The Sacramento River () is the principal river of Northern California in the United States and is the largest river in California.
Rising in the Klamath Mountains, the river flows south for  before reaching the Sacramento–San Joaquin River Delta and San Francisco Bay.
The river drains about  in 19 California counties, mostly within the fertile agricultural region bounded by the Coast Ranges and Sierra Nevada known as the Sacramento Valley, but also extending as far as the volcanic plateaus of Northeastern California.
Historically, its watershed has reached as far north as south-central Oregon where the now, primarily, endorheic (closed) Goose Lake rarely experiences southerly outflow into the Pit River, the most northerly tributary of the Sacramento.
The Sacramento and its wide natural floodplain were once abundant in fish and other aquatic creatures, notably one of the southernmost large runs of chinook salmon in North America.
For about 12,000 years, humans have depended on the vast natural resources of the watershed, which had one of the densest Native American populations in California.
The river has provided a route for trade and travel since ancient times.
Hundreds of tribes sharing regional customs and traditions inhabited the Sacramento Valley, first coming into contact with European explorers in the late 1700s.
The Spanish explorer Gabriel Moraga named the river Rio de los Sacramentos in 1808, later shortened and anglicized into Sacramento.
In the 19th century, gold was discovered on a tributary of the Sacramento River, starting the California Gold Rush and an enormous population influx to the state.
Overland trails such as the California Trail and Siskiyou Trail guided hundreds of thousands of people to the gold fields.
By the late part of the century mining had ceased to be a major part of the economy, and many immigrants turned to farming and ranching.
Many populous communities were established along the Sacramento River, including the state capital of Sacramento.
Intensive agriculture and mining contributed to pollution in the Sacramento River, and significant changes to the river's hydrology and environment.
Since the 1950s the watershed has been intensely developed for water supply and the generation of hydroelectric power.
Today, large dams impound the river and almost all of its major tributaries.
The Sacramento River is used heavily for irrigation and serves much of Central and Southern California through the canals of giant state and federal water projects.
While it's now providing water to over half of California's population and supporting the most productive agricultural area in the nation, these changes have left the Sacramento greatly modified from its natural state and have caused the decline of its once-abundant fisheries.
Course
Upper river
The Sacramento River originates in the mountains and plateaus of far northern California as three major waterways that flow into Shasta Lake: the Upper Sacramento River, McCloud River and Pit River.
The Upper Sacramento begins near Mount Shasta, at the confluence of North, Middle and South Forks in the Trinity Mountains of Siskiyou County.
It flows east into a small reservoir, Lake Siskiyou, before turning south.
The river flows through a canyon for about , past Dunsmuir and Castella, before emptying into Shasta Lake near Lakehead in Shasta County.
The McCloud River rises on the east slope of Mount Shasta and flows south for  through the southern Cascade Range, roughly parallel to the Upper Sacramento, eventually to reach the McCloud Arm of Shasta Lake.
The Pit River, by far the largest of the three, begins in Modoc County in the northeastern corner of California.
Draining a vast and remote volcanic highlands area, it flows southwest for nearly  before emptying into Shasta Lake near Montgomery Creek.
Goose Lake, straddling the Oregon–California border, occasionally overflows into the Pit River during wet years, although this has not happened since 1881.
The Goose Lake watershed is the only part of the Sacramento River basin extending into another state.
Unlike most California rivers, the Pit and the McCloud Rivers are predominantly spring-fed, ensuring a large and consistent flow in even the driest of summers.
At the lower end of Shasta Lake is Shasta Dam, which impounds the Sacramento River for flood control, irrigation and hydropower generation.
Before the construction of Shasta Dam, the McCloud River emptied into the Pit River, which joined the Sacramento near the former mining town of Kennett, submerged when Shasta Lake was filled.
The Pit River Bridge, which carries Interstate 5 and the Union Pacific Railroad over the reservoir, is structurally the highest double-decked bridge in the United States (although most of the bridge piers are submerged under Shasta Lake when the reservoir is full).
The Upper Sacramento River canyon also provides the route for I-5 and the railroad between Lakehead and Mount Shasta.
Sacramento Valley
Below Shasta Dam the Sacramento River enters the foothills region of the northern Sacramento Valley.
It flows through Keswick Dam, where it receives about  of water per year diverted from the Trinity River.
It then swings east through Redding, the largest city of the Shasta Cascade region, and turns southeast, entering Tehama County.
East of Cottonwood it receives Cottonwood Creek – the largest undammed tributary – from the west, then Battle Creek a short distance downstream.
Below Battle Creek it carves its last gorge, Iron Canyon, emerging from the hills at Red Bluff, where a pumping station (which replaced the Red Bluff Diversion Dam) removes water for irrigation.
Beyond Red Bluff the river reaches the low floodplain of the Sacramento Valley, receiving Mill Creek from the east and Thomes Creek from the west near Los Molinos, then Deer Creek from the east near Vina.
thumb|right|Sacramento River above Sacramento Southeast of Corning, the Sacramento forms the boundary of Tehama County to the west and Butte County to the east.
A few miles downstream it forms the border of Butte County and Glenn County to the west.
Stony Creek joins from the west in Glenn County, near Hamilton City and about  west of Chico.
The river then forms the Glenn–Colusa County line for a short distance before crossing entirely into Colusa County.
It passes by the Sutter Buttes, a group of volcanic hills that rise abruptly from the middle of the Sacramento Valley, where it receives Butte Creek from the east at Colusa.
