Interesting photo, at least to a B&Mer.  The USRA car on top of the pile has Ajax brakes but still sports the rectangular herald (as does 72721).  Other photos suggest that the Ajax application (along with AB brakes) coincided with the adoption of the Minuteman herald in 1946.  This configuration of the USRA car suggests a time stamp not too far from 1946, unless the prior evidence is in error.

Couldn't find 72721 in Ken Akerboom's transcription of the B&M's car books, but there are some gaps in that data (or maybe the car was repaired rather than scrapped?).
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Dave Parker
Swall Meadows, CA