The Pony Express was a “mail” service delivering messages, newspapers, mail and small packages from St. Joseph, Missouri across the Great Plains, over the Rocky Mountains and the Sierra Nevada Pass, to Sacramento, California by horseback, using a series of relay stations.
Officially operating as the Leavenworth and Pike’s Peak Express Company of 1859, in 1860 it became the Central Overland California and Pikes Peak Express Company by the freighting business. During its 19 months of operation, it reduced the time for messages to travel between the Atlantic and Pacific coasts to about 10 days. From April 3, 1860 to October 1861, it became the West’s most direct means of east-west communication before the telegraph was established and was vital for tying the new state of California with the rest of the United States. (from Wikipedia)