I believe that the nature preserve is only in Pokemon black 2 and white 2. If you have that version, you can't get to it until you have seen all of the Pokemon in the unova region. Then this area is available, but is not put on the map, simply because there is not enough room. You can go there, and find shiny Haxorous in a clearing somewhere. I am not sure if other shinies appear there, but apparently Haxorous is just standing there and you can battle it without searching through grass for it. I'd bet that you can probably find some other cool Pokemon there though.