This is a very perceptive question concerning this unforgettable story. Mostly this tale is taught as a great example of the first-person point of view and necessarily limited account that first-person point of view supplies us with. As I am sure you can see, this is crucial to the impact of the story. Because we are only able to see the landscape and the action through John's eyes, we have to piece together the various clues that we are given about the setting much like a jigsaw, until we are able to discern that we are seeing a future dystopian world where some kind of nuclear holocaust has destroyed civilisation as we know it and reduced man to living like a caveman once more. Consider the following hints we are given:
It is a great Dead Place - greater than any Dead Place we know. Everywhere in it there are god-roads, though most are cracked and broken. Everywhere there are the ruins of the high towers of the gods.
Because of the limitations of the first person point of view we as the reader are left puzzled by what John refers to by "Dead Place," "god-roads" and "the high towers of the gods." It is this aspect of the point of view of this story that makes it so successful and really heightens the impact as bit by bit we realise that we are presented with a possible future of our world and our race that could occur if we are not careful with "eating" knowledge "too fast."