Posting a bit late today. This was taken as I was riding the train and heading to Silverton on the Durango & Silverton Railway. As we crossed this bridge the engineer blew down the boiler. The boiler gets blown down to clear out scale and debris to get it to operate more efficiently. You have to do it in short bursts when running like this because it uses up a bunch of water and you don't want the level to get too low. In these short bursts over a bridge like this, it puts on a show for the people riding because the steam burst looks fairly impressive.