Below Colusa the river flows south-southeast, forming the border of Colusa County and Sutter County to the east.
About  further downstream, the Sacramento River reaches the Tisdale Weir.
During floods, water overtops the weir and flows east into the Sutter Bypass, the first of two major bypass channels that temporarily store and move floodwaters downstream to reduce pressure on the main channel of the Sacramento.
The Sacramento River and the Sutter Bypass flow parallel for over , rejoining on the border of Sutter County and Yolo County near Knights Landing.
The Feather River, the largest tributary of the Sacramento, joins from the east at Verona directly below the Sutter Bypass.
A second flood control structure, the Fremont Weir, diverts flood waters from both the Sacramento and Feather Rivers into the Yolo Bypass, which parallels the Sacramento River down the west side of the valley.
Cache Creek and Putah Creek, two major tributaries which formerly joined the Sacramento River from the west, are now intercepted by the Yolo Bypass via man-made channels.
The main channel of the Sacramento flows south, forming the Yolo–Sacramento County line.
Lower river
As the river continues south it approaches the Sacramento metro area, the largest population center in the watershed.
Sacramento International Airport is located on the east bank of the river near Fremont.
Near downtown Sacramento it receives the American River from the east, then passes under the historic Tower Bridge and Interstate 80 Business.
The California State Capitol sits less than half a mile (0.8 km) east of the river where the Tower Bridge crosses it.
Shortly downstream, the Port of Sacramento is located on the west side of the Sacramento, connected to the river by a lock.
The Sacramento River Deep Water Ship Channel provides access to the port from the Pacific, bypassing about  of the winding lower Sacramento.
The channel runs parallel to the Sacramento several miles to the west, and also forms the eastern boundary of the Yolo Bypass.
The manually operated Sacramento Weir, located across from downtown Sacramento on the west side of the river, serves to relieve floodwater pressure from the American River by allowing it to drain west into the Yolo Bypass instead of continuing down the Sacramento River.
thumb|left|Aerial view of the Delta region, showing the Sacramento River (above) and the San Joaquin River.
Downstream of Sacramento, the river enters the Sacramento–San Joaquin River Delta, a vast tidal estuary and inverted river delta of over  which receives the entire run-off of the Central Valley, a region covering a third of California.
The Sacramento is by far the largest contributor of fresh water to the Delta; in an average year, it accounts for more than 80 percent of the fresh water inflow.
At Walnut Grove, the manmade Delta Cross Channel connects the Sacramento to the Mokelumne River channel, allowing a portion of the water to be pumped south toward Clifton Court Forebay, the receiving reservoir for the main CVP and State Water Project aqueducts which irrigate millions of acres and supply water to over 23 million people in the San Joaquin Valley, the San Francisco Bay Area and Greater Los Angeles.
Although river levels are tidally influenced here and occasionally as far north as Verona, the water stays fresh in all but the driest years.
Saltwater intrusion from the Pacific Ocean was one of the main reasons for the construction of the federal Central Valley Project (CVP), whose dams maintain a minimum flow in the Sacramento to keep seawater at bay.
Below Rio Vista, the lower Sacramento River is rejoined by the Deep Water Ship Channel and the Yolo Bypass and curves southwest along the base of the Montezuma Hills, forming the border of Solano and Sacramento Counties.
This part of the river is dredged for navigation by large oceangoing vessels and averages three-quarters of a mile (1.2 km) across.
North of Antioch and Pittsburg, the Sacramento and San Joaquin Rivers join at the head of Suisun Bay, marking the official end of both rivers.
The combined waters flow west through Suisun Bay and the Carquinez Strait into San Pablo Bay and San Francisco Bay, joining the Pacific at the Golden Gate.
Discharge
Following the Columbia River, the Sacramento is the largest river by discharge on the Pacific coast of the continental United States.
The natural runoff of the river is 22 million acre feet (27 km3) per year, or about .
Before dams were built on its tributaries, the river flooded up to  during the rainy season, equal to the flow of the Mississippi River.
Late summers of particularly dry years could see flows drop below .
Large volumes of water are withdrawn from the Sacramento River for irrigation, industry and urban supplies.
Annual depletions (water not returned to the river after use) are about 4.72 million acre feet (5.83 km3) for irrigation and  for urban use.
An additional 7.61 million acre feet (9.39 km3) is reserved for environmental uses, primarily to maintain a minimum fresh water outflow in the Delta to combat salinity.
thumb|right|Flooding on the Sacramento River, January 24, 1970 The U.S. Geological Survey (USGS) has stream gauges on 25 locations along the Sacramento River, although not all of them are currently operational.
The ones currently in operation are at Delta, California (near the source at Mount Shasta), at Keswick (near Redding), Colusa (about halfway down the river), Verona, and Freeport.
The Freeport gauge, which sits just downstream of Sacramento, provides a relatively good metric of the annual outflow from the Sacramento River Basin.
The average flow between 1949 and 2013 was .
The maximum recorded flow was  on February 19, 1986; the lowest was  on October 15, 1977.
Flow in the Yolo Bypass, a relief channel designed to carry a portion of the flood waters in order to protect the Sacramento area, is not measured by the Freeport gauge.
A separate gauge on the bypass recorded an average throughput of  between 1939 and 2013, mostly from December–March.
The highest recorded flow was  on February 20, 1986.
During the dry season of July through September, the bypass carries low to zero flow.
