There are many object (tree) courses in the Flagstaff area. The most popular being the “Lake Mary” course and the “Old Munds” course.
Here is a map of the Old Munds course (PDF).
***Please be aware that object courses on private land and forest service land are illegal by nature. The Forest Service considers an object-style disc golf course an unauthorized use of Forest Service property. Officially, the Forest Service has a process for introducing new activities onto the forest – you have to apply for a special use permit, conduct an NEPA (environmental impact) study, plus more red tape. It’s a law put there to regulate what happens on federal lands.