Hi, Ms X. Hope my answer is not late. Anyway, As I know, Autumn to Spring of the next year is the beat season to get though the desert, and late October to mid-November is the golden season, the low season of Hetian River. People usually start their trip from the south to the north, ,moving with the stream of the river. In addition, you can admire the poplar trees at their best time to see. It is a challenging work, although there are the dersert highway. Good Luck and take care.