Ahjumawi Lava Springs State Park. Hat Creek and Burney Creek, spring-fed from the Lassen Peak area, supplied a further to the Pit River. The aquifers in the Pit River basin may hold as much as in storage and are consistently replenished by winter precipitation seeping through the watershed's porous volcanic rocks and soils. The water typically emerges at points of lower elevation where the surface layers encounter harder metamorphic and sedimentary rock. The U.S. Geological Survey (USGS) operates a stream gage on the Pit River at Montgomery Creek, directly below Pit 7 Dam and above Shasta Lake. This gage measures streamflow from an area of , or 70 percent of the total watershed. The average streamflow between 1966 and 2012 was , with a maximum of recorded on January 24, 1970, after heavy rainfall. A short minimum flow of occurred on July 12, 1975 due to construction work at Pit 7 Powerhouse requiring temporary cessation of releases. The minimum 7-day flow was , on September 5–12, 1966. Before the damming of Shasta Lake in the 1940s, the annual flow of the Pit River was about four times the size of the Sacramento at their confluence, making it the true hydrological source of the Sacramento River system. Measured at the mouth, the river's natural discharge likely exceeded , a figure which includes the McCloud River and Squaw Creek contributing about of additional flow below the Montgomery Creek gage. Dams The lower course of the Pit River is one of California's most significant hydroelectric rivers, not just because of its consistent perennial flow, but because of its steep drop: in the between Fall River Mills and Shasta Lake, the Pit descends some , or a gradient of per mile, which is quite considerable for a river of its size. Because of the dependable flow, large reservoirs are not needed to regulate releases for power generation, unlike other major hydroelectric schemes in California. The combined generating capacity of powerhouses on the river and its tributaries is approximately 770 megawatts. As of 2004, the annual generation from main stem powerhouses is approximately 2.64 billion KWh. Including powerhouses on tributaries, the total rises to 3.67 billion KWh, or approximately 13 percent of California's total hydropower. The first dam on the Pit River proper is Pit 3 Dam, which forms Lake Britton near Burney about downstream from Fall River Mills. Water is diverted via a tunnel