Rainbow Bridge


Rainbow Bridge

Rainbow Bridge,
located above Smith's Ferry on the North Fork of the Payette River
Courtesy Idaho State Historical Society


The Rainbow Bridge, located on Highway 55 above Smith's Ferry, is listed in the National Register of Historic Places. As early as 1933 the bridge was recognized as one of the most beautiful in the state. The Idaho Statesman, which criticized bridges as the time as "stark, graceless structures," observed that the Rainbow Bridge complimented its natural settings.

In 1926, the U.S. Bureau of Public Roads approved a highway numbering system that assigned even numbers to east-west roads and odd numbers to north-south roads. The Payette Highway was designated State Highway 15, and later State Highway 55. Although modern improvements to the Payette Highway reflecting new developments in road construction equipment began in the early 1920s, portions of State Highway 55 still consisted of graveled roads as late as 1938. Much of the work was done in the 1930s during the Great Depression.

In 1933, President Franklin D. Roosevelt implemented federal measures to help combat the economic crisis. Under the Public Work Administration, the Idaho Bureau of Highways received almost eight million dollars between 1932 and 1934 for "emergency" road projects.

The concrete bridge spanning the North Fork of the Payette River above Smith's Ferry was built in 1933 with emergency relief funds. It exhibits an open-spandrel design introduced to Idaho in the 1920s and used in several locations throughout the state. Unlike other bridges of this type, the Rainbow Bridge, originally called the North Fork Bridge, has not been altered over the years.

Charles A. Kyle designed the North Fork Bridge. He was Idaho's chief bridge engineer from 1919, when the Idaho Bureau of Highways was established, until his death in 1936. The bridge, which cost $74,000, was built by C.F. Dinsmore & Company, an Ogden construction firm with previous experience building bridges in Boise.