California Code, Penal Code - PEN § 2622

When the order for personal appearance is not made pursuant to Section 2620 or Section 2621 the deposition of the prisoner may be taken in the manner provided for in the case of a witness who is sick, and Chapter 4 (commencing with Section 1335) of Title 10 of Part 2 shall, so far as applicable, govern in the application for and in the taking and use of that deposition.  The deposition may be taken before any magistrate or notary public of the county in which the prison is situated;  or in case the defendant is unable to pay for taking the deposition, before an officer of the prison designated by the board, whose duty it shall be to act without compensation.  Every officer before whom testimony shall be taken under this section, shall have authority to administer, and shall administer, an oath to the witness that his or her testimony shall be the truth, the whole truth, and nothing but the truth.