California Code, Penal Code - PEN § 939.71

(a) If the prosecutor is aware of exculpatory evidence, the prosecutor shall inform the grand jury of its nature and existence.  Once the prosecutor has informed the grand jury of exculpatory evidence pursuant to this section, the prosecutor shall inform the grand jury of its duties under Section 939.7.  If a failure to comply with the provisions of this section results in substantial prejudice, it shall be grounds for dismissal of the portion of the indictment related to that evidence.

(b) It is the intent of the Legislature by enacting this section to codify the holding in Johnson v. Superior Court, 15 Cal. 3d   1 248, and to affirm the duties of the grand jury pursuant to Section 939.7.