Drinking deep draughts of diesel fuel, canary-yellow behemoths dig their steel buckets deep into the valley floor.
The shovels, which drop 36-ton loads of soil into trucks the size of a two-story house, are not merely digging the foundation for a dam at the Eastside Reservoir Project here. They are burrowing back through time, opening a unique window on creatures that grazed and hunted more than 30,000 years ago on this inland patch of southern California.
On maps, each end of this arid hollow has a name - the Domenigoni or Diamond Valley. But to fossil experts from the San Bernardino County Museum, the 4-1/2-mile-long basin has become known simply as the Valley of the Mastodons.
In June, the site more than lived up to its name when team member Steven Kesler spied a fossil bone poking up through the soil. Over the next three weeks, that bone would point the way to the most complete mastodon ever uncovered on the West Coast.
By the time members of the team had safely carted away the last bits of the creature, dubbed Little Stevie, preliminary measurements gave the mastodon a height of 9-1/2 feet at the shoulder. In size, Little Stevie bows only to 10-foot Max, another fossilized mastodon uncovered at the reservoir in 1995 and thought to be the largest specimen from the Western United States.
The valley might most accurately be called Pleistocene Park, as paleontologists discover a rich mix of Ice Age plants, birds, insects, fresh-water marine life, and mammals. The mammal fossils span the food chain and include species never before reported in southern California's interior, from ancient long-horned bison and the North American lion to ground sloths and early horses.
"There are lots of late-Pleistocene assemblages all over North America," says Eric Scott, the paleontologist in charge of field operations at the reservoir. "But there aren't many with the large assemblage of species we have."
The granddaddy of them all is Los Angeles's La Brea tar pits, which trapped creatures big and small in ink-black goo. With some 4 million fossils ranging in age from 11,000 to 40,000 years and extremely well-preserved, "La Brea is the No. 1 richest locality for terrestrial Ice Age fossils anywhere on the planet," says Mr. Scott. He cut his paleontological teeth there as a volunteer when he was 16 years old, and continued working there as a professional until hired by the San Bernardino County Museum in 1990.
Yet as paleontology expands to include efforts to reconstruct ecosystems and the creatures that lived there, as well as their skeletal remains, sites like the Valley of the Mastodons are becoming increasingly important. La Brea's collection, for example, has an overabundance of meat-eaters like saber-toothed cats, which got mired as they tried to feast on the prey trapped in the tar. The collection emerging from the Valley of the Mastodons, by contrast, represents a broader rendering of the mix of Ice Age creatures at a site.
Not bad for a site where the dam project's environmental impact report held that people were unlikely to find fossils of any scientific value.
"We'll never have several million fossils" or ones that match La Brea's degree of preservation, Scott acknowledges. "But in this valley, we're finding a more accurate cross section" of the plant and animal life that shared this area.
A mammoth-sized project
The researchers' efforts here represent the largest fossil-mitigation, or salvage, effort in the United States, according to Kathleen Springer, the lead investigator on the dig. Federal, state, or local regulations require such projects to ensure that important evidence about a site's natural history isn't lost forever to pipelines, housing tracts, shopping malls, or landfills.
At the Valley of the Mastodons, she says, the goal is to record and gather as broad a sample of these ancient remains as possible before 1999, when the Metropolitan Water District (MWD) of Southern California begins pumping 269 billion gallons of water into what will be the region's largest reservoir.
Tight construction schedules and the immense bites of soil the shovels take guarantee that the vast majority of fossils will vanish or be reburied as part of three earth-fill dams.
Standing on a broad mound where Little Stevie was found deep in the footprint of the East Dam, "Bison" Bob Gonzales estimates that he and his colleagues who scout for fossils are gathering perhaps 5 to 10 percent of the material that exists. Look closely as the oversized shovels unload their cargo, he says, and you can see pieces of bone mixed in with the soil as it falls into the huge dump trucks.
Mr. Gonzales, who teaches high-school English and history in San Bernardino, Calif., joined the museum's field team in April and has discovered the remains of three bison never before seen here. "I smell 'em in the ground," he quips.
Check any romantic notions of fossil-hunting at the gate. Here, pith helmets and wide-brimmed hats from the Indiana Jones Boutique have yielded to Construction Chic - steel-toed boots, hard hats, and orange vests for visibility. Even in the hottest weather, long pants are mandatory. One ear is tuned to the walkie-talkie to monitor construction communications while the other is tuned for the relentless beeping of a 300-ton dump truck on 17-foot tires running in reverse.
"You really learn develop eyes in the back of your head," says the museum's Ms. Springer.
The tools are familiar to geologists and amateur rock hounds. As if to demonstrate, Shannon Kerrett holds up a fist-sized clay clod and taps it with her rock hammer. As the clod splits open, tiny white shards appear among the crumbled debris.
"Fresh-water clamshell fragments?" asks a visitor. No, she replies, holding one up and bending it. Instead, they are specimens of Holocene polymer, or bits of plastic.
Dig a little faster, please
Rotating in shifts, a team of field "paleos" is on site whenever the MWD digs - which is about 20 hours a day. Field paleontologists either pick through the rubble left behind by the big shovels, or patiently hike behind huge scrapers as the machines work back and forth, skimming the top 6 to 12 inches of soil from the surface. Anyone who finds a fossil stakes it so excavators can avoid it and surveyors can plot its position. Then they unearth it as quickly as possible.
Some 90 percent of the fossils they find can be unearthed within an hour of discovery. In other cases, they have to settle for getting what they can as fast as they can.
"My wife was working on this project early on when she found a mammoth," Scott recalls. The skeleton was relatively complete. Unfortunately, it was buried atop an island of dirt that was relentlessly being eaten away by a monstrous excavator. They didn't get as much out as they would have liked.
Typically, he continues, the MWD is very good about giving the "paleos" wide berth until their work is finished. But because the Holland loader wasn't needed anywhere else on the site and is costly to run, the MWD told the team it wouldn't shut it down while members worked on the mammoth. "We had 24 hours to get this out," he says. "You see this shark-fin thing coming closer and closer and we're digging and digging."
History rebuilt, piece by piece
Little wonder that the recovered fossils often come in pieces. Thus the excitement over Little Stevie, which was 40-percent complete. "Our job is to recover the fossils that are significant and to preserve them for study," adds Scott. "It's not to come up with showy specimens."
Indeed, the emphasis is on research rather than a museum display. With the large volume, it's all the team can do to keep up with identifying, cataloging, and storing specimens. They have little time to interpret.
Even so, their growing collection of fossils bears mute witness to a time when the now-arid landscape was cooler and wetter, chilled by mile-thick ice sheets that covered much of North America. While the ice sheets never reached this far south, their influence can be read in the fossils of manzanita shrubs and Ponderosa pine from the valley - plant life that today is found on nearby Mt. San Jacinto at elevations above 4,500 feet.
Back in the basement of the museum, sitting amid bison skulls, horses' teeth, and Little Stevie's plaster-jacketed thigh bone, Springer describes other fossil-mitigation projects the museum has undertaken in the area, as well as other researchers' explorations nearby that earlier had yielded Pleistocene fossils dating back 2-1/2 million years.
Fossils from the Valley of the Mastodons will fill "a huge data gap," she says. "We'll be able to look at the big regional picture from 2-1/2 million years ago to about 11,000 years ago. That's why this site is to incredibly important to southern California paleontology."