Idaho Code § 25-1907

Any person owning or having charge of sheep, who herds, grazes, or pastures the same, or permits or suffers the same to be herded, grazed or pastured, on any cattle range previously occupied by cattle, or upon range usually occupied by any cattle grower, either as a spring, summer or winter range for his cattle, is guilty of a misdemeanor; but the priority of possessory right between cattle and sheep owners to any range, is determined by the priority in the usual and customary use of such range, either as a cattle or sheep range.