As I biked, I kept noticing great places to camp, which is allowed. Just bring your own water for the western segment.
Take Highway 36 to Westwood, turn north onto Lassen County Road A-21 and continue 3 miles to County Road 101 (just before the railroad tracks). Follow County Rd 101 a half mile until you reach Mason Station trailhead. There is ample parking at the station. You will see a large sign with trail brochures near a restroom and the trailhead. Follow the path from the trailhead for a quarter mile until you reach the railroad grade.
To reach the Susanville Depot, follow Highway 36, which becomes Main Street in Susanville. Continue on Main Street through Historic Uptown Susanville to Weatherlow Street, at the first stoplight at the base of the hill. Turn right on Weatherlow (which becomes Richmond Road) and continue a half mile to the Susanville Railroad Depot Trailhead Visitor Center. The trail begins at the depot, which has parking.