Gettin' cold, ain't it?
You've just hit the Rockies and it is late October. You were lucky to have warm weather.
That is going to change this week - - big time. 40s for highs; teens for lows.
I would STRONGLY recommend that you get to lower elevation - not head straight for Cedar City.
There is an excellent straight shot from Bluff, Utah to Cameron, Ariz which will take you to Grand Canyon.
The North Rim is mostly closed now with few to no services - i.e. 45 miles away in Jacob Lake.
If you get to the South Rim, you can ride down to Williams - -
Then take Old Route 66 via Peach Springs, Oatman, and Needles to Amboy, Calif.
There is a remote, paved cutoff road from Amboy to Joshua Tree.
The direct, low route into L.A. is rather unpleasant along I-10 - sometimes even using I-10 - bleah!
If you are willing to suffer, head up into the San Gabriels via Big Bear.
The ride along the Angeles Crestcoming down into Glendale and head out to Santa Monica pier.
(Or, you can stay north of the San Gabriels and loop thru Santa Clarita via Soledad Canyon.)