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This page is about the California river. For the river in Mexico, see Sacramento River (Mexico).

{{Geobox|River}} The Sacramento River is the largest river of northern California in the United States. It begins in the Klamath Mountains, near Mount Shasta and flows south through the agricultural Sacramento Valley (the northern half of the Central Valley), to the Sacramento–San Joaquin River Delta where it empties into the Pacific Ocean via Suisun Bay. Sacramento, the state capital, is named for the river and sits at the confluence of the Sacramento and American rivers. The Sacramento River is 400-mile (640 km) long, draining a watershed of 26,500 square miles (69,000 km²) in nineteen California counties.

For most of its course, the river flows across a broad fertile floodplain consisting of alluvial sediments up to 5 miles (8.0 km) thick. Once home to enormous wetland and riparian habitats, and one of the largest Chinook salmon runs in North America, the Sacramento River basin has been populated by Native Americans for about 12,000 years. Spanish colonization of California starting in the 1700s largely avoided the Sacramento Valley due to the difficulty of navigating its swamps and seasonal channels. The river was named by Gabriel Moraga during an unsuccessful expedition to find suitable mission sites in the Central Valley. In the 1800s, fur trappers established trade routes through the Sacramento River watershed along old Native American trails.

Large-scale settlement by Europeans did not occur until after the Mexican-American War when California became part of the United States. In 1848 gold was discovered along a tributary of the Sacramento River, starting the Gold Rush which brought hundreds of thousands of people to California within a few years, establishing the Sacramento River as an important trade and travel route via steamboats, and accelerating the conversion of the Sacramento Valley to agriculture. High demand for fertile land in the valley led to conflicts with Native Americans and their eventual expulsion to reservations. Settlement along the river was not easy, due to its tendency of catastrophic flooding. The Great Flood of 1862, which destroyed Sacramento and turned the Central Valley into a 300-mile (480 km) long lake, was the impetus for construction of water works that would greatly transform the Sacramento River in the late 19th and 20th centuries.

The Sacramento River is the largest river by volume in California and is a key statewide water resource. Since the 1930s the watershed has been intensely developed by massive state and federal water projects, with the primary purpose of impounding floodwaters and delivering it to the drier parts of central and southern California. The Sacramento River irrigates 6 million acres (24,000 km²) of farmland and provides domestic water supply to over 20 million people, including parts of the San Francisco Bay Area and Los Angeles. As a consequence of this development, most of the original wetlands of the Sacramento Valley have been lost and the salmon run has massively declined. Many current water conservation efforts focus on environmental restoration, especially in the sensitive Delta region, but are controversial due to the potential impact on water supplies.

Geography

Sacramento River system
To source at Mount Shasta Pit River Trinity Dam Shasta Dam Trinity River diversion at Lewiston Dam Whiskeytown Lake diversion Keswick Dam SR 44 at Redding Clear Creek I-5 at Anderson Cow Creek Cottonwood Creek I-5 SR 36 at Red Bluff I-5 Tehama-Colusa Canal pumping station Mill Creek SR 32 at Hamilton City Lake Almanor Stony Creek, Black Butte Lake Big Chico Creek Oroville Dam SR 162 at Butte City, Oroville Moulton Weir to Butte Creek Proposed Sites Reservoir Colusa Weir to Butte Creek New Bullards Bar Dam Butte Slough SR 20 at Meridian, Yuba City Yuba River Tisdale Weir to Sutter Bypass Bear River SR 113 Indian Valley Reservoir Clear Lake Sutter Bypass, SR 99 Feather River Fremont Weir to Yolo Bypass/Cache Creek I-5 Sacramento Weir to Yolo Bypass I-80 at Sacramento Lake Berryessa Nimbus Dam (Folsom South Canal head), Folsom Dam Port of Sacramento, American River Locks (inoperational) Sutter's Mill (historical site) Putah Creek Mouth of Yolo Bypass Sacramento Deep Water Ship Channel SR 12 at Rio Vista Head of Sacramento-San Joaquin River Delta Suisun Bay San Joaquin River (from south)

The Sacramento River drains the largest watershed entirely in California, covering much of the northern third of the state. 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. The endorheic (closed) Goose Lake drainage basin, which extends partly into Oregon, has been known to overflow into the Pit-Sacramento River system during particularly wet years.

