Before there was Iowa Interstate, there was Iowa Railroad. They did not enjoy the success that IAIS later had, but they did preserve service over an extensive section of CRI&P. Their power was a very mixed bag, as this photo shows. It shows the westbound return leg of the daily Bureau turn passing through Tiskilwa behind a BN SD7, an orange ICG GP28, and a Milwaukee GP9.
The EMD SD (special duty) series are a strong and reliable kind of locomotive which still serve America's rails today. They have proved themselves reliable by clocking in several million miles of freight service.