track realignments on original Santa Fe main line

[MBTA3247]

While riding the Southwest Chief a few weeks ago, I noticed a number of places between La Junta, CO and Albuquerque, NM (the route over Raton Pass) where the track had been realigned at some point to ease the curves, with the original roadbed still clearly visible off to the side. When did the Santa Fe do this realignment work?

[JimBoylan]

These links claim that one of the dates was in 1945:

http://www.shorpy.com/node/17758" onclick="window.open(this.href);return false;

http://gbcnet.com/ushighways/US66/66_co ... river.html" onclick="window.open(this.href);return false;

[MBTA3247]

Those only deal with a single bridge that's 2 states away from the section I'm interested in, and make no mention as to whether the bridge replacement was part of a larger track realignment program.