Workers tunneling through Mount Baker Ridge "hole through" on April 16, 1940.

  • By John Caldbick
  • Posted 10/05/2021
  • Essay 21321
See Additional Media

On April 16, 1940, workers digging from opposite ends of the north bore of the Mount Baker Ridge Tunnel break through the last eight feet of blue clay separating them. This "hole-through" marks a milestone in the construction of the twin tunnels, each approximately 1,465-feet long (sources differ somewhat on the exact measurement). The tunnels are essential components of the first Lake Washington Floating Bridge project linking Seattle to the cross-Cascades Sunset Highway. The successful completion of the entire project a few months later will vindicate the imagination and doggedness of Seattle engineer Homer More Hadley (1885-1967), who in 1920 had conceived a plan to span Lake Washington with a bridge floating on reinforced-concrete pontoons, an idea that some later labeled "Hadley's Folly." Undeterred by skeptics and working alone and on foot, Hadley had also located the most suitable place for tunnels that would pierce Mount Baker Ridge and feed traffic from Seattle's commercial core to the cross-lake bridge he envisioned. Two decades later, the finished project incorporated many of his ideas, but his contributions weren't formally acknowledged for nearly 50 years.

Joining East and West

The Sunset Highway opened in 1915, the first automobile route over the Cascade Mountains. It crossed at Snoqualmie Pass, went west to Issaquah, turned south around the south end of Lake Washington, then north into Seattle proper. For the first time, Washington's dominant city was linked by road with the other half of the state, albeit by a meandering and time-consuming route.

In 1921 the South Mercer Island Improvement Club started lobbying for a bridge between the island and the western shore of Lake Washington. That same year, by pure coincidence, Homer Hadley, an engineer then working for the Seattle School District, presented to the American Society of Civil Engineers his concept to use reinforced-concrete pontoons to float a major span across the lake. The idea first came to him in 1920, and he was convinced that such a span would overcome conditions that made other types of bridges problematic, including the depth of the lake and the thick layer of soft clay mud at its bottom. His ideas received some public notice at the time, most of it negative, and critics later called it "Hadley's Folly." They eventually would repent their hasty judgment.

In late 1923 a wooden span was built across the East Channel of Lake Washington to link the northeast shore of Mercer Island with the mainland in south Bellevue. Islanders could now access Seattle by automobile, crossing the East Channel and taking the Sunset Highway around the south end of the lake, or the longer-still route over the north end. Easier access brought increased population to the island, and the calls for a bridge to Seattle grew more insistent, if no more fruitful. It would be 1937 before a plan was approved and financing secured, and when it came it was as Hadley had envisioned 17 years before. But he also had another contribution to make, and it would prove key.

Mount Baker Ridge

Much of the land facing Mercer Island along the western shore of Lake Washington is elevated. A highway over the obstruction was not feasible due to the steep grades. Hadley realized early on that the most direct route into Seattle would require a tunnel, and that the location of the tunnel would dictate the site of the western end of a floating bridge. Tunneling is expensive, and Hadley knew that the shorter the tunnel, the more likely his plan would gain support. One Saturday in the early 1920s, the precise date unknown, Hadley rode the trolley to Madison Park and walked more than three miles south along the east side of Mount Baker Ridge, which at its highest was about 260 feet above the lake's western shore. He was looking for the ridge's narrowest place, and he found it near Atlantic Street. There the slope on the west side of the ridge dropped steeply rather than gradually, allowing for a shorter tunnel. Interviewed in 1964, Hadley recalled:

"I felt like Balboa when I discovered this place. I was aware that the site of any future bridge would be an important factor in negotiations because of the high cost of constructing an approach. The spot I found is over the existing tunnel, exactly 1,445 feet long. To have bored it a few hundred feet away on either side would have involved much greater expense" ("The Inspiration ...").

Still, no one was listening.

Years of Frustration

Between 1921 and 1928 there were a number of applications by private companies for a franchise to build a toll bridge across the lake. Many, if not most, suggested Seward Park as the western starting point, which offered the shortest route by far to Mercer Island. This was an unpopular choice, particularly with the Seattle Parks Department and the wealthy folks in neighborhoods near the park, which still was home to a large and increasingly rare stand of old-growth timber. Such influential opposition was no doubt a factor in the long delay in getting a bridge built.

