The are 38 million people in California. Studies show that only 41 million of them will have to use the high speed rail between LA & San Francisco every year to make it economically viable.
All of AMTRAK in the USA only services about 2.5 million passengers per year. 41 million passengers is 16.4 times higher than AMTRAK's total national ridership.
Costs projections suggest it will cost $100 billion. So the project was cut back to "only" $68 billion.
Outside of the Great Pyramid in Egypt, it will be the biggest government project in all of history.