Cal. Evid. Code § 240

(a) Except as otherwise provided in subdivision (b), “unavailable as a witness” means that the declarant is any of the following:
1. (1) Exempted or precluded on the ground of privilege from testifying concerning the matter to which his or her statement is relevant.
2. (2) Disqualified from testifying to the matter.
3. (3) Dead or unable to attend or to testify at the hearing because of then-existing physical or mental illness or infirmity.
4. (4) Absent from the hearing and the court is unable to compel his or her attendance by its process.
5. (5) Absent from the hearing and the proponent of his or her statement has exercised reasonable diligence but has been unable to procure his or her attendance by the court’s process.
6. (6) Persistent in refusing to testify concerning the subject matter of the declarant’s statement despite having been found in contempt for refusal to testify.
(b) A declarant is not unavailable as a witness if the exemption, preclusion, disqualification, death, inability, or absence of the declarant was brought about by the procurement or wrongdoing of the proponent of his or her statement for the purpose of preventing the declarant from attending or testifying.
(c) Expert testimony that establishes that physical or mental trauma resulting from an alleged crime has caused harm to a witness of sufficient severity that the witness is physically unable to testify or is unable to testify without suffering substantial trauma may constitute a sufficient showing of unavailability pursuant to paragraph (3) of subdivision (a). As used in this section, the term “expert” means a physician and surgeon, including a psychiatrist, or any person described by subdivision (b), (c), or (e) of Section 1010.
The introduction of evidence to establish the unavailability of a witness under this subdivision shall not be deemed procurement of unavailability, in absence of proof to the contrary.