Cal. Prob. Code § 13206
(a) If property is transferred to a transferee under this chapter, and the decedent’s personal representative later determines that another person has a superior right to the property by testate or intestate succession from the decedent, the personal representative may request that the transferred property be restored to the estate. Subject to subdivisions (b), (c), (d), (e), and (g) if the personal representative makes that request, the transferee is liable for all of the following:
(c) Subject to subdivision (d), if the transferee made a significant improvement to the transferred property in the good faith belief that the transferee was the successor of the decedent to that property, the transferee is liable for whichever of the following the decedent’s estate elects: