Unlike the East, South, and Midwest, most of the Western United States is Federal land (Bureau of Land Management, USDA/National Forest Service, National Parks, et cetera), and while some of it is occupied there are large swaths of remote areas that receive few visitors. Of course, you do need to know where to go lest you drive down a presumably unused desert road or jeep trail only to find yourself in the middle of the local party spot or an amateur astronomer’s haven, but some scouting with USDA Forest maps and Motor Vehicle User Maps will give you a good idea where ‘the middle of nowhere’ is.
As for disposing of a body, the desert is full of scavengers that will dig for a meal, and while in the pre-genomic sequencing days a few weeks of exposure would reduce a corpse to being identifiable only by dental records and old bone fractures, really ‘erasing’ a body is much more difficult than you’d imagine. Cremating a body to ash requires intense heat—far more than you could generate with a normal bonfire or high temperature kiln—and digging a deep grave is exhausting work. Many people make the mistake of thinking that a body weighted down will stay under water without considering that wave action and decomposition can easily allow enough remains to surface and be blown to shore for identification. Walter White’s favored method of corpse disposal of reduction using hydrofluoric acid is certainly workable but HF is pretty dangerous stuff to handle in large quantities and it isn’t as if you can just dump the result down the drain without thoroughly neutralizing it, and if you are ordering large quantities to a private residence someone is going to be asking questions.
Comparatively, if you have a nearby desert or bog, disposing of the body by finding a remote location and letting nature do its work is difficult to trace provided you aren’t seen coming or going. And every year people go missing in the desert, in national parks, and out in the ocean, and their bodies aren’t found for years if ever even when it turns out that they are only a few miles from civilization.