I've been traveling from Oregon to California and back and from AZ to Calif and back for at least 20 years and I am positive that you are not supposed to bring fruit or plants into Calif. It's OK to take them out of Calif.
Sometimes the check station is not open and you can get by with taking fruit into Calif. Every time that the station is open they have asked me if I have any fruit or plants. I've had fruit taken away because I was honest and told them. I'd not finished my lunch before getting to the border. They do look thru the vehicle in a cursory way, anyway.
The reason for the rule is that Calif has had a great deal of difficulty with plant disease and this is their way of reducing the risk. Frankly I would understand if we were not allowed to take fruit across all state lines but as far as I know Calif is the only state who does this.