Although the Sacramento River nominally begins near Mount Shasta, the true hydrological source of the Sacramento River system is the Pit River, which is by far the largest of the three rivers flowing into Shasta Lake.
At the USGS Montgomery Creek gauge, the average flow of the Pit River was  for the period 1966–2013.
By comparison, the Sacramento River at Delta gauge, a few miles above Shasta Lake, recorded an average of  for the period 1945–2013.
The McCloud River had an average discharge of  for the 1967–2013 period.
Since the 1960s, the McCloud River flow has been reduced and the Pit River flow increased due to diversion of water for hydropower generation; however the total volume of water entering Shasta Lake remains the same.
Before Shasta Dam was built, the volcanic springs feeding the Pit and McCloud Rivers provided the majority of river flow in dry summers when the Upper Sacramento and other tributaries slowed to a trickle.
Monthly combined discharge of Sacramento River at Freeport and Yolo Bypass near Woodland (cfs)
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thumb|left|The Sacramento River below Shasta Dam
The Sacramento River's watershed is the largest entirely in California, covering much of the northern part of the state.
The endorheic (closed) Goose Lake drainage basin in southern Oregon, however, has been known to overflow into the Sacramento River system during particularly wet years.
The Sacramento River basin generally lies between the Sierra Nevada and Cascade Range on the east and the Coast Ranges and Klamath Mountains in the west, although the part of the basin drained by the Pit River extends east of the Cascades.
The Pit River, has the distinction of being one of three rivers that cut through the main crest of the Cascades; its headwaters rise on the western extreme of the Basin and Range Province, east of major Cascade volcanoes such as Mount Shasta and Lassen Peak.
The other two are the Klamath River and Columbia River.
By discharge, it is the second-largest contiguous U.S. river draining into the Pacific, after only the Columbia River, which has almost ten times the flow of the Sacramento.
The Colorado River, which reaches the Gulf of California just south of the US-Mexico border near the southeast part of the state, is far larger than the Sacramento in terms of length and drainage area but has a slightly smaller flow.The Columbia River has a flow of , seven times that of the Sacramento.
There are other rivers that come close to the Sacramento's discharge such as the Skagit River, with , or the Klamath River, with .
The Colorado River, which is heavily drawn from for irrigation and municipal water supply, no longer reaches the sea; even its historic flow of  did not come close to the Sacramento.
The Sacramento, when combined with the Pit, is also one of the longest rivers in the United States entirely within one state—after Alaska's Kuskokwim and Texas' Trinity.
The major drainage basins bordering that of the Sacramento are that of the Klamath in the north, the San Joaquin and Mokelumne to the south and the Eel River in the west.
The Russian River also lies to the west and the endorheic (closed) Honey Lake and Eagle Lake basins to the north.
On the east side are many endorheic watersheds of the Great Basin including the Truckee River and Carson River.
Parts of the Sacramento watershed come very close to, but do not extend past, the border of California and Nevada.
Physiography
The basin's diverse geography ranges from the glacier-carved, snowcapped peaks of the Sierra Nevada to the sea-level (and often lower) marshes and farmlands of the Sacramento-San Joaquin Delta.
The highest point is  at Mount Shasta, a dormant stratovolcano near the headwaters of the Sacramento River.
The Sierra Nevada peaks generally decrease in height from south to north—from over  in the headwaters of the American River near Lake Tahoe, to  in Lassen County where they adjoin the Cascade Range.
On the west side, the Coast Ranges are the opposite, increasing in height to almost  in the north.
The arid volcanic plateaus in the northeast, which are characterized by alternating hills and large sedimentary basins, typically lie at elevations of .
Most of the Sacramento Valley is below  in elevation; in its lower course, the Sacramento River drops only about  per mile.
Between the bajadas or alluvial slopes extending from the foothills of the Sierra Nevada and Coast Ranges, are the low floodplains of the Sacramento River.
The river flows at an elevation somewhat higher than the surrounding terrain due to deposits of sediment over millennia that created raised banks (essentially natural levees).
The banks separate the river from the lowlands to the east and west that once served as vast overflow basins during winter storms, creating large areas of seasonal wetlands.
Since the 19th century, artificial levee systems have been constructed to enable farming in the fertile flood plain.
Today there are  of irrigated farmland in the Sacramento Valley.
Due to the reduction of the floodplain area, the speed of flood flow in the Sacramento River has increased, creating a significant hazard for the farms and towns along its course.
By the early 20th century engineers had realized not all the floodplains could be safely reclaimed, leading to the intentional creation of flood bypasses where development is limited to annual crops and recreational uses.
Further south, much of the Delta region is actually below sea level: subsidence caused by wind erosion and intensive farming have caused the land in the delta to gradually sink since the late 19th century.
Many of the delta islands would be underwater if not for the maintenance of the levees and pumps that keep them dry.
Some of the "islands" are now up to  below the adjacent channels and sloughs.
Land use
The Sacramento River watershed is home to about 2.8 million people; more than two-thirds live within the Sacramento metropolitan area.
Other important cities are Chico, Redding, Davis and Woodland.
The Sacramento River watershed covers all or most of Shasta, Tehama, Glenn, Butte, Plumas, Yuba, Sutter, Lake and Yolo Counties.
It also extends into portions of Siskiyou, Modoc, Lassen, Lake (in Oregon), Sierra, Nevada, Placer, El Dorado, Sacramento, Solano and Contra Costa Counties.
