This spot is located in the Prescott Basin.
The Prescott Basin is an area immediately south and west of Prescott, Arizona and encompasses approximately 59,000 acres (about 4% of the Prescott National Forest).
Dispersed camping is camping outside of developed campgrounds. In contrast to camping in developed campsites, dispersed camping is more primitive, and generally has no amenities such as trash collection, water or toilets.
A map of the area can be found here: https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3797787.pdf
This is a good hike. It has some great views of Prescott and the surrounding area. I didn't get any pictures while on the hike itself, but I got some on Senator Highway.
Thumb Butte Loop was super rough to travel on. If you plan to go past site 15 I'd strongly suggest something with high ground clearance. Sites 1, 2, and 3 were not clearly marked from the road. Sites 4 and 5 were immediately on the roadside. Most of the pictures posted are from site 7 which is more high desert than most of the other sites. This site accommodated quite easily backing in to the site with a camper. Sites 6 and 7 are on the outside of a switchback and had some dropoffs on the sides. Some of the spaces have rock fire rings and other have metal fire rings. There was a porta potty at sites 9, 10, and 11 (one group area) but that was the only bathroom I saw. Sites 16 and 17 are laid out to accommodate a very large group and could handle a few trailers. There is a giant (like 6 ft) fire ring in between the sites but it was FULL of broken bottles so I assume a popular local hangout. We also found a few handfuls of nails thrown across the road at this point on the road. Towards the south side of the road between sites 20 and 21 the road gets narrow and goes up the side of a mountain to Sierra Prietta Overlook and has quite the drop off.