1911,1918 Fernbridge over Eel River near Fortuna, CA, was largest concrete bridge

(Archived Bridge Hunter; Bridge Hunter; Historic Bridges was broke; Satellite)

Bridges Now and Then posted
"Building Fernbridge (Fortuna, California) in 1911. When this 1320-foot bridge was built in 1911, it was referred to as the world’s largest all-concrete span. Also called Eel River Bridge, Fernbridge is listed on the National Historic Register for its engineering significance during the period of 1900 to 1924." (USGS)

BridgeHunter has the stats of 2408' (734m) long with a span of 195' (59.4m). It also provides a rehabilitation date of 1918. 

BridgeHunter

BridgeHunter

That strikes me as rather shallow arches.

BridgeHunter

BridgeHunter

BridgeHunter

BridgeHunter, 2009 photo by Craig Philpott

BridgeHunter, 2018 photo by Mike Goff

I wonder what rehabilitation work was needed just 7 years after it was built. I checked out Wikipedia. The work replaced wooden approaches with the current concrete ramps. I also learned that this bridge "is still the longest functional poured concrete bridge in operation in the world."