The state has to consider whether it is capable of doing this at all (obviously, it isn't).

The state is capable, it is just unwilling to leverage its power to achieve a meaningful outcome. This is relatively normal across the country; NIMBYs and small landowners have outsized influence and ability to delay.

China builds high speed rail at half the cost of the US.

European countries of comparable size and GDP to California do not experience own-goals of this magnitude.

The state in the US, especially California, is not competent.

The state in China, is competent.

What is the best evidence that it is capable? I believe it isn't, as demonstrated in this and other areas.

For comparison, the construction cost of AlBoraq 200mph bullet train in Morroco is $5.3–5.7 billion in today's dollars. The line length is 200 miles.

https://en.wikipedia.org/wiki/Al_Boraq