The river itself flows through Siskiyou, Shasta, Tehama, Butte, Glenn, Colusa, Sutter, Yolo, Sacramento, Solano and Contra Costa, often forming boundaries between the counties.
Many of the mountainous regions of the watershed are administered by the U.S. Forest Service.
The Sacramento River watershed includes large areas of coniferous forests in the Mendocino and Trinity National Forests in the Coast Ranges, Shasta and Lassen National Forests in the southern Cascades and the Plumas, Tahoe and Eldorado National Forests on the western slopes of the Sierra Nevada.
The watershed also has Lassen Volcanic National Park, which covers  centered on Lassen Peak, the southernmost Cascade volcano.
Whiskeytown-Shasta-Trinity National Recreation Area, which is over  in size, straddles much of the upper Sacramento and Trinity Rivers, and is named for the three local reservoirs (Shasta Lake, Trinity Lake and Whiskeytown Lake) which are popular tourist areas.
Many other state parks and recreation areas lie within the watershed.
Geology
By geologic standards, the Sacramento is a fairly young river; the borders of its watershed began to form only a few million years ago as magma welling up below the Earth's crust pushed up by the Pacific Plate colliding with the North American Plate caused the formation of the Sierra Nevada.
Although mountains had existed as early as 100 million years ago in this region (before then the land was probably submerged under the Pacific), they were worn by erosion, and the present-day range only formed about 4 million years ago.
The northern part of the Sacramento watershed is more ancient, and was formed by intense volcanic activity over 25 million years ago, resulting in lava flows that covered and created the Modoc Plateau, through which the Pit River flows.
Mount Shasta and Lassen Peak are among the numerous Cascade Range volcanoes that still stand in the area.
As the Sierra rose, water erosion and glaciation carved deep canyons, depositing massive amounts of sediment to form a coastal plain between the mountains and the Pacific Ocean.
About 3 million years ago, multiple terranes were formed and smashed into the North American Plate from the Pacific Plate, causing the uplift of the California Coast Ranges, enclosing the Sacramento Valley and forcing the streams within to flow south instead of west, forming the ancestral Sacramento River.
(The Klamath Mountains, which enclose the northwest part of the Sacramento Basin, were formed in the same way but are much older, dating back 7.5 million years.)
It is possible that the river once had its outlet in Monterey Bay, and may have played a part in the formation of the  Monterey Submarine Canyon when sea levels were lower during the Ice Ages.
The Monterey Bay outlet of the Sacramento and San Joaquin rivers was blocked off by uplift about 2 million years ago, and runoff from the Sierra began to transform the Central Valley into a gigantic lake, called Lake Clyde.
This lake stretched  north to south and was at least  deep.
About 650,000 years ago the lake catastrophically overflowed, draining into San Francisco Bay and creating the Carquinez Strait, the only major break for hundreds of miles in the Coast Ranges.
The narrow outlet trapped some of the sediments of the rivers in the Central Valley, forming the inland Sacramento-San Joaquin River Delta.
Since then, this inland sea has periodically reformed during times of intense flooding, the most recent being the Great Flood of 1862.
Dams, levees and floodways constructed during the 20th century have thus far prevented this phenomenon from re-occurring.Kelley and Kelly, pp.5–15 History
Native Americans
The Sacramento River and its valley were one of the major Native American population centers of California.
The river's abundant flow and the valley's fertile soil and mild climate provided enough resources for hundreds of groups to share the land.
Most of the villages were small.
Although it was once commonly believed that the original natives lived as tribes, they actually lived as bands, family groups as small as twenty to thirty people.
The Sacramento Valley was first settled by humans about 12,000 years ago, but permanent villages were not established until about 8,000 years ago.
Historians have organized the numerous separate original native groups into several "tribes".
These are known as the Shasta, Modoc, and Achomawi/Pit River Tribes of the volcanic plateaus in the north; the Wintu and Hupa in the northern Klamath and Trinity mountains; the Nomlaki, Yuki, Patwin, and Pomo of the Coast Ranges; the Yana, Atsugewi, Maidu, Konkow, and Nisenan in the Sierra and their western foothills; and the Miwok in the south.
Most of the Sacramento Valley's native peoples relied on hunting, gathering and fishing, although agriculture was practiced in a few areas.
Settlement size ranged from small camps to villages of 30–50 permanent structures.
Acorns were a staple food, and the Sacramento Valley's riparian zones, which supported seven species of native oaks, provided these in abundance.
Native Americans pounded the acorns into flour, which they used to make bread and cakes.
Abundant salmon and steelhead runs in the Sacramento River and its tributaries were harvested using fishing weirs, platforms, baskets and nets.
The river also provided shellfish, sturgeon, eel and suckerfish They also hunted waterfowl, antelope and deer which all existed in huge numbers in the rich valley bottom and marsh lands.
Before European contact, the indigenous population of the Sacramento Valley has been estimated at 76,000 people.
European exploration and settlement
thumb|right|Mt. Shasta and the Sacramento River by Frederick A. Butman (1820-1871)
The first outsiders to see the river were probably the members of a Spanish colonial-exploratory venture to Northern California in 1772, led by Captain Pedro Fages.
The group ascended a mountain, likely in the hills north of Suisun Bay, and found themselves looking down at the delta of the Sacramento and San Joaquin Rivers.
However, due to their vantage point, neither Fages nor any of his men saw the Sacramento clearly.
They assumed that the San Joaquin, coming from the south, was the largest of the merging rivers they saw.
