All orders and notices issued by the county board of appeals or any county official pursuant to the authority of this chapter shall be served on the person to whom they are directed, either by registered mail or by personal delivery to such person. Service on nonresidents and persons who cannot be found in the county shall be made by publication of such order or notice once in a newspaper of general circulation in the county and by posting the same on the tree concerned in a conspicuous manner. Service shall be deemed to have been made on the day of such mailing, publication or posting. (Mont. Co. Code 1965, § 113-8.)