Every railroad corporation operating its lines of road or any part thereof within this state, between the fifteenth day of July and the first day of November of each and every year, upon each side of its line of road, shall plow as a fire guard a continuous strip of not less than six feet in width, which said strip of land shall run parallel with said line of railroad and be plowed in such a good and workmanlike manner as to effectually destroy and cover up the vegetation thereon and be sufficient to prevent the spread of fire. In addition thereto all such railroad corporations shall cause to be burned, between said dates, all the grass and vegetation lying between the said plowed strips and the track of said road, and the outer line of said strip of plowed land shall be upon the outer line of such corporation's right-of-way or, if upon land owned by said corporation, one hundred feet on either side from the center of the road. Such fire guard to be so plowed need not be constructed within the limits of any town or city, nor along the line of a railroad running through the mountains, nor in other lands where plowing would be impracticable, but the provisions respecting the burning of a strip on each side shall be duly conformed with whenever any vegetation is found along such line of road. The boards of county commissioners of the various counties of the state shall prescribe for their respective counties where the plowing of such fire guard and burning shall be done.