Frederick W. Panhorst Bridge, Concrete open-spandrel deck arch bridge in Mendocino County, California

The Frederick W. Panhorst Bridge, commonly called the Russian Gulch Bridge, is a reinforced concrete open-spandrel deck arch bridge on California State Highway 1 in Mendocino County. Its 73.2 m main span springs from the two rocky headlands flanking Russian Gulch Creek, with no buttresses; total length is 160.6 m. Henry E. Kuphal designed it.

The bridge was completed in 1940 to replace a wooden trestle from 1911 that could no longer handle growing traffic volumes. This replacement was part of broader improvements to California's coastal highway.

The name honors Frederick W. Panhorst, chief of the Bridge Section of the California Division of Highways from 1931 to 1960 and a director of the American Society of Civil Engineers. The California Senate renamed the structure for him in 1974 by Concurrent Resolution 145; before that it was known simply as the Russian Gulch Bridge.

The bridge is on Highway 1 inside Russian Gulch State Park; the deck is narrow and carries about 10,500 vehicles a day, so drivers should expect little shoulder room. Walkers reach the bridge and the creek mouth from the park's day-use parking off the highway. The 1911 wooden trestle it replaced stood on the same crossing.

Retired bridge engineer Arthur Elliott called it the most beautiful of California's concrete arch bridges, and it is frequently photographed. Its column spacing widens as the columns lengthen, a detail visible from below. In 2007 Caltrans engineer Barton Newton called it functionally obsolete because of its narrow deck, though structurally sound.