California Code, Revenue and Taxation Code - RTC § 1642

(a) An assessee of mining or mineral property located in more than one county and alleged to be unitary property, may, within the time specified in Sections 1603 and 1605, request a hearing before a panel comprising one assessment hearing officer from each county in which that unitary property is located by filing in each county concerned a multicounty application for reduction of assessment. The board of supervisors of each county in which the unitary property is located shall appoint one assessment hearing officer pursuant to Section 1636. In the event that the unitary property is located in an even number of counties, the assessment hearing officers shall designate one additional assessment hearing officer who shall be included in the panel. If the assessment hearing officers fail to designate the additional hearing officer within 60 days after the application is filed, the Office of Administrative Hearings shall designate the additional assessment hearing officer.

(b) Hearings before the panel of assessment hearing officers shall be conducted pursuant to Article 1 (commencing with Section 1601) governing equalization proceedings by county boards of equalization. All counties in which the unitary property is located shall be parties to the hearing. Hearings shall be held at the place or places as a majority of the panel shall designate.

(c) Section 1638 shall apply to the hearings by the panel.

(d) The presence of all members of the panel shall be necessary to constitute a quorum.