Porcupine Spring Trail follows an old retired forest road that is gradually reverting back to singletrack. In the first 3.5 miles, the trail climbs only 400'. Wildlife is frequently seen along the entire length and the views of the Salmon River Mountains are breathtaking.
This is a popular out-and-back ride with Salmon locals seeking to escape the summer heat in the valleys but not seeking hair-raising challenges. Most riders, however, follow this trail as part of a shuttle ride to Twelvemile Meadow Trail #101
and Lime Creek Trail #100
Look for a cairn after 3.5 miles marking the start of Twelvemile Meadow Trail #101
and the steep climb there up to Twelvemile Meadows and the top of the Lemhi Mountains.
After about five miles, the road steepens but is still very rideable, topping out at about six miles in a broad saddle that is the north end of prominent Gold Bug Ridge. There is a "kelly hump" just to the left and the road continues beyond this. Fight through the saplings there and follow the now very rocky roadbed further to get a gander of the mighty Salmon River far below.
There are plenty of old spur roads along the way if your curiosity is piqued to explore.