It could be one of two things - if it's a fairly recent map, it might be confusing because the line runs under I-35W / Hwy 62 junction, and 35 runs north to downtown Minneapolis. It might look like the line goes all the way downtown.
If it's an older map (pre-1954), the tracks are probably the Twin City Rapid Transit streetcar line. The MN&S was blocked for many years of going into Minneapolis, and their tracks in Richfield ended where Richfield ended at 54th st. This was as far south as the streetcar line on Nicollet Ave. went. It was possible in the 30's to take the streetcar from DT Mpls to 54th and Nicollet, cross the street, and get on an MN&S train to Northfield or Randolph MN. (Richfield now ends at 62nd st.)
The line now goes parallel to Pleasant Ave., and serves Model Stone Co. just inside Minneapolis, and ends at LeJeune Steel just off of 60th and Nicollet.
BTW I've lived on this line in Richfield since 1958.
