Near Sun Valley, the 4 mile Proctor Mountain Loop is a hardcore mountain bike climb of 2,000 feet over 2 miles. Although it really starts at the paved bike path along Sun Valley Road from in town, it is recommended to drive to the Trail Creek Cabin parking area. From here, cross Trail Creek on the XC ski bridge and head upstream on the dirt road behind the ampitheatre. Once in the trees, follow the trails to the right. This leads up the mountain. Themountain bike route back down is awesome.
Overall, Proctor Mountain Loop is the 55th most popular mountain bike trail of all 63 mountain biking rides in Idaho.