High speed rail between San Francisco and Los Angeles isn't economically viable. California HSR will cost at least $30 billion to construct and California's own estimates claim it will cost $700-$874 million per year to operate.[1] Around four million passengers fly between SF and LA every year. Assuming every single one of them takes the train instead of flying, you're looking at $175-$218 per ticket just to pay for operations. If you wanted the project to pay for itself in 20 years, you'd have to charge $550-$600 per ticket. For comparison, airfare between the two cities starts at $80 round trip. Also the train will take 3 hours while flying takes 1.5 hours. Even including the time it takes to get to/from the airport and get through security, flying is faster.
1. https://hsr.ca.gov/wp-content/uploads/docs/programs/san_jose...