Northwest of Smiths Ferry in the Boise National Forest, the Joes Creek Trail (2.5 mi / #137) provides access to the West Mountain Trail (10 mi / #131). These routes are shared by hikers, mountain bikers, off-road motorcycle and horseback riders. A good starting point is Sagehen Reservoir.
Note: As of September 2007, ATV riding on Forest Service roads is permitted only on designated roads. All ATVs must have a valid ATV registration. In addition, there is an extensive list of regulations that also must be met. Make sure to call the Boise National Forest HQ prior for a complete list (208) 373-4039.
Overall, West Mountain / Joes Creek is the 42nd most popular ATV riding trail of all 55 ATV trails in Idaho.