NPR has a great story on the controversies that Steinbeck's The Grapes of Wrath inspired . This story chronicles how the book was banned and burned in a number of places, including Kern County, California (the endpoint of the Joad family's migration). Listen to or read the story here. The NPR page also features Rick Wartzman's book Obscene in the Extreme: The Burning and Banning of John Steinbeck's The Grapes of Wrath, which covers this history in greater detail.
And, as I mentioned in class, here's the link for Bruce Springsteen's "The Ghost of Tom Joad," which underscores the popular resonance of Steinbeck's tale.