By discharge, it is the second-largest river on the Pacific coast of the continental United States , after only the Columbia River, which is almost seven times larger than the Sacramento. The Sacramento River watershed is bordered by the drainage basins of the Klamath River to the north, the San Joaquin River to the south and the Eel River and Russian Rivers to the west. The east side borders endorheic watersheds of the Great Basin, including those of Eagle Lake, Honey Lake, the Truckee River and the Carson River. Parts of the Sacramento watershed reach almost to the border of California and Nevada.

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 counties, often forming boundaries between the counties.

Upper river

Upper Sacramento River at Castle Crags State Park

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 14,104-foot (4,299 m) Mount Shasta, at the confluence of North, Middle and South Forks in the Trinity Mountains of Siskiyou County. Shasta, a dormant stratovolcano, dominates the geography of the area, rising considerably above the surrounding 5,000-to-7,000-foot (1,500 to 2,100 m) Cascade Range peaks. The river flows east into the small reservoir of Lake Siskiyou before turning south. It flows through a canyon for about 60 miles (97 km), past Dunsmuir and Castella, before emptying into Shasta Lake near Lakehead in Shasta County.

The headwater area is densely forested, with the exception of the farming valleys at the foot of Mount Shasta, and receive some of the heaviest rainfall in the watershed (65.4 inches (1,660 mm) annually at Shasta Lake). The McCloud River flows largely parallel and to the east of the upper Sacramento. It rises on the east slope of Mount Shasta and flows south for 77 miles (124 km) through the Cascade mountains, eventually to reach the McCloud Arm of Shasta Lake. Like the upper Sacramento, the McCloud flows through deep canyons. While the Upper Sacramento River canyon provides the route for Interstate 5 and the Union Pacific Railroad (formerly Southern Pacific) between Lakehead and Mount Shasta, the McCloud flows through wilder and more inaccessible landscapes.

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 300 miles (480 km) before emptying into Shasta Lake near Montgomery Creek. In contrast to the Sacramento headwaters, the Pit River country has an arid semi-desert climate, with alternating rocky hills and large sedimentary basins, at elevations of 3,000 to 5,000 feet (910 to 1,520 m). Goose Lake, straddling the Oregon–California border, can overflow into the Pit River during wet years, although this has not been observed since 1881. The Goose Lake watershed is the only part of the Sacramento River basin extending into another state.

Sacramento River at Shasta Dam

Unlike most California rivers, the Pit and the McCloud Rivers are fed by volcanic springs, ensuring a large and consistent flow in even the driest of summers. Before the construction of large dams and reservoirs, the Pit-McCloud system provided most of the base flow in the main stem of the Sacramento River during late summer and fall when other, more seasonal tributaries would slow to a trickle.

At the lower (southwest) 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 old 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).

Sacramento Valley

Below Shasta Dam the Sacramento River enters the foothills region of the northern Sacramento Valley. Most of the Sacramento Valley is below 300 feet (91 m) in elevation; in its lower course, the Sacramento River drops only about 1 foot (0.30 m) per mile. The valley is a large sedimentary basin rimmed by high mountains. On the west, the Coast Ranges generally rise in elevation from south to north, where they reach heights of nearly 10,000 feet (3,000 m) in the Klamath Mountains. On the east side, the Sierra increase in height from north to south, with an average of 6,000 to 7,000 feet (1,800 to 2,100 m) in the Feather River watershed to more than 11,000 feet (3,400 m) along the Sierra Crest between the American River and Lake Tahoe. The north side is bordered by mountains formed by the intersection of the Coast and Cascade Ranges. The south is open to the San Joaquin Valley, the southern continuation of the Central Valley.

Sacramento River in the Sacramento Valley

Keswick Dam

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 more than 2,000,000 acres (8,100 km²) 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.

Near Keswick, the river flows through Keswick Dam, where it receives about 1,200,000 acre-feet (1.5 km³) 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 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.

