Pacific Mastodon Tooth Unearthed in San Mateo County Creek (2026-09-16)
A nearly nine-inch Pacific mastodon tooth found in a San Mateo County creek has been donated to Stanford University after a chance discovery during habitat restoration work.
A fossilized tooth belonging to a Pacific mastodon, an extinct elephant-like relative that once ranged across North America, has been recovered from a creek in San Mateo County, offering researchers a window into the Bay Area's Ice Age past.
The tooth, measuring close to nine inches, was spotted by Brigid Lynch, a geomorphologist at Balance Hydrologics, while she was working on a habitat restoration project. It lay partly submerged in the middle of the creek, on land managed by the Midpeninsula Regional Open Space District.
Lynch said the object stood out immediately because it resembled none of the surrounding rocks. Unsure what she had found, she turned to a reverse image search, which identified it as a Pacific mastodon molar fossil. She noted that the match was nearly identical to a previously documented specimen.
"I keep joking it wasn't hard to find," Lynch said. "It was just sitting there in the middle of the creek, halfway in, half out of the water."
The fossil has since been donated to Stanford University's Doerr School of Sustainability. Chrissy Garcia, curator at the Stanford Geoscience Specimen Collection, said the discovery was unexpected, given that the tooth was found in a creek rather than a more typical fossil-bearing deposit.
Researchers describe the specimen as being in unusually good condition, with both the crown and root intact. Scientists plan to establish its age and produce a 3D replica for use in public education.
Garcia said the tooth's value extends beyond its initial study, noting that future technologies and shifting scientific questions could unlock new information from the specimen. She also pointed to broader discussions among researchers about reintroducing extinct species or their ecological functions into modern ecosystems, while cautioning that much work remains to understand the implications of such efforts.
Officials said the find underscores the scientific and educational importance of preserving open spaces in the region.