Cal. RTC § 6487.3

(a) (1) For persons that elect to report qualified use tax in accordance with Section 6452.1, except in the case of fraud, intent to avoid this part or authorized rules and regulations issued by the department, or the gross understatement of qualified use taxes, every notice of a deficiency determination with respect to the qualified use tax shall be served within three years after the last day for which an acceptable tax return is due or filed, whichever occurs later.

(2) In the case of a gross understatement of qualified use tax, every notice of a deficiency determination with respect to the qualified use tax shall be served within six years after the last day for which an acceptable tax return is due or filed, whichever occurs later.

(3) For purposes of this subdivision, a “gross understatement of qualified use tax” is a deficiency that is in excess of 25 percent of the amount of qualified use tax reported on a person’s acceptable tax return. In the case of married individuals filing separate California personal income tax returns, the total amount of qualified use tax reported will be considered in determining whether there is a gross understatement of qualified use tax.

(4) For purposes of this section, “acceptable tax return” means a timely filed original return that is filed pursuant to Article 1 (commencing with Section 18501), Article 2 (commencing with Section 18601), Section 18633, Section 18633.5 of Chapter 2 (commencing with Section 18501) of Part 10.2, or Article 3 (commencing with Section 23771) of Chapter 4 of Part 11.

(b) This section applies to reporting of purchases of tangible personal property made on or after January 1, 2010, in taxable years beginning on or after January 1, 2010.