The Shasta River is a tributary of the Klamath River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map, accessed 9 March 2011 in northern California in the United States. It drains the Shasta Valley on the west and north sides of Mount Shasta in the Cascade Range.
The river rises in southern Siskiyou County on the edge of the Shasta-Trinity National Forest, approximately southwest of Weed. It flows generally northwest through the Shasta Valley, past Weed, through Lake Shastina, and past Montague. It joins the Klamath from the south approximately north-northeast of Yreka.
The Shasta Valley is dominated by nearby Mount Shasta and underlain with volcano basalt from eruptions of the mountain in recent geology time. Pluto's Cave is an example of voids remaining after highly fluid lava drained from underground conduits which were fed by volcanic vents to the east. The Shasta Valley is covered with small hillocks extending from the base of Mt. Shasta north to just beyond the city of Montague, that are the debris from the liquefication of the ancestral Mount Shasta sometime within the past 400,000 years.
Bypassing Big Springs from the mouth, the river picks up more agricultural runoff as it meanders north between irrigated fields. The river then passes between Yreka and Montague, from the mouth, crossed by California State Route 3 and Interstate 5 for the final time. It then enters a canyon in the Klamath Mountains, from the mouth, and begins to parallel California State Route 263. Its mouth is on the left bank of the Klamath River, at the junction of State Route 263 and State Route 96.
Receiving just of rain yearly on average, the -wide Shasta River Valley receives most of its surface water flow from groundwater, and now, agricultural return flows. It also receives some water from snow runoff at Mount Shasta - which flows out of lava tubes as springs and feeds east-side Shasta River tributaries such as Big Springs Creek.
Today, less than 10% of this population still returns, and recent droughts have severely hampered survival rates of juvenile fish.
The river also supports coho salmon and steelhead.
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