From Gainesville, go west on SR 20 to Hawthorne. Take the exit for US 301, but just before US 301, turn right onto SE 221st Street, aka Johnson Street (the main drag through Hawthorne). Go through the four way stop, and take the next right onto SE 71st Ave, aka SE 2nd Ave (if you cross the railroad tracks you have overshot). There will be a sign announcing the Gainesville Hawthorne Trail just after you turn. A little ways down turn left into the trailhead parking lot.
