The Great Flood of 1862 was the largest flood in the recorded history of California, Oregon, and Nevada, inundating the Western United States and portions of British Columbia and Mexico. It was preceded by weeks of continuous rains and snows that began in Oregon in November 1861 and continued into January 1862. This was followed by a record amount of rain from January 9–12, and contributed to a flood that extended from the Columbia River southward in western Oregon, and through California to San Diego, as well as extending as far inland as the Washington Territory (now Idaho), the Utah Territory (now Nevada and Utah), and the western New Mexico Territory (now Arizona).
The event dumped an equivalent of 10 feet (3.0 m) of precipitation in California, in the form of rain and snow, over a period of 43 days. Immense snowfalls in the mountains of far western North America caused more flooding in Idaho, Arizona, New Mexico, as well as in Baja California and Sonora, Mexico the following spring and summer, as the snow melted.
The event was capped by an intense, warm storm that melted the heavy snow load that had accumulated during the earlier storms. The resulting snow-melt flooded valleys, inundated or swept away towns, mills, dams, flumes, houses, fences, and domestic animals, and ruined fields. It has been described as the worst disaster ever to strike California. The storms caused an estimated $100 million (1861 US dollars) in damage, roughly equal to $3 billion in 2021. The governor, state legislature, and state employees were not paid for a year and a half. At least 4,000 people were estimated to have been killed in the floods in California, which was roughly 1% of the state population at the time.
Background
The weather pattern that caused this flood was not from an El Niño–type event. From the existing Army and private weather records, it has been determined that the polar jet stream was to the north because the Pacific Northwest experienced a mild rainy pattern for the first half of December 1861. In 2012, hydrologists and meteorologists concluded that the precipitation was likely caused by a series of atmospheric rivers that hit the Western United States along the entire West Coast, from Oregon to Southern California.
An atmospheric river is a wind-borne, deep layer of water vapor with origins in the tropics, extending from the surface to high altitudes, often above 10,000 feet, and concentrated into a relatively narrow band, typically about 400 to 600 kilometres (250 to 370 mi) wide, usually running ahead of a frontal boundary, or merging into it. With the right dynamics in place to provide lift, an atmospheric river can produce astonishing amounts of precipitation, especially if it stalls over an area for any length of time.
The floods followed a 20-year-long drought. During November, prior to the flooding, Oregon had steady but heavier-than-normal rainfall, with heavier snow in the mountains. Researchers believe the jet stream had slipped south, accompanied by freezing conditions reported at Oregon stations by December 25. Heavy rainfall began falling in California as the longwave trough moved south over the state, remaining there until the end of January 1862, causing precipitation to fall everywhere in the state for nearly 40 days. Eventually, the trough moved even further south, causing snow to fall in the Central Valley and surrounding mountain ranges (15 feet (4.6 m) of snow in the Sierra Nevada mountains).
Impact by region
Oregon
There was an excessive amount of precipitation in November 1861 over most of Oregon, less so in the extreme northwest. It was cold enough at the higher elevations that much snow fell in the Cascade Range, which, when later melted by the warm rains, produced a great quantity of water that flooded into the Willamette River and other streams in the Cascades. Tributaries of the Willamette originating in the Oregon Coast Range did not rise as high. A tropical depression that came in at the beginning of December produced strong, warm southerly winds in Oregon, with extremely heavy rain. Flooding was heaviest on rivers with tributaries arising from the snow-covered Cascade Range. The crest of the Willamette flood was reached at Salem on December 3; at Oregon City on the 4th; at Milwaukie, between Oregon City and Portland, on the 5th; at Albany on December 8. The crests at Albany and Salem were the highest ever known at any time. In Oregon, the flood was one of the largest in the recorded history of the Willamette Valley and the rest of Western Oregon.
An article in the December 14, 1861, Oregon City Argus, described the course of the flood at Oregon City:
During the month of November the rain had been falling almost continuously, and a vast amount of snow must have accumulated in the mountains...
Tuesday evening a gloom settled on a scene such as probably never was witnessed in our Valley before. The ceaseless roar of the stream made a fearful elemental music widely different from the ordinary monotone of the Falls; while the darkness was only made more visible by the glare of torches and hurrying lights, which with the shouts of people from the windows of houses surrounded by the water, all conspired to render the hour one of intense and painful excitement. The flood has covered the highest mark of January '53, and is still rapidly rising. As late as anything could be seen the mills were still standing, but the insatiate monster is still creeping up inch by inch, winding its swelling folds round the pillars and foundations of all the houses in its way, crushing and grinding them in the maw of destruction, and sweeping the broken fragments into a common vortex of ruin. All night as on the night previous, people whose homes were being invaded hurried to places of security, glad to escape even with the sacrifice of all their goods.
The light of Wednesday morning revealed a scene of desolation terrible in its extent no less than in its completeness. The Oregon City and Island Mills, Willamette Iron Works, Foundry and Machine Shop were all gone...
Flood waters were so high that at Oregon City at the flood's crest on December 5, the steamer St. Clair was able to run the falls, and steamers were able to visit points at some distance from the normal river channel. Although large amounts of wheat and flour were swept away, some was recovered when Oregon City's Island Mill was found on Sauvie Island downriver from Portland. The nearby town of Linn City was completely destroyed by flooding and was not rebuilt. The flood destroyed the historic towns of Champoeg, site of the first provisional government in Oregon, and Orleans, across the Willamette River from Corvallis. Neither was rebuilt.
