Wawona Covered Bridge, Wawona California

Date added: February 03, 2024 Categories: California Covered Bridges Queenpost Truss

North end and west elevation of bridge (1991)

The Wawona Covered Bridge, spanning the South Fork of the Merced River, is one of the oldest covered bridges in California, and the only covered bridge in the western region of the National Park System. The bridge was built by Galen Clark in 1868, and was converted to a covered bridge about ten years later. It is the oldest surviving bridge in Yosemite National Park.

The South Fork of the Merced was first crossed by the Mann Brothers' Trail (or Mariposa Trail), a toll route wide enough for the passage of pack horses, about 1855. The first crossing was a large log about 6' in diameter. The Manns replaced it with a crude bridge they called "Clark's Crossing" after Galen Clark, who had settled nearby in 1855. This bridge was reportedly often rebuilt due to flooding on the river. Following an 1862 flood that destroyed the bridge, some trees were felled across the river as a replacement.

Clark settled on the South Fork of the Merced River in the present Wawona area soon after his first visit to the Yosemite country in 1855. Wanting to attract visitors to a rustic hostel he established on the South Fork, he soon commenced road-building operations from his location toward Yosemite Valley.

Although numerous park publications and the interpretive display at the Pioneer Yosemite History Center State that Clark built the bridge in 1857 or 1858, the structure was apparently not built until the late spring of 1868. In May of that year, Clark received permission from the Mariposa County Board of Supervisors to erect a bridge across the South Fork. On 1 June, the Supervisors gave permission for Clark to collect tolls:

It is ordered by the Board that Galen Clark be permitted to collect toll on the completion of the Bridge across the South Fork of the Merced River on the Yosemite Trail for the term of one year at the following rates,

Saddle horses and mules....... $1.00
Pack animals, loaded ......... $1.00
Loose horses or mules ........ 25¢
Sheep or swine ............... 2¢
Loose cattle ................. 10¢

On 31 July, the Mariposa Gazette reported that the bridge was nearly finished:

We learn from Mr. Galen Clark, that by tomorrow he will have his bridge completed across the South Fork of the Merced River, on the trail between this place and the Yo Semite Valley. He will then as speedily as possible thoroughly repair the trail between the Mariposa Grove of 8ig Trees and Yo Semite Valley. Nearly one hundred dollars was raised in this place last week to assist in this public enterprise. Parties visiting the Mariposa Big Tree Grove and Yo Semite Valley by this route, will find the trail in as good and safe a condition for travel in ten days from now as ever heretofore.

Later that month, a correspondent to the same paper wrote of crossing "the skeleton of a new bridge, on a plank" at Clark's, while her horses were swum across the river."

Clark was still collecting tolls on the bridge in 1873, when the Supervisors warned him that he had received permission to collect tolls only for one year, and ordered him to desist.

The costs of the road-building venture were instrumental in forcing Clark to sell his holdings. In late 1874, his holdings at the South Fork (along with those of his son, Alonzo, and their partners, Edwin Moore and Henry S. Rockwell) were acquired by Albert Henry Washburn and two partners.

The Washburn group covered the bridge in about 1878, giving it its basic present appearance. The wood was cut at the Washburn's nearby sawmill. A sash saw was used to cut the lumber into 12" cants, and a circular saw cut these cants into boards. The Washburns may have roofed over the bridge to protect the wooden trusses, due to the heavy snowfall to which the Wawona area is prone; however, a display at the bridge suggests that they may have covered it to recreate a common form from their native New England. Possibly, it was a combination of the two reasons.

The bridge has been altered or reconstructed on several occasions. As noted, the bridge began as an open-deck pony truss but was changed to a covered bridge in about 1878. The Washburns also replaced the old wooden abutments with a new set at an undetermined date. In 1900, the approaches were lengthened by the inclusion of short 10' approach spans at either end. After automobiles were introduced in the park, the Washburns installed runnerboards for the car wheels. In 1935, the park engineer reported that one of the bottom transverse struts was cracked, and that one of the stringers was broken; a 1½-ton load limit was placed on the structure. More repairs were done in 1937 by the Civilian Conservation Corps; as part of this project, additional stone was added to the timber crib foundations. The new Wawona Road was placed in service at this time, and the principal traffic loads were diverted away from the covered bridge to a new bridge over the South Fork.

Severe floods in the winter of 1955 "mortally wounded" the covered bridge. An inspection by F. P. Cordero, field engineer for the California Department of Highways, noted that the bridge was sagging by 3-4', that two of the floor beams had been broken by drifts, and that most panel points were distorted. The floorboards were decaying, and the inner chords were failing due to rot. Cordero warned that the bridge was in danger of collapsing from its own weight.

Park superintendent John Preston warned Lawrence C. Merriam, Director of the National Park Service's Region IV (and a former Yosemite superintendent), that the bridge was in imminent danger: "The situation is so critical at present that several inches of new snow upon the bridge could cause it to collapse. We fear that if immediate aid is not forthcoming, the only covered bridge in the National Park System will be lost forever."

