Upon further research this was not a bridge. It was called the Milwaukee trench or the Trent Avenue trench/tunnel. It was 850 foot long. Trent Avenue ran across the top and the Chicago, Milwaukee and St. Paul RR ran double track inside the tunnel. Also, a few 100 feet away was a 750 foot long wood trestle. It seems that they demolished these structures and others to make way for the 74 Worlds Fair. I've tried all the libraries in Spokane and no one has any pictures. What a shame, this was really an exciting construction project built in 1915. They built bridges over the railroad, under the railroad, a tunnel, wood trestles across many street and the even built concrete bridges over some of the alleys. It seems that Americans no longer care about our history. These pictures if they exist should be in a museum.