Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a nature run amok movie where all of the animals have gone wild, including the snakes. We are told that fluorocarbon gases used in aerosol spray cans are seriously damaging the Earth's protective ozone layer. That was something everybody worried about a lot in the '70s before Climate Change started getting all the press. So due to the loss of the ozone, animals that live above the altitude of 5,000 feet have become overly-aggressive. We see a group of hikers and their guides flown out of town on helicopters and dropped off in the mountains for a two week hiking trip. Almost immediately they are attacked by wolves, bears, cougars, and vultures and other large birds. After several of the hikers are killed the rest try to get back to town, but that's not easy when you are being chased by bears.
One of the men, a lawyer named Frank who watched his wife get her eyes pecked out by vultures then fall off a cliff, finds a little girl and the two of them hike out of the woods and make it back to a road. He is excited when he sees a pickup truck on the road. He puts his hand on the truck, then pulls it away just in time to avoid a striking rattlesnake. He then sees that the bed of the truck is full of snakes. As he and the girl run away we see snakes falling out of the truck onto the road, as if they are trying to chase them.
Frank and the girl walk into town and sit inside another vehicle when a wild dog comes at them. The town is full of vicious pet dogs looking for human blood. Frank exits the truck with a hammer to confront the dog. The growling dog follows him away from the vehicle and he decides to go inside a VW to escape the dog. Without seeing what's inside the car, Frank puts his arm inside the window and it is immediately struck by rattlesnakes. We then see that the car is full of snakes. He screams and drags some snakes out of the car that are hanging onto his arm, then the dog gets him.
We see quite a few rattlesnakes of different species - Western, Western Diamond-backed, and Red Diamond Rattlesnakes. There are also lots of harmless snakes in the vehicles, including Gopher snakes, Rat snakes, and Corn snakes. How and why do so many snakes that should not be found in the mountains at this altitude gather together inside motor vehicles? Are they planning on driving somewhere? Has the lack of ozone made them crazy? They don't really act much different from most snakes in movies. Why are there so many snakes in town? When did wolves return to the Sierra Nevada Mountains? It's just not worth asking intelligent questions about a movie like this.
RiffTrax did a parody of this movie, which you might still be able to watch on YouTube.