I remember a trip out to the Mojave desert in the 70's. Highway 15 has some summits along the way back to Los Angeles. When we topped one of the summits we could see the entire Los Angeles basin. It appeared to be encased under a perfectly spherical dome of green glass.
Kind of beautiful in a sci-fi sort of way, but horrifying to know that we were soon going to be dropping down into there and having to breathe that air.