Cal. Rev. & Tax. Code § 439.1
For purposes of this article "restricted historical property" means qualified historical property, as defined in Section 50280.1 of the Government Code, that is subject to a historical property contract executed pursuant to Article 12 (commencing with Section 50280) of Chapter 1 of Part 1 of Division 1 of Title 5 of the Government Code. For purposes of this section, "qualified historical property" includes qualified historical improvements and any land on which the qualified historical improvements are situated, as specified in the historical property contract. If the historical property contract does not specify the land that is to be included, "qualified historical property" includes only that area of reasonable size that is used as a site for the historical improvements.
Ca. Rev. and Tax. Code § 439.1