The trailhead is Susanville has a gravel parking area and sits across the street from the old Susanville Railroad Station, from which the building and an old train car still remain.
The South Side Trail is a more technical, single track route paralleling much of the length of the Bizz Johnson Trail. You'll see several forks with it over the course of the rail trail.
Goumaz Campground marks the approximate halfway point of the full length of the trail. Turning around here will make the out and back distance from Susanville around 27 miles.