California Codes, Code of Civil Procedure - CCP, Part 2 — Of Civil Actions, Title 13 — Appeals in Civil Actions, Chapter 1 — Appeals in General, Section 909

In all cases where trial by jury is not a matter of right or where trial by jury has been waived, the reviewing court may make factual determinations contrary to or in addition to those made by the trial court. The factual determinations may be based on the evidence adduced before the trial court either with or without the taking of evidence by the reviewing court. The reviewing court may for the purpose of making the factual determinations or for any other purpose in the interests of justice, take additional evidence of or concerning facts occurring at any time prior to the decision of the appeal, and may give or direct the entry of any judgment or order and may make any further or other order as the case may require. This section shall be liberally construed to the end among others that, where feasible, causes may be finally disposed of by a single appeal and without further proceedings in the trial court except where in the interests of justice a new trial is required on some or all of the issues.