Wikipedia to the rescue:
https://en.wikipedia.org/wiki/Aerotrain_(GM)
The Rock Island paint job on the picture threw me, but it appears that some ended up in service with Rock Island in commuter service after the major rail lines gave up on them.
The picture at the Wikipedia link more clearly shows the 1950s style bus windows and the doors at what would have been the front of the bus.
That is it. Little Colorado town I was in school was not a stop, we just saw it sail by.