36 CFR § 2.19 - Winter activities.
(a) Skiing, snowshoeing, ice skating, sledding, innertubing, tobogganing and similar winter sports are prohibited on park roads and in parking areas open to motor vehicle traffic, except as otherwise designated.
(b) The towing of persons on skis, sleds, or other sliding devices by motor vehicle or snowmobile is prohibited, except in designated areas or routes. This paragraph shall not apply to sleds designed to be towed behind snowmobiles and joined to the snowmobile with a rigid hitching mechanism.
(c) Failure to abide by area designations or activity restrictions established under this section is prohibited.