Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
IMDB lists this as a comedy/mystery/romance. It's part con man movie, part western adventure, part ghost story, and part cringey romance between a 13-year-old girl and a man three times her age.
Peter Fonda is Beau the grifter (and he directed the movie) and a 13-year-old Brooke Shields plays a girl he wins in a poker game who tells him that she wants to be a singer and her stage name is Wanda Nevada. She develops a crush on him and though it is made clear that the relationship between them is purely platonic it's a little disturbing how sexualized Shields is throughout the movie at such a young age. This isn't the first movie she made that does that - "Pretty Baby" made the previous year and "Blue Lagoon" made the following year are notorious for sexualizing the young actor. But as cringe-worthy as it might be, she's really the best reason to watch the movie. She gives a great performance and lights up the screen in many glamorous close-ups. There's also some great western scenery, and, of course, I watched it for the rattlesnakes.
When the two are in a bar they observe an old prospector who shows everybody a bag of gold he found in the Grand Canyon. Wanda gets hold of a map he made to where he found the gold then she and Beau trade in his car for a mule train and supplies and ride down into the canyon to find the gold, pursued by bad guys and Apache ghosts.
Their path leads to a narrow gap in the rocks that Beau can't fit through so Wanda goes inside. She immediately sees two rattlesnakes on the ground and pulls out her gun. (It's funny that we hear the snakes rattling loudly for the entire scene, but when we see them their tails are not moving at all.) He nags her to hurry up but she is more concerned with carefully getting past the snakes. Eventually she squeezes past them with no harm to her or the snakes.
When I saw her pull her gun I thought we were going to see her shoot her way out. That would happen in most other movies, but not here. She just slowly walks right past them. I congratulate Fonda for playing the scene this way. Not all tension in a movie needs to be resolved with gunshots. There is plenty of other gun shooting in the movie, along with arrows shot by Apache ghosts.
They did a good job of making it look like Shields was with actual rattlesnakes, but I'm not sure how they did it. I doubt they would have put her so close to live rattlesnakes. When we see an actor with the snakes, it could be a stunt double, they could have use a piece of glass between the snakes and the actor, or maybe the snakes we see with her are not alive.