Cal. Welf. and Inst. Code § 626.6
Notwithstanding Section 626.5, any peace officer who takes a minor who is 14 years of age or older into temporary custody under Section 625.3 shall take the minor without unnecessary delay before the probation officer of the county in which the minor was taken into custody, or in which the minor resides, or in which the acts took place or the circumstances exist which are alleged to bring the minor within the provisions of Section 602, and deliver the custody of the minor to the probation officer. The peace officer shall prepare a concise written statement of the probable cause for taking the minor into temporary custody and the reasons the minor was taken into custody and shall provide that statement to the probation officer at the time the minor is delivered to the probation officer.
Ca. Welf. and Inst. Code § 626.6