First responders located the man below the center of the bridge, on the river's rocky shore, with injuries to one or both legs.
The 25-year-old man was on a day hike, slipped and slid about 20-30 feet down the steep slope.
A rescue team made up of personnel from the Mason County Sheriff's Office and two or more Mason County fire districts responded.
A rescuer was lowered 420 feet from the bridge to the river below and then hauled the man back up. He was taken to Mason General Hospital in Shelton for treatment of a possible broken leg, along with cuts and scrapes.
The bridge, located in the Olympic National Forest about 20 miles north of Shelton, was built in 1929 by the Simpson Logging Co. and is considered the highest bridge in the state.