There is one grade of any note, for about a mile - on 44 east of the town of Old Station. The highway climbs up the Hat Creek Rim. Right at the top of the grade is a short paved spur to a scenic overlook with interpretive signs explaining the volcanic geology. The rest of the road is mostly flat to very gentle rolling, and mostly straight with a few gentle curves.
September is usually warm and sunny, with cool nights. Although snow can occur, it is not common.
The forest is well roaded, with many unpaved roads leaving the highway in to the woods. Lots of boondocking opportunities if you are looking for a place to spend the night. Drive down one of the side roads until you are out of sight and sound of the highway.
There are no services between Old Station and Susanville. One large developed rest area with RV lanes about halfway, at the Bogard Ranger Station.
I live there (Lake Almanor area). If you want more specifics PM me.
=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=
So many campsites, so little time...
~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~
