That's according to the state parks department, which runs the California Mining and Mineral Museum.
Officials say as many as three staff members were inside the building Friday afternoon when it was robbed.
Witnesses told the Mariposa Gazette two men armed with a pick-axe ran in and forced employees to one side of the museum before going into the vault.
That triggered an alarm, and the suspects got out just before the vault locked. Authorities are still searching for the robbers. It's not clear yet exactly what they were able to steal.