California is a country of its own when it comes to what to visit.
#1 for me is Yosemite, but try not be there on the weekend in the summer as it way too crowded these days.
San Francisco and the Bay Area is a nice place to see. If you're into it, you can go a couple hours north to Sonoma or Napa.
North of there you have a lot of nature for the most part. Big trees and nice remote coasts and mountains.
South you have the standard LA mess. There's things to see there, but it's still a mess of people. Personally, I would spend minimal time there, especially if wanting beaches, and head to San Diego where it's not as crowded (getting there.)