Atmospheric rivers of 1862 trigger devastation in Sierra, Northern Nevada

Tahoe Dam in Tahoe City recorded maximum outflow of 2,690 cfs in January 1997. | Mark McLaughlin

An ARkStorm (1,000-year weather event) swamped the Pacific Coast with historic amounts of rain and snow during the winter of 1861-62.

Potent and relentless, a 43-day atmospheric river triggered devastating floods up and down California, inundating the immense Central Valley with an inland sea nearly 300 miles long and 20 miles wide. San Francisco was lashed by more than 24 inches of rain in January 1862 alone. Locations throughout the foothills were deluged by up to 9 feet of rain in just 60 days.

The high watermark of 1862 is an astonishing 12 feet above [Lake Tahoe’s] natural rim of 6,223 feet that occurred where there was no dam to restrict outflow into the Truckee River.

Arid and less populated, Southern California also suffered. In Los Angeles an estimated 66 inches of rain fell that year, compared to an average of 15, which caused mass destruction.

State newspapers reported that dozens of communities were destroyed and thousands of people died, many swept away by deep torrents of muddy water. An estimated 200,000 cattle drowned, nearly one quarter of the Golden State’s total livestock. It took six months for flood waters to recede from the city of Sacramento. When legislators finally returned to the state capitol that summer, they faced a crushed economy and a bankrupt government.

The megafloods that devastated the state, especially in northern California, were exacerbated by post-Gold Rush activities, land development and steep population growth along volatile waterways. In the 1850s, settlers and local officials ignored physical evidence that the strikingly flat Sacramento Valley was essentially a vast hydrological escape valve for the flood-prone Sacramento River. The vast flood plain had previously been submerged by deep water.

The valley was also a catch basin for engorged streams and rivers cascading down out of the immense watersheds of the Sierra Nevada. Millions of tons of fractured rock, cobbles and gravels from hydraulic gold-mining debris filled these streams and choked riverbeds causing them to quickly overflow their natural channels. Sand, mud and sediment even reached the California Delta.

Wet mantle events devastating
Preceding the flooding, a series of cold Gulf of Alaska-bred storm systems had repeatedly dumped heavy snow in the mountains during December, at times down to sea level in Northern California. In January 1862 warmer Pacific-sourced rain followed and the burgeoning snowpack began melting rapidly, releasing the water it contained from earlier storms. Modern-day hydrologists call this a wet mantle event, where extended periods of steady rain wash out a winter snowpack. Nothing melts a mountain’s frozen mantle of ice and snow faster than high-elevation rain from a strong atmospheric river.

Famed California environmentalist John Muir was aware of wet mantle events. In 1900 he wrote: “The Sierra Rivers are flooded every spring by the melting of the snow as regularly as the famous old Nile. Strange to say, the greatest floods occur in winter, when one would suppose all the wild waters would be muffled and chained in frost and snow…. But at rare intervals, warm rains and warm winds invade the mountains, and push back the snow line from 2000 to 8000 [feet in elevation] or even higher, and then come the big floods.”

Rain, snowmelt overwhelm
In the Tahoe Sierra, rivers and streams were overwhelmed by the massive influx of runoff. In 1862 there was no dam to hold back water at Lake Tahoe’s sole outlet in Tahoe City, but the overload of incoming precipitation, melting snow and runoff from the surrounding watershed pumped levels up to the highest ever recorded.

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Lumberjacks working in the Tahoe Basin at the time observed the shoreline encroachment and estimated that Big Blue rose to 6,235 feet in elevation, about 6 feet higher than today’s federally mandated maximum limit of 6,229.1 feet (Lake Tahoe Datum) when the lake’s storage volume is partially controlled by a 17-gate concrete buttress dam.

The high watermark of 1862 is an astonishing 12 feet above the lake’s natural rim of 6,223 feet that occurred where there was no dam to restrict outflow into the Truckee River. It’s hard to fathom how much water that is.

Miles downstream the Truckee River inundated Reno, Nev., where houses, structures and livestock were engulfed and destroyed. Myron C. Lake’s wooden toll bridge, hostelry and his assorted buildings were all swept away. Considered the founder of Reno, Lake rebuilt his enterprise that summer.

Weather along the relatively protected eastern Sierra Front was miserable. Two brothers grazing cattle in the Owens Valley noted that for 54 consecutive days after Dec. 24, 1861, there was not one day without a downpour of either rain or snow: “Not continuous,” Barton McGee wrote in his journal, “but at no time did it quit for a whole day, snowing to a depth of two feet or more and then raining it off. The whole country was soaked through, and all the hills were deeply covered. All the streams became impassible, while the Owens River was from one-fourth to one mile in width, about half ice and half water, and sweeping on to the lake.”

Eyewitness accounts partially reveal the extent of damage in the Carson Valley. In a letter from Carson City, dated Feb. 22, 1862, Uriah Allen wrote: “We have had one of the most severe winters ever known. Not so cold, but from Dec.1 to Feb.1 it stormed almost incessantly. It is impossible to estimate the amount of property destroyed in this Territory besides a great loss of human life — all the bridges upon the rivers were washed away. [Nevada did not become a state until 1864.] So great a destruction of property has injured all kinds of business, money is scarcer than ever before known.”

But, typical of the idealistic pioneer mentality of the time, Allen added: “This state of things cannot last, and I have no doubt that within a few months we shall prosper as old.”

Across the Nevada-California border east of the Bodie mining district was the gold-mining boomtown of Aurora with 5,000 residents. In January, a three-day rain melted the deep accumulated snowfall surrounding the district and nearly all the community’s adobe and stone buildings were wiped out. Lives were lost one night when Bodie Creek burst over its banks and swept several miners away. Weather records from Nevada Territory’s Fort Churchill — on the Carson River east of Carson City — indicate that the fort picked up nearly 9 inches of precipitation in two months, about double what the bone-dry area receives in an average year.

Hydrologists and climate scientists understand that powerful ARkStorms have long impacted the West Coast of North America and doubtless will again. Modern flood protection systems in the mountains and valleys are not designed to handle extreme weather events of this magnitude.

Referring to 1862, former California State climatologist Bill Mork said, “It was just an astounding year. It’s highly unlikely we’ll ever see anything like that in our lifetime.”

We better hope so.