The La Brea Tar Pits Have Been Sucking in Visitors for Millennia. Paleontologists Are Still Finding Out What Lies Within the Ooze

Unusually for a major tourist attraction, the phrase “death trap” features prominently in the signage and the lore at the La Brea Tar Pits, the celebrated fossil site in the heart of Los Angeles. “Death Trap for Meat-Eaters” says the sign at one site, though in truth it’s a death trap for plant-eaters, too. Over the past 60,000 years or so, animals by the millions, including giant ground sloths, saber-toothed cats, dire wolves and ten-ton Columbian mammoths were stuck in the goo and died here—and were quickly preserved in exquisite detail by the same stuff that killed them.

For scientists, the La Brea death trap matters because the animals entombed here, now mostly extinct, are remnants of a lost North America. Not so long ago, big, scary animals, both predator and prey, dominated the landscape, much as they still do in parts of Africa today. Their abrupt disappearance roughly 13,000 years ago makes La Brea a tantalizing window into the American past, what the International Union of Geological Sciences calls “one of the most important fossil localities in the world.” Emily Lindsey, a La Brea paleoecologist with a passion for the strangeness of giant ground sloths, goes further: “There is almost nothing on Earth of any time period that can match the number of fossils and the diversity of fossils.”

This range includes megafauna and microfossils, plants, insects, snails, even fungi, all preserved together. Lindsey and Regan Dunn, a former river guide and ski instructor turned paleobotanist, are the scientific leads at La Brea. The big question researchers hope these fossils can answer is why such a world suddenly disappeared when it did—and what, if anything, those findings can tell us about our own world. 

For nonscientists, though, La Brea’s “death trap” image has a different appeal. “Lots of screenwriters live in the area,” says Dunn. Her eyes widen but do not quite roll. “You sometimes see them around with their laptops.” 

Act I, Scene 1 often takes place at the sizable “Lake Pit” by La Brea’s front gate, just off Wilshire Boulevard. The location is production friendly, just 15 minutes from major Hollywood studios, and suitably apocalyptic, with methane bubbling ominously from the surface and a statue of a desperate mammoth mired hip-deep in tarry liquid. In the recent NBC television series “La Brea,” a sinkhole opens here and drops attractive people into a primeval underworld. And in the 1988 movie Miracle Mile, a boy-meets-girl, boy-loses-girl, boy-finds-girl story, the happy couple are racing away from a nuclear apocalypse when their helicopter suddenly spins down into the tar. As the goo rises around them, they console themselves with the thought that their fossilized remains might someday be displayed in a museum. 

Such depictions may be Hollywood kitsch, but they live in the hearts of fans. “This is right where the movie Volcano happened, right?” exclaims a middle-aged man in a cowboy hat to two pals one morning as they stride past the tar pit, bound for the George C. Page Museum on the La Brea grounds. In that 1997 movie, La Brea gives rise to a volcano, which flings flaming “lava bombs” and sends a river of molten rock flowing through the city. Perhaps as a nod to the site’s morbid reputation, the man in the cowboy hat has dressed for his La Brea visit in a black T-shirt printed with lyrics from the heavy metal group Venom: “We suck the blood of the beast and hold the key to death’s door.” 

For visitors, the first clue that there’s something different about the land around the museum is in the bare patches among the trees, where the exposed earth is a little too dark and dead leaves are stuck in place. On one such patch, a stray soccer ball waits like an invitation to come closer. Don’t. In fact, there are fences to keep you away.

These dark patches have always been the real hazard, not the lake out front. Lindsey, who is the excavation site director, dismisses the lake as a giant hole in the ground left behind by commercial mining in the late 19th century. The almost ordinary patches of ground are more deadly for being less obvious. What they hide beneath the leaves is not a lake, or even a pit, but a shallow seep. The dirt is saturated with asphalt, the lowest grade of crude oil. Long before commercial mining, Native Americans harvested the asphalt here to waterproof baskets and boats. Early Spanish colonists likewise used the asphalt to seal their roofs. They were the ones who named the place “La Brea,” which means “the tar.”

The oil pushes up through narrow cracks in the rock from oil deposits between 500 and 1,000 feet underground. The asphalt didn’t pull its victims down into the earth, as Hollywood likes to suggest. Even a shallow puddle was enough to lock creatures in its adhesive grip, where they died of exposure or starvation, or were finished off by predators that then often got trapped themselves. As did many scavengers following behind. Inside the museum, schoolchildren and parents flock to an exhibit that invites them to pull up on the handle of a shaft stuck in tar and see what being trapped might have been like. These encounters suggest that most of these people would have gone the way of the perished mammoths.

