10c Green, Ty. II (32).
Tied by large "Paid" grid, small red "Boston Sept. 18" circular datestamp on blue 1860 cover to San Francisco, endorsed "Per Mail Steamer & Isthmus Rail Road"
at lower left, some slight toning, Very Fine, east to west directives are unusual, by Dec. 17, 1859 the "Via Panama" route was replaced by the Butterfield route as the default sending unless other instructions were given as in the case here
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