Whenever the board of supervisors and the assessor of any county determine that, in order to maintain the equality of the assessment of property within the county, an appraisal of all or any class of property is required, the clerk of the board of supervisors and the assessor shall certify this determination to the State Board of Equalization. Thereupon, the assessor, the chairman of the board of supervisors, and the member of the State Board of Equalization from the district which includes the county constitute an appraisal commission to conduct the appraisal.