I find this fascinating, too. I'm in western Ohio near an abandoned line that connected Indianapolis, IN to Springfield, OH. The line is still very apparent in satellite photos nearly 50 years after the last bits were retired. Likewise, in the property records, the "scar" the line left on the land is clearly visible.
In a few places landowners purchased the parcels on both sides of the line and "reconnected" them, but mostly the line's legacy is a bunch of oddly-shaped property lines cutting across a grid of 80 or 160 acre fields. In those "reconnected" places it's interesting to see how the crops and soil have a slightly different appearance (or not-so-slight, in some cases).
Many of the little towns along the line have a "Railroad Street", too. The town I grew up in did, but I'm old enough to remember when the abandoned rails were still there.
Similar to the railroads leaving their mark, a few years ago I got a bit obsessed with the Hetch Hetchy aqueduct. I spent a few evenings laying in bed "flying" the line with Google Earth, seeing where the pipes diverge and following their separate paths, and seeing where they meet up again. Seeing how San Jose and Palo Alto are situated on top of the line is interesting. I'm resolved to visit the Pulgas Water Temple and any public spaces I can walk on top of Hetch Hetchy next time I'm in the Bay area.