Colorado- " Great sand dunes national park" in colorado.  Most of the film was shot close by in creed colorado.  They have the largest dune in the USA measured in vertical feet rise.  Its about 750 foot vertical rise for one big dune ( the second tallest dune at 700 feet is here in Utah-sand mountain little sahara)   The bad thing about colorado is there are no motor vehicles allowed on the dunes --such a wast of big sand.