Is the car reg. I paid tax deductible?

The registration fee is not deductible, but, if your state charges ad valorum or property taxes, the taxes are deductible.

Did I mention I was in California?

Does not matter for the federal return; it is still NOT deductible.

I suspect the same is true for the California return.

In Montana the Co-Opt amount and Light vehicle registration fee is deducted on Schedule A property tax