The attorney-client privilege is one of the most closely guarded layman-professional relationships, but California takes it to a whole new level. It even has codified the attorney-client privilege (unlike other states which rely on rules derived from the ABA rules) in Cal. Evid. Code section 900 et seq.
It turns out that even when privilege has been used for abuse, California jurisdiction is highly unwilling to question the practice. In the case of Dp Pham, LLC v. Cheadle, a prima facie showing of privilege turned out to be one heck of a shield against disclosure.