Until you hit the almost certin lawsuits that even if you were successful would take years if not longer to resolve.
Not to mention the fact that no one lives in the national and state parks (meaning that there's no intermediate customers or long-distance commuters), none of the state or national parks are actually on any kind of sensible route from Los Angeles to San Francisco (or Los Angeles to San Diego, or Sacramento to San Francisco or...you get the idea), and that nearly all of the state and national parks are in rugged, mountainous terrain or deserts that would be even more expensive to build through than the Central Valley for physical reasons. It's a great way to ensure failure, though.
This attitude seems to be strong. I made a thread about
Metro Transit that got little interest. People want to focus on the shiny new HSR and not talk about what you need for it to make any sense at all. For HSR to make any sense at all you have to have decent metro. If you have to rent a car after you arrive at the train station you might as well drive all the way.
And yet people do not, in fact, "drive all the way" just because "they have to rent a car." Just look at how many people
in fact fly from, for example, Houston to Dallas every year (over 3 million--granted, about 4 million automobiles but that still means that 3 out of 7 travelers take a plane), or how popular many other air corridors are that are short enough to drive in principle (about a fifth of the top fifty air corridors in the world are under 500 km, although one of those, Seoul-Jeju, connects to an island). A lot of people are willing to "rent a car" if it means getting to their destination faster.
Additionally, if you look at actual HSR systems, often they
do successfully connect to cities with much smaller and less expansive metro systems than you seem to imagine. Lyon, for instance, the destination of the very first French HSR line, had a mere two metro lines (along with a rack railway line) when the LGV Sud-Est connected to it in 1981, which only covered the city center at that time (since then they have greatly expanded the system and built a parallel light rail system). Other cities connected to other parts of the LGV network, like Le Mans and Tours, didn't have
any kind of rail transit when they were linked up (they did both eventually build
light rail systems, opening about a decade after the LGV Atlantique that connected them up). It's true that Paris has quite a large and extensive metro system, but most other French cities
don't. In short, while a good metro system (or public transit in general) may be
helpful for the success of an HSR line, it is very far from a prerequisite. Which makes sense, because HSR is more like an airplane than a bus, and like I said earlier plenty of people are willing to fly to destinations with poor or no public transit even if it means having to rent a car.