Oregon City bridge (#0173)

Oregon City bridge, just north of the Williamette Falls, was completed in 1922. Though it doesn’t look like, it is actually a steel bridge. Due to the sulfur dioxide emissions that came from the paper mills that were at the Falls, the steel was coated with gunite (shotcrete) to prevent corrosion. See Wikipedia for more details: en.wikipedia.org/wiki/Oregon_City_Bridge