Depending on which route you decide to take, you could stop at Twentynine Palms and perhaps drive through Joshua Tree NP as part of the onward journey to SD, or a more direct route and you could stop in Barstow. Both are closer to 6 hour drives. If you can find suitable lodgings in Blythe and it's just for an overnight that should be fine too.

A few options back up to SF from theme parks to beaches in the LA area to more sedate seaside towns like Cambria and San Simeon, where you could book a Hearst Castle tour, if that's your thing. Maybe Santa Barbara, Cambria and Monterey would make suitable stops. [?]