Avoiding the mountains of CA

The mountains from Diego to SF is no big deal, if that bothers you wait till you head East on I-15 into Nevada or I-70 East into Reno..

5, 405, 101 with just a few small hills.

That's pretty tough to do. San Diego's in a hole. Just ask any commercial airline pilot. It's one of the toughest airports to land in. But, heading north, in a vehicle, you're going to run into hills and small grades, no matter which freeway you take. They're not overbearing, but, it's not Kansas either.

I-5 wiggles around and up and down mildly all the way from downtown San Diego, all the way to L.A. The "Grapevine", on the north side of L.A. is about the toughest climb I think you'll see, in that section of the drive. From that point on, if I recall, it's pretty flat for quite a while. I can't recall just where or when any larger climbs take effect after that.

I-15 is even more wild and hilly, right from the San Diego area. Plus, you can't take it all that far, without it heading NE so, you'd be sort of heading in an off direction. Don't know if this helps any. Good luck.
Scott

San Diego to San Francisco only has one major pass and that's the grape vine on I5. North of L.A. and it's no big deal but if your worried about it then in L.A. take the 101 north.