This park is mostly for mountain biking, though it gets some equine use also. I use the park as a proving-ground for new backpacks, boots, etc... The park stretches from the north side of Tempe Town Lake all the way to the Phoenix Zoo. From the zoo you can also get to the Papago Buttes trails. There are so many trails cut through this area that you need not worry about losing your way. Eventually all these trails find their way to the zoo or to the actual park at the southern part of the range. These trails are heavily used, especially on weekends, and are easy to find and follow. There are facilities (bathrooms and drinking fountains) at the southern end of the park and at the zoo.
There are various difficulty levels of trails available; it all depends on how hard you want to work. Even though this area is in the middle of the city there are still a number of wild-life viewing opportunities. If you are out early in the morning, close to sunset, or any time few people are around, you can see coyotes, jackrabbits, ground squirrels, and a variety of plant life along the trails.
This trail system is a nice connector between some of the other various parks in the area. The Scottsdale Greenbelt Park and Papago Park are connected by the trails around Tempe Town Lake. You can also get to Camelback from Papago via the canal that cuts through Papago. Aside from the Zoo, there are also the botanical gardens just up north and east of the zoo, also accessible from Papago. This is a good hiking (or mountain biking) area for short inner-city jaunts down the trail or for getting into shape for those longer, more difficult hikes.
Check out the Official Route and Triplogs.