California Code, Revenue and Taxation Code - RTC § 19308

(a) The taxpayer has, within the period prescribed in Section 19306, agreed in writing, under Article 3 (commencing with Section 19031) of Chapter 4, to extend the time within which the Franchise Tax Board may propose a deficiency assessment.

(b) The taxpayer has agreed with the United States Commissioner of Internal Revenue for an extension (or renewals thereof) of the period for proposing and assessing deficiencies in federal income tax for any year.