The Susan River (Northeast Maidu: Pam Sewim, bush creek)[3] is a northeastern California river of approximately 67 miles (108 km) length[4] 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.

It flows eastward, curving southeasterly as it enters the Great Basin, where it is joined on the left by Bridge Creek and dammed to form McCoy Flat Reservoir, approximately 11 miles northwest of Susanville.

After being joined by Willow Creek from the left, the Susan River passes below Litchfield and is extensively modified by a complicated system of canals and levees for irrigation of the surrounding ranching areas.