I have had several communications with historians in the greater Fort Smith area regarding the "bridge" that I saw going across the Poteau River into Carnall Avenue near downtown Fort Smith.
It is now clear to me that the 1887 Poteau River crossing shown on the USGS map was "FERRY SERVICE" and not a two-span Beale bridge, which I incorrectly perceived. I note other ferry crossings along the Arkansas River shown on the map, as has been pointed out to me.
Gene McCluney has recently sent me a 1887 Perspective (bird's eye) picture of downtown Fort Smith which also clearly shows the FERRY SERVICE from Carnall Avenue across the Poteau connecting to a road in Indian Territory. In 1887 the ferry service connection ran underneath a new overhead railroad bridge. A large underground drainage tunnel (large storm sewer) with surrounding fill materials now supports the railroad yard.
The new evidence does show, however, that the Butterfield Overland Stage Route of 1858-60, which Beale tried to follow as much as possible, connected into downtown Fort Smith at the Carnall Avenue Ferry.
There is much to still be written about the Beale Bridges of 1860. It is beginning to appear, after talking to Jack Beale Smith and Gene McCluney, that what was published in Eastern newspapers and journals (which I referenced) was Beale's Initial Plan for his six bridges, but is not necessarily where all the Whipple bridges were finally installed, especially the one "at" Fort Smith. The 1887 USGS survey shown in the 1890 map depicts "a Bridge" across the Poteau about seven miles south of downtown Fort Smith near the old Texas Road" crossing site (US271, OK9). Gene McCluney has provided me with several old Fort Smith newspaper clippings which indicate that an old government iron bridge was located there across the Poteau River. The Whipple-plan, two-span, Beale Bridge may have been diverted by local government officials at the last moment and placed (in whole or part) seven miles upstream at/near the site shown in the 1890 USGS map. Jack Beale Smith notes that the federal project was underfunded and federal support was waning as the last and largest bridge (at Fort Smith) was about to be constructed.