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 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.William H. Brewer, Up and down California in 1860–1864, New Haven, Connecticut: Yale University Press, 1930, p. 243. 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 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 ( 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:
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 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 , and on January 10 and 11 alone, it rained over .
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:
Two years later William H. Brewer saw, near Crescent City, the debris of the flood:
Central Valley The entire Sacramento and San Joaquin valleys were affected. An area about long, averaging in width, and covering was under water. The water flooding the Central Valley reached depths up to , 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.
In Knights Ferry, in the foothills of the Sierra Nevada astride the Stanislaus River, about 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.Mildred Brooke Hoover, H. E. Rench, E. G. Rench, Historic Spots in California, Third Edition, Stanford University Press, Stanford, 1966. pp. 540–541 Knight's Ferry. 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.
Sacramento
Sacramento, sited at the junction of the Sacramento and American Rivers, was originally built at above low-water mark, and the river usually rose almost every year. The New York Times reported on January 21, 1862, that a trapper who had spent more than 20 years in California had frequently boated over the city's site, and in 1846, the water at the location was deep for sixty days. On 27 December 1861, the Sacramento River reached a flood level of above the low water mark, after rising during the prior 24 hours.
By 1861, the Sacramento flood plain had quickly become inhabited by a growing population during the Gold Rush, and had begun to serve as the central hub for Valley commerce and trade and as the home of the California State Legislature. The landscape was recognized as a flood-prone landscape located at the confluence of the American and Sacramento River. John Muir noted the extent of seasonal flooding in Sacramento, "…The greatest floods occur in winter, when one could suppose all the wild waters would be muffled and chained in frost and snow…rare intervals warm rains and warm winds invade the mountains and push back the snow line from 2000 to 8,000 feet, or even higher, and then come the big floods."Muir, J. (1894). The Mountains of California: Chapter 11 The River Floods. The Century Co., New York.
However, the series of storms that led to the Great Flood of 1862 averaged precipitation levels that records show only occur once every 500 to 1,000 years. The geographical range of flooding in the state was noted by a traveling geologist from Yale University, William Brewer, who wrote that on January 19, 1862,
From December to January 1862 the series of storms carrying high winds and heavy precipitation left city streets and sidewalks underwater. Photographs show canals in place of city streets and boats docked to storefronts.