Saturday, June 3, 2023
HomeFeaturesEverything You Ever Wanted to Know About the Bly Tunnel! (But Were...

Everything You Ever Wanted to Know About the Bly Tunnel! (But Were Afraid to Ask) – Part Two

Did you miss the other parts in our series?

Here are links so you can catch up and read them all

Part One Where we detail the physical aspects of the lake and the earliest records of exploration

Part TwoIn which we will begin to look at historic lake levels and the different natural factors which have caused Eagle Lake to rise and fall… including earthquakes!

Part ThreeIn which we retrace our steps and take a look at the various attempts to tap the lake, including 3 tunnels you never knew existed!

Part FourIn which we find out where all of this water was supposed to be going! Featuring the lush garden regions of Amedee, Standish and Litchfield.

Part FiveAbsolutely everything else you need to know about the Bly Tunnel up till now.

Everywhere we go these days people are talking about the Bly Tunnel at Eagle Lake. We all read the pertinent articles in the Lassen County Times, try and absorb facts and figures and listen to the arguments in what has become an incredibly divisive issue.

Why does this particular controversy raise the ire of so many? Just attempting to put a lot of these facts down in writing is a scary proposition given the extreme nature of the arguments. We have tried to exhaustively track down as many prima facie documents as possible, relying on the opinions or studies by experts.

Along with those opinions we hope to give you our own SusanvilleStuff primer on the colorful history, unique geology and over 150 years of political battles surrounding California’s second largest natural lake.

Eagle Lake at its highest level ca.1916

Part Two – In which we will begin to look at historic lake levels and the different natural factors which have caused Eagle Lake to rise and fall… including earthquakes!

Because of the peculiar nature of Eagle Lake its depth has fluctuated to extremes since long before man attempted to tap the water for irrigation.

We are very much indebted to Dr. Owen Bateson for his meticulous research and data skills and we have relied for the most part on his data for the rise and fall of the lake, contrasted against his record of precipitation totals. Dr. Bateson has put a great deal of time and effort into his study of the lake and is a wealth of resources about the many facets of the issue.

In 1870 the United States Government Land Office placed elevation of the lake at 5,109 feet above sea level, and it slowly rose through the early 1880’s flooding developed lands and forcing settlers to abandon homes and ranches. This increase was tied directly to the above-average precipitation.

But on June 19th, 1889 something happened to change the very nature of the lake. A substantial earthquake with 28 aftershocks, centered directly under the lake, rocked the area.

A letter from a correspondent to the San Francisco Call, written shortly after the quake reads, “The series of earthquake shocks that commenced here on the evening of the 19th inst. have been continued at intervals up to the present. Although the first shock was by far the hardest, there have been a number since that have made things quite lively, and indicating that the force that creates these commotions is active still.”

“Since the first shock some curious phenomena have developed. The spring from which the town of Susanville is supplied with water has been largely increased in its volume of water, as also many others in this vicinity. The waters are of a milky whiteness. The water of Eagle Lake has been greatly disturbed and is quite muddy.”

“At the south of Eagle Lake and extending many miles is a range of high volcanic hills, covered generally with timber and chaparral. A number of persons who were near or on these hills last Friday heard loud rumblings to the west, accompanied by loud detonations like the firing of very heavy artillery, while the earth seemed to keep up an almost uninterrupted trembling motion. A slight trembling is also noticed much of the time here in town.”

A composite photo of Susanville in 1895 from Inspiration Point – Click for a larger version!

Thomas Ford, editor of the Bieber Mountain Tribune, who was travelling through the Willow Creek Valley at the time of the quake, gave a firsthand account of four shocks, the waters of Willow Creek were higher than ever before, the water in local reservoirs turned muddy, ashes were found in wells, beer shot up 15 feet out of the tank of Frank Runge’s brewery and more.

Springs on the Willow Creek side of the mountain increased in flow, and water from Cady Springs, Bunnel’s Springs and on the south slope of Roop Mountain doubled.

And then, immediately after the quake and without warning, Eagle Lake dropped two feet.

