Others will come on to verify, but it would be Hwy 89 East through McCloud for about 80 miles and then to Hwy 44 for maybe 50 miles to Hwy 36 and East (left) to Susanville.....There is nothing out of the ordinary as for terrain. There is no way to figure September weather but generally never any problems. It is a nice drive in my opinion. Probably 140 miles total if my memory is correct.