In 1926 Hadley joined the league of franchise hopefuls, claiming in his application that "a company comprising Seattle capital is now being organized to push the project" ("Council Get Third Request ..."). Maybe, maybe not. In any event, a combination of jurisdictional issues, bureaucratic inertia, and financing difficulties ensured that no proposal was accepted until 1928, when both the Seattle City Council and the King County Commission granted a 35-year franchise to the Seattle Toll Bridge Company, a Delaware corporation (and subsidiary of the Puget Sound Bridge and Dredging Company). Oddly, neither the location nor the type of bridge was specified in the offer, the details to be provided only after further study. But by the time the company got its act together, the Great Depression had begun. The national bond market was broken, and private financing simply unavailable. Still, the Seattle Toll Bridge Company muddled along for seven years before King County, frustrated by little or no progress, took direct control of the project in 1935. By spring 1936 it had settled on a plan for a 3,400-foot steel cantilever span from Seward Park to Mercer Island, once again raising fervent opposition from the parks department, people living near Seward Park, and The Seattle Daily Times.

At Long Last

In 1933 Lacey Van Buren Murrow (1904-1966), the older brother of famed broadcaster Edward R. Murrow (1908-1965), had become head of the Washington State Highway Department at age 28. His agency was one of the state's biggest providers of relief work for the unemployed during the ongoing Depression. Four years later, in 1937, the Washington State Legislature established the Washington Toll Bridge Authority (WTBA), giving it the sole authority to build toll bridges constructed upon any public highway in the state. The WTBA was empowered to issue "revenue bonds for the purpose of obtaining funds ... required for such construction" (1937 Wash. Laws, ch. 173, sec. 6). The creation of this agency broke the longstanding logjam and opened a path to financing the project. Finally free of the albatross, relieved King County commissioners happily turned the entire matter of a bridge across Lake Washington over to the WTBA.

Murrow took on the additional role of chief engineer for the WTBA. He didn't like the county's proposed route, and ordered new surveys. Hadley reached out to Murrow, and on June 10, 1937, the two engineers met for lunch. Hadley described his proposal for a concrete-pontoon bridge and the optimal tunnel route into Seattle. In his daily diary he noted, "Murrow clicked and said to go ahead ... and he would have me loaned [by the Portland Cement Association]" ("The Inspiration ..."). Murrow directed his staff to conduct new surveys, which established that Hadley's route was indeed the best in all relevant respects -- directness, grade, cost, and accessibility.

Hadley played no further part in the realization of his vision. Since 1921 he had been associated with the Portland Cement Association ("Portland" referring to the type of cement used to make almost all concrete), a nonprofit organization representing the cement trades. By 1937 he was the consulting engineer for the association, among whose stated goals were "to increase the quantity of cement used in established fields, and to develop new fields" ("Moments"). Murrow feared that opponents of the project would use Hadley's ties to the association to impugn his motives, and he asked Hadley to play no further role. To soften the blow, Murrow assured him that he would be given credit for his contributions. This promise was not fulfilled until 1989, 23 years after Murrow's death, when the third floating bridge to cross Lake Washington was named the Homer M. Hadley Memorial Bridge.

Getting Started

A $3,794,400 grant from the New Deal's Public Works Agency (PWA) and the sale by the WTBA of revenue bonds totaling $5,060,000 financed the project. Work was divided into 11 units, with each unit let for separate bids. Unit 2 comprised the Mount Baker Ridge Tunnel and the connecting approaches at either end. Original plans had called for a single-bore tunnel, but were upgraded to specify two tunnels, each with a 24-foot-wide roadway and a pedestrian sidewalk. (Note: Although there are two tunnels, they are usually referred to by the singular noun.) The contract was awarded to Chicago's Bates and Rogers Construction Corporation on a bid of $1,372,320.11. This was about 2 percent over the WTBA's estimate, but deemed acceptable. The final plans called for continuous bores from east to west. Right-of-way disputes caused a 115-day delay in the start of the work. To meet the project's scheduled finish date (July 1, 1940), an additional $30,000 was allocated on January 25, 1940, for equipment to also bore a short distance from west to east.

Mount Baker Ridge is composed of tight blue clay of glacial origin, with a 28 to 35 percent water content. Its consistency ranges from fairly dry and lumpy to wet and slippery. Tunnels through rock typically have an arched roof and straight side walls. Tunnels through clay, which is plastic and tends to flow, use one of two forms -- circular (as viewed in cross-section) or horseshoe shaped, a modified version of which used for the Mount Baker Ridge Tunnel.

