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Finding Fossils in San Diego Area Easy as Kicking Rocks

June 28, 1987|HILLIARD HARPER | Times Staff Writer

SAN DIEGO — 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.

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

Armored Creatures

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 does not 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 meeting 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.

Laid Out Near Surface

Instead of having to dig 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. In the last 15 years, he and his wife, transplanted Los Angeles residents, have found 300 to 400 fossils working as amateur "prospectors."

"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.

Patchens Have Permit

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

As significant to fossil collectors 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 said. "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.

"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.

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