I was thinking more along the scale of a string of bunker-blasters!
Not like that plan to make a freeway cut all the way through the Bristol Mountains (Mohave desert) all at once! (to build I-40, a more direct replacement for Route 66).
Caltrans' in-house newsletter had a different description of that proposal than what I see on Wikipedia. According to an interview with a former chief design engineer, AEC visited and offered their instant-pass proposal. Caltrans thought it was a crackpot idea and that's as far as it got.
I think one thing critical to Caltrans but not considered by AEC is a roadway needs a stable base, building on rubble of uneven depth will never be stable and worst-case could fail like this spillway. Plus perhaps the earthmoving required to clean up the blasting mess might be as great as the earthmoving required for conventional construction so no overall benefit/cost. Then there's the radiation-in-the wind issue.....