CAIS and NAIS (Ca. Ass’n of Independent Schools and National Ass’n of Indie Schools have lists.
CA is a big state. Where? How big? Tradtional Liberal Arts, small, big, Quaker school, coed, etc? What other qualities does this kid have besides being bright? Where is his brother at school? Is money an issue? What about student diversity?
Harvard-Westlake school in LA is a typical, high-end, competitive independent day school. It does have a diverse student population.
I went to an excellent public HS outside of NYC. My kids went to an Independent Day School owne an operated by The Society of Friends. They had a better experience socially, intellectually and in terms of a moral and social-service background that they will keep forever.