The Riverside Press-Enterprise reports the owner of the Ford Flex found thedevice after leaving the JCPenney store in
City spokesman Carl Baker says a few hundred people were evacuated from seven businesses as a bomb squad investigated.
A robot was used to detonate the pipe bomb in an area behind the stores that is bordered by an empty field.
No arrests have been made. A sheriff's bomb dog sniffed the parking lot for other devices but found nothing dangerous.
Baker declined to discuss what the woman may have told police about who she suspected may have planted the pipe bomb or the motive.