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 15 miles (24 km) 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 20 miles (32 km) 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 40 miles (64 km), 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. 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 (inoperational since 2004). The Sacramento River Deep Water Ship Channel provides access to the port from the Pacific, bypassing about 42 miles (68 km) 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.

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 1,000 square miles (2,600 km²) 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. 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 25 feet (7.6 m) below the adjacent channels and sloughs.

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 30,000 cubic feet per second (850 m³/s). Before dams were built on its tributaries, the river flooded up to 650,000 cubic feet per second (18,000 m³/s) during the rainy season, equal to the flow of the Mississippi River. Late summers of particularly dry years could see flows drop below 1,000 cubic feet per second (28 m³/s). 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 491,000 acre-feet (0.606 km³) 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.

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 23,330 cubic feet per second (661 m³/s). The maximum recorded flow was 115,000 cubic feet per second (3,300 m³/s) on February 19, 1986; the lowest was 3,970 cubic feet per second (112 m³/s) 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 4,809 cubic feet per second (136.2 m³/s) between 1939 and 2013, mostly from December–March. The highest recorded flow was 374,000 cubic feet per second (10,600 m³/s) 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 4,760 cu ft/s (135 m³/s) for the period 1966–2013. By comparison, the Sacramento River at Delta gauge, a few miles above Shasta Lake, recorded an average of 1,191 cu ft/s (33.7 m³/s) for the period 1945–2013. The McCloud River had an average discharge of 775 cu ft/s (21.9 m³/s) for the 1967–2013 period. It should be noted that 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)

Geology

The modern path of the Sacramento River was once occupied by a shallow sea along the west coast of North America. Starting about 165 million years ago, as the Pacific plate subducted under the North American plate it pushed up rocks of the Franciscan assemblage where the Coast Ranges stand today. To the east, the Nevadan orogeny created a volcanic arc (similar to today's Cascades) in the current location of the Sierra Nevada. The forearc basin created between the two gradually filled with sediment eroded from the ancestral Sierra volcanoes, depositing the 40,000-foot (12,000 m) thick Great Valley Sequence which underlies the flat floor of the Sacramento Valley. The Klamath Mountains which form the northern boundary of the Sacramento Valley were created by a series of terranes (crustal fragments) that were uplifted and metamorphosed between the Coast Range and Cascade Range, during the Paleozoic and Mesozoic periods.

Mount Shasta, created by eruptions between 600,000–300,000 years ago, is the highest point in the Sacramento River watershed.

Volcanism also created the Modoc Plateau, the area drained by the Pit River to the northeast of the Sacramento Valley, at least 25 million years ago via massive basaltic lava flows. Active volcanoes still exist in the Cascade Range, at Mount Shasta and Lassen Peak (in Lassen Volcanic National Park, near the headwater of the Feather River). The ancestral volcanic Sierra Nevada was ultimately eroded away; today's Sierra were formed not by volcanic activity but by the tilting of a massive crustal block forming a regional slope to the west, starting around 10 million years ago. The Sutter Buttes are a volcanic anomaly in the middle of the otherwise flat Sacramento Valley, formed about 1.6 million years ago along a now-inactive fault line.

The Sacramento valley floor today consists mainly of sediment deposited during the Cenozoic, from 66 million years ago to the present. By the mid-Cenozoic, about 30 million years ago, regional uplift and continued sedimentation had raised the valley enough to push the coastline westwards, exposing the valley floor and establishing a large, southward-flowing stream, the ancestral Sacramento River. Tributaries eroded deep canyons into the Sierra Nevada and Coast Ranges, depositing more and more sediment into the valley, where it was distributed by annual floods of the Sacramento River to form today's extensive floodplain.

The lower Sacramento River has seen constant morphological changes in the last 2.5 million years due to ice ages and interglacial periods during the Quatenary glaciation, which caused large fluctuations in sea level. During glacial periods the sea level was much lower, and the Sacramento River continued well past its current Suisun Bay terminus; the Carquinez Strait, San Francisco Bay and the Golden Gate are a ria, part of the Sacramento River valley that was ultimately drowned 14,000 years ago at the end of the last ice age. A large shallow bay formed at the junction of the Sacramento and San Joaquin Valleys, which was ultimately filled in by sediment, creating the Sacramento–San Joaquin delta, a rare example of an inverted river delta which accumulated in an upstream rather than downstream direction.

