Upper Pit River Watershed.
The Upper Pit River Watershed is located in northeastern California at the eastern edge of the Great Basin Province. The north and south forks of the Pit River drain the northern portion of the watershed. The North Fork of the Pit River originates at Goose Lake, an enclosed basin except during rare events when it spills over into the Pit River. The North Fork headwaters include a number of tributaries in the Warner Mountains. The South Fork of the Pit River originates in the south Warner Mountains at Moon Lake in Lassen County. The north and south forks of the Pit River converge in the town of Alturas flows in a southwesterly direction into Shasta Lake in Shasta County and into the Sacramento River. The southern limit of the Upper Pit River is marked by the confluence of the Pit River and Fall River in eastern Shasta County. The Upper Pit River Watershed includes approximately 3, 415 square miles or 2, 767,000 acres, 21 named tributaries totaling about 1,050 miles of perennial stream, and 4,054 river miles.
The Upper Pit River Watershed, from the headwaters to the historical confluence with Fall River, is within the Modoc Plateau Geomorphic Province. The Modoc Plateau is bordered on the west by the Cascade Range, to the south by the Sierra Nevada, and the east by the Basin and Range geomorphic provinces.
The Upper Pit River is a run off dominated river with substantial snowmelt from the Warner Mountains. Flows are augmented by spring discharge in some reaches. As the Upper Pit River crosses the Modoc Plateau, it loses water through its stream channel to the underlying groundwater. According to Norris and Webb (1990), they concluded that the Upper Pit River and its tributaries lose water to groundwater from Goose Lake to Fall River. Springs associated with the Fall River system collectively produce a nearly constant discharge of approximately 1,100 to 1,200 cubic feet per second (USDA, 2002). This system is among the largest freshwater spring systems in the United States (Meinzer, 1972).