Cal. Const. art. VI, § 3

The Legislature shall divide the State into districts each containing a court of appeal with one or more divisions. Each division consists of a presiding justice and 2 or more associate justices. It has the power of a court of appeal and shall conduct itself as a 3-judge court. Concurrence of 2 judges present at the argument is necessary for a judgment.

An acting presiding justice shall perform all functions of the presiding justice when the presiding justice is absent or unable to act. The presiding justice or, if the presiding justice fails to do so, the Chief Justice shall select an associate justice of that division as acting presiding justice.