Dec 1st through Mar 31st, or as posted, a valid Washington State Sno-Park Permit is required in certain areas.
Salmon La Sac Trailhead
Snowmobiling
https://www.fs.usda.gov/recarea/okawen/recarea/?recid=57781
Easton Reload Sno-Park
Snowmobiling
https://parks.wa.gov/find-sno-parks/easton-reload-sno-park