We're literally right now building a huge high speed rail project that is planned to link san diego to san francisco through LA, bakersfield and fresno. Progress is made on it daily. https://www.youtube.com/CAHighSpeedRail
So slow, in fact, many countries have faster regular rail.
Phase 1 from SF to LA is estimated for 2035-2040. They might do end-to-end service before that with existing tracks and slower speeds, especially from Palmdale to LA. The SF and LA segments require tunneling to get over the mountains.
But, hey, you'll be able to go really fast between California's 6th and 80th largest cities!