There are however other, quieter ways to approach La Brea. The museum is part of Hancock Park, a 23-acre refuge from the traffic and chaos of central Los Angeles. Parents wander with a child or two down winding paths shaded by live oak trees. School groups picnic under date palms. An exercise class works through its routine at the foot of a slope. Visitors can amble in through the museum’s back gates and visit Project 23, a fenced-in area where a paleontological excavation is in progress. 

The crates in Project 23 came to the museum from the Los Angeles County Museum of Art, which began building an underground parking lot next door in 2006 and excavated 16 pockets, loading the contents into 23 crates. The largest weighed 123,000 pounds. 

Now a wooden crate stands open, revealing what looks like a crude sculpture roughly five feet tall. It’s a tableau of death, a cataclysmic mix of blackened ankles, teeth, femurs and skulls jammed together. This mass grave was carefully excavated and set aside during construction at the site. The bones in the crates are still embedded in asphalt, just as they were underground. Before removing them from the crates, Sean Campbell, a paleontological preparator at the museum, uses a laser to measure each one and carefully documents its position relative to the others. 

Next, Campbell goes to work excavating a large rib, spraying on solvent to soften the asphalt that holds it in place. The asphalt yields to gentle scraping with dental tools and accumulates in glistening little heaps like couscous cooked in motor oil. “So far,” Campbell says, as he works, “I have a baby ground sloth, a baby bison, a baby horse.” 

Visitors often pay special attention to the babies in the collection. “People are just like, ‘Oh, God, that’s so terrible.’ And I’m like, ‘Yes, but they would have died 40,000 years ago by now anyway. But at least they’re now present for the scientific record, for us to study and analyze them and learn more about their lives.’” He continues with his roster of the dead in the crate: “One deer, a few dwarf pronghorns, tons of coyotes, at least three adult dire wolves and at least one subadult saber-­toothed cat. A partially articulated rodent …”

Time and geological upheaval below ground have left many of the bones battered, including the rib. Campbell wraps it in aluminum foil to keep it intact as he gently rocks it back and forth, out of the dirt. Then he brings it to a bench and wraps it again, this time in orthopedic casting tape. A half-hour in the sun will harden it, leaving it ready to be cleaned up and repaired more durably at a lab inside the museum.

What comes out of the ground here is true buried treasure. A nearly intact saber-toothed cat skull, unearthed nearby in the 1960s, sold at auction in 2009 for $334,600. But the museum doesn’t sell its discoveries. A volunteer named Lynne Schneider, retired from a career as a government contractor, has been “working for months on a dire wolf skull that’s very broken up.” Now, she says, she’s almost getting to “the point where I can start consolidating the bone and gluing it together.” Barbara Hill, another volunteer and a former aerospace worker, stands on the opposite side of the same blackened mass of bones. Both women volunteer two days a week. Hill divides her time between Project 23 and the prep lab inside the museum, though that schedule can change depending on where she is needed most. “It feels like a custody battle,” Hill jokes of her split schedule.

At the lab, preparators stand at a long, horseshoe-­shaped bench facing out into the public area. Visitors watch through plate glass windows. Jars of Q-tips, toothpicks and foam-tip makeup applicators stand at the ready for the cleaning and sorting process. Manicure sticks, the kind beauticians use for pushing back cuticles, “are very nice for removing stubborn matrix,” says Connie Clarke, a staff preparator, referring to the sediment that hardens around fossils. “An electric toothbrush is good for removing a clay layer.” Alongside the bone consolidants and glues are degreasers for cleaning the bones. “In the old days, they used boiling kerosene,” Clarke says. But boiling a flammable liquid, she adds, is “not ideal.” 

Like Schneider and Hill, the other preparators are mostly longtime volunteers—an anthropologist, a veterinarian, a software developer. “A fun mix,” Clarke says. Today, they’re working not on large, easily recognizable bones but on shallow dishes of debris scooped from a gallon paint can. It’s the oily couscous that originally surrounded the bones out at Project 23, now dried and thoroughly cleaned. When the preparators view them through a microscope, items in the mix sharpen into bits of sticks, shells, bones, plants and insects. They use the bristles of a fine artist’s paintbrush to nudge pieces to one side or another, sorting them by type.