At this point, the National Park Service considered replacing the bridge with an all-concrete bridge, a steel beam bridge with a concrete deck, or a wooden beam bridge with a laminated wooden deck. But due to the bridge's historical significance, considerable debate ensued as to whether or not the historic structure should be replaced or rebuilt. Park Service Director Conrad L. Wirth initially felt the bridge would have to be replaced.

Superintendent Preston was a strong advocate for the bridge's reservation, or if that proved impracticable, for its reconstruction in kind. He was supported by landscape architect Thomas C. Vint, the Park Service's Chief of Design and Construction, who stated "The bridge at Wawona is the only covered bridge under the jurisdiction of the Service and for that reason, if for none other, we are interested in its preservation." After considerable discussion between different park agencies, a decision was reached to reconstruct the covered bridge as part of the National Park Service's ten-year "Mission 66" development program.

To protect it against collapse, a temporary pier was placed beneath the bridge, and on 26 November 1956, the structure was pulled to the north bank of the river for repairs. At this point, the bridge was measured and then dismantled. Rotted materials were discarded. To remove the roof shingles, fourteen bundles of 20 percent dynamite were exploded beneath the rafters to loosen the roofing nails.

The earlier stone-filled log cribs were replaced with new abutments of reinforced concrete faced with rock rubble masonry. New upper and lower chords were hand-hewn from ponderosa pine, and other boards and beams were cut or hewn from Douglass fir. All materials matched the ones originally used, even the square nails. Many of the original members were reused. The reconstruction was strong enough that some materials might have been omitted, but all were included for the sake of historical authenticity. The work was done by contractor Glen M. Gordo of Catheys Valley, California under the supervision of National Park Service Assistant Engineer Norris Udell and Yosemite National Park Resident Engineer Luther Peterson.

The trusses were reassembled on wooden rollers atop steel I-beams which served as tracks. When all work was completed except for the exterior siding, floorboards, and roof shingles, the bridge was pulled back across the river, and the I-beams were removed. The final work was done with the bridge in Place. Some of the materials used were salvaged from other park structures. Superintendent Preston found some handmade shakes for the roof in the park, and the replacement boards for the exterior came from the Civilian Conservation Corps structures being dismantled at nearby Camp Hoyle.

The bridge reconstruction project heightened the interest of park officials in other historic structures in the park and a decision was made to establish a reconstructed pioneer "village." The Pioneer Yosemite History Center, another Mission 66 project, was created around the covered bridge, with several historic buildings from around the park relocated to the site.

Several more timbers were replaced in 1961. In the early 1970s, the bridge needed further work. A draft environmental statement in June 1972 stated that one of the main timbers required replacement; the report warned that the bridge might collapse if the timber failed. In 1974, two of the transverse stringers were replaced and the floor reconstructed above them. A wooden temporary pier was constructed to support the bridge, and a coffer dam utilized to divert the water away while the work was completed. Total cost of the project was $6,553.11.

By 1977, further deficiencies had manifested themselves. A bridge safety inspection conducted by the Federal Highway Administration (FHwA) in October reported rotted floor beams and loosened panel points. The report recommended the replacement of five floor beams and the use of wooden shims or wedges to tighten connections. It also identified severe seasoning checks or splits in the ponderosa pine main truss members. Although their replacement was not yet mandatory, the report suggested that they should be, as if any of the compression members split full-length, the truss would not be capable of supporting even the bridge's dead weight.

In 1983, the Federal Highway Administration provided drawings and specifications for major repair and reconstruction work for the covered bridge. These plans called for the replacement of the heavy ponderosa pine truss frame, floorboards, and several stringers. This work was carried out, but the main members are now suffering from checking and lateral splitting, and pose a future problem.

Bridge Description

The Wawona Covered Bridge spans the South Fork of the Merced River at the Pioneer Yosemite History Center in Wawona, Yosemite National Park. The structure is a modified Queen-post truss constructed with native woods braced by steel tie rods. The overall length of the structure is 130 feet, 4 inches: overall width is 16 feet, 6 inches. A pair of longitudinal stringers spans between the trusses. The trusses and stringers me supported by a system of seven transverse floor beams, or outriggers. The covering structure, added in 1878; a decade after construction of the original bridge, has an internal frame with timber siding. The total height of the bridge is 30 feet, measured from the peak of the gable-roofed covering structure to the top of the transverse floor beams.

The principal truss members are made of hand-hewn Ponderosa Pine; the vertical and diagonal elements of the truss are made of plain-sawn Douglas fir. The internal frame covering structure is made of plain-sawn Douglas fir with a roof consisting of hand-split sugar pine shakes. The piers and abutments are composed of concrete with stone facing. The property was meticulously rehabilitated in 1956, reusing all salvageable materials and replacing deteriorated materials in-kind, regarding species, dimension, and hand-hewn method of preparation. The bridge remains at its original location in the Wawona region. Because of this accurate approach to the bridge retains integrity of design, location, workmanship, rehabilitation, feeling, and association. The interior structure is currently in good condition. The covering structure is in good condition, with many original siding boards extant.

