Cal. Public Utilities Code § 310

No vacancy in the commission impairs the right of the remaining commissioners to exercise all the powers of the commission. A majority of the commissioners constitutes a quorum for the transaction of any business, for the performance of any duty, or for the exercise of any power of the commission. Any investigation, inquiry, or hearing which the commission may undertake or hold may be undertaken or held by or before any commissioner or commissioners designated for the purpose by the commission. The evidence in any investigation, inquiry, or hearing may be taken by the commissioner or commissioners to whom the investigation, inquiry, or hearing has been assigned or, in his, her, or their behalf, by an administrative law judge designated for that purpose. Every finding, opinion, and order made by the commissioner or commissioners so designated, pursuant to the investigation, inquiry, or hearing, when approved or confirmed by the commission and ordered filed in its office, is the finding, opinion, and order of the commission.