Found these current regulations from Forest Service and BLM regarding mechanisms in wilderness areas:
FOREST SERVICE: Mechanical Transport. Any contrivance for moving people or material in or over land, water, or air, having moving parts, that provides a mechanical advantage to the user, and that is powered by a living or nonliving power source. This includes, but is not limited to, sailboats, hang gliders, parachutes, bicycles, game carriers, carts, and wagons. It does not include wheelchairs when used as necessary medical appliances. It also does not include skis, snowshoes, rafts, canoes, sleds, travois, or similar primitive devices without moving parts.
BUREAU OF LAND MANAGEMENT. Regulations governing wilderness areas administered by the Bureau of Land Management provide in essence the same definition, but do not even refer to living/non-living power sources: Mechanical transport means any vehicle, device, or contrivance for moving people or material in or over land, water, snow, or air that has moving parts. This includes, but is not limited to, sailboats, sailboards, hang gliders, parachutes, bicycles, game carriers, carts, and wagons. The term does not include wheelchairs, nor does it include horses or other pack stock, skis, snowshoes, non-motorized river craft including, but not limited to, drift boats, rafts, and canoes, or sleds, travois, or similar devices without moving parts.
Well, there goes my zipline idea...