Bridges presentation
over the South Fork of the Yuba River near Grass Valley,
California (USA), has two parallel trusses based on the Howe
patent of timber and iron rods, flanked by solid wooden arches cut
to the curves and reflected in the exterior siding. It is the second
longest covered wooden bridge span in the USA, after the
Blenheim Bridge (1855) in New York State, which is 210ft (64m).
Jet Lowe, HAER Collection
European engineers visiting the New World during the 19th century marvelled at the spans achieved
by American timber bridges. Especially noteworthy was Louis Wernwag's 340ft (104m) arch truss of
1812, the "Colossus," over the Schuylkill in Philadelphia, the longest spanning bridge in the world at
the time. Covered bridges, sheathed in wood to keep the structural timbers from deteriorating, are an
icon of the American landscape. Outstanding spans that survive today include the Cornish-Windsor
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