I second Salt's recommendations for the coast drive and some beautiful areas in NorCal. I visited all of the places he mentioned when we lived up north, and all are definitely worth a visit!
If they're hoping to spend time on the beach, I'd recommend beaches south of Los Angeles. They're more laid back, often less crowded and the water's typilcally warmer the further south you go. I like several beaches in San Diego county, and there are some nice places in Orange County, too. DM me if you/they want specifics; we spend a lot of time on the beach, and have visited many
Should be an awesome trip for them! Is this their first visit to California?