Cal. Veh. Code § 23635
When an allegation of a violation of Section 23152 is dismissed by the court, an allegation of a different or lesser offense is substituted for an allegation of a violation of Section 23152, or an allegation of a separate conviction is dismissed or stricken, the court shall specify on the record its reason or reasons for the order. The court shall also specify on the record whether the dismissal, substitution, or striking was requested by the prosecution and whether the prosecution concurred in or opposed the dismissal, substitution, or striking.
When the prosecution makes a motion for a dismissal or substitution, or for the striking of a separate conviction, the prosecution shall submit a written statement which shall become part of the court record and which gives the reasons for the motion. The reasons shall include, but need not be limited to, problems of proof, the interests of justice, why another offense is more properly charged, if applicable, and any other pertinent reasons. If the reasons include the "interests of justice," the written statement shall specify all of the factors which contributed to this conclusion.
Ca. Veh. Code § 23635