In any district or part of a district within San Bernardino and Riverside Counties, bears may be taken at any time with traps within a good and substantial fence, as such fence is described in Section 17121 of the Food and Agricultural Code, surrounding beehives, if no part of the fence is at a distance greater than 50 yards from a beehive, and if a conspicuous sign is posted and maintained at each entrance to the enclosed premises to give warning of the presence of the traps. No iron or steel-jawed or any type of metal-jawed trap shall be used to take bear under this section.