Cal. Rev. & Tax. Code § 17010

“Taxable year” means the calendar year or the fiscal year upon the basis of which the taxable income is computed under this part. If no fiscal year has been established, “taxable year” means the calendar year.

“Taxable year” means, in the case of a return made for a fractional part of a year under this part or under regulations prescribed by the Franchise Tax Board, the period for which the return is made.