The deep sedimentary layers in the valley are home to one of the largest contiguous aquifers in the United States. Although groundwater is an important source for irrigation in the Sacramento Valley, groundwater levels have remained relatively stable since the 1960s, in contrast with precipitous declines in the drier San Joaquin Valley further south. This was one of the primary reasons for the construction of massive works to move surface water from the Sacramento River to the San Joaquin Valley.

Human history

First peoples

The Sacramento River and its valley were one of the most densely populated areas of North America prior to the arrival of Europeans. Abundant water, fertile soil and a mild climate provided enough resources for hundreds of Native American groups to share the land. The Sacramento Valley was first settled about 12,000 years ago, but permanent villages were not established until about 8,000 years ago. Most of the villages were small. Although it was once commonly believed that the original natives lived as tribes, they actually lived as bands, or family groups as small as twenty to thirty people. 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.

Life for Native Americans in the Sacramento Valley was relatively simple and involved little warfare. Most relied on a hunter-gatherer or fishing lifestyle. Settlement size ranged from small camps to villages of 30–50 permanent structures. As with people in the San Joaquin Valley and throughout much of California, the acorn was a staple food. The historic abundance of live oak and valley oak in the Sacramento Valley was capable of supporting a large population. Native people pounded the acorns into flour, which they used to make bread and cakes. They also consumed a variety of other foods—wild roots, seeds, berries, and game animals such as fish, deer, rabbits, and birds. Most of California's original 275,000–300,000 Native Americans are believed to have lived in the Sacramento and San Joaquin Valleys.

European exploration and settlement

Mt. Shasta and the Sacramento River by Frederick A. Butman (1820-1871)

The first known Europeans to see the river were 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. Due to their vantage point, the explorers incorrectly assumed that the San Joaquin, coming from the south, was the larger of the merging rivers they saw. In 1808, Spanish army officer and explorer Gabriel Moraga, on a journey to find suitable sites for missions in the Central Valley, became the first European to actually reach the river. Judging its huge breadth and volume 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 in 1817.

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 vicinity of Mount Shasta in 1826. By this time, California was under Mexican rule, although few Mexican settlers had come to the Sacramento Valley; they mostly settled in the small pueblos and ranchos along the south and central coast. The fur trappers and 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 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 linking the West Coast.

Gold Rush

"California Gold Diggers, Mining Operations on the Western Shore of the Sacramento River," lithograph published by Kellogg & Comstock, date unknown.

Chrysopolis was one of many large steamboats that transported miners on the river during the Gold Rush

In 1841, Swiss pioneer John Augustus Sutter and his men built a fortress at the confluence of the Sacramento and American Rivers and the Mexican government granted him almost 50,000 acres (200 km²) of land surrounding the two rivers, the future site of the city of Sacramento. Naming it New Helvetia, Sutter began to build an agricultural empire in the lower Sacramento Valley, attracting several hundred settlers to the area, and conscripting Native Americans as field workers. Sutter had mixed relationships with the local native groups. He was friendly with some groups, and paid their leaders generously for supplying workers, but others were seized by force.

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 initially held on to their Mexican land grants. 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 more than 300,000 hopefuls from all over North America and the world, starting the California Gold Rush. People flocked to the region by the Oregon Trail-Siskiyou Trail, California Trail and other established trails which crossed into the Sacramento River basin via various Cascade and Sierra passes. Sea routes through the Isthmus of Panama and around southern South America connected to steamboat services from the San Francisco Bay to the Sacramento River, carrying miners from the port of San Francisco to the gold fields.

Native American conflicts

As 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. 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, 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.

