The Pony Express operated in the American West from 1860 to 1861. Prior to the completion of the transcontinental railroad, riders on horseback would deliver mail across frontier country. The mail service allowed a letter to travel from the Atlantic to the Pacific in 10 days.
To make the best time and expedite mail delivery, riders would relay bags to one another while at a full gallop.
This is my first foray into Western MOCs. I loved the TV show "The Young Riders" as a kid - it was about the adventures of Pony Express riders.