Cool Finds

A Geologist in California Found Something Strange Sticking Out of a Creek. A Reverse Image Search Told Her It Was an Ancient Mastodon Tooth

Pacific mastodons roamed parts of North America before disappearing along with other Ice Age megafauna around 11,700 years ago

Margherita Bassi | Daily Correspondent

September 15, 2026 3:04 p.m.

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It’s big and multi-faceted, with strange protrusions sticking out of the main body. Brigid Lynch, a geomorphologist at Balance Hydrologics, spotted it in a creek in California’s San Mateo County and thought it could be an animal. “I was like, ‘Do you think we should touch it?’” she tells the New York Times.

The mysterious object in question turned out to be an exceptionally well-preserved ancient mastodon molar and a reminder of the megafauna that once roamed the region. Lynch and a colleague had been conducting field surveys for a conservation project for California red-legged frogs, a federally threatened species, and Lynch had no idea that she’d found and photographed something so special.

Then, however, "she did a reverse Google image search and found out that it might be a molar of an Ice Age mastodon,” Wayne Thompson, a paleontologist and CEO of the fossil mitigation company Pacific Paleontology, tells Sooji Nam for CBS News Bay Area.

The Midpeninsula Regional Open Space (Midpen)—an independent district in the greater Santa Cruz Mountains that cares for 70,000 acres of public open space—asked Thompson to confirm the “gigantic” finding. "I confirmed it was a mastodon tooth. And everybody is pretty excited about it, because these don't show up all that often," Thompson adds.

Lynch discovered the intact tooth in one of Midpen’s preserves in San Mateo County. The fossilized molar belonged to an adult Mammut pacificus, or a Pacific mastodon. Mastodons are now-extinct elephant-like herbivores that were shorter and stockier than mammoths and also had shorter and straighter tusks. Another differing factor has to do with their diets: mammoths fed on grasses, while mastodons were browsers, meaning they ate vegetation or fruits from tall plants.

Pacific mastodons are the most recently recognized mastodon species, and they have narrower teeth, thicker leg bones and different tusks than the more established American mastodon (Mammut americanum).

Experts theorize that Pacific mastodons moved across modern-day California, Oregon, the northern Rocky Mountain region of the western United States and parts of Mexico. They lived from 2.5 million years ago to approximately 11,700 years ago, joining a host of other Ice Age megafauna that went extinct around the time.

In what is now California, Pacific mastodons would have existed alongside other bygone species, including Jefferson’s ground sloths, western camels and Columbian mammoths, as well as animals that still exist, like gray foxes, Steller’s jays and spotted owls.

“The tooth itself is in immaculate condition. It's the most complete mastodon molar from our area, and the most spectacular mastodon molar that I've ever seen. I had chills and shivers up and down my spine,” Thompson says in a Midpen statement. “It's another puzzle [piece] in the Ice Age saga that we can put into place.”

What’s more, the puzzle piece in question “wasn’t hard to find,” Lynch tells the Associated Press’ Jamie Stengle. “It was just sitting there in the middle of the creek, halfway in, half out of the water.” The fossil’s rare intact nature indicates that the mastodon’s skull must also be close by, Thompson points out to CBS News Bay Area.

But mastodon fossils aren’t especially rare. They “pop up with some degree of frequency, depending on where you live,” Ron Tykoski, vice president of science and curator of vertebrate paleontology at the Perot Museum of Nature and Science in Dallas, tells the AP. In 2023, for example, a woman in California found another mastodon tooth on a beach.

After it was retrieved from the creek, Midpen staff put the molar in a bucket of creek water, according to the New York Times. Molars decay quickly after they are taken from a water environment, Thompson explains to the outlet. Midpen donated the fossil to Stanford University’s Doerr School of Sustainability, where researchers will figure out exactly how old it is and create a replica to use for public outreach and education.

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.