California Code, Revenue and Taxation Code - RTC § 24945

(a) The statutory period for the assessment of any deficiency, for any taxable year in which any part of the gain on such conversion is realized, attributable to such gain shall not expire prior to the expiration of four years from the date the Franchise Tax Board is notified by the taxpayer (in such manner as the Franchise Tax Board may by regulations prescribe) of the replacement of the converted property or of an intention not to replace; and

(b) Such deficiency may be assessed before the expiration of such four-year period notwithstanding the provisions of any other law or rule of law which would otherwise prevent such assessment.