In 1808, explorer Gabriel Moraga, on a journey to find suitable sites for the construction of missions, became the first foreigner to see the river clearly.
Judging its huge breadth and power he named it Rio de los Sacramentos, or "River of the Blessed Sacrament".
In the following years, two more Spanish expeditions traversed the lower part of the river, the last one in 1817.Exploring the great rivers of North America, p. 126
The next visitors were Hudson's Bay Company (HBC) fur trappers exploring southwards from the disputed Oregon Country, starting in the 1820s.
The first organized expedition, led by Peter Skene Ogden, arrived in the area of Mount Shasta in 1826.
By this time, California was under the control of Mexico, although few Mexican settlers had come to what would later become the state, mostly settling in the small pueblos and ranchos along the south and central coast.
The HBC mountain men created the Siskiyou Trail out of several Native American paths that ran through the mountains between Oregon's Willamette Valley and the northern part of the Sacramento Valley.
In the years to come, this path, which eventually extended from San Francisco to Portland, Oregon following parts of the Sacramento, Willamette, Klamath, Rogue, and other rivers would become an important trade and travel route.Harton and McCloud, p.8 Gold Rush
Although just one of thousands of American emigrants that poured into California over the next few years when California became part of the United States, John Augustus Sutter's arrival marked a turning point in the history of the Sacramento Valley, and California as a whole.
In 1841, Sutter and his men built a fortress at the confluence of the Sacramento and American Rivers and the Mexican government granted him almost  of land surrounding the two rivers.
Naming it New Helvetia, he created an agricultural empire in the lower Sacramento Valley, attracting several hundred settlers to the area, and relied on Native American labor to maintain his domain.
Sutter had something of a two-faced relationship with the many Native American groups in the area.
He was friendly with some of the tribes, and paid their leaders handsomely for supplying workers, but others he seized by force to labor in the fields.Royce and Wells, p.33
thumb|alt=Black-and-white photo of a pair of steamboats moored at a dock; smoke is issuing from one of the boat's funnels; the masts of several sailing ships are visible in the background|Chrysopolis, one of several large steamboats that served for transportation on the river during the California Gold Rush After the Bear Flag Revolt of 1846 and the Mexican–American War, in which California became part of the United States, Sutter and other large landholders in California held on to their properties.
In 1848 Sutter assigned James W. Marshall to build a sawmill on the South Fork American River at Coloma, where Marshall discovered gold.
Although Sutter and Marshall originally intended to keep the find a secret, news soon broke attracting three hundred thousand hopefuls from all over North America, and even the world, to the Sacramento River in search of fortunes, kicking off the California Gold Rush.
People flocked to the region by the Oregon Trail-Siskiyou Trail, California Trail, Southern Emigrant Trail and various land and/or sea routes through the Isthmus of Panama and around southern South America by ship.
Steamboats traveled up and down the Sacramento River carrying miners from San Francisco to the gold fields.
As the miners expanded their diggings deeper into the Sierra Nevada and Klamath Mountains, Native Americans were pushed off their land and a long series of skirmishes and fights began that continued until intervention by the state and national governments.
Post-Gold Rush development and effects
The influx of migrants brought foreign diseases like malaria and smallpox, which American Indians had no immunity to.
These diseases killed off a large proportion of their population within a few decades of the arrival of Sutter and the following settlers,Exploring the great rivers of North America, p. 129 the start of the gold rush, not to mention the numerous battles fought between the settlers and native bands as well as the forced relocation of some of the tribes to Indian reservations in several places scattered around the Sacramento Valley, mainly in the Coast Ranges.
In the early 1850s, several treaties were signed between the U.S. government and the Native Americans involving their relocation onto a reservation in the Sierra foothills; this promise was broken.
Therefore, in 1863, the tribes from the area surrounding the middle Sacramento and Feather rivers, the Konkow group, were removed and marched forcibly to the Round Valley Indian Reservation near the Eel River.
A total of 461 people were forced from their homes, but only 277 made it to the reservation; the others perished of disease, starvation or exhaustion.
As mining developed from simple methods such as panning and sluicing to a new form of commercialized extraction, hydraulic mining, profits from the petering gold rush made a second leap, earning more profits than placer miners in the early years had ever made.
The city of Sacramento, founded on the original site of Sutter's fort, began to flourish as the center of an agricultural empire that provided food to feed the thousands of miners working in the hills as well as a place of financial exchange of all the gold that was mined.
Sacramento was officially established in 1850 and was recognized as the state capital in 1854.
As the economy of the Sacramento Valley grew, the Southern Pacific Railroad established tracks along the river to connect California with Oregon following the ancient path of the Siskiyou Trail, in the 1880s and 1890s.Harton and McCloud, pp.
26–27 Many parts of the railroad were treacherous, especially in the mountainous areas north of Dunsmuir.Harton and McCloud, pp.
27–31
It was not long after Sacramento surpassed a population of 10,000, then the Great Flood of 1862 swept away much of it (and almost everything else along the Sacramento River) and put the rest under water.
The flood waters were exacerbated by the sediments washed down by the millions of tons by hydraulic mining, which filled the beds of the Sacramento, Feather and American rivers up to  in Sacramento and also covered thousands of acres of Central Valley lands.
A flood in 1875 covered the city of Marysville and when it subsided the town's streets were filled with debris and rocks washed down from the "hydraulicking" going on upstream.
Repeated floods and increased demand for Sacramento River water saw a plethora of massive changes to the environment beginning in the 20th century.
