The Pit River or Pitt River is a major river watershed draining Northeastern California into the State's Central Valley. The Pit, the Klamath and the Columbia are the only three rivers in the U.S. that cross the Cascade Range.
The longest tributary of the Sacramento River, it contributes as much as eighty percent of their combined water volume into Lake Shasta; the junction of their Lake Shasta arms is four miles northeast of Shasta Dam. The Pit River is approximately 315 miles long (measuring from its longest source as is standard USGS practice.) This 58 mile South Fork Pit River - West Valley Creek - Cedar Creek source originates just southeast of Buck Mountain in the Warner Mountains in the extreme southeastern corner of the Modoc National Forest nine miles west of the Nevada border.
The Pit River drains a sparsely-populated volcanic highlands area, passing through the south end of the Cascade Range in a spectacular canyon northeast of Redding. The river is so named because of the pits the Achumawi dug to trap game that came to water at the river.
The combined river flows WSW in a winding course across Modoc County, past Canby and through the Modoc National Forest in a narrow gorge called Stonecoal Valley. It turns south to flow past Lookout and into northern Lassen County, past Bieber to emerge into the ranching region of Big Valley. North of Little Valley it runs east into northeastern Shasta County, passing through the Cascades in a serpentine canyon in the Shasta National Forest. It flows past Pittville, McArthur, and Fall River Mills to join the Sacramento River as the eastern arm of Shasta Lake reservoir, approximately 15 mi (24 km) north of Redding. The lower 30 mi (50 km) of the river now forms the longest "arm" of the five of Lake Shasta, which is formed by Shasta Dam on the Sacramento downstream from the original confluence.
Goose Lake was once the source of the North Fork Pit River, but it now usually an enclosed basin. During rare high water levels, the lake still spills out into the Pit River system.
The river is a popular destination for fly fishing, rafting in its lower reaches, and is used for hydroelectric energy both in the powerhouses below Fall River Mills and at Shasta Dam. It is also used extensively for irrigation and conservation purposes.