California Code, Family Code - FAM § 3171

(a) If a stepparent or grandparent has petitioned, or otherwise applied, for a visitation order pursuant to Chapter 5 (commencing with Section 3100), the court shall set the matter for mediation.

(b) A natural or adoptive parent who is not a party to the proceeding is not required to participate in the mediation proceeding, but failure to participate is a waiver of that parent's right to object to a settlement reached by the other parties during mediation or to require a hearing on the matter.