Historic photographs of the bridge taken in the 1880s indicate that the appearance of the structure is essentially the same as the present structure. Galen Clark, original steward of the Yosemite Grant, built the bridge as an open-deck structure in 1868. The bridge used a modified Queen-post truss with main members composed of hand-hewn Ponderosa Pine, reinforced with vertical iron tie rods. Following acquisition of the bridge by the Washburn Group (consisting of Albert Henry Washburn, William F. Coffman, and Emery W. Chapman), the bridge was covered in 1878, using lumber prepared in the Washburn Group's nearby sawmill. Anecdotal evidence found in the National Park Service archives suggests that the bridge was covered to emulate popular covered bridges in Henry Washburn's native Vermont. More likely, the bridge was covered to protect its timber elements from the heavy rains and snows found in its mountainous location. The covering structure was of internal frame design with plain-sawn Douglas fir structural elements and siding and a gable roof finished with hand-cut sugar pine shakes. The original foundation for the bridge consisted of timber cribs filled with stone.

The bridge has undergone a series of alterations since the early Twentieth Century. In 1900, both approaches were lengthened approximately 13 feet, with new abutments installed. Running boards for the handling of automobiles were added in the 1930s. The bridge, which served the original Wawona Stage Road to Yosemite Valley, was taken out of automobile service in 1937, as the Wawona Road was routed over a new bridge located approximately 200 yards southwest of the original bridge. The covered bridge was kept in service for local and pedestrian traffic. In that same year the Civilian Conservation Corps undertook repair work to several transverse floor beams, replacement of some of the wood siding, and the addition of stone to the timber crib foundations.

The bridge suffered severe damage from the floods of 1955 that ravaged the Yosemite region. Following inspections by Park engineers, the bridge was determined to be in poor condition and replacement was recommended, Park engineers evaluated several options, but Park Superintendent John Preston recognized the historical significance of the structure and pursued methods to save it. Along with landscape architect Thomas Vint, who was head of the Park Service's Office of Design and Construction, the two officials successfully lobbied for rehabilitation of the bridge, which began in 1956. The bridge was pulled to one shore using an ingenious system of rails, cables and pulleys. The entire structure was field surveyed, with careful measurements of all timber elements taken. Photographs of this process exist in the records of the Yosemite Research Library. Severely damaged elements were replaced using the same wood species, dimension and historical method of preparation. The bulk of the original siding was reused; the sugar pine shake roof was replaced. Despite the flood damage, the bridge was still robust enough to withstand the use of dynamite suspended under the roof to loosen the old shingles. The following structural elements were replaced: both truss lower chords, all transverse floor beams, and all knee braces. The timber crib substructure was replaced with concrete piers and abutments faced with stone. Articles appearing in local newspapers and journals, hailed the rehabilitation for its historical accuracy.

Various structural elements have been repaired since 1956. In 1972, Yosemite Park crews replaced five transverse floor beams. Five transverse floor beams were replaced in 1978 as well, with three of the 1972 transverse floor beams replaced. The above dates are approximate, as there is some contradiction in actual dates of replacements in the archives. In 1983, replaced elements included the stringers of the approach spans, several transverse floor beams, several truss elements, all knee braces and the wood decking. The 1983 restoration work also included replacement of the original iron tie rods with steel tie rods. In 2001, 5 transverse floor beams were repaired with sistered wood bolted to the existing fabric. The two inner stringers that span between the south abutment and south pier were replaced at this time. Rehabilitation work in 2002-2003 replaced additional transverse floor beams and compression members of the truss.

Current Appearance of the Wawona Covered Bridge

In form, materials, and many details, the Wawona Covered Bridge retains its historic appearance. The 1956 rehabilitation duplicated the original wood structural elements in-kind, using measurements taken from the original structure. The dimensions of the principal structural elements are as follows: top chord 13" x 14": bottom chord and stringers 14" x 16"; transverse floor beams 14" x 14; knee braces 4" x 6." Wherever possible, the 1956 rehabilitation reused sound timber structural elements. However, due to subsequent replacements, it appears that the clear-span interior stringers are the only principal supporting elements that are original. However, it appears that greater than 50% of the original siding for the covering structure is extant.

Several alteration campaigns have compromised the original appearance of the bridge. The 1956 rehabilitation changed the appearance of the abutments, which are presently composed of concrete faced with stone. The stringers replaced in 1983 duplicated the original dimensions accurately, but used a faux method of wood preparation, in which the timbers were sawn first and then dressed on the surface to give an appearance of hand hewing. The 1983 structural strengthening campaign is the only work documented by existing construction drawings. These drawings indicate that the grade of steel used in the existing tensioning rods could not be verified, thus the steel reinforcing rods were replaced with sizes from 1¼" to 1¾" in diameter, tied to the wood structural elements using 1" bearing plates and hex nuts. It is not clear from historic photographs of the first bridge if the reinforcing rods used a similar system of attachment to the wood structure.