An early project was undertaken to raise the entire city of Sacramento about  above its original elevation.
This was followed by much bigger engineering projects to control and store the floodwaters of the Sacramento River; the building of these public works would radically transform the river during the 20th century.
Dams and water use
From the late 19th century through the 20th century, California experienced an economic boom that led to the rapid expansion of both agriculture and urban areas.
The Central Valley was becoming a heavily developed irrigation farming region, and cities along the state's Pacific coast and the Sacramento and San Joaquin rivers were growing rapidly, requiring river control to prevent flooding on the one hand, and to ensure a consistent supply of water on the other.
The U.S. Army Corps of Engineers and the State of California completed reports as early as the 1870s and 1880s which outlined future development of the Sacramento, Feather, Yuba and Bear rivers.
In 1873, Colonel B.S. Alexander of the Army Corps of Engineers surveyed the Central Valley's hydrology and irrigation systems and proposed a great network of pumps and canals that would take water from the Sacramento River in the north, and transport it to drought-prone central and southern California, especially the San Joaquin Valley.
The Sacramento River basin receives "two-thirds to three-quarters of northern California's precipitation though it has only one-third to one-quarter of the land.
The San Joaquin River watershed occupies two-thirds to three-quarters of northern California's land, but only collects one-third to one-quarter of the precipitation."
The topography of the Sacramento River watershed makes it particularly prone to flooding.
Storm water runs quickly off the steep mountains flanking the Sacramento Valley, but with few exceptions the alluvial valley floor is strikingly flat, slowing down the runoff and causing it to overflow the river banks.
Before flood control works were built, the winter floods frequently transformed the valley into an inland sea.
In 1880 State Engineer William H. Hall developed the first flood control plan for the Sacramento River.
Hall recognized that with the combination of flat topography and extremely heavy winter runoff volumes, a system of levees alone could not hope to contain flooding, as had been proven time and again in the flood prone city of Sacramento.
Sacramento River Flood Control Project
thumb|right|Sacramento Weir is one of several structures along the Sacramento River designed to drain excess floodwaters.
The Sacramento River Flood Control Project was authorized by the federal government in 1917.
While it intended to contain minor floods in the river banks by strengthening the existing levee system, the main feature was a series of bypasses, or sections of the valley intentionally designed to flood during high water.
Weirs placed at strategic points along the Sacramento River release water into the bypasses when the river reaches a certain stage, relieving the pressure of floodwaters on the main channel.
The bypasses are then allowed to drain slowly once flood crests have passed.
For most of the year, the bypasses remain dry and are used for annual crops such as rice.
Some of the principal features are the Butte Basin, Colusa Basin, Sutter Bypass and the Yolo Bypass.
The Butte Basin is a large lowland area on the east side of the river between Hamilton City and Colusa; the geographically similar Colusa Basin is located to the west.
The Sutter Bypass begins at Colusa and runs parallel to the east side of the Sacramento River until reaching the confluence with the Feather River.
The Yolo Bypass, located on the west side of the river, starts at the confluence of the Feather and rejoins the Sacramento in the Delta.
Although termed "bypasses", the system essentially reconnects the Sacramento with a portion of its historic flood plain, which it would have naturally flooded had the levee system not been in place.
Central Valley Project
thumb|left|alt=A crane lifts material used in the construction of a large concrete dam, which is still notched in the center to let the water flow through.
Several pipes for future water conveyance use are visible on the left.
|Construction work on Shasta Dam in June 1942
During the Great Depression in the 1930s, the first concrete proposals for a statewide water engineering project emerged, but when the state government could not sell the necessary bonds to fund the project, the federal government took over.
The Central Valley Project, one of the largest irrigation projects in the world, was constructed by the U.S. Bureau of Reclamation beginning in 1935.
Ultimately, the system would distribute 7 million acre feet (8.6 km3) to irrigate 3 million acres (1.2 million ha) of land in the Sacramento and San Joaquin Valleys.
Construction of Shasta Dam, the principal water storage facility in the Sacramento River system, started in 1938 and was completed in 1945.
Controlling runoff from the upper  of the Sacramento River watershed, Shasta greatly reduces flood peaks on the middle and lower parts of the Sacramento River.
Flood waters are stored for irrigation in dry years as well as navigation and electricity generation.
In the following decades, more huge reservoirs – capable of storing a combined  of water – were constructed on the Sacramento's main tributaries, enabling the regulation of water for irrigation and hydroelectric power.
Starting in the late 1950s, two major canals were extended to irrigate the western side of the Sacramento Valley – the Tehama-Colusa and Corning Canals.
Starting at the Red Bluff Diversion Dam on the Sacramento, the canals are  and  long respectively, and divert a total of over  of water to irrigate some .
State Water Project
In 1960, construction began on the State Water Project, whose primary purpose was to deliver water to Los Angeles and the San Francisco Bay Area.
Oroville Dam – the tallest dam in the U.S. – was built on the Sacramento's largest tributary, the Feather River.
A series of channels were enlarged in the Delta to facilitate water flow from the Sacramento to the Banks Pumping Plant and the California Aqueduct, which can carry as much as 4.2 million acre feet (5 km3) of water each year.
From its origin at the Delta the canal runs  southwards through the west side of the San Joaquin Valley, providing irrigation water to farmlands along its length, and lifted almost  over the Tehachapi Mountains via four large pumping stations.
