This is the Parker truss bridge that spans the Animas River over a portion of NM-550, less than 1/2 mile from the Colorado border. It is no longer used but can be walked by foot. Being that Michael was a mechanical engineer for 30+ years and Bridget has industrial artistic tastes, we like the contrast of these old bridges against the landscape and photograph them often.
With the ongoing modernization of the freeway system, they someday will not be here.
A Pratt truss includes vertical members and diagonals that slope down towards the center. The Pratt truss was invented in 1844 by Thomas and Caleb Pratt. This truss is practical for use with spans up to 250 feet and was a common configuration for railroad bridges as truss bridges moved from wood to metal. As you can see across the river, the concrete supports from the train still exist.
These types of bridges were common in the United States between 1844 and the early 20th century. A Parker truss bridge is a Pratt truss design with a polygonal upper chord. A "camelback," like what you see here, is a subset of the Parker type, where the upper chord consists of exactly five segments.
We love the contrast that the old truss bridges make against the floodplain landscape.