It has a river rock case about 12" deep then a layer of landscaping fabric followed by 8" of rough sand.Absolutely beautiful!!! I have some trimming clients that are looking to refurbish a small outdoor arena. I know nothing at all about arenas but it's obvious that you do. What is under the sand? What depth do you aim for with the sand? Is it just basic run of the mill sand?? Any and all help would be greatly appreciated!!!!