Cal. Code of Civil Procedure § 2031.240

(a) If only part of an item or category of item in a demand for inspection, copying, testing, or sampling is objectionable, the response shall contain a statement of compliance, or a representation of inability to comply with respect to the remainder of that item or category. (b) If the responding party objects to the demand for inspection, copying, testing, or sampling of an item or category of item, the response shall do both of the following: (1) Identify with particularity any document, tangible thing, land, or electronically stored information falling within any category of item in the demand to which an objection is being made. (2) Set forth clearly the extent of, and the specific ground for, the objection. If an objection is based on a claim of privilege, the particular privilege invoked shall be stated. If an objection is based on a claim that the information sought is protected work product under Chapter 4 (commencing with Section 2018.010), that claim shall be expressly asserted. (c) (1) If an objection is based on a claim of privilege or a claim that the information sought is protected work product, the response shall provide sufficient factual information for other parties to evaluate the merits of that claim, including, if necessary, a privilege log. (2) It is the intent of the Legislature to codify the concept of a privilege log as that term is used in California case law. Nothing in this subdivision shall be construed to constitute a substantive change in case law.