What is the name of the film or cinema-plex or what-have-you that had very large and spectacular footage of the US countryside (like the Grand Canyon etc) relatively early in film history?

I think you are taking about IMAX theaters. They still exist.

Even before IMAX, there were shows like that… the local amusement park near me had it. I forget what they called it back then, but the audience stood inside the done and would sway with the camera motion. IMAX shows are remarkable… go to IMAX.com to find a theater near you.

inside the dome

circlevision 360 at the old Disneyland that had eight cameras in a circle it preceded imax

you can rent IMAX movies on DVD for home viewing

Nope, it was only one place and it was the first and it presented footage of the grand canyon and other famous american sites. It was in some obscure state like colorado or something. :-) I give up.