If all you want is tumbling material, go here. There are two mines that allow fee digging. The first on the road in is Teddy Ridge. Some people have found nice schillers and reds here. They are the exception rather than the norm.
Most people find smaller clear, straw, and light copper schiller.
If you want some larger stones than the public area has to offer, by all means dig here. The Dust Devil is the premiere fee digging site for sunstones in the world. Mine owner Don Buford will show you where to dig. The best way is to screen the loose rock that is ripped up from the floor and walls of the pit by their D-9. You can also dig the walls if you have the energy.