Which work of Mark Twain is the beginning of modern literature?

Mark Twain is one of the earliest "non-East Coast" famous writers. There is a view that the East Coast is, after all, the place where British immigrants settled, and it is deeply influenced by Europe, or so-called "English literature". The local characteristics, dialects and folk stories of the western United States and the Mississippi River like Mark Twain are the real American local literature. So Hemingway said that all modern American literature originated from Mark Twain's The Adventures of Huckleberry Finn.