What are some characteristics that help to make John Steinbeck's novel East of Eden a typical work of modern American literature?

Various characteristics help to make John Steinbeck’s
novel East of Eden a representative work of modern American
literature.  Among those characteristics are the
following:

• It is set in California; the most
  prominent works of nineteenth-century American writing tended not to be set on the west
  coast, since that coast was still in the process of development. Steinbeck is one of the
  first great writers from California (Jack London being
  another).


• It is fairly frank in its treatment of sexual
  matters, including the illicit sexuality of Cathy. Such frankness tended to be frowned
  upon in earlier American literature. Indeed, Kate Chopin never even tried to publish her
  provocative story “The Storm,” which seems rather tame by today’s standards but which
  was not tame at all by the standards of the generally genteel nineteenth
  century.


• Much of the novel is set in the early twentieth
  century and is therefore modern, by definition, in some of its subject matter. Sometimes
  the novel even calls attention to its modern setting, as in the following
  sentences:

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Also, to start the engine of a modern car, you
just do two things: turn a key and touch a starter. Everything else is
automatic.

As these two
sentences suggest, part of the theme of the novel is historical change, and specifically
how the world of nineteenth-century America evolved, in numerous ways, into the modern
American period.

• An Asian-American person is a
  prominent character in the book, a fact that suggests the broadening of perspective that
  was typical of much modern American fiction. Members of minority groups began to play
  increasingly important roles in American fiction of the twentieth century, not only as
  characters but as writers and audiences.


• World War I –
  perhaps the decisive event of the twentieth century in many ways – is one of the topics
  dealt with in the book.


• The structure of the novel is
  highly complex in ways that are often typical of modern fiction. Modern fiction often
  tried to puzzle and challenge its readers rather than presenting them with simple,
  straightforward stories, and in this sense, too, East of Eden might
  be called a representative work of modern
  fiction.