Over 150 years after the riders of the Pony Express carved their place in the history of the Western United States, a new generation saw the innovative mail system of the old west come alive Friday afternoon in Casper.

It was a quick stop shortly before 3 p.m. at the National Historic Trails Interpretive Center, sitting on a ridge on the south edge of town.

Two riders crossed the Platte River and rode uphill from the south, stopping at the top as dozens of folks looked on. The saddle bag full of mail was secured to a fresh horse before the next rider -- one of nearly 700 participating in this year's re-ride -- climbed into the saddle and took off to the west.

The Casper exchanges, like all the others, didn't take much time -- something the riders don't have much of, as they make the 1,966-mile trip from St. Joseph, Missouri, to Sacramento, California in just 10 days.

April 1860 saw the beginning of the original Pony Express. It was only in service for 19 months, but left an immutable brand on the American West.

Casper is the northernmost stop of the Pony Express Re-Ride, which largely follows the Pony Express National Historic Trail through eight states: Missouri, Kansas, Nebraska, Colorado, Wyoming, Utah, Nevada and California.

This year marks the 37th re-ride held by the National Pony Express Association, which was organized in 1966. In 1960, the National Pony Express Centennial Association was formed and worked with state committees to put on a 100th-anniversary re-ride.

The 2017 ride followed the Old Glenrock Highway into Casper and made several stops in town before arriving at the Trails Center. Riders will spend an estimated 55 hours crossing Wyoming.

Wyoming contains the intersection of four major trails, and all of them played a significant role in American settlement of the western United States. The Oregon, Mormon Pioneer, California and Pony Express Trails all headed for South Pass at the northern end of the Rocky Mountains.