Late 19th and 20th centuries

Environmental damage caused by hydraulic mining near Downieville, on the North Yuba River

In the second stage of the gold rush, mining switched from simple panning and sluicing and methods to the highly commercial enterprise of hydraulic mining, earning even more profit than placer miners in the early years. As a consequence of hydraulic mining, millions of tons of sediment were washed down the Sacramento, Feather and American rivers and raised the river bed up to 7 feet (2.1 m) in Sacramento and also covered thousands of acres of land in the Sacramento Valley in "spoils" such as those at the Yuba Goldfields. Some parts of the river channel became so shallow that steamboats were unable to pass through; the debris eventually washed down to Suisun Bay, where much of it remains today and poses a hazard to shipping.

The city of Sacramento, founded on the original site of John Sutter's fort, experienced a population boom soon after the start of the Gold Rush, as the center of agricultural markets that provided food for the thousands of miners working in the hills, and a place of financial exchange for all the gold that was mined. Sacramento was formally incorporated in 1850 and was recognized as the state capital in 1854. As the regional economy grew and diversified in the late 19th century, the Southern Pacific Railroad established tracks along the Sacramento river to connect California with Oregon following the ancient path of the Siskiyou Trail. Many parts of the railroad were treacherous, especially in the mountainous areas north of Dunsmuir.

The Great Flood of 1862 was the largest on record along the Sacramento River and completely inundated Sacramento, which at the time had just reached a population of 10,000. Sacramento's levee system was completely overwhelmed; in fact, some levees that withstood the initial damage trapped water in the city, and had to be intentionally breached after the floodwaters outside had receded. The flooding was exacerbated by hydraulic mining debris that clogged the river channel and reduced its capacity. After the 1862 flood, a massive effort was undertaken to raise downtown Sacramento about 11 feet (3.4 m) above its original elevation. In 1916 the Sacramento Weir was constructed as a relief channel bypassing Sacramento. The weir was the first of many massive 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.

Water projects

Shasta Dam

From the late 19th century through the 20th century, California experienced an economic boom that led to the rapid expansion of agricultural and urban areas. The Central Valley was on its way to becoming the most productive farming region of the United States, and cities along the Sacramento and San Joaquin rivers were growing rapidly, requiring river control for two purposes: to prevent flooding in the winter, and to ensure a consistent supply of water in the summer. The U.S. Army Corps of Engineers (USACE) and the state of California completed reports as early as the 1870s which outlined future development of the Sacramento, Feather, Yuba and Bear rivers. In 1873, USACE Colonel Barton S. Alexander surveyed the Central Valley's hydrology and proposed a large network of pumps and canals that would take water from the Sacramento River in the north, and transport it to the drier central and southern parts of the state. This was the first of many proposals to move water from north to south, which would eventually culminate in the great federal and state water projects of the 20th century.

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, 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, levees alone could not hope to contain flooding, as had been proven time and again in the flood prone city of Sacramento. In order to provide the necessary level of protection, a system of large reservoirs, flood basins and relief channels would be needed to operate in conjunction with levees to protect cities and farms from flooding.

The second major issue was water supply in the dry summer and fall. Although Northern California experiences a much wetter climate than the south, rainfall is still remarkably seasonal, with almost no measurable precipitation between May and September. As farming in the Sacramento valley increased, more water was needed for irrigation, leaving only a minimal freshwater flow into the delta and Suisun Bay. During high tides, saltwater pushed in from the Pacific Ocean and compromised the water supply in estuary cities such as Pittsburg and Antioch. A teredo (saltwater worm) infestation in the 1930s caused massive damage to ships and piers in Suisun Bay. After the construction of a barrier across the Carquinez straits was deemed impractical, the focus was shifted to building water storage on the Sacramento River, which would ensure enough water supply for both irrigation and protection against salt-water intrusion.

Sacramento River Flood Control Project

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 height, 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 (drained by Butte Creek is a large lowland area on the east side of the river between Hamilton City and Colusa; the similarly sized 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

Construction work on Shasta Dam in June 1942

Main article: Central Valley Project

The Central Valley Project (CVP) originated out of the 1919 Marshall Plan, which proposed Kennett Dam (later to be known as Shasta Dam) on the Sacramento River to control floods and prevent saltwater intrusion. During the Great Depression in the 1930s, the California government could not sell the necessary bonds to fund the project and 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 Central Valley.