The project irrigates  of land in the San Joaquin Valley and serves 22 million people in Central and Southern California.Exploring the great rivers of North America, p. 130
Over the years, several other plans materialized to divert rivers from California's North Coast into the Sacramento watershed, as future demand was projected to exceed supply.
The only one to be built was the Trinity River Project (which would become part of the CVP), sending over 90 percent of the flow of that river into the Sacramento via a tunnel under the Klamath Mountains.
Due to environmental damage and fish kills in the Trinity River, the volume of diverted water has been limited by law since the 1990s.
Other, larger projects ultimately failed to take root.
One of the most notorious, the Klamath Diversion, proposed to send the entire flow of the Klamath River into the Sacramento River through a system of large reservoirs, canals, pumping stations and tunnels.
Similarly, the Dos Rios Dam project would have diverted a considerable portion of the Eel River to the Sacramento.
Both projects were defeated by local resistance, opposition from environmentalists, as well as the high capital cost.
Navigation
The Sacramento River Deep Water Ship Channel was completed in 1963, and was built to facilitate navigation of large oceangoing ships from the Delta to the port of Sacramento.
The channel bypasses the winding lower part of the Sacramento River between the state capital and the Delta thus reducing water travel times.
It also serves to discharge floodwaters from the lower end of the Yolo Bypass.
Built by the Army Corps of Engineers, the canal is  long and is maintained to a depth of .
Ecology and environmental issues
The Sacramento River and its drainage basin once supported extensive riparian habitat and marshes, in both the Sacramento Valley and the Delta, home to a diverse array of flora and fauna.
Due to the reclamation of land for agriculture and the regulation of seasonal flooding, the amount of water-based habitat declined greatly during the 20th century.
Other human impacts include the heavy water consumption for agriculture and urban areas, and pollution caused by pesticides, nitrates, mine tailings, acid mine drainage and urban runoff.
The Sacramento supports 40–60 species of fish, and 218 species of birds.
The basin also has a number of endemic amphibian and fish species.
Many Sacramento River fish species are similar to those in the Snake–Columbia River systems; geologic evidence indicates that the two were connected by a series of wetlands and channels about 4-5 million years ago.
Located along the Pacific Flyway, the sprawling wetlands of the Sacramento Valley are an important stop for migratory birds; however, only a fraction of the historic wetlands remain.
Seasonally flooded rice paddies in the Sacramento Valley comprise a large portion of the habitat currently used by migrating birds.
Native bird populations have been declining steadily since the 19th century.
Species that were once common but now are endangered or gone include the southwestern willow flycatcher, western yellow-billed cuckoo, least Bell's vireo, and warbling vireo.
Another reason for dropping numbers are the introduction of non-native species, such as the "parasitic" cowbird, which lays its eggs in the nests of other bird species causing its hatchlings to compete with the others for food.
There were once 9 species of amphibians that used the Sacramento River, but some have become extinct and most other populations are declining due to habitat loss caused by agriculture and urban development.
Amphibians originally thrived in the marshes, sloughs, side-channels and oxbow lakes because of their warmer water, abundance of vegetation and nutrients, lower predator populations and slower current.
This population once included several species of frogs and salamanders; the foothill yellow-legged frog and western spadefoot are listed as endangered species.
Riparian and wetlands areas along the Sacramento once totaled more than ; today only about  remains.
Much of this consists of restored stretches and artificially constructed wetlands.
Levee construction has prevented the river from changing course during winter and spring floods, which was crucial to the renewal of existing wetlands and the creation of new ones.
Since the late 19th century the river has been mostly locked in a fixed channel, which once could shift hundreds of feet or even several miles in a year because of floods.
In 2010, about  of the river's riparian forests are undergoing active restoration.
Anadromous fish
thumb|right|Current and historic range of winter chinook salmon Second only to the Columbia River on the west coast of the United States in Chinook salmon runs, the Sacramento and its tributaries once supported a huge population of this fish.
Millions of salmon once swam upstream to spawn in the Sacramento; as recently as 2002 eight hundred thousand fish were observed to return to the river.
The Sacramento and San Joaquin River systems are home to the southernmost existing run of chinook salmon in North America.
Starting in the 20th century, dam construction blocked off hundreds of miles of salmon-spawning streams, such as the upper Feather and American Rivers, and the entirety of the Pit and upper Sacramento rivers.
Pollution from farms and urban areas took a heavy toll on the river's environment, and heavy irrigation withdrawals sometimes resulted in massive fish kills.
Since 1960, when the big pumps at the head of the California Aqueduct in the Delta began their operation, the pattern of water flow in the Delta has been changed considerably leaving the fish confused as to where to go, resulting in many generations dying off because they have not been able to find their way upstream.
In 2004, only 200,000 fish were reported to return to the Sacramento; in 2008, a disastrous low of 39,000.
In 1999, five hydroelectric dams on Battle Creek, a major tributary of the Sacramento River, were removed to allow better passage of the fish.
Three other dams along the creek were fitted with fish ladders.
The river is considered one of the best salmon habitats in the watershed because of its relatively cold water and the availability of ideal habitat such as gravel bars.
By the late 20th and early 21st centuries, the government blamed crashing fish populations on overfishing, especially off the Northern California and Oregon coast, which lie directly adjacent to the migration paths of Sacramento River salmon.
This has resulted in a ban on coastal salmon fishing for several years since 2002.
The Red Bluff Diversion Dam, although not a large dam and equipped with fish passage facilities, also presents a major barrier.
