Auburn to Pine Grove to Dauphin - Reading RR
This 51-mile section was built in the 1800s and was knows as the Auburn & Susquehanna Bridge RR.  It ended up at part of the Reading.  It extended from Auburn to Summit and on through Pine Grove where it intersected the West End Branch of the Reading.  The line then proceeded further SW through Grantville, Manada, and Linglestown to Dauphin on the Susquehanna River where it intersected the Pennsylvania RR.  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 ROW can be made out in Pine Grove and in areas SW of Pine Grove if you know what you are looking for.  The old raised ROW as it crosses Tulpehocken Street in Pine Grove played a big part in the Hurricane Agnes floods of 1972, and the ROW served to dam up water from the flooded Swatara Creek and created worse problems.
The old ROW in Pine Grove, looking W from Tulpehocken.  Being used as a lane for several hundred yards in this area.
(Photo from June 2001)
W of Pine Grove and I-81 along Oak Grove Road.  To the N of Oak Grove Road, a section of fill or possibly a trestle has been removed (probably fill).  The cut can be seen in the distance.  Behind the photographer the ROW is evident - it has been converted into a dirt road.  In this section the ROW is difficult to make out, but once you "tune" your eyes to what you are looking for, it can be found relatively easily.  The section was abandoned in the 1940s or early 1950s (let me know if you have an exact date or more info on this line.
(Photo from June 2001)