These are not in any order.
1. A beach--which one? See other threads.
2. The Getty in Brentwood
3. The Huntington in San Marino, despite the admission price.
4. Mulholland Drive on a sort of clear night starting near the 101 freeway.
5. The San Diego Safari Park (? formerly the Wild Animal Park) in Escondido
6. Knott's Berry Farm--especially for the Scary Farm and especially for the Scary Farm in late September
7. Either presidential library (I like Reagan's more than Nixon's, but both are worthwhile for history buffs.)
8. The Getty in Malibu
9. The LaBrea Tar Pits (for an hour or 90 minutes for the bone buffs)
10. The Norton Simon art museum in Pasadena
11. The Griffith Park Observatory
12. A hike on a mountain after riding the palm Springs Aerial Tramway
13. This is cheating because it's four hours from Pasadena & not in CA, but Las Vegas!
14. A hike near Mount Baldy
15. La Jolla (N. of San Diego--dodge waves on the rocks near the Cove, and check out the view of S.D. from Mt. Soledad.)
16. Universal Studios Hollywood.
What would you add?