This F7 A unit locomotive was built in March 1950 by EMD for ATSF as part of order 3020B. It was rebuilt in October 1973 when 231L was converted to CF7. ATSF ordered many of their F7 A and B units to be run in groups of four and had them numbered the same with letter designators to indicate their relative position when working together: “L” designated the ‘lead’ unit; “C” the cab, or second A unit, and A, B or C for the B units. The 231L unit likely started its work on the rails followed by A unit 231C and B units 231B and 231C.