This trail is an extension of the Waterline Trail (hence the name) which parallels Orofino Gulch and eliminates the need to walk on the road to access trails further up the road. Driving up Orofino from Helena, watch for the Waterline trail on your left. This trail will eventually turn into the Waterline Extension and continue to roughly parallel the road.
The trail will pop out onto the shoulder for 20 meters just before Arrastra Gulch. Turn onto Arrastra Gulch and watch for the trail on your right just a short 10 meters down the road. The trail will eventually cross Orofino Gulch and pick back up for a short distance before connecting to Barking Dog Trail