I hate to sound cocky (*sound* cocky that is) but I am not at all surprised by the river flowing West because this story, like The Fifth Head of Cerberus (generally) and The Book of the New Sun (very much) is a new myth -- based on the cosmic heavens and the precession of the equinox. Wolfe was inspired to follow this schema through most of his career based on the admonitions and theory-spinning of the book "Hamlet's Mill" (the only 20th century literature cited from - quoted directly, in fact). But perhaps others as well.
The Cassionsville is located in the night sky and the river is the Milky Way, which flows from east to west each night.
The significant event of a Hamlet's Mill "true myth" is the precession of the equinox at the moment the expected stars do not rise up on their assigned date. Mythologically speaking then those stars (gods or heroes) have descended to the underworld, or beneath the waters, or been burned up in fire, or retreated beneath the hills. When that happens the solar ecliptic is described as shifting cataclysmically -- tower falls or shifts, a giant topples, the sky (Ouanos) is untethered from the Earth, or starry eyed Argo's throat is cut - his head shifting,
OR a tree falls. Or a stack of orange drink boxes topple.
"It is not the history of technology; it is, if anything, science fiction that can bring in the adventures of the future. Science fiction, when it is good, is a wholly valid attempt at restoring a mythical element, with its adventures and tragedies, its meditations'" on man's errors and man's fate."
"Hamlet's Mill," History, Myth and Reality