SD - Palm Springs... that's tough. There are a lot of bike-unfriendly roads between those two points.
Do you have your heart set on a point-to-point tour?
Here is the SoCal Route repository. (Click.)
You could string together a lot of great rides East of North San Diego County. Jabantik in here is a pretty gung-ho camping/adventure cyclists in here. He'd be a good source, I'd PM him.
Good luck and let us know where you end up going and how it turns out!