Originally Posted by
fietsbob
Gobi desert, maybe Namibia?
Fall in the US is among the hottest periods in (southern-hemisphere) Namibia. I cycled through at end of April 2013 and was surprised at how much it reminded me of deserts in Nevada. So except for the timing/cost this could be a good choice for someone who enjoyed deserts in Nevada, particularly if you are ok with some gravel road cycling.
One of the two photos below was taken near Panamint Springs in Death Valley and the other was taken in Namibia...
As far as other choices in the US west, most have been mentioned, but I'm partial to some of the canyon country in UT and would probably include them in a loop and take in a few of the parks like Capital Reef or Arches.