Kirk Trailhead gives you options. Travel 3 miles to Deadwood. Travel 5 miles to Englewood Trailhead. Or ride the fantail loop to Sugarloaf Trailhead, then loop around back to Kirk. This is the only section of the Mickelson Trail with a loop, allowing you to park in one place and ride without backtracking.
Use of the trail does require a Mickelson Trail Pass for all users over age 12. You can purchase the pass at the trailhead or online. The exception to this would be when you are using the trail within city limits.