Riding thru Vegas is tough - tougher recently that I-15 had major washout damage.
If you choose to go via US 6 - stay on the Western Express to Ely.
Then take US 6 via Tonopah to Bishop - - even more remote than US 50.
Then follow US 395 and/or side roads to Hwy 14 - runs along the eastern escarpment of the Sierras.
Hwy 14 has some expressway section with parallel service roads.
Then Soledad Pass Road to Santa Clarita.
Or you can turn south at Tonopah and ride thru Death Valley - still hot.
Reconnecting to US 395 and Hwy 14.
Or if you are in a hurry -
From Cortez, Colo - head west on McElmo Road to Bluff, Utah.
Then take US 163 thru Monument Valley - tough but very scenic.
Then US 160 to Tuba City and US 89 / Hwy 64 to Grand Canyon.
Continue on Hwy 64 to Williams - then you have to ride I-40 a few miles.
Get on to Old Route 66 thru Peach Springs to Kingman -
Then take Old Route 66 over the pass to Oatman and Needles.
Another short stretch of I-40 - then Old Route 66 via Amboy to Barstow.
These are the best preserved stretches of Old Route 66 - lots of roadside history.
BUT, BUT - - you need to be aware of temperatures and water in the Amboy stretch.
The Amboy Café is kinda reopened - you should be able to get water, but check first.