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The Great Flood of 1861–62

History repeats itself once again.

In the winter of 1861–62, a 43-day run of storms filled California’s Central Valley with water and left parts of the state flooded for up to six months.

A levee road running through a flooded plain at sunset
Timeline

How it unfolded.

  1. December 1861

    The storms begin.

    A series of storms starts hitting California. It doesn’t let up for 43 days.

  2. January 10, 1862

    Sacramento goes under.

    Floodwater sweeps through the capital on the day Leland Stanford is to be inaugurated as governor. The ceremony goes ahead. He gets there by rowboat.

  3. January 22, 1862

    The government leaves.

    Unable to work in a flooded city, the legislature gives up and moves to San Francisco to wait out the water.

  4. The months after

    An inland sea.

    Water covers the Central Valley across an area at least 300 miles long and 20 miles wide. In the south, the Santa Ana River spreads into a sheet of water four feet deep around Anaheim. It stays for four weeks.

  5. The seven years after

    Sacramento rebuilds higher.

    The city raises its downtown district by 10 to 15 feet.

Source for this timeline: Scientific American, “California Megaflood: Lessons from a Forgotten Catastrophe.”
An eyewitness
“The entire valley was a lake extending from the mountains on one side to the coast range hills on the other.”
William H. Brewer, botanist, in a letter dated January 31, 1862.
The long record

Ten megastorms in 1,650 years.

A flood this size leaves a layer of silt behind. Scientists have read those layers in the Santa Barbara Basin, San Francisco Bay, the Sacramento Valley and the Klamath Mountains. They show megastorms in these years.

  1. 212
    The earliest one found so far.
    Stronger than 1861–62
  2. 440
    228 years later.
    Stronger than 1861–62
  3. 603
    163 years later.
    Stronger than 1861–62
  4. 1029
    426 years later. The longest gap.
    Stronger than 1861–62
  5. c. 1300
    About 271 years later.
  6. 1418
    About 118 years later.
    Stronger than 1861–62
  7. 1605
    187 years later. At least 50% more powerful than any other on record.
    The strongest
  8. 1750
    145 years later.
  9. 1810
    60 years later.
  10. 1861–62
    51 years later. The shortest gap.
51 to 426 years
The shortest and longest gaps between megastorms. On average, one has come every 100 to 200 years.
6 of the 10
were more severe than the flood of 1861–62, according to the U.S. Geological Survey. Offshore sediment near Santa Barbara dates them to 212, 440, 603, 1029, 1418 and 1605.
160+ years
since the last one. The last four came in 1605, 1750, 1810 and 1861–62, with gaps of 145, 60 and 51 years. By that pace, the next one is overdue.
Sources: U.S. Geological Survey, ARkStorm Scenario. Dettinger and Ingram, “The Coming Megafloods,” Scientific American, January 2013, as summarized on Wikipedia.
Then and now

Same valley. A hundred times the people.

380,000
People living in California at the 1860 census.
39 million
People living in California today, roughly.
100–200 years
How often a flood this size used to come, based on river sediment records and climate models.
UCLA Newsroom, 2022

Next: what would that storm do now?

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