The Willow Creek War — Robert Leininger

Returning home to Wyoming from college back east with a civil engineering degree, Andy Stillman finds that his father has been murdered and his ranch, the Bar-O, is under siege by a rival ranch, the Circle-K. Unwilling to risk the lives of his hired hands and family to fight the much larger ranch, Andy protects them by firing his ranch hands and sending his young brother and sister to Cheyenne, two hundred miles away. Now a lone, almost invisible target, Andy fights the Circle-K and its hired guns in a stealthy, violent guerilla war, using his recently-acquired engineering skills.