California has always had some of the worst highways in the country. The state is broke and has little funds to keep up with its infrastructure but that's a debate for a different forum!
I-10 west through Banning area feels like bad washboard on a dirt road.
Here in AZ the highways are mostly great. The only interstate I know of thats really bad is I-40 east of Kingman. Bone jarring potholes. I was pulled over once for driving in the left lane. Was told to use the left lane only for passing and that it must be kept clear in case of emergency vehicles. I mentioned to the officer that I'd rather keep my vehicle and bones in one piece as the right lane had massive potholes. Left with a warning.