Tunnels were relatively common, but a bridge floating on concrete was completely novel, even suspect to many. Almost all local press attention focused on the bridge, with only brief and scattered mentions of the Mount Baker Ridge Tunnel, at least until the final days before its completion. Fortunately, the story of the tunnel was twice researched and documented by the Historic American Engineering Record (HAER) -- in 1980 in preparation for listing on the National Register of Historic Places (NRHP), and again in 1993, when the tunnel was rehabilitated after 53 years of service. The 1993 report has by far the most detailed description of the methods and conduct of the work, which can be only briefly summarized here.

The Dig

Site preparation began in April 1939. At least one house located on Lake Washington Boulevard was moved to make way for the dig. Fifty thousand cubic yards of material was sheared off the east side of Mount Baker Ridge to form a steeply inclined face, and work on both tunnels began simultaneously. Large amounts of water would be released from the clay as the tunneling progressed, and it had to be dealt with. The answer proved simple -- since the tunnels would have a slight, 1.5 percent uphill grade from east to west, all but a short portion of each bore would be dug from the east. This allowed the water to flow downhill into Lake Washington, obviating the need for pumps.

Because no rock was encountered during the dig, no mechanical drilling or explosives were required. In the first phase of digging, hand-operated pneumatic air spades (nozzles that blast out high-pressure compressed air) were used to excavate a series of seven 9-foot by 8-foot "pilot drifts" at what would be the highest point, or crown, of the finished tunnel ("About Tunnelling"). Their purpose was to explore ground conditions and to provide access for bracing the roof before the bulk excavation began. This temporary bracing comprised ten-inch-square timbers at 6-foot intervals that rested on equally large timber plates driven deep into the tunnels' side walls.

Behind the air spades blasting out the pilot drifts, excavating machines called electric shovels, which produced no noxious exhaust gasses, were used to dig out the complete tunnel cores. Rail tracks were installed in each tunnel's center, and an electric locomotive hauled out cartloads of excavated clay. Only after the tunnels were completed and opened did Charles E. Andrew, the entire project's principal construction engineer, reveal that the great weight of the ridge above had crushed the 10-inch timber wall plates down to a thickness of four inches, delaying the work due to concerns that the shafts could collapse.

The workers building the reinforced-concrete linings for the tunnels worked no more than 150 feet behind those doing the digging. Six steel arches in a row, totaling 32 feet from end to end, were mounted on a traveling frame that moved on rails mounted on either side of each tunnel near the walls. The frame could be lowered or elevated with hydraulic jacks. Once  fitted in place, the temporary timber framing was removed and reinforcing steel put in place in preparation for the pouring of the tunnels' concrete lining. When the lining forms were completed, a three-foot-wide pneumatic gun pumped concrete behind the forms in 32-foot pours, each taking about 60 hours. The forms were dismantled after the concrete reached a breaking stress of 600 pounds per square inch (psi), usually in about 40 hours. After 28 days of curing this increased to 3,400 psi. The thickness of the lining averaged 24 inches.

As the project neared completion in June 1940, and to the amused delight of many, concrete and other materials were hauled into the tunnel by horses after workmen complained of exhaust fumes. Wrote the Post-Intelligencer, "Old Dobbin won a sweeping victory on one front of this mechanized age yesterday" ("Old Dobbin in Comeback ...").

Since the tremendous pressure from the ridge above could force wet clay down the sides of the tunnel and undermine the roadway, the lower portion (called the invert) of each tunnel was excavated as each section of the lining was completed. To prevent water infiltration from below, a 24-inch protective "cradle" of concrete, heavily reinforced with steel was poured (see illustration at left). The invert was then refilled with dirt and laid over with eight-inch concrete pavement sections.


By March 1940 there were 460 men working on the tunnel in four six-hour shifts. It is unclear how far the tunnels from the west progressed before they met the much longer segments coming from the east, but one source suggests that it may have been as little as "a distance of some 400 feet" (Clarke, 8). On April 16, 1940, The Seattle Times reported, "Daylight showed today at both ends of the north vehicular tunnel being built to serve the Lake Washington Pontoon Bridge, after workmen, who have been burrowing through the earth since last June projected two exploratory drifts through the west side of the hill." With the pilot drifts holed through, engineers were able to confirm that "they had run the tunnel 1,446 feet under the hill with only one-eighth inch of error" ("Lake Tunnel Is Through ..."). (Note: The Seattle Post-Intelligencer­ recorded a breakthrough four days earlier, so the precise date remains unclear.)

The south tunnel was lagging the north by about 100 feet, and there were just 76 days to go until the contractual finish date of July 1, 1940. Crews rushed to meet the deadline, and the tunnels were ready for automobile use when the project was officially dedicated and opened for traffic on July 2. Later that month crews temporarily closed first the north tunnel and then the south for the installation of the walkways, and by August 10  both were complete.

