RICHMOND -- A backpack found in a parking lot brought two bomb squads out to the Chevron refinery early Tuesday afternoon.

Both the Walnut Creek and the UC Berkeley Police Departments bomb squads were called to the refinery shortly after the package was discovered around 12:50 p.m., said Melissa Ritchie, a spokeswoman for Chevron in Richmond. The package, Ritchie said, was in a parking lot adjacent to the refinery. Though it was not near any of the processing units, the parking lot area was evacuated as a precaution.

The bomb squads determined around 4:30 p.m., however, that the package was a backpack and that there was no threat.

Federal investigators believe that at least one of the pressure-cooker bombs detonated last week at the Boston Marathon was hidden inside a backpack.

Contact Katie Nelson at 925-945-4782 or follow her at Twitter.com/katienelson210.