Battle for Cedar Creek by J. P. Yelen

A generation ago a natural disaster devastated billions, and world governments collapsed. But life, although different, goes on for the hard working, innovative, self-sufficient townsfolk of Cedar Creek. That, however, is about to change. Cedar Creek has been invaded by a nihilistic biker gang, intent on rape and pillage, led by a violent and ruthless sociopath and backed up by the scary leader of the biker women and the sadistic self appointed sheriff who has a score to settle. But this is a new world, and the people of Cedar Creek have been tempered on the anvil of independence. The survivors of the first violent and abusive attacks escape into the mountains, and there follows a war of attrition to win back their town.