@divebuddy
//yeah, I know, so why live in a desert then//
The theory I was alluding to was predicated on the fact that archaological remains of day-to-day living were known from the area, which proves long-term habitation.
The obvious question arises: how the heck did they manage such a lifestyle in a wasteland like this? They sought more remains and found evidence of farming and sea fishing, as opposed to hunter/gatherer culture.
Next question: if they farmed, where had all the soil gone and what was seasonal rainfall like, in that region (it has quirks of terrain etc.) thousands of years ago? Finding a suitable proxy for "paleoclimate" is not easy and I've forgotten how they pulled that off. I can return to this point, if need be.
End result: changed weather patterns was the emerging story. The meso-american culture who carved a town out of a cliff face similarly went extinct due to changed rainfall patterns but a lot later, 1000AD or thereabouts.
Or, if you prefer, the aliens took a dislike to humans grovelling at their feet all the time and demanding things be magicked up for them and meddled with their weather until their land was laid waste.