Finished with a Flourish

On January 25, 1940, the same day that Charles Andrew had announced a $30,000 increase in the tunnel budget, he also revealed that Lloyd Lovegren (1906-1989), the chief architect on the project, had designed a decorative scheme for the tunnels' east portal. As described by Andrew: "It will bear the inscription 'Seattle: Portal to the North Pacific' in the center, and the words 'Alaska' and 'The Orient' at the sides, with symbolic designs including an Alaskan totem and an Oriental dragon" ($30,000 More Sought ..."). When completed, the portal was both a bit less and a lot more than Andrew had described.

The 1993 study by the Historic American Engineering Record identifies the engineering significance and artistic importance of the Mount Baker Ridge Tunnel:

"In the context of Western tunneling, it is remarkable both for the material it was driven through (clay), and the form it took (twin bore). It ranks as the world's largest diameter soft earth tunnel. The highly stylized treatment of the east portal demonstrated the way in which Modernistic Architecture was applied to engineering structures" (Clarke, "Mount Baker Ridge Tunnel ...").

While the bridge and the tunnel were both engineering marvels, it was the design and execution of three illustrative panels at the eastern portal that captured the public's attention, admiration, and affection. They expressed in sculpture the significance of the entire project to the economy and growth of the Northwest, and particularly Seattle.

The art was a collaboration of three men, and financed by the New Deal's Federal Art Project. Lovegren designed the layout of the east portal, including the Art Deco nested arches at each tunnel's entrance, reinterpretations of classic Gothic semi-circular arches. Adjacent to the outer edge of each tunnel, and in the space between them, a rising, stepped tier of inverted trapezoid shapes, each smaller than the one beneath, terminated at the main wall of the facade, drawing the eyes to the portal's pièces de résistance ­-- three dramatic, cast-concrete sculptures symbolizing Seattle's place as the inevitable link between East and West.

Lovegren recruited James FitzGerald (1910-1973), an associate instructor of painting at the University of Washington, to design the triptych of concrete panels, which would be FitzGerald's first public sculptures. In collaboration with Lovegren, he simplified the decorative panels somewhat, removing the words "THE ORIENT" from the southernmost one and the word "ALASKA" from that on the north side, confident that the artwork alone would convey the meaning. But on the central panel, the words "CITY OF SEATTLE" and "PORTAL TO THE NORTH PACIFIC" remained.

After the design was complete, Lovegren and FitzGerald tapped James A. Wehn (1882-1973), a well-known Seattle sculptor, to cast the decorative panels in concrete. Wehn 28 years earlier had sculpted the city's iconic, life-sized bronze statue of Chief Seattle, which still stands in Tilikum Place at 5th Avenue and Denny Way. The east-portal panels he cast were said to be the largest sculptures cast in concrete up to that time, each one measuring 25 feet high and 12 feet wide (another source has them somewhat smaller, at 22 1/2 feet by 11 feet). Though displayed on a north-south axis, the triptych represents the relationship between the East and the West. The southernmost panel, with a stylized Chinese dragon, signifies the Far East. The northern panel signifies the lands of the North Pacific, with figures based on a totem pole in Alaska, rendered in Native American style.

Between the two tunnels' entrances, the central panel has the words CITY OF SEATTLE at the top, followed by an equally stylized sperm whale, representing the Pacific Ocean. Beneath the whale are the words PORTAL OF THE NORTH PACIFIC.

A Monument to Innovation, Progress, and Civic Pride

Since their opening in 1940, and despite a sinking and the normal ravages of age, the original Lake Washington Floating Bridge (renamed the Lacey V. Murrow Floating Bridge in 1967) and the Mount Baker Ridge Tunnel have played a huge part in securing Seattle's role as a vital link between Asia and North America and in the growth and development of the thriving communities on the eastern side of Lake Washington. In 1989 a new and wider tunnel was added north of the originals, with a double-decked roadway and a bicycle/pedestrian path above the traffic lanes. Over its east portal are the words SEATTLE - PORTAL TO THE PACIFIC. This tunnel connects to the Homer M. Hadley Memorial Bridge. 

The Lacey V. Murrow Memorial Bridge and the east portal of the tunnels were designated a Seattle Landmark on June 11, 1979, and the entire Mount Baker Ridge Tunnel was added to the National Registry of Historic Places in 1982. The twin shafts were fully rehabilitated and their systems brought up to date in 1993. As of 2021 the tunnels were still in service, with no end in sight.

