Anyone heading to Okemah should read Bound for Glory by Woody Guthrie — his lightly fictionalised autobiography, opening in Okemah during the boomtown oil years and following him through the Dust Bowl to California. It is the single best primer on the town and the man.
Ramblin' Man: The Life and Times of Woody Guthrie by Ed Cray is the standard biography: thorough, balanced, and unsentimental. It fills in the parts Woody left out and traces his complicated political life through the 1940s and 50s.
For the Oklahoma context, The Grapes of Wrath by John Steinbeck takes the same Dust Bowl migration Guthrie wrote songs about and turns it into one of the great American novels. The Joad family leave from just up the road in Sallisaw.