How long would it take a rider to deliver mail from Walla Walla WA to Hell Gate (MT) in mid 1860's? I am writing a historical fiction novel based on the completed Mullan Road. Young rider on a Morgan horse (used by Pony Express, I understand). Would 50 miles a day be reasonable?
Pony Express riders frequently traveled 75 mile per day routes, although they would change horses every 15-25 miles or so. The idea was to travel a 1900 mile route within ten or eleven days.
However, given time to train (let's say three months or so), you could push a Morgan to 30 or 40 miles but it would take you quite literally the entire 24 hours without pause to cover it.
Arabians have been cornering the miles-per-day market for a number of years now, being the most popular and effective endurance riding breed to date.