Following my earlier theme, this is a cover originating from the early Pre-Colorado mining region. The so-called Pikes Peak Gold Rush.
It is franked with a pair of 12c #36s paying the 24c British Open mail rate to Britain.
I think that this is an extremely interesting cover, as it is -
1) The earliest known foreign use from the Mining area
2) From Auraria, Kansas Territory - now part of Denver, Co.
One of the earliest PO's established in the region. They had a hard time securing a mail contract with anyone though. Jones & Russell was carrying most of the mail at this time to and from the area at adjacent Denver City. The fact that this did not go by J&R, and instead went north, via Ft Kearney is indicated by the Council Bluffs postmark. The Auraria origin is determined from the docketing (applied by recipient), in ink of the period. Also numerous other covers from the very early mining region entered the mails as this did, at Council Bluffs.
3) I am told that this is the earliest known use of this particular Portland, Me exchange office marking. An agreement with Canada about mail carriage had just been signed in November. As a result this likely went via the Canadian Grand Trunk Railway, maybe via Detroit, which is how it managed to get to Portland ME, instead of Boston or New York.
4) Outgoing Foreign mail that went through the Portland ME exchange office is not nearly as common as that which went through, say Boston or New York. In a census of about 500 Portland exchange covers, only 60 are outbound. Most mail posted in the East would default to Boston or NYC, while that posted centrally or West might find its way through the Detroit or Chicago exchanges. Those last two exchanges, however, were formed in December of 1859, for British Treaty Mail. So this letter was mailed just prior to those offices opening and bypassed them as a result. The Portland exchange was opened in Feb 1859.
Richard Frajola has a good write-up of this cover here:
https://www.philamercury.com/covers.php?id=28941
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