The Susan River is a northeastern California river of approximately length that drains from an arid plateau of volcanic highlands along the Great Basin Divide to intermittent Honey Lake. The river flows from eastern Lassen County from east of Lassen Volcanic National Park generally east past Susanville and emerging into a ranching valley to enter the north end of Honey Lake. Along with Fredonyer Pass, the Susan River is the northern boundary of the Sierra Nevada.