Welf. & Inst. Code, § 653.7

If the probation officer does not take action under Section 654 and does not file a petition in juvenile court within 21 court days after the application, or in the case of an affidavit alleging that a minor committed an offense described in Section 602 or alleging that a minor is within Section 602, does not cause the affidavit to be taken to the prosecuting attorney within 21 court days after the application, he or she shall endorse upon the affidavit of the applicant the decision not to proceed further and the reasons therefor and shall immediately notify the applicant of the action taken or the decision rendered by him or her under this section. The probation officer shall retain the affidavit and the endorsement thereon for a period of 30 court days after the notice to the applicant.