Free Dry Camping at Aqua Fria National Monument
On Highway I-17 between Flagstaff and Phoenix you can dry camp or boondock free for 14 days. Entrance to the monument on Bloody Basin Road, exit 259 of I-17. There are some toilets there, but not much else.
The Agua Fria National Monument covers an area of high desert around the boundary between the Sonoran cactus lands and the grass-chaparral belt, it is about 1/3 of the way between Phoenix to Flagstaff.