Most of the photos on this site were extracted from reference images (high-resolution tiffs, 20 to 200 megabytes in size) from the Library of Congress research archive. (To query the database click here.) Many were digitized by LOC contractors using a Sinar studio back. They are adjusted by your webmaster for contrast and color in Photoshop before being downsized and turned into the jpegs you see here.

Santa Fe R.R. yard at night, Kansas City, Kansas. March 1943. 4x5 Kodachrome transparency by Jack Delano. <View full size. to see the light trails made by the yard workers' torches in this time exposure, as well as a phantom number (3167, at right) that must have been on a train that paused in front of the camera.
The streak in the upper left is a crescent moon, being occasionally obscured by clouds in a very long exposure. Nifty!
For a long time, it was thought best to keep the new and high maintenance diesels in the yard, where they could do less damage if they broke down. Also, it was thought that diesel-electrics were not well siuted to hauling main line fast freight. The EMD (originally EMC) FT demonstrator tour had a lot to do with changing that attitude, by proving that a stock diesel locomotive design could replace steam locomotives in everyday road service all over the country.
I'm surprised that all the shunters are diesel/electric. I would've expected that they would've been the last changed, not the first.
The number 3167 was most likely from an engine. The boxcar numbers would not have been that large, and the font is the same as the other engines.