And don't forget Utah 12 from Torrey to Bryce Canyon. It's a fantastic road and Bryce Canyon is stunning
Ill echo that, I'll also say don't bother going as far south as LA and head inland somewhere around Morro Bay. I'll also add that whilst everybody goes to the GC , Zion and Bryce ( I do like Bryce, so nice I went twice ) i've fonder memories of Canyon de Chelly which isn't too far south from Monument and also Mesa Verde NP further north . Canyon de Chelly is largely unspoilt , beautiful and you get a real sense of what it must have been like to live there before the white men came, likewise the cave dwellings at Mesa Verde.
if you want to avoid the crowds at GC i was told the North rim was quieter , however the HW67 down to the rim (which in itself is supposed to be a great road ) was closed due to snow and the JAcobs Lake campground was shut so i took one of the many trails down to the rim and was on my own at a fantastic lookout. I then rode the 60-70 miles up to Kanab & stayed there the night and never saw another car en route.
There is just too much to see in the Western USA . HAve a great trip
EDIT : Just posted and then saw your last post , what a bummer