Factual error: Burt claims his watch updates its time "by connecting directly to the cesium clock in Colorado via ultrasonic frequency." Later the graboids home in on him by the ultrasonic sound emitted by his watch. Firstly, radio controlled watches update their time by receiving signals, but they don't emit any signals - the battery would be way too weak for two-way communication. Secondly, they work on radio waves, not sonic waves. Thirdly, if a hypothetical time transmitter did work on ultrasonics, the smallest distance between Colorado and Nevada is some 435 km (around 270 mi). An ultrasonic signal strong enough to reach that far would probably be deadly within a sizable range around the transmitter.
Factual error: When Miguel gets knocked over the hillside by the ass-blaster, the camera shows how/where he falls - the speed of his fall is no more than 1/3 of how a body would really fall. Also, he falls right next to the cliff; bit when the gang goes down, he is right behind the truck, which we know is about 50-60 feet away from the cliff.
Factual error: Burt hands a bolt-action rifle to Jodi when the group heads to the canyon to clean up the Shriekers, and she ends up using it to fire at the first Assblaster they encounter. She begins rapidly firing off rounds from this rifle as if it were a semi-automatic rifle, not the bolt action, single shot rifle that it is.
Revealing mistake: When the group comes across the first ass-blaster, it hops out from behind the fence. Pay attention to its right leg when it jumps out and you'll see a rock on the ground just appear behind it. After it spots them, it stomps a few times. While it's stomping, pay close attention to the rock and you'll see it and some of the ground around it just disappear after a few frames. This rock also isn't visible in any other part of the scene.