The Pony Express National Historic Trail was used by young men on fast paced horses to carry the nation's mail across the country, from St. Joseph, Missouri to Sacramento, California, in the unprecedented time of only ten days. Organized by private entrepreneurs, the horse-and-rider relay system became the nation's most direct and practical means of east-west communications before the telegraph. Though only in operation for 18 months, between April 1860 and October 1861, the trail proved the feasibility of a central overland transportation route, and played a vital role in aligning California with the Union in the years just before the Civil War.

Most of the original trail has been obliterated either by time or human activities. Along many segments, the trail's actual route and exact length are matters of conjecture. However, approximately 120 historic sites may eventually be available to the public, including 50 existing Pony Express stations or station ruins.