There is a wonderful John Ford biography (amazon/local library?) narrated by Bogdonavich, Speilberg and Eastwood that tells of Ford’s style and film effects accomplishments. One — is his use of the “horizon line” — spelled out perfectly by Speilberg.
As I remember the scene where Stewart and Ladd are alone by the river (I think one lighting a cigarette) is ad-libbed.
Oops - “Stewart and Widmark” (not Ladd)