wonderful strike of the rare "Carmine Pony" handstamp on reverse of cover to Boston, blue "Pony Express San Francisco Aug 25" running pony handstamp ties 1859 10c Green (35) with second strike alongside, endorsed "Per Pony Express ½", entered the mails with blue "Saint Joseph Mo. Sep 6 1860" datestamp, stamp with tiny tear at top right corner (mentioned on certificate but does nothing to detract from this cover's appearance), one of just 10 covers with the Carmine Pony handstamp, just six of which are eastbound and only four of which have a 10c adhesive, a great Pony Express rarity, 2022 Philatelic Foundation certificate (Frajola-Walske-Kramer census #E16)
The Second Rate Period (August 15, 1860 to April 13, 1861) reduced the rates for letters weighing between one-quarter and one-half ounce to $2.50.