A car number would almost certainly answer the majority of the questions about when where and why. I have plenty of C&S information and I'm sure y'all have plenty of RGS information.
I mentioned earlier these cars could be on their way to Alaska. But that would have been 1943. In that case this photo makes perfect sense in that the 1943 batch came from Leadville (via Salida since there was no longer a South Park Route). However the problem here is the stock car. There were no stock cars in Leadville after the South Park had been taken up. Also I don't see any coal cars. Now that doesn't really mean too much but it would seem if these were Leadville cars there would have been a few in this string. On the other hand the Miller took no coal cars. Thus the more I look at this picture the more I believe it was 1938 or, as you pointed, out 1942. A single readable car number would likely clear that up.