Got a call saying that it was important to call back, that it was regarding taxes. Not to ignore this call and call back. It is a scam call - if the IRS was to call, they would leave a different message, and the ID would say so, not California. Usually you would get a certified letter from them anyways.
Received a call and message (twice today) with the urgency that it was the IRS calling and not to disregard it. Same as Ryz, I know that IRS would contact you by mail FIRST, never a phone call.