For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
The Joads travel west on Route 66, in search of a better life in California.
Act II
The Joads discover that there are very few jobs to be had in California, and that wages keep dropping. California is not a happy place, but they have nowhere else to go.
Act III
The Joads survive hunger, sickness, floods, and loss.