Idaho Postal History
Most of the material in this web page will pertain to Idaho or at least the Pacific Northwest.
An RPO is a post offce that is in a railroad car. Mail was picked up at a rail station and sorted on the train.
I need a lot more information to put in here. This is just a start. What I really want are some covers showing the WIM markings. Covers are kept in the Idaho/Latah binder