The Pueblo Division subdivisions 1A and 1B are  originally the Denver & Salt Lake Railway subdivisions 1 and 2.  The Denver & Rio Grande Western Railroad bought control of the D&SL and built the Dotsero Cutoff, a connection between the D&SL at Orestod and the D&RGW at Dotsero.  The D&SL was officially merged into the D&RGW in 1947.  The Pueblo division was divided into two employee timetables, this series covering the 'Moffat' route, and another series covering Pueblo west and the remaining narrow gauge lines.