In MGM's epic 1962 western "How the West Was Won", in what battle of the Civil War does Yankee soldier Zeb Prescott (George Peppard) encounter a rebel deserter (Russ Tamblyn)?

In MGM's epic 1962 western "How the West Was Won", in what battle of the Civil War does Yankee soldier Zeb Prescott (George Peppard) encounter a rebel deserter (Russ Tamblyn)?