Stand on Donner Summit Bridge on a summer afternoon and you’ll see much of what makes the area so special. Below, rock climbers inch their way up granite walls, cyclists grind through the final stretch of Donner Pass Road’s steep ascent, and to the east, Donner Lake shimmers. Now, for a century, the bridge has offered travelers one of the Sierra Nevada’s most iconic viewpoints.
On Saturday, August 22nd, Donner Summit Bridge, also called Rainbow Bridge, marked its 100th anniversary. The California Lincoln Highway Association hosted a special Driving Tour and Re-Dedication Ceremony, celebrating the bridge’s role in California transportation history and the enduring legacy of the Lincoln Highway — America’s first transcontinental automobile route.
Rainbow Bridge during its dedication ceremony 100 years ago. Photo from the Norm Sayler collection.
Much of the bridge’s history has been preserved by the Donner Summit Historical Society, whose archives document the construction, significance, and preservation of the landmark structure. According to DSHS, travelers crossed Donner Summit on the old Lincoln Highway before the graceful concrete arch of Rainbow Bridge was built. The winding roadway featured grades of up to 8%, and as automobiles and trucks became more common during the 1920s, it struggled to accommodate growing traffic and the transportation demands of the region’s expanding lumber industry.
State officials began constructing a new highway in 1923, promising easier grades and safer travel. The final 3.7 miles over Donner Summit, including the bridge, were built by the U.S. Bureau of Public Roads using federal forest highway funds. The bridge and final parts of the highway were finished in 1926 for $450,000.
The graceful lines of Donner Summit Bridge incorporate a continuous grade and a compound curve. Photo by Paul Hamill.
While the bridge reflected a common bridge design of the 1920s, similar to structures built at Yuba Gap, Big Sur, Redding, and Folsom, it was unique in one important respect: its location. To accommodate the challenging location, engineers incorporated both a continuous grade and a compound curve into the design, a landmark engineering achievement. It replaced a treacherous section of the original Lincoln Highway and has provided one of the Sierra Nevada’s most photographed vistas of Donner Lake for a full century.
A 1920s bus travels over Donner Summit Bridge, also known as Rainbow Bridge, with Donner Lake in the background. Photo from the Norm Sayler collection.
DSHD says the bridge’s 1925 final construction report states, “The alignment consists of a series of compound curves; there being a 360-foot radius curve over the arch and a 145-foot radius over each approach span.
However, its future wasn’t always guaranteed. By the early 1990s, decades of harsh winters and deferred maintenance had left Rainbow Bridge in deteriorating condition, and Nevada County was evaluating several options, including demolition. Community members organized fundraisers, attended public hearings, and wrote letters in support of preserving the bridge.
Donner Bridge on a recent winter day. Photo by Mark Loper.
Fortunately, California State Parks had $500,000 available for historic bridge rehabilitation projects, and the funding application for repairs to Donner Bridge was successful, with Nevada County supervisors eventually backing the preservation project. The county then contributed $1.6 million toward the rehabilitation, which was completed in 1993.
Crews carefully color-matched the replacement concrete so the restored bridge would retain its historic appearance. The only significant change was reducing the size of the railing openings to improve safety.
One hundred years after its completion, Donner Summit Bridge remains more than a transportation structure. It serves as a gateway to Donner Summit, carrying visitors to recreation areas throughout the entire year, and standing as a monument to early highway engineering and the community effort that ensured its survival.