A couple of police officers on Mars need to transport a criminal to a remote mining settlement. When they get there it turns out all the miners have been possessed by Martian ghosts. A siege ensues.
This movie is as close as you can get to being a Western as possible with out actually having it set in the old west, using horses or having the heroes fight "injuns." Still wondering when John Carpenter's just going to make that Western he seems to want to make.
Also of note it features a score by John Carpenter (on synthesizer) and a bunch of heavy metal guitarits, including Robin Finck, Steve Vai and Buckethead, and the rest of Anthrax.