What is the burden of proving a valid arbitration agreement?

A party who petitions to compel other parties to an arbitration agreement to arbitrate a dispute bears the burden of proving the existence of a valid arbitration agreement by a preponderance of the evidence. (Jones v. Jacobson (2011) 195 Cal.App.4th 1, 15.) A nonsignatory who seeks to enforce an arbitration agreement against a signatory has the burden to show that the nonsignatory is a party to the arbitration agreement covering the dispute. (Ibid.)

"There is no uniform standard of reviewing for evaluating an order denying a motion to compel arbitration. [Citation.] If the court's order is based on a decision of fact, then we adopt a substantial evidence standard. [Citations.] Alternatively, if the court's denial rests solely on a decision of law, then a de novo standard of review is employed. [Citations.]" (Robertson v. Health Net of California, Inc. (2005) 132 Cal.App.4th 1419, 1425.)