In all cases in which a boundary marker along the right-of-way of a public highway has been disturbed or removed by a public agency of the State or a county in connection with the widening, construction, or maintenance of the highway, the public agency which caused the disturbance or removal shall, if requested by an owner of land a boundary marker of which has been so affected, restore the boundary marker or set a new one at the point of intersection of the affected boundary of the owner’s land with the boundary of the right-of-way; provided that no boundary marker shall be restored or set unless its proper location has been established by law or by agreement of all persons having an interest in the location thereof; and provided further that this section shall not apply to markers disturbed or removed prior to January 1, 1950.