Descriptions of the variety and number of horses used by the Pony Express became distorted during the course of its history since November 1861. In general, the type of horse used for carrying the rider and mail depended greatly on the region. The more fleet-footed thoroughbred horses worked fine on the central prairies, but the strength and endurance of half-broken mustangs were needed to cross the arid deserts and rugged mountain ranges of the West. Alexander Majors, one of the three founders of the Central Overland California and Pike's Peak Express Company's Pony Express, chose the California mustang for its strength and endurance, describing it "as alert and energetic as their riders."
As each of the more than 100 stations spread along the route, relays of horses needed to be kept in sufficient numbers to meet the demands of the relay system. As the C.O.C.&P.P.E.C prepared for the "start-up" of the Pony Express, the company estimated that it would take approximately 75 horses to make the nearly 2,000 mile trip from Missouri to California.
A little more than two months before the first riders left from St. Joseph and Sacramento, the firm of Russell, Majors, and Waddell began purchasing 500 of the best horses available, paying as much as $200 a head for some stock. One ad, posted in the Kansas Leavenworth Daily Times, asked for "200 grey mares, from four to seven years old, not to exceed fifteen hands high, well broke to the saddle and warranted sound ..."
So, just how far and how long can a horse run? A modern-day horse in good shape can travel at a full gallop on flat terrain for maybe five to eight miles. Over the mountainous terrain in the Sierra Nevada, a horse and rider may be able to cover five miles. Pony Express mustangs could travel at speeds of about 10 miles an hour, but at times could gallop at speeds up to 25 miles per hour. At a full gallop, the distance that the horse could travel before becoming exhausted depended on several variables—if it was a hot or cool day, state of health, and when the horse last had a drink of water.
A good Pony Express rider rode his horse at a steady spring and generally galloped the horse only to get out of harm's way. None were easy to ride, but all agreed that in a race for life and mounted on a half-broken mustang, the express rider could leave danger far behind.
"There were about eighty pony riders in the saddle all the time, night and day, stretching in a long, scattering procession from Missouri to California, forty flying eastward, and forty toward the west, and among them making four hundred gallant horses earn a stirring livelihood and see a deal of scenery every single day of the year."—Mark Twin, Roughing It, 1872
"The worst imps of Satan in the business. The only way I could master them was to throw them and get a rope around each foot and stake them out, and have a man on the head and another on the body while I trimmed the feet and nailed the shoes on ... It generally took half a day to shoe one of them."
—Pony Express Farrier and Station Keeper, Levi Hansel, in 1901 describing his experience shoeing half-wild California mustangs at Seneca, Kansas. Photograph—D.B. Young, wild mustangs near Simpson Springs Pony Express Station, January 2010.