CCP §638: A referee may be appointed upon the agreement of the parties filed with the clerk, or judge, or entered in the minutes, or upon the motion of a party to a written contract or lease that provides that

A referee may be appointed upon the agreement of the parties filed with the clerk, or judge, or entered in the minutes, or upon the motion of a party to a written contract or lease that provides that any controversy arising therefrom shall be heard by a referee if the court finds a reference agreement exists between the parties: (a) To hear and determine any or all of the issues in an action or proceeding, whether of fact or of law, and to report a statement of decision. (b) To ascertain a fact necessary to enable the court to determine an action or proceeding. (c) In any matter in which a referee is appointed pursuant to this section, a copy of the order shall be forwarded to the office of the presiding judge. The Judicial Council shall, by rule, collect information on the use of these referees. The Judicial Council shall also collect information on fees paid by the parties for the use of referees to the extent that information regarding those fees is reported to the court. The Judicial Council shall report thereon to the Legislature by July 1, 2003. This subdivision shall become inoperative on January 1, 2004.