RCW 46.10.300
Definitions.
The following definitions apply throughout this chapter unless the context clearly requires otherwise.
(1) "All terrain vehicle" means any self-propelled vehicle other than a snowmobile, capable of cross-country travel on or immediately over land, water, snow, ice, marsh, swampland, and other natural terrain, including, but not limited to, four-wheel vehicles, amphibious vehicles, ground effect or air cushion vehicles, and any other means of land transportation deriving motive power from any source other than muscle or wind; except any vehicle designed primarily for travel on, over, or in the water, farm vehicles, or any military or law enforcement vehicles.
Then we go to,
46.09.450
Authorized and prohibited uses for off-road vehicles.
(1) Except as otherwise provided in this section, it is lawful to operate an off-road vehicle upon:
(a) A nonhighway road and in parking areas serving designated off-road vehicle areas if the state, federal, local, or private authority responsible for the management of the nonhighway road authorizes the use of off-road vehicles;
(b) A street, road, or highway as authorized under RCW
46.09.360; and
(c) Any trail, nonhighway road, or highway within the state while being used under the authority or direction of an appropriate agency that engages in emergency management, as defined in RCW
46.09.310, or search and rescue, as defined in RCW
38.52.010, or a law enforcement agency, as defined in RCW
16.52.011, within the scope of the agency's official duties.
(2) An off-road vehicle operated on a nonhighway road or on a street, road, or highway as authorized under RCW
46.09.360 and this section is exempt from both registration requirements of chapter
46.16A RCW and vehicle lighting and equipment requirements of chapter
46.37 RCW.
(3) It is unlawful to operate an off-road vehicle upon a private nonhighway road if the road owner has not authorized the use of off-road vehicles.
(4) Nothing in this section authorizes trespass on private property.
(5) The provisions of RCW
4.24.210(5) apply to public and private landowners who allow members of the public to use public facilities accessed by a highway, street, or nonhighway road for recreational off-road vehicle use.
[
2013 2nd sp.s. c 23 § 15; 2011 c 171 § 27; 2010 c 161 § 221; 2006 c 212 § 2; 2005 c 213 § 4. Formerly RCW
46.09.115.]
Washington makes a distinction between wheeled and non wheeled off road vehicles but never mentions tracked vehicles.
RCW 46.04.546
Snowmobile.
"Snowmobile" means a self-propelled vehicle that is capable of traveling over snow or ice that (1) utilizes as its means of propulsion an endless belt tread or cleats, or any combination of these or other similar means of contact with the surface upon which it is operated, (2) is steered wholly or in part by skis or sled type runners, and (3) is not otherwise registered as, or subject to, the motor vehicle excise tax in the state of Washington.
So by the letter of the rule the Tuckers with skis on the front are snowmobiles. So is Mr Loggah's Lombard.
http://www.snocobra.com/trail-use/
This website breaks down what each state considers a snowmobile.
If the Washington State legislature changed a few words you could register and operate a fully tracked snowcat as a snowmobile and possibly operate on groomed trails.
Or operate as a non-wheeled ATV.
Then there is the Fed's take on it.
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3799973.pdf
(Sorry for the rambling. It's Sunday.)