In Game Description
"The 6th Street Viaduct was the last of LA's grand river bridges to be built, connecting the Downtown and Boyle Heights areas when it opened in 1932. Two thirds of a mile long, its twin steel arch design comes from the Classical Moderne school of architecture."
A badge in the Badge Pursuit Challenge can be found here. Go under the 6th Street Viaduct and look for the entry point into the Los Angeles River canal that is directly under the Viaduct. Between the two central pylons, you should see a ladder. Cross the shallow patch of water and climb up the ladder to find the badge.