Part of my high school was in South Dakota, and Willa Cather's Prairie Trilogy, especially My Ántonia, is a big part of English education in South Dakota. However, I happen to have come in just in time to miss her completely. I don't have a copy of My Ántonia, but I do have a copy of Cather's Death Comes for the Archbishop, which I've also never read. So that's the next one up.
Willa Cather was born in Nebraska, where she graduated from the University of Nebraska; she then went east, first to Pittsburgh, then to New York. She is famous for writing novels about frontier life. The latter part of her life is actually somewhat sad: she was acclaimed brilliant for a great part of her career, but towards the end of her life, literary fashions changed, and she began to be sharply criticized and dismissed as out of date, stuck in the past, and, in short, a has-been who, incapable of writing about contemporary life, wrote romances about an idealized past. Faced with such criticisms, Cather became a recluse. Of course, there's no evidence that Cather's literary ability had faded; at least, the arguments of the critics don't really seem to point to any. It's just that the critics of the thirties and forties had no more taste for it.
Death Comes for the Archbishop is, in a sense, Cather's last great victory before her reputation was swept away by the barbarians. Published in 1927, it has repeatedly been listed as one of the great American novels. It's set in New Mexico territory, so that will make for quite a change of scenario from the Mediterranean setting of the last book.