This is a Disney movie about a dog named Savage Sam, who is the son of Old Yeller, the dog from the 1957 Disney Movie. A snake is shown briefly along with some other animals in a sequence which I found interesting since it is used to illustrate some cowboy weather predictions.
After a boy and a girl are kidnapped by some renegade Apaches, a group of ranchers use Sam to track their trail. At one point on their journey they see a snake crawling on the ground, along with a snapping turtle and some tarantulas. When a man mentions the snakes and spiders the boy's uncle Beck (Brian Keith) tells him that means it's going to rain. Shortly after a strong wind starts blowing and it begins to rain and hail and the men and their horses take shelter in a giant cave.
The snake is interesting to me because it's a Desert Kingsnake, a species that is appropriate for the Texas setting and one that I don't remember ever seeing in a film. The movie was filmed in California and the animals we see in the scene are probably library footage.