From it's trailhead at Forest Road 492 (Santiam Sourdough Road) the trail climbs moderately for about 0.4 miles to it's junction with Twenty Mile Cutoff Trail #884, after which the grade levels off as the trail works it's way up Twentymile Creek Canyon.
About 1.4 miles past the last junction you reach the junction with Alaska Ridge Trail #856. This trail is unmaintained and hard to see. The junction is marked by a sign indicating that the Twentymile Creek Trail continues in either direction. Shortly after the junction the trail passes the ruins of an old cabin on the left, before dropping down to Twentymile Creek. There was once a bridge at this crossing, but it collapsed and was subsequently washed out.
At the time of this writing it is possible to walk downstream of the ford and cross on a segment of the bridge which is caught in a small logjam. After crossing the creek the trail passes a small meadow on the right before beginning to climb through heavy brush to its junction with Driveway extension trail #881.