The flooding was also severe in other parts of Oregon; to the south, the Umpqua River had the greatest flood known even to the oldest Native Americans, and water was 10 to 15 feet (3.0 to 4.6 m) higher than the 1853 flood. It rose from November 3 to December 3, subsided for two days, then rose again until the 9th. At Fort Umpqua, communication upriver was cut off above Scottsburg, and the river was full of floating houses, barns, rails and produce. The Coquille River swept away settlers' property, and there was also great damage on the Rogue River and on other small streams."
Economic losses from flood damage were severe, as the rivers in Oregon were the main routes of travel. The riverfront was the building site of mills, freight depots, and storehouses for grain and other foodstuffs. Business houses and many residences were near the landings. Farm buildings were mostly on sites convenient to the rivers and supplies of feed for livestock. Loss of so much wheat flour and the new demand coming since 1860 from the recently opened Idaho gold fields caused a spike in its price from $7 to $12 per barrel.
Idaho
In the interior of Washington Territory, in what is now Idaho, the storm creating the flood in Oregon dumped its precipitation as an unprecedented snowfall. Flooding on the Columbia River and the snow in the mountains closed off supplies to the new mining towns on the Salmon River, causing starvation among the miners of Florence, who were cut off from December until May 1862. By early July, as the heavy burden of snow in the mountains finally melted, the runoff caused great flooding. The Boise River flooded from extremely high runoff and is believed to have been four times larger than its largest recorded flood in 1943. Flood waters made the river expand to a couple of miles wide. It washed away or covered the original route of the Oregon Trail in the river valley.
California
California was hit by a combination of incessant rain, snow, and then unseasonably high temperatures. In Northern California, it snowed heavily during the later part of November and the first few days of December, until the temperature rose unusually high and it began to rain. In San Francisco, there were 35 inches of precipitation in December 1861–January 1862, and almost 50 for the season. There were four distinct rainy periods: The first occurred on December 9, 1861, the second on December 23–28, the third on January 9–12, and the fourth on January 15–17.
Native Americans knew that the Sacramento Valley could become an inland sea when the rains came. Their storytellers described water filling the valley from the Coast Range to the Sierra Nevada.
Northern California
Fort Ter-Waw, located in Klamath Glen, California, was destroyed by the flood in December 1861 and abandoned on June 10, 1862. Bridges were washed away in Trinity and Shasta counties. At Red Dog in Nevada County, William Begole reported that from December 23 to January 22 it rained a total of 25.5 inches (650 mm), and on January 10 and 11 alone, it rained over 11 inches (280 mm).
At Weaverville, John Carr was a witness to the sudden melt of snow by the heavy rain and onset of the flood in December 1861 on the Trinity River:
From November until the latter part of March there was a succession of storms and floods... The ground was covered with snow 1 foot [30 cm] deep, and on the mountains much deeper... The water in the river ... seemed like some mighty uncontrollable monster of destruction broken away from its bonds, rushing uncontrollably on, and everywhere carrying ruin and destruction in its course. When rising, the river seemed highest in the middle... From the head settlement to the mouth of the Trinity River, for a distance of one hundred and fifty miles, everything was swept to destruction. Not a bridge was left, or a mining-wheel or a sluce-box. Parts of ranches and miners cabins met the same fate. The labor of hundreds of men, and their savings of years, invested in bridges, mines and ranches, were all swept away. In forty-eight hours the valley of the Trinity was left desolate. The county never recovered from that disastrous flood. Many of the mining-wheels and bridges were never rebuilt.
Two years later William H. Brewer saw, near Crescent City, the debris of the flood:
The floods of two years ago brought down an immense amount of driftwood from all the rivers along the coast, and it was cast up along this part of the coast in quantities that stagger belief. It looked to me as if I saw enough in ten miles along the shore to make a million cords of wood.... One I measured was 210 feet [64 m] long and 3 1/2 feet [1.1 m] at the little end, without the bark.
Central Valley
The entire Sacramento and San Joaquin valleys were affected. An area about 300 miles (480 km) long, averaging 20 miles (32 km) in width, and covering 5,000 to 6,000 square miles (13,000 to 16,000 km2) was under water. The water flooding the Central Valley reached depths up to 30 feet (9.1 m), completely submerging telegraph poles that had just been installed between San Francisco and New York. Transportation, mail, and communications across the state were disrupted for a month. Water covered portions of the valley from December 1861, through the spring, and into the summer of 1862.
The rainy season commenced on the 8th of November, and for four weeks, with scarcely any intermission, the rain continued to fall very gently in San Francisco, but in heavy showers in the interior. According to the statement of a Grass Valley paper, nine inches of rain fell there in thirty-six hours on the 7th and 8th inst.... the next day the river-beds were full almost to the hilltops. The North Fork of the American River at Auburn rose thirty-five feet, and in many other mountain streams the rise was almost as great. On the 9th the flood reached the low land of the Sacramento Valley.
In Knights Ferry, in the foothills of the Sierra Nevada astride the Stanislaus River, about 40 miles (64 km) east of Modesto, the town's homes, its mill, and most of its businesses were ruined by the flood. The bridge spanning the river initially withstood the flood waters but was destroyed when the debris of the bridge at Two-Mile Bar, only a short distance up river, was torn from its foundation and crashed into the Knights Ferry Bridge, crushing the truss supports and knocking it from its rock foundation. All Sacramento excepting one street, part of Marysville, part of Santa Rosa, part of Auburn, part of Sonora, part of Nevada City, and part of Napa were under water. Some smaller towns like Empire City and Mokelumne City were entirely destroyed.