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 monster movie about an archeologist who is trying to discover why the ancient Anasazi Indians disappeared hundreds of years ago when he unearths the alien monster that destroyed most of them before they managed to bury it alive. Probably the most interesting thing about the movie is that the heroes are two women (two improbably beautiful women, of course, but they're strong characters) - the sheriff (Emmanuelle Vaugier) and a Native American woman who studies plant DNA and takes care of her grandfather (Tonantzin Carmelo). When she runs some chemicaltests on a part of the monster, she concludes, with one of the unintentionally-funniest lines of the movie, that it's "a bonified unnatural organism."
After cows and then people are disembowled the town drunk who is also the sheriff tries to figure out what's happening. She meets two girls headed for Hollywood fame and a stranded cowboy they gave a ride to, and a man from Detroit, all of whom are stranded at a gas station after a gasoline tanker truck crashed and blocked the highway. They're only in the movie to give us enough bodies for the monster to tear up.
The snake shows up after the monster shows up and kills a few people and blows up the gas station. The survivors drive up to an archeologist's camp to try to get him to fly them to safety in his helicopter, but he holds them at gunpoint until they eventually knock him out and tie him up. The sheriff demands the keys to his SUV and he tells her they're behind a rock. The wanna-be actress reaches out between some rocks to find the keys by touch since she can't see where she's reaching (never a good thing to do in rattlesnake country), and a snake bites her. The cowboy then grabs the snake and throws it. Everybody is so angry at the archeologist that they're about to kill him when he tells them he'll go get some anti-venom if they set him loose. As he stabs her with a needle he says that she was bitten by a baby rattler. The snake-bit woman wanders around afterwards slightly dazed wearing make-up that makes her look sick with dark circles under her eyes, but she survives long enough to hear an old rancher tell her that he got bit by a rattler once and it hurts like a bitch.
The snake is not really a rattlesnake, it's a gopher snake or a bull snake.