A little reading on a nearby bridge gives the date, 1886, and explains the names.
My guess would be that it was built in the late 1800s. All I know is that CKW built the route, and that the CKW was bought by the ATSF around 1901.
Any idea how long ago the RR was built? The 1903 KS RR map also shows AT&SF but I don't know anything about when this line was built or by whom. I don't have much access to RR history, so your info source would be interesting to look at. I'm always curious what else might be out there undiscovered.
The bridge would have been built by the Chicago, Kansas and Western Railroad. http://bridgehunter.com/ks/chautauqua/ckw-cedar-creek/
The RR was shown as the AT&SF on the 1936 county highway map.
The photo showing a pier in the middle of the river, just north of the Cedar Creek Bridge is from a railroad bridge and is the same railroad that built the stone arch bridge, just west of Elgin that is pictured elsewhere on this site. The railroad was removed in the late 30's. There are also stone abutments on either end to the east and west of the pier in the middle of Cedar Creek.
AT&SF subsidiary, Chicago, Kansas and Western, erected this bridge ca. 1886. This was part of the Santa Fe's Cedar Vale branch, which meandered in a southerly and westerly direction from Havana, Kansas. At the time of its construction, the Santa Fe and Missouri Pacific were in a territorial dispute, as both companies vied for supremacy in the region. Track crews of the CK&W and MoPac subsidiary, Denver, Memphis & Atlantic, raced each other westward through Chautauqua County, with the DM&A beating its rival to the Chautauqua/Cowley County line at Cedar Vale. The Santa Fe declined to continue the fight, leaving Cedar Vale as the western terminus of the line. At least one map from the time period shows the Santa Fe continuing westward, but it was not to be. The Cedar Vale branch reached its zenith during the first decade of the twentieth century, when cattle shipping in and out of Elgin kept the line busy. Following years of decline, Santa Fe scrapped the Cedar Vale branch ca. 1938. My grandad claimed that, as a kid, he'd swim under this bridge when trains passed overhead.