This cover was mailed from Cristobal, Canal Zone to the US Army Armory in West Saint Paul, Minnesota.
The sender lived in Rainbow City, but Cristobal is just a short drive of about four miles from Rainbow City, and the sender may have dropped off the letter while doing errands in the shopping center of Cristobal.
What is unusual about this cover is that it has been given a cancel (the one that covers the stamp) that says “PAQUEBOT” in the lower arc of the Circular Date Stamp (CDS). This postal marking is intended for items that were posted on board a ship while it was en route from one port to another.
Because the sender of the letter was living in the Canal Zone at the time it is most likely this was a mistake. I suspect this is why the stamp was re-cancelled with the proper cancel for regular postal service (there were no special cancels for Air Mail postal service at this time)
The stamp on the cover is Scott# C49 and as two sides of the stamp are straight, rather than perforated, we can tell this stamp came from a booklet pane of four. This particular stamp was issued in both sheet and booklet format. This stamp was put into use in 1971, one year prior to the sending of this letter.
The 11ยข rate was the appropriate Air Mail rate to the United States at this time.
I am rather curious about the number “2398” written on the left margin of the cover with what appears to be a black felt-tip pen.
It is interesting to note that the name of Rainbow City was the only city name chosen by popular vote in the Canal Zone. It was previously called Silver City.
Canal Zone Postal History 