It happened after a backhoe operator hit-up against a hard object -- 20 feet below ground level.
That's when he unearthed a gigantic tusk.
Paleontologists from the San Diego History museum are taking over what's now being called an excavation.
Scientists uncovered a skull and other bones.
They say it appears to be the remains of a Columbian mammoth which roamed the Earth half a million years ago.
The dig is expected to take several days.
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