Cal. Sts. & High. Code § 26082

Upon the receipt of a petition in writing, signed by at least 25 percent in number of the registered voters residing within the district, the California Transportation Commission shall declare the position on the commission held by the county surveyor or county engineer, as the case may be, vacant, and nominate and appoint a person to fill the vacancy who is a civil engineer and who, in the opinion of the California Transportation Commission, is qualified to serve on the commission.