The transcontinental Pony Express operated a ten-day mail route between St. Joseph, Missouri, and Sacramento, California, using pony relays. Because it operated for only nineteen months, not much surviving mail is known. A census of known Pony Express covers published in 2005 included only 180 eastbound and seventy-one westbound covers.
Pony Express mail can be divided into four distinct rate periods.
1. The service began on April 3, 1860, under the management of The Central Overland California & Pikes Peak Express Company (COCPP), which charged five dollars per .5-ounce ounce for the ten-day express between San Francisco, California, and St. Joseph, Missouri.
2. Starting July 31, 1860, (westbound) and August 15, 1860, (eastbound) COCPP charged $2.50 per .25-ounce in an effort to increase the volume of mail carried by the Pony Express.
3. Starting April 1, 1861, (westbound) and April 15, 1861, (eastbound) Wells, Fargo & Company began managing the route and introduced a two-dollar per .5-ounce rate.
4. On July 1, 1861, Wells Fargo reduced the rate to one dollar per .5-ounce.
Eight major types of Pony Express markings were used. These included San Francisco's 'Running Pony' and COCPP markings; Sacramento's 'Pony Express' marking; St. Joseph's 'Running Pony', COCPP, and 'oval in circle' markings; and New York's two varieties of 'California Pony Express' markings. These markings occurred variously in black, blue, red, or green colors.
In the third and fourth rate periods, Wells Fargo issued stamps and franked envelopes to facilitate prepayment of Pony Express fees The stamps issued for weight progressions above .5-ounce are very rare when used on cover.
1. Two dollars per .5 ounce third rate period: 2-dollar red and 4-dollar green Wells Fargo stamps were used on eastbound mail, and the Type 1 Wells Fargo franked envelope was used to prepay the two-dollar rate on westbound mail.
2. One dollar per .5 ounce fourth rate period: 1-dollar red, 2-dollar green and 4-dollar black Wells Fargo stamps were issued for eastbound mail. The Type 2 Wells Fargo franked envelope was used to prepay the dollar rate on westbound mail, and the 1-dollar 'garter' stamp was used on westbound mail for weight progressions above .5 ounce.
The Pony Express was discontinued by notice from Wells Fargo on October 26, 1861. The last westbound pony left St. Joseph on October 24, and the last eastbound pony left San Francisco on October 23.