Wyo. Stat. § 24-1-121
The board of county commissioners of every county, wherein is situated any mountain road or highway or portion thereof, which would be liable to receive unusual injury and damage by driving over the same herds of cattle, horses or flocks of sheep, shall have the power, by order entered in the records of such board of commissioners, to designate so much of such road or highway as would be so liable to receive unusual injury and damage, as, not a highway for herds of horses, cattle or flocks of sheep, a notice of which designation shall be posted at convenient and conspicuous places along, and in the vicinity of the portion of such road or highway so designated, which notices shall likewise reasonably point out the lieu road or highway laid out as hereinafter provided.
W.S. 24-1-121