Gov. Code, § 65101

(a) The legislative body may create one or more planning commissions each of which shall report directly to the legislative body. The legislative body shall specify the membership of the commission or commissions. In any event, each planning commission shall consist of at least five members, all of whom shall act in the public interest. If it creates more than one planning commission, the legislative body shall prescribe the issues, responsibilities, or geographic jurisdiction assigned to each commission. If a development project affects the jurisdiction of more than one planning commission, the legislative body shall designate the commission which shall hear the entire development project.

(b) Two or more legislative bodies may:

(1) Create a joint area planning agency, planning commission, or advisory agency for all or prescribed portions of their cities or counties which shall exercise those powers and perform those duties under this title that the legislative bodies delegate to it.

(2) Authorize their planning agencies, or any components of them, to meet jointly to coordinate their work, conduct studies, develop plans, hold hearings, or jointly exercise any power or perform any duty common to them.