Idaho
Idaho has more than two dozen well defined groomed trail systems spread out from one end of the state to the other.
There are probably as many as that or more spots where you can explore with nary a groomed trail in sight. Most of these are on BLM or forest service land and just like the groomed trail systems scattered across the state, the out-of-the-way places you can sled are found in just about every corner of Idaho at every elevation.
One of those areas is the Owyhee Mountains in southwest Idaho. There is no groomed trail system even close and cross country riding rules here. When the snows are right there is lots of excellent backcountry riding. And you can get a good look at Silver City, one of Idaho's most famous mining towns. Contact the BLM (208-384-3300) for more information.
In the southcentral part of the state are the Mount Bennett Hills, north of Gooding, roughly following the Gooding-Camas county border. This riding area is about 20 miles north of Gooding off State Highway 46.
Another great spot that is popular among several snowmobilers is Swan Valley, which is east of Idaho Falls and kind of west and north of Palisades Reservoir. Technically this area is in Bonneville County but it really is its own little area. Extreme riding rules here. Sheep Creek is a local favorite among the big horsepower crowds.
If you're in the Island Park area there is Mt. Jefferson, which is for experienced riders only. It offers some of the best backcountry riding in all of Idaho and is famous for its steep bowls and rugged terrain.
On the other side of the state, west of Council and hugging Hells Canyon, is the Seven Devils, another extreme riding area that might just be one of the best in the state. There are some dedicated followers who love this area for its hillclimbing and challenging boondocking. This area is not for the faint of heart or small horsepower sleds.
In central Idaho, a great backcountry ride is out of Yellow Pine. You follow the Stibnite Road (ungroomed) east out of Yellow Pine along the East and then South Fork of the Salmon River and there is some great drainage riding as well as climbing and sidehilling. Just be aware that you're close to a Wilderness area once you get farther back in, where you can't ride.
Another option is a couple of state parks where snowmobiling is allowed, including Priest Lake and Bear Lake. Sledders might not travel to Idaho just to ride one of these state parks, but if you're sledding in a nearby area, you should check them out. For more information go to the Idaho Parks and Recreation website http://parksandrecreation.idaho.gov.
One more riding area worth mentioning is the City of Rocks National Reserve, in southcentral Idaho. Snowmobiles are allowed on the unplowed roads during the winter and you can see some great rock formations in this reserve. For more detailed information, check out the listing below. The riding elevation here is between 5,500-8,867 feet. For more information, contact the City of Rocks National Reserve (208-824-5519).
We just scratched the surface of the backcountry riding that is available in Idaho. Although it primarily focuses on groomed trail systems, Idaho has a decent website dedicated to snowmobiling. Check out www.visitidaho.org/winter/.