Rockwood is now designated yard limits, and was so at the beginning of the season in 2011 if I remember correctly. Train speed is 10 MPH inside of those limits, and an engineer must be able to stop within one half his line of sight.
Basically, flagging a stopped train is not required within those limits. Same as Durango or Silverton. That's not to say the crew did anything wrong by placing torpedoes and presumably a flagman with a red flag, or leaving an unattended red flag to warn and stop the following train. They were taking an extra precaution and I probably would have too. Prior to this season flagging would have been required here, and as they say, old habits die hard.
At the D&S (and I'm sure most other railroads) positive radio communication does NOT take the place of flagging. Even if everyone on the railroad listening to a radio knows where and why you're stopped, you still have to lay down protection.
-Jon