California Code, Revenue and Taxation Code - RTC § 19060

(a) If a taxpayer fails to report a change or correction by the Commissioner of Internal Revenue or other officer of the United States or other competent authority or fails to file an amended return as required by Section 18622, a notice of proposed deficiency assessment resulting from the adjustment may be mailed to the taxpayer at any time.

(b) If, after the six-month period required in Section 18622, a taxpayer or the Internal Revenue Service reports a change or correction by the Commissioner of Internal Revenue or other officer of the United States or other competent authority or files an amended return as required by Section 18622, a notice of proposed deficiency assessment resulting from the adjustment may be mailed to the taxpayer within four years from the date the taxpayer or the Internal Revenue Service notifies the Franchise Tax Board of that change or correction or files that return.