You're right, the proper name for that detour is Mormon Immigrant Trail.
I thought I remembered that when the bulldozers met in the middle they said they were above so many layers of ice and snow that they were 12 ft above the pavement. But that seems so incredible that I didn't mention it above. Do you remember what was in the news at the time?
More Sierra storms trivia - when I was a little kid I remember the passenger train from the east, the City of San Francisco, disappeared in 1952. It was 3 days before rescuers reached it. A tiny avalanche had blocked its forward motion and it was snowed in so badly that it couldn't back up. Finally the storm let up and US-40 got plowed so that the passengers could walk out to the highway. To a little kid the breathless news updates seemed like the sinking of the Titantic or something!