On a couple branchlines here in Oregon some recent rail replacement projects have pulled up rails dating as far back as the 1890s - when the particular route was re-laid to standard gauge!
One such route was a former Southern Pacific branchline (now the Willamette Valley Railway) in Aumsville, just east of Salem. Another route that I visited just a few weekends ago was the former Spokane, Portland & Seattle Railway's Astoria Line in St. Helens - a recent CWR project (intended for an ethanol plant that didn't last very long) ripped up some rails from when the track was first laid around 1910. And on yard tracks and sidings, such rails are still relatively easy to find.
However thanks to the shortlines taking over the branchlines, the demand for heavier cars (centerbeams, fully loaded grain hoppers), larger locomotives (up to SD45s and run-through UP/BNSF mainline power such as C44-9Ws and SD70s), and programs like ConnectOregon which have provided state funding for many of the track upgrades - the light stick rail is harder to find. The Bailey Branch from Corvallis south to Monroe has some really old 75 pound rail on the "mainline", but the line is out of service and likely to be abandoned soon. There's also a short stretch of rail in Tualatin (P&W Westside District, former SP Newberg Branch) just west of the Tualatin River bridge that has some very light rail. In the last few years, the P&W's Seghers District (Hillsboro to Gaston) and Willamina District (Amity to Willamina) has received CWR replacing the old 75-90 pound iron; the Westside District from McMinnville to Independence was upgraded shortly after P&W took over and a CWR welding plant was actually set up right next to the line (now mothballed).
On the lines that warranted SP investment back in the 1970s and early 1980s (Westside Line north of Corvallis, parts of the Newberg Branch over Rex Hill, much of the Tillamook Branch from Milwaukie to Hillsboro, the Toledo Branch) the rail was often pulled up from the Valley Main and relaid, so the branches would get the 1940-1960 era rail that was welded into CWR when the mainline got the newer rail.
Erik Halstead - Portland, Oregon