I keep hoping we'll get SLC <-> LA via Las Vegas. We have commuter rail from SLC down about 100 miles, and there are some fairly popular destinations along that route that could benefit from train access (lots of National and State parks, St. George is a popular retirement and vacation destination, etc).
But to be viable, it has to be competitive with airline travel, and that means fast trains. It currently costs more to go from SLC <-> SF than by airplane, and it takes a full day (18 hours or so, I forget exactly) to get there vs 2 hours or so by airplane and 10 hours by car. If it was 4-6 hours (120-200mph), it would be competitive with airlines if you take into account security and baggage on both ends. I know I would take Amtrak if that were the case, but for now, I'm only going to take it as a vacation in itself.
There are a lot of companies in CA that have offices in Utah now, so improving the train system between them may make sense if they can get speeds to be reasonable.
So, you're either blasting a giant gap in the Sierras, blasting a giant tunnel under the Sierras, or have some novel HSR technology that'll run over the Sierras.
For a much less useful route, it'll probably be more expensive than the actual full proposed CA HSR system.
Not saying it is worth it, but I did want to point out a massive tunnel below mountains has been done before[1]. The Gotthard tunnel train below the Alps cost about $12 billion to tunnel about 35 miles. Pretty awesome engineering.
For reference, the LA<->SFO train was last estimated about $75-100 billion to complete before it was canceled. Of course, there's almost no way anyone could build such a train tunnel in the USA for the same price as they did in Switzerland.
But to be viable, it has to be competitive with airline travel, and that means fast trains. It currently costs more to go from SLC <-> SF than by airplane, and it takes a full day (18 hours or so, I forget exactly) to get there vs 2 hours or so by airplane and 10 hours by car. If it was 4-6 hours (120-200mph), it would be competitive with airlines if you take into account security and baggage on both ends. I know I would take Amtrak if that were the case, but for now, I'm only going to take it as a vacation in itself.
There are a lot of companies in CA that have offices in Utah now, so improving the train system between them may make sense if they can get speeds to be reasonable.