A 10,000-year-old mastodon molar discovered in a San Mateo County creek has stunned scientists, offering a rare glimpse into the Ice Age ecosystem of California.
Brigid Lynch’s discovery began as an odd-shaped rock in a creek bed, but it quickly revealed itself as a remarkably preserved molar from a Pacific mastodon, an extinct relative of modern elephants. The 9-foot-tall creature roamed western North America during the Ice Age, and its fossil—described as “immaculate” by paleontologist Wayne Thompson—has become a critical piece of the ecological puzzle.
The Discovery and Initial Reactions
Lynch, a geomorphologist with Balance Hydrologics, stumbled upon the fossil while conducting field surveys for the Midpeninsula Regional Open Space District in March 2026. It really stuck out,
she said, recalling the moment. I had no idea what it was. I thought maybe it was a mollusk or something, but that didn’t make sense since it wasn’t near the ocean.
The tooth itself is in immaculate condition.
It’s the most complete mastodon molar from our area,
he said, adding that the find is another puzzle in the Ice Age saga that we can put into place.
The Midpeninsula Regional Open Space District, which manages over 70,000 acres of preserved land, has declined to disclose the exact location of the discovery. We don’t really want people digging around in the creek looking for other fossils,
said spokesman Ryan McCauley. However, the agency acknowledged the find’s significance, with McCauley comparing it to “Jurassic Park” in its imaginative potential.
Scientific Significance and Expert Reactions
Christine Garcia, curator of Stanford University’s Geoscience Specimen Collection, emphasized the rarity of the discovery. It’s pretty rare to just stumble across a fossil like this,
she said, noting that most such finds come from construction projects. The molar, now housed at Stanford’s Doerr School of Sustainability, will undergo carbon dating and 3D scanning to determine its age and study the mastodon’s diet and environment.
He highlighted the species’ distinct features, including narrower teeth and thicker leg bones compared to the American mastodon. Unlike mammoths, which were also present in the region and fed on grasses, mastodons were considered browsers, using their massive trunks to strip leaves, soft shoots or fruits of high-growing, generally woody plants,
he explained.
The fossil’s condition suggests it was not in the creek for millennia.
Educational and Research Implications
The discovery also ties into broader efforts to study prehistoric life in California. In 2023, a similar find—a mastodon molar—was uncovered at Rio Del Mar State Beach near Santa Cruz.
A Puzzle in the Ice Age Saga
The mastodon’s existence in the Bay Area challenges common perceptions of the region’s prehistory. This isn’t that long ago—only about 10,000 years,
McCauley said. It boggles the mind.
The creature lived during the Pleistocene epoch, when the area was home to mammoths, saber-toothed tigers, and other megafauna. It’s another puzzle in the Ice Age saga that we can put into place,
Thompson said.
The fossil’s journey from a creek bed to a university lab underscores the intersection of chance and scientific expertise. Lynch’s ability to recognize the molar’s significance, combined with the collaboration of researchers and conservation agencies, highlights the value of interdisciplinary efforts in preserving natural history.
As Stanford prepares to analyze the specimen, the discovery serves as a reminder of the hidden stories embedded in the Earth. For Garcia, the molar represents not just a scientific breakthrough but a chance to connect the public with the deep history of their surroundings. Fossils are our only opportunity to see into past biodiversity,
she said. We can study fossils to better understand Earth’s past, past wildlife and the ecosystem they were a part of, and to help us make better predictions and better decisions about how to help our ecosystems and biodiversity thrive into the future.
