I looked at this bridge – the Upper Pine Creek Bridge on the Zion-Mount Carmel Highway in Washington County, Utah – as I was browsing through the HABS/HAER records because I was curious why it had “I-beams” as a keyword in its description. I’m using it here because I thought the picture above was dramatic.
That doesn’t look like a bridge with steel beams. A look at the underside makes it clear how this very simple structure works:
It’s four short spans totaling less than 130 feet, so really any form of structure would have worked. The decision in 1929 to go with this simple form almost certainly helped with cost but it was also a wise choice to let the natural aesthetics govern. The same bridge built today would probably be two spans and might have concrete beams, but would likely look much the same.