COB = Council Bluffs makes perfect sense. UP had other exchange points with RI including nearby Denver, so COB in the routing instructions was specifying most of the western leg to be on UP, with RI handling only the Council Bluffs to Chicago portion.
If it were me writing the waybill, I would've routed it UP->CNW and not RI if I was wanting to get it there reasonably. In 1978 "The Rock" was breathing its dying breaths.