We quite enjoy that are starting about mid September to mid to late November. You have to be prepared though, as by late October you could end up with a cold snap, or it might be warmer than expected. You tend to get swings in temp. For the Moab area, it's always wise to check the web calendar of events to make sure there are no bike ride event, atv, 4X4 or even car shows going on as it can get quite crowded during the many events that take place there.