San Diego? San Francisco?
Why not start from Los Angeles or Ventura?
a) You can head out of Sunland via Big Tujunga Rd and up the Angeles Forest Road
(But that road is murderously steep and nearly impossible with panniers.)
b) Or you can head up from San Fernando to Santa Clarita
c) Or you can ride/take the Surfliner to Ventura and then follow the Santa Clara Valley east
With b or c there are a number of great bike trails that follow the river around Santa Clarita
Then you top out at Soledad Pass just south of Palmdale.
Follow the Sierra Highway (Old Calif 14) along the RR tracks all the way to Mojave
Stay on Calif 14 a few miles north of Mojave
Turn right (east) on Calif City Blvd
In Calif City take Randsburg Road to US 395
a) You can head up thru either the Owens Valley via Bishop
b) Or thru Death Valley via Beatty, NV
Death Valley is getting very hot by late May/early June.
If you do decide to go via Death Valley - ride at sunrise and evening.
The Owens Valley has the snow-capped Sierras this time of year.
But US 385 is mostly 4-lane and busy.
One variation is to head up CA 178 towards Death Valley and cut back on CA 190 and CA 136.
A little longer, but much more peaceful.
Then thru Tonopah, NV -
East on US 6 to Warm Springs -
East on NV 375 to Hiko Junction -
North on US 93 (mostly east) to Caliente and Panaca
East on NV 319 to Utah border
East on UT 56 to Cedar City
The Nevada section is VERY remote.
See journal for photos: