You can ride on certain public lands managed by government agencies. You can view these riding areas on the online trail-mapping program. Once you find a riding area, you can print or download the map. You can also get maps from local U.S. Forest Service and Bureau of Land Management offices. These offices and their contact information can be found on page 4 of the Idaho Department of Parks and Recreation Off-Highway Vehicles brochure.
Check out these Moscow, ID ATV/OHV resources: