The Fall River, a major tributary of the Pit River, is located in north-eastern Shasta County approximately 60 miles northeast of Redding in the Fall River Valley. It courses between the Sierra Nevada and Cascade Mountain ranges with Mt. Shasta visible to the northwest and Mt Lassen to the south.
The river originates at Thousand Springs (elevation approximately 3,320 ft) – a series of springs rising from lava beds northeast of Dana – and flows 21.3 miles in a southerly direction before joining the Pit River below Fall River Mills.
Since 1922 most of the flow has been diverted at the Pacific Gas and Electric Pit No. 1 Forebay, located just upstream from Fall River Mills (Federal Energy Regulatory Committee Project No. 2687). For the forebay, flow is diverted via tunnel to Pit 1 Powerhouse on the Pit River.
Location & Geology
The Fall River Watershed lies within the volcanic terrain of the Modoc Plateau geomorphic province, and is the largest sub-drainage in the middle reach of the Pit River.
The river drains a 612-square mile area, but due to the porous volcanic nature of the region, most of the stream flow originates from springs within the valley. Bear Creek represents the only significant surface flow contribution to the Fall River.
The Tule River, another tributary to the Fall River, originates as a series of large springs known as Ahjumawi Lava Springs.
The Fall River is a moderate sized, slow moving, meandering meadow stream. It varies in width from 50 ft in narrower stretches near its headwaters to 300ft in its lower reaches. Depths generally range from approximately 2 ft in some shallow runs to an estimated 20 ft in deeper pools. The mean gradient is less than 1ft/mile.
Flows are relatively stable throughout the year due to the stream’s spring origins. At the USGS gauge near Dana, the river has a summer flow of about 450 cfs. Extreme flows recorded for the 1958 to 1967 period were 353 and 3,910 cfs (USGS survey, 1968).
Peak flows originate primarily form flood events on Bear Creek. Bear Creek flows into Fall River just below Thousand Springs, but is intermittent in its lower reaches during the summer.
In its uppermost 5 miles above Spring Creek, Fall River is about 75 ft wide as it flows through ponderosa pine forests interspersed with wide, flat meadows. At 5.2 miles below Thousand Springs, Spring Creek contributes more cold, clear water to the river.
Below Spring Creek, the river broadens to about 100 ft and meanders the remaining 16 miles through an open valley.
Approximately 7 miles below Spring Creek, Fall River is joined by the Tule River, which flows out of Big Trout and Eastman (Tule) Lake. These tributaries bring the total summer flow to about 1,200 cfs and channel widths to about 300 ft in the lower 9.3 miles of Fall River above the Pit No. 1 Intake.
The large volumes of spring water inflow maintain Fall River water temperature at near optimum ranges for trout production, even during mid-summer. At the Island Road Bridge, mid-summer temperatures are generally in the low to mid 50s F and, near Glenburn and the Pit No. 1 Intake, in the low to mid 60s.