On paper, the Highline Trail is one, long 51-mile backpack trip. In reality, it's a series of connected trails.
The great hike along the Highline Trail is a 10.75-mile section that begins at See Canyon Road (Forest Road 284) to the fish hatchery (Forest Road 289). The best way to hike this is by parking a car at each end.
The hike is long and strenuous if you aren't in good shape, but, if you are, the views are incredible.
Detailed descriptions of the hike are available in "Day Hikes and Trail Rides in Payson's Rim Country" available in the Forest Service office.