I've followed a number of the adventures in the Long Rider's Guild.
Bernice Ende is a colorful character who sort of makes a living of traveling the west with her horses and dog. She is not particularly out to prove anything, so she has no reservations about taking up an offer to put the horses in a trailer and bypass some horrible bridge or congested metro area.
The Unbranded adventure was a wilderness trip on the Continental Divide trail by a bunch of college kids. Their ambition to produce the movie was nearly as audacious as their trip. By any measure they were hugely successful, but their trip illustrates the physical risk to horses and relational strains of people as the unknown unfolds. A different way of tackling the Continental Divide trail was recorded by former Minnesota Governor Al Quie in his book, Crossing the Divide. Quie started from the north and did the route over a series of summers, often with different people at each stage.
Some of the journeys I read about ended badly due to disagreements along the way. (Not exactly Donner Party level disagreements, but it seems that putting people together in a stressful situation can sever relationships.) One of the saddest was a pair of young women who planned to ride to the Pacific Coast from the Dakota badlands. By the time they got as far as Billings the more experienced rider of the two was sick of the whole thing. They eventually made it as far as the Bob Marshall Wilderness, which was a huge accomplishment, but after that they split up. The bored horsewoman took up with a Montana cowboy and left the other poor girl to hitch a ride to Oregon with her mule.
My favorite of the stories I followed live was the cross country trip of Linny Kenney, who rode an Arab gelding 3,700 miles from Los Angeles to New Hampshire. Amusingly, once she reached her childhood home after 8.5 months of riding, she had no desire to go the final 120 miles to the Atlantic. And she really did ride or walk every step of the way. Her friend drove an old compact pickup truck along the route, hauling supplies and arranging lodging as they went. He also turned out to be a masterful photographer, which greatly enhanced the updates as they were posted to the web. Kenney now handcrafts and sells high end custom leather goods from her web site.