The mastodon molar was donated to Stanford University in California.

Brigid Lynch, a scientist who studies the Earth’s surface, was walking through a Midpeninsula Regional Open Space District (Midpen) preserve in San Mateo County when she stumbled upon a major find: a giant tooth from the ice age.

Lynch was working in a creek bed on a field survey for the threatened California red-legged frog when she spotted the “oddly shaped rock” in the water. Paleontologists later confirmed it was a molar of an adult Pacific mastodon, a huge herbivore that resembled an elephant and roamed the Earth for 2.5 million years before going extinct around 11,000 years ago.

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