It was built there during WWII to have steel fabrication closer to ship building on the West coast.
The other reason it is there is that the contingency plan for a Nazi landing and invasion of the East Coast was to retreat behind the Rocky Mountains.
Hitler started WW2 5 years before the German navy was built-up, and most of their aviation was for close air support.
Even the English Channel ended up being too much.
In summary, both Germany and Japan declared war on a country they couldn't invade, the USA - how futile is that?
"In the first six to twelve months of a war with the United States and Great Britain I will run wild and win victory upon victory. But then, if the war continues after that, I have no expectation of success." – Yamamoto, head of the Japanese Navy, and architect of the Pearl Harbor attack
That's the first time I've heard of that plan. Would love to read more about that if you have any resources for it. A quick cursory search online wasn't too successful. Retreating behind the Rockies would leave a huge amount of space and resources available, and presumably the majority of the citizens. Would places like steel mills or other industrial facilities be sabotaged so they could not be used by the opposition?
The Corporation : A Centennial Biography of United States Steel Corporation, 1901-2001 https://www.amazon.com/dp/1887969128/
To answer your other question, there were plans in place to evacuate most of the capital via rail behind the Rockies as well. The Soviets did this tactic for real during the German invasion and were quite successful at it.
You’d hope the outcome would be that unpopular wars are avoided, but it seems that the real outcome is only that big ones are. Our leaders have discovered that small wars that don’t require major sacrifices from the general population can be highly unpopular and it just doesn’t matter.