This is a poster from a 1971 re-release of the film, orginally made in 1965.  The tag line of course references Easy Rider, released in 1969, which had made Nicholson a marketable personality.  The film was financed by Roger Corman and made back-to-back with another Hellman Western, The Shooting, near Kanab, Utah.  The films were then sold to a distributor who sold them directly to television.  Ride In the Whirlwind was subsequently released theatrically on a couple of occasions and became a huge hit in France, especially among cinéastes there, who have lionized Hellman ever since.