I always pick the "backest -of the back roads" that is pavement. I am terrified of heavy traffic. I like shoulders, but if there isn't much traffic shoulders aren't necessary. I sure you can find a California bike map on-line that gives local traffic volumes. Pick the least one and you should be set.

This isn't so much a problem in the Mid-West or Western States (other than California). Seems to me that when I rode from S.F. to Tahoe (20yrs ago) I didnt have any problem with using a state map from the gas station. No problem at all.