The Thetis Plague — Mark Onspaugh

When a NASA probe crashes in the California desert releasing toxic spores, an unholy plague is unleashed, creating an army of walking dead that cannot be stopped. Tom Meyers has seen these horrors first-hand, as the girl he loves is torn apart and devoured and dead friends return to scratch at his door. Now Tom with a motley band of brothers must fight their way to a rumored haven in the North. As they travel the countryside filled with the rotting and ravenous dead, they find themselves immersed in a perilous new world where people will do anything to survive.