This bridge was built in 1932 when California was opening State Route 1 along the coast by building bridges across seven wide canyons near Big Sur.
The photograph was taken on a weekend when Caltrans and Lawrence Livermore Labs were attaching instruments on the bridge to obtain its natural periods of vibration. The periods (and mode shapes) would be checked against a computer model of the bridge to make sure it was okay. All the bridges along the coast were being retrofitted (by Buckland and Taylor) and this was an independent check of the retrofit strategy (similar to the one discussed for the Buena Vista Bridge).
Arch Bridges: Bixby Creek Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.