California gives you an automatic filing extension through October 15, 2019. You don't need to file any form to have an extension.
Please note that this is only an extension of time to file your return. Any tax owed still must be paid by April 15, 2019 or else you may accrue interest on the amount owed.
To estimate and pay your tax owed, use Form 3519 . You may also pay the amount owed with your credit card by going to Official Payments