Next to the gallon can, the results of recent sortings occupy clear plastic boxes. Clarke carefully opens a box full of the glossy blackened heads of insects, some smooth, some pitted, their rounded skull-like shapes resembling the singed aftermath of a mass catastrophe. “Sometimes a sneeze or a deep sigh will send things rocketing away,” she warns. 

Dung beetle fossils have lately become Hill’s specialty. A paleontologist helpfully told the volunteers that the underside of a dung beetle’s head looks like a toilet seat, and so far, in a few days of microfossil sorting, Hill has found two dung beetle heads that may represent previously unknown species; she hopes to find another today. “It’s treasure!” Hill says playfully, giving herself a pep talk. “You’re going to find it! Open a whole new page of history!”

The big animals that thrill the popular imagination may have died at La Brea only once or twice in a decade. But across millennia, those numbers added up. In the museum’s collection rooms, saber-toothed cat skulls fill a line of cabinets 8.5 feet high and 50 feet long, while drawers full of saber-toothed cat astragali (or ankle parts) and other bones are lined up like spoons. A public display wows museum­goers with 400 dire wolf skulls in almost military formation. Another 430 are stored in back for scientific research. 

“Is it real?” a visitor demands, in front of a massive skeleton of a Harlan’s ground sloth. It’s a standard question at La Brea, and Becca Prater, an educator on staff, confirms that, yes, it’s real. “We have found over 9,000 of their fossils. So we do have a fully articulated skeleton of a Harlan’s ground sloth here.” Then, scrupulously, she adds that those 9,000 bones probably came from about 60 individuals. Like nearly all skeletons at natural history museums, this one is a composite. The bones of individual animals rarely turn up intact, or even in the same place. “So who​ever had that skull never knew the guy with those ribs, and probably never was friends with the sloth that now holds his legs up. So we Frankenstein them all together, and build these big composite skeletons with the pieces we find.” The viewer goes away satisfied. But the “is it real?” question will inevitably recur.

The challenge for La Brea, says Lindsey, is that it’s “a spectacle, and it’s also in the middle of the worst city to be a spectacle. People come to L.A. expecting to see made-up experiences”—­like Universal Studios or Disney’s Holly­wood Land, which bills itself as a place “where movie moments come to life.” When they come to La Brea, Lindsey says, “They’re like, ‘Oh, it’s the La Brea Tar Pits Experience.’” It doesn’t always fully register that these fossils are real, and they’re still coming out of the ground in the third-largest city in North America. 

Several seeps on the property are active enough to require fencing. Other, smaller seeps turn up from time to time, and green traffic cones labeled “Sticky” and “Gooey” warn pedestrians away. Workers scoop asphalt out of inconvenient areas and empty it into the Lake Pit, which is periodically pumped out by a hazmat service. There are seeps outside the museum grounds, too. Nearby homeowners who do not realize they live above an oil field sometimes call to complain: “Your tar is coming up in my garage.”

Old seeps, now cut off from their source, also lie buried in pockets around the neighborhood. As preparators continue to sort through the original batch of 23 crates, construction for a new wing of the Los Angeles County art museum recently brought 37 more crates to the museum. Faced with so many specimens, some seemingly insignificant, when does a paleontologist decide to stop excavating? La Brea is planning a major redesign with a new center for Ice Age research that will emphasize lessons from microfossil research. The aim is to get it done in time for the 2028 Olympics in Los Angeles. 

 “Microfossils are really cool, really important,” Dunn, the botanist, tells an evening audience of museum donors. “They’re super abundant if you look hard enough, and if you know how to look for them. And these small critters are really important for ecosystem function.” While the monsters for which La Brea is now celebrated roamed widely across the region, size kept their smaller counterparts mostly local. “We study them to interpret what the environment was like right here at the tar pits and the surrounding area. And these small fossils tell really big stories.” 

A 2023 paper, published in the leading journal Science, shed new light on the abrupt disappearance of species including the Western horse, the American lion, a bison species, saber-toothed cats and dire wolves. Lindsey and Dunn’s collaborators at Marshall University and the University of California, Irvine, used updated techniques to remove all traces of asphalt from the fossils, which is crucial for accurate carbon dating. “And then,” says Dunn, “they said, ‘Oh my God, we know the timing of the extinction event.’” 

But what was the extinction event? Botanists like Dunn thought that phytoliths might hold the answer. These infinitesimal stones form when plant species take up silica from groundwater and channel it into shapes that are visible only under a high-­powered microscope, and then only after grinding up stony matrix and running it through a series of acid baths and heavy liquid flotation treatments. 

