The South Fork Eel River Viaduct is an abandoned portion of the early Redwood Highway located between Leggett and Confusion Hill in Mendocino County. This span was constructed in 1923 and is more popularly known as "The Slab." The South Fork Eel River Viaduct is 525 feet in length and served as part of US Route 101 from 1926 until 1982. The structure was ultimately bypassed by an inland cut and left abandoned.
Part 1; the history of the South Fork Eel River Viaduct
The South Fork Eel River Viaduct is a former component of the early Redwood Highway located between Leggett and Confusion Hill. This structure is often referred to as the "The Slab" by abandoned highway enthusiasts.
The history of what would become the Redwood Highway (later US Route 101) begins with the approval of the 1909 First State Highway Bond Act. The First State Highway Bond Act was approved by voters during 1910 and was the genesis point of some of the most notable highways in California. Legislative Route Number 1 as originally configured was a then new State Highway which was designated between San Francisco north to Crescent City.
Legislative Route Number 1 would be extended to the Oregon State Line during the 1919 Third State Highway Bond Act. The planned alignment of Legislative Route Number 1 can be seen between Garberville of Humboldt County and Cummings along the South Fork Eel River in Mendocino County on the 1917 California State Automobile Association Map.
Prior to the construction of Legislative Route Number 1 wagon borne traffic heading north from Cummings to Humboldt County had to ascend the treacherous Rattlesnake Grade (also known as the Bell Springs Grade). The Rattlesnake Grade is described in the
July 1916 California Highway Bulletin as being only passable during the summer months. The initial northward climb on the Rattlesnake Grade ascended grades as high as 20% the from Cummings to the 4,100-foot-high Bell Springs Mountain. The descent from Bell Mountain to Dyerville (now on California State Route 254/Avenue of the Giants) is described as having grades as steep as 30% amid an elevation drop of just over 3,900 feet. The construction of Legislative Route Number 1 (then known as the Mendocino State Highway) sought to follow the Eel River watershed to bypass the Rattlesnake Grade.
The completed Redwood Highway/Legislative Route Number 1 between Cummings and Garberville can be seen on the
1920 Clason Highway Map of California.
During 1923 much of the Redwood Highway between Leggett and Piercy would be widened. The cliffs above the confluence of the South Fork Eel River and Bridges Creek were too narrow for a conventional highway widening. Subsequently the South Fork Eel River Viaduct was installed as it was able to provide a 24-foot-wide road deck through the difficult terrain.
During November 1926 the US Route System was created by the American Association of State Highway Officials. US Route 101 from San Francisco north to Crescent City was aligned over the Redwood Highway. Both US Route 101 and the Redwood Highway between Garberville and Cummings can be seen on the 1927 Rand McNally Highway Map of California.
US Route 101 can be seen crossing the South Fork Eel River Viaduct north of Leggett in Township 24 North, Range 17 West on the 1935 Division of Highways Map of Mendocino County.
US Route 101 can be seen passing over the South Fork Eel River Viaduct on the 1950 United States Geological Survey map of Piercy.
The 525 foot long South Fork Eel River Viaduct was featured in the
January/February 1967 California Highways & Public Works. The structure is noted to be a substandard piece of US Route 101 which was in need of modernization due to carrying 5,000 vehicles a day in summer months.
Construction of an inland bypass of the South Fork River Viaduct broke ground in 1980. During
1980 the Bridges Creek Bridge was replaced with a box beam span. The bypass of the South Fork Eel River Viaduct needed to be excavated from a rocky cliff and was opened to traffic in 1982.
Upon being bypassed the South Fork River Viaduct was abandoned by Caltrans District 1. The older alignment of US Route 101 may have been open to traffic for a time until it became sufficiently covered in rockfall.
Part 2; a visit to the South Fork Eel River Viaduct
The abandoned South Fork Eel River Viaduct can be found on northbound US Route 101 just beyond the Bridges Creek Bridge at Postmile MEN M97.64. Traffic can pull off the roadway in front of gate immediately in front of the viaduct structure.
These views are along the South Fork Eel River Viaduct facing southward. The concrete viaduct design has an obvious slab-like aesthetic which lends itself well to the "The Slab" nickname. Rockfall has covered much of the structure and knocked out some of the railings.
These views are facing northward from the South Fork Eel River Highway towards modern US Route 101. The rails on this structure were once were painted white, but it has gradually been stripped away.
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