Saguaro National Park in Tucson, Arizona, has two segments, one east of town and one west of town. If you want a tough workout on paved roads in a gorgeous setting, head east. You have to pay the daily walk-in fee to enter the park, but then you can run relatively traffic free (if you go early)on a loop of 8-9 miles through beautiful desert scenery with the Rincon mountains in the background. But be warned, this course is tough, with lots of ups and downs, but well worth it for the views! Bring water if it's hot!