This kind of reminds me of a plot element in Stephenson's "Fall; or, Dodge in Hell". Main character dies, consciousness is uploaded to a computer where he kind of becomes a God. He makes his own world, manifesting the "firmament" (has anyone else noticed that Stephenson loves the word "firmament", not just in this book).
But he creates all this land, and eventually new consciousnesses are uploaded to the same realm and one of the guys was a geologist. He realizes everything isn't real because something like "it's impossible for this type of a mountain to be next to this type of river".
