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 first act of the book begins with the funeral of John's grandfather and lasts until the boys steal back Blevins's horse. After that point, there's no turning back—the boys are connected by the crime, no matter what they might think of each other. Rawlins's warning about giving up on a course of action before you commit to a course that will make you do something stupid is no longer valid.
Act II
The second act follows the boys' escape from Encantada to their comparatively idyllic life on the ranch, and eventually takes a dark turn to their hopeless nights in the Saltillo prison.
Act III
The third act sees the boys escape from prison, follows John's desperado play at both love and horses, and then watches him wander off into the Texas sands.