36 CFR § 2.16 - Horses and pack animals.
The following are prohibited:
(a) The use of animals other than those designated as “pack animals” for purposes of transporting equipment.
(b) The use of horses or pack animals outside of trails, routes or areas designated for their use.
(c) The use of horses or pack animals on a park road, except: (1) Where such travel is necessary to cross to or from designated trails, or areas, or privately owned property, and no alternative trails or routes have been designated; or (2) when the road has been closed to motor vehicles.
(d) Free-trailing or loose-herding of horses or pack animals on trails, except as designated.
(f) Obstructing a trail, or making an unreasonable noise or gesture, considering the nature and purpose of the actor's conduct, and other factors that would govern the conduct of a reasonably prudent person, while horses or pack animals are passing.
(g) Violation of conditions which may be established by the superintendent concerning the use of horses or pack animals.