Toothrock and Eagle Creek Viaducts
Curving around a promontory near Tooth Rock, west of Eagle Creek along an abandoned section of the Historic Columbia River Highway, Multnomah County, Oregon, beginning at mile post 42.24.
Date of Construction
K. P. Billner or Lewis W. Metzger, designing engineers, Oregon State Highway Department
Unknown; probably the Pacific Bridge Company or The Construction Company, both of Portland
Oregon Department of Transportation
Abandoned, 1937, reopened as pedestrian walkway ____.
One of several half viaducts constructed on the Historic Columbia River Highway. Part of the first section of the route made redundant by a new water-level grade for U.S. 30, later a portion of Interstate 84.
Toothrock and Eagle Creek Viaducts
As locating engineers on the Historic Columbia River Highway neared the eastern end of Multnomah County they encountered perhaps some of their greatest natural obstacles. Even though they had already laid out the route through the difficult “Waterfalls Section,” dropping several hundred feet from Crown Point to Latourell Falls, and then over several bridges and viaducts, the outcropping behind Tooth Rock, a small “tooth-shaped” pillar, presented itself as one of the greatest obstacles to continuing the road to the east.
American Indians believed that the promontory was the southern abutment of the mythical Bridge of the Gods, part of the great divide of the Cascade Range spanning the present path of the Columbia River. Modern geologists see it as a cliff immediately downstream and across the river from remnants of the Cascade landslides of about A.D. 1260. This landslide deposited a 1/2 cubic mile of material from the river’s northern shore into the river and diverting its flow a mile to the south, eventually damming the river and creating a natural barrier. Eventually the lake behind the slide broke through, creating the rapids later known as the Cascades of the Columbia. For early Oregon Pioneers, the outcropping behind Tooth Rock was a barrier to overland travel to Portland as much as the Cascades were a barrier to river traffic.
In order to maintain a maximum 5 percent grade and a minimum 200′ tuning radius on the Historic Columbia River Highway, which were the standards agreed upon at the road’s inception, locating engineers saw no alternative in overcoming the bluff other than “hanging” the road around it. The easiest, but by far the most expensive alignment alternative was to cut down the rock slope to form a wide ledge to carry the highway around the promontory. It involved time-consuming and costly drilling and blasting basalt from the outcropping, some 200* above the Columbia and the Oregon-Washington Railroad and Navigation Company (OWRN) main line at the river’s edge. Another alternative might have been a tunnel, as was used at Oneonta Gorge. As a compromise, the highway department cut a 12′ ledge into the cliff side, or half as wide as the needed roadway, and for the other 12′ relied on sections of half viaducts.
Design and Description
Either K. P. Billner, or his colleague and successor, Lewis W. Metzger, designed the Toothrock and Eagle Creek viaducts in 1915. Both were accomplished and talented draftsmen who worked under the direction of Oregon State Bridge Engineer Charles H. Purcell. They were accomplished engineers who had created all the bridges constructed on the HCRH up to this point. They were accustomed to difficult problems and solved them with many one-of-a-kind structures.
Bids were opened on May 3, 1915 for the Toothrock and Eagle Creek viaducts. The outcome is unknown, for construction files no longer exist, but it is highly likely that one of two Portland firms built these viaducts. Both the Pacific Bridge Company and The Construction Company had already completed all the bridges and viaducts constructed in Multnomah County on the Historic Columbia River Highway in 1914.
For a distance of about 224′, the highway skirted around Toothrock on half-viaducts and a ledge. The engineers designed two reinforced-concrete structures 12′ wide, of deck girder spans, supported on the outside of the roadway on concrete columns carried down the cliff face, and on the inside by the solid rock roadbed. Floor beams were carried on one side by the girder system and on the other in notches cut out of the cliff. Because the half-viaducts permitted construction of 12’ of the 24′ roadway out of the basalt cliff, they greatly reduced excavation costs.
The portion of the structure west of the point itself is know specifically as Toothrock Viaduct, while the portion east of the point is known as Eagle Creek Viaduct. The real differences between them were the railing treatments and the span lengths. Designers of the HCRH, including Lancaster, were very aware of the need to construct an economical, efficient road, but they never lost sight of their belief in the need for aesthetic considerations in its design. On the Toothrock Viaduct, the railing details consisted of a concrete spindle and cap arrangement as seen on other Historic Columbia River Highway structures, namely, Latourell Creek Bridge, Shepperds Dell Bridge, and Moffett Creek Bridge. The somewhat fragile looking railing contrasted well with Toothrock’s rugged appearance. On the Eagle Creek Viaduct, designers used a rubble masonry rail with semicircular drainage cutouts and a screeded concrete coping. It complimented the surrounding landscape and continued without interruption the adjacent masonry guard rails and retaining walls. Its basalt materials blended well in color and texture with the natural surroundings; the rock likely came from a nearby quarry.
An additional component of the Toothrock and Eagle Creek Viaducts was the inclusion of a pedestrian observatory at the midpoint, between the two structures. Here, masonry parapet walls and concrete benches provide motorists with an ideal location to stop on the roadside to take in majestic vistas of the Columbia Gorge from a high vantage point. It was appropriately named “Eagle’s Nest” because of its tree-top perch.
Repair and Maintenance
Maintenance records for Toothrock and Eagle Creek viaducts no longer exist. Plans for construction of Bonneville Dam in 1933 called for backwaters that would flood the OWRN main line near Eagle Creek. The U.S. Bureau of Public Roads decide to reroute the tracks over portions of the HCRH, creating the need to realign the highway with a 837’ tunnel through the outcropping behind Tooth Rock and new bridge over Eagle Creek. Construction of the tunnel’s east portal included cutting away a portion of the HCRH east of the Eagle Creek Viaduct and replacing it with a temporary 90′ timber truss bridge. Once the new structures opened in 1937, the Toothrock and Eagle Creek viaducts were closed.
In the past two years (1993-1994), an Oregon Department of Transportation mason has been repairing both viaducts and reconstructing Eagle’s Nest as part of a departmental rehabilitation program for portions of the HCRH that were abandoned in the 1930s and 1950s. He has recast spindles on the Toothrock Viaduct and rebuilt masonry walls on the Eagle Creek Viaduct. Plans call for a new span above the Tooth Rock Tunnel’s east portal to connect the eastern end of Eagle Creek Viaduct with the HCRH as it approaches Eagle Creek Bridge from the west.
Excerpted from Historic American Engineering Record, Sandy River Bridge at Troutdale, HAER OR-36-N.
Historian: Robert W. Hadlow, Phd., September 1995.
Transmitted by: Lisa M. Pfueller, September, 1996.