Why does Steinbeck begin "Of Mice and Men" with a detailed description of the countryside before the characters enter?

John Steinbeck is setting the scene for George and Lennie before they enter.  Actually, each chapter begins with Steinbeck's use of sensory imagery.  This brings the reader into the scene and allows him/her to experience that setting as the characters might.  Also, in chapters 1 and 2, Steinbeck uses 19 animal references.  These act as symbols that both characterize George and Lennie as well as foreshadow later events in the plot.  For example, a water snake slithers by in chapter one.  The snake symbolizes transmutation (change) because a snake sheds its skin and leaves the old one behind.  This could foreshadow changes in the relationship between Lennie and George.  The snake reappears in Chapter 6, but is eaten by a water heron.  The change for George and Lennie is disastrous, and nothing will ever be the same for these characters.  If you make a list of all the animal references and then use a dictionary of animal symbolism, you can make connections to the characters and the plot.