“Single mile of track” is one of the dumbest memes ever. Yes, they lay the tracks last, because that is by far the easiest part of the project and there’s a machine that can poop out HSR tracks at 1km/hour.
Sigh. Though there are definitely automated track laying machines in the US, some pieces might not meet the needs of the project and may want other machines. You can of course ship them.
Did you think CAHSR was going to lay the track by hand?
Uh... not in the US, there isn't.