Big Timber Creek holds some amazing trails. They may be called "primitive" in an era when "flowy" is the norm. These are great trails nonetheless and harken back to a day not so long ago when trails were not judged by how easy they were to ride but a means to an end. This ride is a remote gem in the Gem State.
This is true Idaho backcountry so be prepared for anything from injury to weather to mechanicals to wildlife. Bring a map, bring a GPS, bring a saw, and have a plan and have a backup plan. Bring some Orange too is it is hunting season.
From the trailhead (a gate across the road) the ride follows Big Timber Creek Trail (Tr 6183.1). This is ridden heavily by ATVs, is rocky and loose, and descends steeply into the Big Timber Creek drainage. Remember this descent and save yourself some heartache because you will be coming back up this at the end of your ride.
Not too far along Big Timber Creek you come to a gate. This gate is the end of ATV access!! It is single track from here. There is still Motorcycle access but the trails are, for the most part, in great shape.
Further along the creek you come to a stream crossing. This is Rocky Creek and just beyond hang a right onto Rocky Creek Trail (Tr 6184). From here you will ride (and hike-a-bike too) along Rocky Creek close to 7 miles and climb about 2200' to a pass. You will Rocky Peak on the right and Junction and Yellow peaks on the left.
At this pass is a junction, go left back on to Big Timber Creek Trail (Tr 6183.1). There is another pass on the shoulder of Yellow Peak and steep, rocky and technical sections on your way 2500' downhill.
Once the Big Timber drainage opens up the trail opens up too. It is about 5 miles in this open valley back to the "ATV" gate. Remember that climb back to the trailhead and hopefully you remembered to stash some beers in a cooler there too. You earned them on this ride.