Mike,
Someone like Earl could better give the exact dates, but I believe 485 rolled into the Salida turntable pit in 1955. As I recall it suffered a broken frame in the mishap. It was also, as memory serves, only recently shopped and so was mostly canniblized for parts and appliances before being scrapped.
1955 was not a good year for the ng. The pipe business was starting to slow on the ALA/DGO portion, the Marshall Pass line was being scrapped and the Monarch branch converted to sg, thus a surplus of "big" engines.
The 483/494 accident was 3 years later.
Earl had a pretty thorough account on the old BBS of the 483 accident, which may or may not be available in the archives.
Thanks,
MAS