Cal. Rev. & Tax. Code § 23504

Where a corporation formerly subject to tax under Chapter 2 (commencing with Section 23101) becomes subject to tax under Chapter 3 (commencing with Section 23501), the tax for the year in which the change occurs will be assessed under Chapter 2 (commencing with Section 23101) and not under Chapter 3 (commencing with Section 23501). For years subsequent to the year in which the change occurs, the tax will be assessed under Chapter 3 (commencing with Section 23501).