A Pony Express cover delayed during the Pauite Indian war is estimated at $75,000-100,000 ahead of Robert A Siegel's June 24 sale in New York.
The war was a short-lived series of assaults on settlers by the Northern Pauite people in May 1860 in which Pony Express riders were deliberately targeted.
The lot is one of four surviving covers from the well-documented incident, which saw mail sent from St Joseph, Missouri to California on the dates May 20, May 27, June 3 and June 10 held in Camp Floyd near Salt Lake City before continuing west.
A June 25, 1860 article in the San Francisco Bulletin reported: "The long missing Pony Express arrived at Carson City last evening, bringing dates from St. Louis to June 10th.
"The Pony Express will arrive here to-night about 10 o'clock, on board the Sacramento steamer. The Express will bring four several letter-bags - the number now due - and will have altogether 300 letters, at least."
The lot features the free frank of "Milton S Latham USS" - one of the few people allocated free use of the Pony Express - and displays the St Joseph Running Pony oval.
The Pony Express operated in the US for a short period between 1860 and 1861, becoming the fastest method of delivering mail from coast to coast until the advent of the telegram.
Some of its riders, such as Buffalo Bill Cody and Robert Haslam (aka Pony Bob), would become international household names.
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