The tax rebates (aka the stimulus payments) that will be issued beginning in May won’t be taxed by California. The Franchise Tax Board announced this last week. The FTB notes (as has the IRS) that in order to claim the rebate you must file a federal tax return. You do not have to file a California tax return in order to claim the rebate.
A few states will be taxing the federal tax rebate. Generally, those states give a deduction for federal tax paid. Alabama and Louisiana are two states that I believe will be taxing the federal tax rebates.