California does not permit you to treat any HSA contributions as pre-tax. Because the entire $4,200 is federally pre-tax (not included at all in your federally taxable income), the entire $4,200 must be applied as an addition on your California income tax return.
Note that the amount on CA Form 540 line 12 is not used in determining your CA taxable income. The calculation begins on Form 540 line 13 with your federal AGI and the $4,200 is added in on line 16.
