Additional info from the Sandia Software D&RG Multimedia Adventure Kit DVD.
"The plate-girders (beams) for the bridge were originally ordered in 1881. However, they were used on the Marshall Pass route at several locations. All the parts eventually found a home at Cascade in 1889.
According to the literature, a German company did the original design of the Cascade trestle. On the upstream side a builders plate says "BUILT IN 1889 BY DETROIT BRIDGE & IRON WORKS DETROIT, MICH." This plate must refer to the builder that erected the assembly at the Cascade site."
Dan