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 6,600 square miles (17,000 km²) 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 13 million acre feet (16 km³) 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 total 132 mi (212 km) in length and irrigate 150,000 acres (610 km²) of farmland. However, the majority of CVP water is diverted south via the C.W. Bill Jones Pumping Plant in the Delta, through the Delta-Mendota Canal to the drier San Joaquin Valley, where it irrigates up to 2.1 million acres (8500 km²) of land and also serves municipal, industrial and environmental demands.

State Water Project

Main article: California State Water Project

In 1960, construction began on the State Water Project (SWP), whose original purpose was to deliver water to Los Angeles and the San Francisco Bay Area, although a large amount of water is also delivered to San Joaquin Valley farms. The principal source of water would be the Feather River, the largest tributary of the Sacramento, which was impounded by Oroville Dam, the tallest dam in the United States. The Banks Pumping Plant diverts water from the Delta to the California Aqueduct, which can carry as much as 4.2 million acre feet (5 km³) of water each year. The California Aqueduct runs 444 miles (715 km) south through the San Joaquin Valley, and is lifted almost 3,000 feet (910 m) over the Tehachapi Mountains via four large pumping stations. The SWP irrigates 750,000 acres (300,000 ha) of land in the San Joaquin Valley and serves 22 million people in Central and Southern California.

Since its inception, the SWP has rarely been able to deliver the full amount of water it was contracted for, due to pumping limitations and constricted river channels in the Delta. The Peripheral Canal was intended to address this problem by diverting fresh water from the Sacramento River in a bypass around the Delta. The Peripheral Canal proposal was highly controversial due to its potential environmental damage, and was ultimately rejected via a ballot measure in 1982. Since then, the state has made several attempts to build a similar project, most recently the California Water Fix and Eco Restore plan, which rather than an open canal proposes to build tunnels under the Delta to deliver the water south.

The SWP also involved some proposals 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. The Klamath Diversion, proposed to reverse the entire Klamath River southward into the Sacramento River through a system of large reservoirs, canals, pumping stations and tunnels. 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, and ultimately poor economic justifications.

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 43 miles (69 km) long and is maintained to a depth of 30 feet (9.1 m).

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, which were 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 River and its riparian habitat support 40–60 species of fish, and 218 species of birds. The basin 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 suggests that the two were connected by a series of wetlands and channels about 4-5 million years ago.

Red Bluff Diversion Dam, which sends Sacramento River water to a pair of irrigation canals near Red Bluff, posed a major barrier to fish movement and migration in the river until replaced with a pumping plant in 2013.

The extensive wetlands of the Sacramento Valley provide important habitat for migratory birds along the Pacific Flyway; 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 at least 9 species of amphibians in 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 marshes, sloughs, side-channels and oxbow lakes because of their warmer water, abundance of vegetation and nutrients, lower predator populations and slower current. The population includes several species of frogs and salamanders; the foothill yellow-legged frog and western spadefoot are listed as endangered species.

Riparian and wetland areas along the Sacramento once totaled more than 500,000 acres (2,000 km²); today only about 10,000 acres (40 km²) remain. Much of this consists of restored or artificially constructed wetlands. Since the late 19th century the river has been mostly locked in a fixed channel, due to levee construction which have prevented the river from changing course during winter and spring floods, which were crucial to the renewal of existing wetlands and the creation of new ones. The river could once shift hundreds of feet or even several miles in a year due to flooding. In 2010, about 100 miles (160 km) of the river’s riparian zones were undergoing active restoration.

Anadromous fish

"The Sacramento River fall chinook stock is the driver of commercial and recreational salmon fisheries off California and most of Oregon."

Pacific Fishery Management Council, 2008

Current and historic range of winter chinook salmon

The Sacramento and its tributaries once supported a huge population of Chinook salmon, second only to the Columbia River on the west coast of the United States. 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-San Joaquin River system is 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 40,000 cubic feet per second (1,100 m³/s). 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

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 69 miles (111 km) 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 90 miles (140 km) 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

Sacramento River in 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 45 miles (72 km) 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 didn’t know that they were hauling a dangerous chemical.