I beleve that the dust is what was formerly known as the salt flats. the reason being is that in the good the bad and the mordecai the imprisoned bandit in the friendship gulag states that he hid his tresure in the salt flats and you find it in the dust. i know the salt flats was more damp and less desert but if you go to the highlands via the dust you will find a dried up riverbed leading to the dust. Prehaps this river fed mosture into the dust until hyperion dammed it off.