Somewhat ironically, since the bridge named for Hadley was completed in 1989, the 1940s tunnels that proclaimed to those entering Seattle that it was the "PORTAL OF THE NORTH PACIFIC" only carry traffic eastbound, away from the city. Perhaps for this reason, by the time the tunnels were rehabilitated in 1993, trees and shrubs were starting to block the view of them. By 2017 the three panels were almost entirely hidden by thick vegetation. By 2021 they could not be seen at all, an atypical concealment of historic public art in a city that values it more than most. But even unseen, the magnificent east portal of the Mount Baker Ridge Tunnel remains one of Seattle's most enduring, significant, and beloved pieces of public art, proof that even the rigorous and unyielding requirements of urban engineering expressed in concrete can be softened and humanized by a touch of beauty.


Lisa Soderberg, "HAER/Washington State Bridge Survey -- Mount Baker Ridge Tunnel" (1980), National Archives Catalog website accessed September  16, 2021 (; Jonathan Clarke, "Mount Baker Ridge Tunnel" (HAER No. WA-109), Library of Congress website accessed September 18, 2021 (; James A. Davis, Eighteenth Biennial Report of the Director of Highways (Olympia: Government Printing Office, 1940); "Toll Bridges" (1937 Wash. Laws, ch. 173); "House  Makes Way for Tunnel," Seattle Post-Intelligencer, April 6, 1939, p. 13; "Tunnel Bore Started at Mount Baker," Ibid., June 2, 1939, p. 19; "Additional $30,000 Allowed for Lake Bridge Tunnel," Ibid., January 26, 1940, p. 17; "Lake Bridge Tunnel nears Finish," Ibid., April 12, 1940, p. 6; "Fete to Mark Lake Bridge Completion," Ibid., April 13, 1940, pp. 1, 3; "Old Dobbin in Comeback at Lake Bridge Tunnel Job," Ibid., June 14, 1940, pp. 1, 5; "Tolls of Lake Bridge Exceed Expectations," Ibid., September 19, 1940, p. 9; "Tunnel Grade Helps Excavators," The Seattle Times, October 20, 1939, p. 38; "How Mt. Baker Tunnel Will Hold a Hill on Its Back," Ibid., October 21, 1939, p. 2; "Work Begins on City Tunnel," Ibid., April 24, 1939, p. 4; "Pontoon Bridge Work Too Slow," Ibid., November 14, 1939, p. 7; "$30,000 More Sought for Bore," Ibid., January 26, 1940, p. 17; "Lake Tunnel Is Through Hill," Ibid., April 16, 1940, p. 13; "South Tunnel to Bridge Opens," Ibid., July 26, 1940, p. 2; "Both Bores to Lake Span Open," Ibid., August 10, 1940, p. 7; Lucile McDonald, "The Inspiration for the First Floating Bridge," Ibid., Sunday Magazine, July 26, 1964, p. 6; Bill C. Dugovich, "Lloyd Lovegren, 83, Architect," Ibid., August 2, 1989, p. H5; "About Tunnelling" (Glossary), ITA website accessed September 13, 2021 (; "Moment," Portland Cement Association website accessed September 18, 2021 (;"Toll Bridges" (1937 Wash. Laws, ch. 173); HistoryLink Online Encyclopedia of Washington State History, "Hadley, Homer More (1885-1967)" (by Phillip Seven Esser), and "Seattle Landmarks: Lacey V. Murrow Memorial Bridge and East Portals of the Mount Baker Tunnels" (by HistoryLink staff), "Lake Washington Floating Bridge (Lacey V. Murrow Memorial Bridge)" (by John Caldbick), "FitzGerald, James (1910-1973) (by Fred Poyner IV), "Wehn, James A. (1882-1973) (by Fred Poyner IV) (accessed September 25 - October 2, 2021).

Licensing: This essay is licensed under a Creative Commons license that encourages reproduction with attribution. Credit should be given to both and to the author, and sources must be included with any reproduction. Click the icon for more info. Please note that this Creative Commons license applies to text only, and not to images. For more information regarding individual photos or images, please contact the source noted in the image credit.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License
Major Support for Provided By: The State of Washington | Patsy Bullitt Collins | Paul G. Allen Family Foundation | Museum Of History & Industry | 4Culture (King County Lodging Tax Revenue) | City of Seattle | City of Bellevue | City of Tacoma | King County | The Peach Foundation | Microsoft Corporation, Other Public and Private Sponsors and Visitors Like You