California Code, Evidence Code - EVID § 1521

(a) The content of a writing may be proved by otherwise admissible secondary evidence. The court shall exclude secondary evidence of the content of writing if the court determines either of the following:

(b) Nothing in this section makes admissible oral testimony to prove the content of a writing if the testimony is inadmissible under Section 1523 (oral testimony of the content of a writing).

(c) Nothing in this section excuses compliance with Section 1401 (authentication).

(d) This section shall be known as the “Secondary Evidence Rule.”