In his book Tim Purdy asks a very interesting question. Did this major 1889 earthquake close the subterranean outlet of the lake, thereby allowing the lake to reach its high level in 1916? By then the lake elevation was 5125.2 feet, an increase of 16 feet since 1899’s low point!

By September of 1896 the stage road which formerly passed around the shore of the lake was covered with water by a depth of twelve feet! An article in the Pacific Rural Press said that the new road, built in its stead, was soon to be submerged as well.

This Engel photo, taken near the turn of the century shows the lake water slowly encroaching on surrounding area.

Evidence left in rings of stumps showed that this was the highest lake level in at least 400 years.

USGS Map showing movement of the 1921 earthquake – Click here for a larger version

Another major quake followed in July of 1921, recorded by the seismograph at UC Berkeley and centered again under the lake. Purdy asks if this earthquake could have re-opened the same outlet allowing water to flow out again.

Computations from the seismograph records of the 1921 quake, according to the USGS report, showed that, “There is no doubt that a subterranean movement occurred along the fault plane on its east shore.”

Purdy notes that Bly’s tunnel was approaching completion at the time of the second major quake and would receive direct responsibility for lowering the lake.

After this point, Purdy says, the lake’s fluctuation was no longer consistent with the annual precipitation.

Purdy’s supposition is backed up by a USGS report from the turn of the century which said, “This lake rises and falls without regard to rainfall, and that when it sinks numerous springs flow actively from the outer slope of its apparent barrier and supply streams that reach Honey Lake.”

“This suggests,” concludes the report, “that the barrier is of porous nature, as a landslide might be, and that the water passages through it are intermittently closed and opened.”

Another California Water Board study done in 1954 opined that perhaps it was a combination of the quake-opened subterranean outlet, the Bly Tunnel and severe drought that drew down the lake to its lowest level.

Dating of stumps along the shore was done by Professor St. Harding who began his study in 1915. The historic lake level was determined by rings on stumps, which on one showed the elevation at 5,115 feet or less from the year 1650 until the tree was submerged in 1895.

After drought and water loss to the Bly Tunnel project during the 1930’s Eagle Lake saw its sharpest decline in water levels. The lake bottomed out at its lowest point in 1936, shortly after the tunnel was abandoned and filled with a sand plug.

This 1948 view from the air shows the lake at around 5,093 feet, with points of land almost meeting in the middle of the lake.

Drought would drop the lake again to severe levels in 1950, after which it slowly rose for more than 30 years.

This Eastman Studios photo of the lake’s south shore shows just how much waters had receded by 1953.
Reno Gazette Journal, 1983


During the wet winter of 1983, worried that the 51 year-old sand plug might fail with absolutely catastrophic effects, the Eagle Lake Interagency Board supported the idea of permanently sealing the Bly Tunnel with a concrete plug.

Engineers determined that if the lake reached 5,110 feet, a level not reached since the tunnel was built, “there is reason to be concerned that there could be a massive failure of the tunnel.”

According to the report, with the lake at that level a failure of the tunnel would drain most of the north and south basins and send large volumes of highly alkali water into the Willow Creek Valley.

Opponents of the project rallied against the BLM’s plan to permanently block the tunnel, citing rising water levels which would inundate home owners and resorts around the lake and flood Highway 139.

In 1984 when the Olympic Torch passed through Lassen County on its way to the Los Angeles Olympics, flood worries at the north end of the lake prompted organizers to reroute the torch over the Eagle Lake Road, making Lassen A-1 the only county road on the torch’s journey. ~From Purdy’s Eagle Lake

In November of 1986, after the lake had reached just two feet from what the BLM considered an emergency, the agency permanently sealed the tunnel, replacing the previous sand plug with a concrete plug in the shaft.


Tomorrow in Part Three of our special series we will rewind back to the 19th century and begin looking at the various attempts to harness the lake. Including four tunnels, two ditches and a big pump!

A comparison of the Bly Tunnel inlet in 1962 and today



Jeremy Couso
Jeremy Couso Publisher/Editor
clear sky
55.2 ° F
55.2 °
55.2 °
58 %
0 %
79 °
82 °
79 °
81 °
81 °
- Advertisment -

Most Popular

- Advertisement -