Different types of plants left behind differently shaped phytoliths. On her computer screen, Dunn points out examples: “You see kind of like a spiky golf ball at the top center? Those are palms. The one on the left, with these parallel lines? That’s a fern. The one that’s like a worm with spirals on it? It comes from the veins in leaves.” Phytoliths are everywhere in the plant world. When you run your hand up a blade of grass and feel a spiky edge, she says, you’re touching phytoliths. And they provide clues about the habitat. Certain phytoliths from the upper surface of a leaf can reveal, for instance, whether the plant lived under forest cover or in open grassland.

By studying fossil phytoliths, seeds, pollen and other plant remains from La Brea, the botanists constructed a timeline of what the habitat there was like in different time periods. The post-glacial pine forests of 54,000 years ago gave way to juniper and oak woodlands 30,000 years ago, and then, about 13,200 years ago, to open habitat populated by drought- and fire-adapted plants. 

But, again, the question is why. The megafauna extinction event didn’t happen only at La Brea. Ice Age fossils found scattered across the continents suggest that it was a global event. La Brea is different mainly because of the abundance and the extraordinary preservation of the evidence there. 

Scientists worldwide have debated possible explanations for the sudden extinction. One is that at the end of the glacial period, the climate rapidly became warmer and drier, changing habitats in ways that put pressure on cold-adapted plants and wildlife. Another commonly cited explanation, the “overkill theory,” is based on the fact that human populations expanded around this time, including in southern California, where evidence suggests that people were present in the Channel Islands by about 13,200 years ago. These growing human populations led to heavier hunting, which intensified the pressure on large animals. A third model, put forward by Lindsey, Dunn and their colleagues in the 2023 paper, emphasizes fire: As humans traveled through this already drying landscape, they made fires wherever they went, causing conflagrations and adding to the stresses on vulnerable species. 

The same asphalt that preserved bones and insect parts so well was terrible at preserving ash and charred materials. But a graduate student at UCLA named Lisa Martinez had been assembling a detailed charcoal record from the critical time period using core samples from nearby Lake Elsinore. Her results were hidden at first behind an embargo, even from Dunn. “And then,” Dunn says, “when I was finally able to see that thesis, and I saw her charcoal record, I just nearly fell off my chair.” Martinez quickly became a co-author on the paper. “What we saw by looking at her record is that there’s hardly any fire in the system—until about 13,200 years ago,” Dunn says. “And I was like, ‘Oh my God, it’s humans.’”

The resulting 2023 study found no evidence for the overhunting theory. Instead, the researchers proposed what they called a “more nuanced” approach, a “climate-human synergy” of humans and wildlife adapting—­with a wide range of results—to a climate that was rapidly changing around them. During previous periods of climate change, Lindsey says, animals were able to move freely to better habitats. If ice sheets were expanding over the northern regions of what is now the U.S., the animals could move south to greener pastures. But once humans began transforming the landscape, the animals faced new barriers.

For Lindsey, Dunn and their co-authors, these findings reveal not just what happened 13,000 years ago but also what seems to be happening now. Over the past century, they noted, southern California’s climate has warmed ten times faster than it did at the time of the extinction recorded in such detail at La Brea. Frequent, prolonged droughts and wildfires are common again, as they were then. Ecosystems’ failure to recover after fire suggests, they warned, “that critical thresholds for re-establishment have already been crossed.”

Last year, wildfires driven by fierce Santa Ana winds raced through neighborhoods all around metropolitan Los Angeles. Over more than three weeks, the fires incinerated more than 58 square miles of habitat for humans and animals alike, destroyed more than 16,200 homes, schools and other structures, placed some 200,000 residents under evacuation orders and killed 31 people. Economists estimated the damage to the local economy at more than $250 billion. A La Brea staff member was among the locals who lost their homes. 

Along with many other institutions, La Brea’s Page Museum shut down for two days. The site itself was unharmed, and as the city gradually came back to life, it was almost possible to go on as if nothing had changed. 

Soon after the fires—let’s imagine—a screen­writer shows up at La Brea. She opens her laptop to a script set at the Tar Pits. Working title: “Death Trap.” Heart-in-throat scenes of escape from catastrophe begin to fill the page. But then she starts to noodle around with a new plot point: What if a small band of determined researchers come out of La Brea with a story powerful enough to save our world?