I think the US already has a better than average rail freight system.
It seems to me the solution is to have a major rail artery which at least allows freight to be delivered to a distribution center farther inland(Ontario, Palm Springs, or somewhere east). That would free the truckers from dealing with LA freeway traffic.
Another option would be a canal up to the Salton Sea. Obviously that's a much more major effort but it has nearly endless economic and ecological benefits.
That would be an obscene undertaking... going a hundred miles THROUGH several mountain ranges.
There would be no ecological benefit. Salton sea will still not have an outlet, so after a one-time dilution, the seas will continue to increase in salinity, endlessly. It needs a massive supply of FRESH water to try to dilute the salt down to acceptable levels. Sea water with salt will just worsen the problem, long-term.
The economic benefits are marginal. You'll be limited to the number of vessels the canal can handle, the size of the port you can build in the desert, and you very quickly overwhelm the roads in the area.
Any malfunction or damage to the canal would be devastating... the unstoppable flooding in the low desert and along the canal zone would be unprecedented.
Okay, so now it's an international construction project, with all the political barriers that brings. And running close to the Colorado river.
> The alternative is, what, a toxic dust bowl
It's the Salton sea that caused the area to become "toxic". Bringing in more sea water with no solution to ever clean it up will provide just a short-term reprieve to the area, but exacerbate the problem long-term.
Your plan is to create a much larger toxic dust bowl.
Or you could build a 20 mile tunnel from the Port of LA/Long Beach to offload the road network. I even know a local guy with a tunnel boring machine company.