Because of inadequate design, roughly 25–40% of the incoming fish get blocked by the dam each year.
The dam has also become a "favorite spot" for predatory fish to congregate, feasting on the salmon that get trapped both above and below the dam.
As of 2010, the salmon run has shown slight signs of improvement, probably because of that year's greater precipitation.
In 1995, a gate on the Folsom Dam on the American River broke open, causing the river's flow to rise by some .
The water traveled down the Sacramento and washed into the Pacific; the influx of fresh water was such that it confused thousands of anadromous fish to begin migrating up the river, thinking that the river had risen because of late-autumn storms.
Whales
thumb|alt=A whale breaches in a light blue body of water in the foreground.
The far shore is steep and heavily vegetated.
|Delta the Whale in the Sacramento River Marine animals such as whales and sea lions are occasionally found far inland after navigating the river for food or refuge and then losing track of how to get back to the Pacific Ocean.
In October 1985 a humpback whale affectionately named "Humphrey the humpbacked whale" by television media traveled  up the Sacramento River before being rescued.
Rescuers downstream broadcast sounds of humpback whales feeding to draw the whale back to the ocean.
On May 14, 2007, onlookers and media spotted two humpback whales traveling the deep waters near Rio Vista.
The duo, generally believed to be mother and calf (Delta, the mother and Dawn, her calf), continued to swim upstream to the deep water ship channel near West Sacramento, about  inland.
There was concern because the whales had been injured, perhaps by a boat's propeller or keel, leaving a gash in each whale's skin.
The whales were carefully inspected by biologists and injected with antibiotics to help prevent infection.
After days of efforts to lure (or frighten) the whales in the direction of the ocean, the whales eventually made their way south into San Francisco Bay, where they lingered for several days.
By May 30, 2007, the cow and calf apparently slipped out unnoticed under the Golden Gate Bridge into the Pacific Ocean, likely under cover of night.
Pollution
thumb|right|Sacramento River flowing through the Sacramento suburbs For a river of its size, the Sacramento is considered to have fairly clean water.
However, pollutants still flow into the river from many of its tributaries and man-made drains or channels.
Pesticide runoff, especially DDT, is one of the largest problems faced today, because of the valley's primarily agricultural economy.
Increased erosion caused by the removal of riparian vegetation and the runoff of fertilizers into the river have led to occasional algae blooms, though the water is usually cold because of the regulation of dams upstream.
Other pollutant sources include urban runoff, mercury and even rocket fuel that was reported to have leaked near the American River from an Aerojet extraction project.
Mercury pollution created by mining and processing activities during the California Gold Rush still has a profound impact on the Sacramento River's environment.
The toxic substance was widely used by miners to separate gold from the surrounding rocks and dirt, and was disposed of by allowing it to evaporate.
Most of the mercury was mined in the Coast Ranges to the west of the Sacramento River; mines in these mountains produced roughly 140,000 tons of mercury to serve the Gold Rush.
When the gold rush ended, most of the mines were closed but toxic acidic water and chemicals continue to leak from within, into west-side Sacramento tributaries such as Cache Creek and Putah Creek.
In the east, mercury that permeated into the ground has contaminated several aquifers that feed rivers such as the Feather, Yuba and American.
Even the evaporated mercury posed problems – so much of it was used that significant concentrations still linger in the air in many places.
Mercury pollution continues today and will probably continue for decades or centuries into the future.
In July 1991, a train derailed near Dunsmuir, California alongside the Sacramento River.
A tank car split open, spilling about 19,500 gallons of the pesticide metam sodium into the river.
The chemical formed a stinking, bubbling, green glob that moved  down the river, killing everything in its path.
More than one million fish were killed, including at least 100,000 rainbow trout, and thousands of other aquatic creatures as well as nearby trees.
Next, the green glob entered Shasta Lake, California's largest reservoir.
Fortunately, a system of aerating pipes at the bottom of the lake had been set up to dissipate the chemical, reducing it to almost nothing by the 29th, preventing further environmental destruction.
The tank car carrying the metam sodium through California was of a type that the National Transportation Safety Board said had "a high incidence of failure" in accidents.
Furthermore, the tank car was not labeled, so the train's crew was unaware of the danger posed by the chemical.
See also
Auburn Dam
Bass Festival
Blue Tent Creek
Delta Dawn
List of crossings of the Sacramento River
List of rivers of California
United States Exploring Expedition
References
Works cited
External links
Sacramento River realtime flows and forecasts
SacramentoRiver.org
Sacramento River Watershed Program
Sacramento River Flooding – Online Video from KVIE Public Television
"A Toxic Nightmare: The Dunsmuir Metam Sodium Spill Revisited"
* Category:Sacramento Valley Category:Rivers of Northern California Category:Tributaries of San Pablo Bay Category:Central Valley Project Category:Geography of the Sacramento Valley Category:San Francisco Bay watershed Category:Rivers of Sacramento County, California Category:Rivers of Contra Costa County, California Category:Rivers of Solano County, California Category:Rivers of the San Francisco Bay Area Category:Rivers of Siskiyou County, California Category:Rivers of Shasta County, California Category:Rivers of Tehama County, California Category:Rivers of Butte County, California Category:Rivers of Glenn County, California Category:Rivers of Colusa County, California Category:Rivers of Sutter County, California Category:Rivers of Yolo County, California Category:Geography of the Central Valley (California) Category:History of Sacramento, California Category:Mendocino National Forest
