Darwinia?

Robert Charles Wilson's Darwinia: A Novel of a Very Different Twentieth Century is just that. The premise is that in 1912, the continent of Europe is replaced by an unearthly wilderness. The geography is the same, but it's been supplanted by a completely new ecosystem. All of Europe's humans and human artifacts have disappeared, and turn-of-the-century America is left to deal with the mystery.

Wilson is good at building up the bizarre situation, and showing how people try to cope with and rationalize something that they will never be able to explain. With that in mind, I would almost rather than Wilson not have explained it; the phenomenon works better as a pure mystery than as the convoluted futuristic plot that develops.

"Darwinia" is a name given the continent as a joke, which somehow sticks in spite of the American embrace of fundamentalism. (I suspect that Wilson just liked the name too much to give it up.)

Character development is decent; the plot starts off with a bracing amount of weirdness, and if it doesn't sustain that, it's nonetheless very readable throughout.