It was a two-hour movie in the beginning, but AMC wanted to develop an original series, so they made it longer (from the book "Difficult Men: Behind the Scenes of a Creative Revolution: From The Sopranos and The Wire to Mad Men and Breaking Bad" by Brett Martin).
Writer Alan Geoffrion drew on the true-life stories of Nebraska rancher Waldo Haythorn - a friend of Duvall's - whose grandfather at the turn of the century took a herd of 700 horses to South Dakota, and of Donaldina Cameron, a San Francisco woman who saved over 3,000 Chinese girls from prostitution during that time.
In a 2007 interview with the DGA, Walter Hill described how he shot a 3-hour western epic in 45 days, which was a shorter shooting schedule than one of his previous westerns, Geronimo: An American Legend (1993): "I don't know how the hell we did it, to tell you the truth. Again, same cameraman, Lloyd Ahern II, and we just sat there and said we have to go like hell. And I printed quite often, one take instead of two, and I held the coverage down to what I thought was an absolute minimum... We scheduled a tremendous amount of work and did it. It was not easy. We also only worked 10 hour days... 5 day weeks... which comes out actually to 39, 40 days and we lost one day to weather. So, how the hell we did it is still a mystery to most of us. We just turned them into the cross-light and kept the backgrounds as neutral as we could, shot the big stuff, and the actors were very good. I mean you know, it's easy to say, 'Well, Lloyd did a wonderful job', which he did, or 'Walter was on his game', which I guess is true, but the actors had to be up to it, and they were."
Robert Duvall previously worked with Walter Hill in Geronimo: An American Legend.