What is the function of Muley Graves?

Muley is a friend of the Joad family who Tom and Casey find hiding out on his land. His family had headed to California while Muley clings to abandoned hoses and shattered dreams. Muley functions on a few levels. He is a bit of ominous foreshadowing of what might be in store for the Joads, or at least the misery. Muley is a "ghost" of a man lurking around in the dust and dodging the officials. He is representative of time that has passed these sharecroppers rendering them redundant in a world that has moved on.