A near-copy of the old Carnall St. Bridge still exists! This near-copy, The Shaw Bridge, is located in upstate New York where most of Whipple's patented bowstring bridges were built.
The Shaw Bridge (1870), located in Claverack, NY, USA, is the only double-span Whipple cast- and wrought-iron bowstring truss bridge still existing in the nation. The two spans are about 80 feet long; whereas, the Carnall Street Bridge into Fort Smith (on Beale Wagon Road, 1860-1861) had two 100-foot spans. The two bridges are otherwise believed to be very similar, if not identical. Pictures of the Shaw Bridge show none of the technical advances seen in later "Whipple-based" enhanced versions, such as various Whipple-Murphy designs, etc. commonly built in the 1870's and later.
See pictures and features of the still existing double-span Shaw Bridge at:
GPS: 42.215079, -73.728734
As you may have noticed in my related Indian Territory posts, the old E-Street Bridge into Fort Smith came 20 years after the Carnall Street Bridge and was located about 1/3 mile south of the Carnall St. Bridge.