late Pliocene (600,000 to 10 million years ago) and early Pleistocene (12,000 to 600,000 years ago) epochs. Known as the Palm Spring Formation, the land was formed when earthquakes twisted and tilted a horizontal section of the earth up to an incline, exposing a cross-section of 1.5 miles of accumulated sediment.

Instead of having to dig down through layers of the Earth, paleontologists can walk across 3,000 meters of layers, laid out virtually on the surface of the land.

Marvin Patchen lives in the Anza Borrego Desert. Over 15 years, he and his wife, transplanted Angelenos, have found 300 to 400 fossils working as amateur “prospectors.”

Trained Eye Is Needed

“It takes a trained eye to differentiate the rocks from the bone,” Patchen said. “But once you get your eye trained . . . then it’s just a lot of hard hiking.”

The Patchens’ preferred method of collecting fossils is to walk narrow ridges so they can look down on both sides.

“Sometimes you find something sitting right there on the surface saying ‘pick me up,’ ” Patchen said. Using only the naked eye, they have found 200 sites.

Public fossil collecting in the park is against the law. The Patchens, who have a special permit, turn their fossils over to a paleontologist.

As significant to fossildom as the Anza Borrego Desert is the San Diego Formation of the Pliocene Epoch (600,000 to 10 million years ago).

Demere stated flatly: “Our Pliocene marine chapter is the best-written in North America.”

This stretch of land, running from Mission Hills to Lemon Grove, has yielded an extremely rich treasure of fossils in the 2-million to 3-million-year age range: whole invertebrates such as scallops, clams, oysters and snails have been unearthed, as well as skeletal remains of mammals such as whales.

For all its richness, San Diego’s “Pliocene chapter” is unfinished, Demere acknowledged. “It’s still in manuscript form,” he said. Although thousands of fossils have been collected, there has been little time to analyze and theorize about what they mean, what clues they may provide to ancient ecological systems and evolution.

Written Record a Must

“If you don’t write about it, it’s not worth collecting,” Demere said. “If you don’t ask questions, you’re just stamp collecting.”

Because San Diego is steadily producing an embarrassment of fossil riches, scientists at the museum have less and less time for paleontological research or for the formation of theories, the real meat of paleontology. Instead, they frequently find themselves forced into a “salvage mode,” collecting more and more fossils that are being turned up almost daily in excavations that are part of San Diego’s building boom.

The California Environmental Quality Act of 1970 requires that land developers hire qualified paleontologists to monitor construction projects likely to unearth fossils. The Natural History Museum benefits from the extracurricular activities of several members of its paleontology department who work as private consultants to developers.

The result is that they are constantly running across fossils.

That’s how Demere and his partners made a whopping discovery in 1985 while working as consultants for EastLake Development Co., which is building a planned residential and commercial community in Chula Vista. No one thought the EastLake site contained any fossils, just volcanic ash and sand, Demere said. He thought the region was in the Miocene Epoch, which ranged from 10 to 25 million years ago.

But one day, while walking behind bulldozers, one of the paleontologists tapped a block of sandstone with a pick and out popped a complete lower jawbone, including teeth, of a hypertragulidae, an ancient mouse deer. The scientists were stunned.

“We were jumping up and down,” Demere said. “It was an unknown time period in San Diego.”

Goldmine of Antiquity

As the grading progressed, they found more jaws, then heads. As the graders tore up the earth, the scientists would cautiously gather blocks of sandstone, some with bones sticking out. They salvaged fossils of camels, lizards, shrews, hedgehogs, birds, rabbits and a mountain beaver. They found bones of a hyaenodon, a bear-like carnivore; a chevrotain, another kind of tiny mouse deer not unlike one now at the San Diego Zoo, and the remains of scores of extinct grazing animals known as oreodonts, a distant relation of the camel.

Because there was a good relationship with the developer, the contractor often provided a bulldozer to assist in the digging.

The EastLake discoveries--some of those fossils are now on exhibit at the museum--never would have been made had the land not been developed. “If the equipment wasn’t grading, we couldn’t work on the rocks,” Demere said.

But the equipment was there, moving literally millions of cubic yards of dirt, exposing rocks that were deposited in a river bed 26 million years ago. The fossils uncovered were donated to the museum.

But for anyone to make any sense of the fossils, they must be carefully removed from limestone, then documented as to precise location, then identified. That all takes time away from research.

When a dinosaur skeleton was discovered this spring at a Carlsbad industrial park, virtually everything else stopped in the museum’s paleontology department.

“It’s like an unexpected guest from out of town who’s going to stay awhile,” Demere said.

It may take museum workers a year to remove the fossil bones from the stone they are embedded in. The bones, which were not found intact, but spread over a 100-square-foot area, must then be sorted before any research based on them can proceed. Nothing can be slipshod.

Preparation Is Vital

“There has to be proper preparation and curation,” Demere said, “or 100 years from now, when all of us are dead and gone, somebody’s going to say, ‘Golly . . ., where does this (piece of bone) go?’ ”

Demere is not engaging in idle speculation. Only last summer, the museum’s staff completed a two-year painstaking cataloguing of an international collection of invertebrates, most of it collected more than 100 years ago.

Although the museum is sending some of the EastLake fossils to other institutions for analysis, Demere agonizes over the thought that much of that material, too, might not be studied for 100 years. It is a very real possibility.

EastLake is only one construction site and the grading there is scheduled to go on for the next 15 years.