The Tejon pass (grapevine) is over 4000 feet. Minimum vertical curve radius on Britain's High Speed Two, with a top design speed of 250mph, is 56 kilometers. This thing will need to operate at an average speed several times that.
As you make the train faster and faster, the route must asymptotically approach a straight line. A straight-ish line that goes over the mountains between LA and the central valley would either require viaducts hundreds, if not thousands of feet tall, or it will require tunneling, or it will require a mixture of both.
But it is not a train. It is a short, tube-shaped vessel inside of another tube and magnetically elevated. I am assuming that the magnetic "elevation" is all around the vessel which would prevent it from slamming side-to-side or top-to-bottom. I'm not saying there won't be problems but I don't think it will need the curve radius like you are thinking for a train.
It has nothing to do with the ability of the train to stay on the tracks, it has to do with the ability of the passengers to keep their lunch in their stomachs.
It's elevated, not below ground. But I think most of your point stands. Just getting through the politics alone would be impressive.