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A system of rapid mail transportation by relays of horses that operated from St. Joseph, Missouri, to Sacramento, California, in 1860-1861.
(Historical Terms) (in the American West) a system of mail transport that employed relays of riders and mounts, esp that operating from Missouri to California in 1860–61
a system of carrying mail by relays of riders on ponies, esp. the system in use between Missouri and California in 1860–61.