Lost River (California)

The Lost River is a river in northern California and southwestern Oregon in the United States, approximately 70 mi (113 km) long. The river flows within an enclosed basin on the volcanic plateau southwest of the Klamath River watershed. Its waters provide irrigation in a farming and ranching region along the California-Oregon border.

It rises in two forks in northern Modoc County, California west of Goose Lake in the Modoc National Forest. The short North Fork and South Fork, each approximately 20 mi (32 km) long, flow west and join east of the Clear Lake Reservoir. The combined stream flows through the Clear Lake Reservoir, then flows in a northward loop through southern Klamath County, Oregon, re-entering California approximately 20 mi (32 km) southeast of Klamath Falls. It enters the north end of intermittent Tule Lake, approximately 7 mi (13 km) south of the Oregon-California border.

The lower reaches of the river near Tule Lake cross a ranching valley where the water of the river is diverted into multiple canals and ditches for irrigation as part of the Klamath Reclamation Project. The ditches intermingle with those of the nearby Klamath River at the northwest end of the valley.

During the mid-1800s, the river was used as the route of a portion of the Applegate Trail, a trail intended as a safer alternative to the main route of the Oregon Trail.

The river was the traditional home of the Modoc during the 19th century. In November 1872 it was the site of the Battle of Lost River, the first battle of the Modoc War.