Cal. Civ. Proc. Code § 2031.230

A representation of inability to comply with the particular demand for inspection, copying, testing, or sampling shall affirm that a diligent search and a reasonable inquiry has been made in an effort to comply with that demand. This statement shall also specify whether the inability to comply is because the particular item or category has never existed, has been destroyed, has been lost, misplaced, or stolen, or has never been, or is no longer, in the possession, custody, or control of the responding party. The statement shall set forth the name and address of any natural person or organization known or believed by that party to have possession, custody, or control of that item or category of item.