Big Timber Creek Trail can be runed as an out-and-back or as a part of several loops, the most common being the Yellow Peak Loop with Rocky Creek Trail. You may want to consider camping if you plan on running the entire trail or adding loops. It has some great, smooth singletrack, some more rugged sections and some unavoidable steeper climbs.
Access to Big Timber Creek is via the Timber Creek Road #105. This is a rough road so many start their run closer to the USFS kiosk board near Swan Basin. It is 4.5 miles from the kiosk to the start of the trail (please take this extra milage into consideration when planning your run).
The official beginning of the trail is at a gate across Big Timber Road just uphill from a shallow stream crossing. It then climbs and follows this road, past another wire gate, about 1/4 mile where a good singletrack bears left away from the road.
This short trail contours down and rejoins the ATV road before descending steeply to parallel Big Timber Creek. The trail is open to ATVs to the next gate.
Once past the ATV gate, the trail is easy to follow and well defined. The trails beyond this gate are still open to MX bikes so don't be surprised to hear some "brap." Soon after the gate is a stream crossing. This is Rocky Creek and the Rocky Creek Trail #6184
takes off to the right just after this crossing.
The trail then follows Big Timber Creek along the valley, climbing gently for about another 4 miles before entering the timber and gaining elevation more quickly. This is a short, wet section of trail near the end of the sage valley in an aspen grove and a little ways above the junction with Cabin Creek Trail.
After entering the timber, the trail gets much more rugged and climbs close to 2000' to the pass between Big Timber and the Park Fork. Much of this section is open sage meadows mixed with steeper more rugged trail.
Near the head of Big Timber Creek, the trail crosses several springs and has been badly washed out. Above the washout, the trail crosses a boggy area then turns and climbs up on a steep bench, passing giant white pine skeletons along the way to the pass.
North of the pass, at 9700', the trail drops 300' vertical across a rocky scree field. There are some beautifully constructed, terraced switchbacks criss-crossed by dirt-bike shortcuts. This makes for a somewhat exposed descent.
Beyond the scree field, the trail rolls and climbs along the edge of the head of the Park Fork of Pahsimeroi's Big Creek to the junction with Rocky Creek Trail #6184
where it ends 11.8 miles in.