Cal. Civ. Proc. Code § 2030.230

If the answer to an interrogatory would necessitate the preparation or the making of a compilation, abstract, audit, or summary of or from the documents of the party to whom the interrogatory is directed, and if the burden or expense of preparing or making it would be substantially the same for the party propounding the interrogatory as for the responding party, it is a sufficient answer to that interrogatory to refer to this section and to specify the writings from which the answer may be derived or ascertained. This specification shall be in sufficient detail to permit the propounding party to locate and to identify, as readily as the responding party can, the documents from which the answer may be ascertained. The responding party shall then afford to the propounding party a reasonable opportunity to examine, audit, or inspect these documents and to make copies, compilations, abstracts, or summaries of them.