This 51-mile section was built in the 1800s and was knows as the Auburn and Susquehanna Bridge Railroad. It ended up as part of the Reading Railroad. It extended from Auburn, through Summit, to Pine Grove where it intersected the West End Branch of the Reading. The line then proceeded further southwest through Grantville, Manada, and Linglestown to Dauphin on the Susquehanna River where it intersected the Pennsylvania Railroad.

The line was abandoned in stages between 1937 and 1959. A remnant across Swatara Creek to a power plant in Pine Grove survived the longest. Sections of the old right-of-way can be made out in Pine Grove and in areas southwest of Pine Grove if you know what you are looking for. The raised former ROW crosses Tulpehocken Street in Pine Grove and played a big part in the Hurricane Agnes floods of 1972 — the ROW served to dam up water from the flooded Swatara Creek, but created worse problems.