Leonard is best known for his crime fiction and thrillers (think "Get Shorty") but actually began his career with Westerns. This is one of those, written in 1959. It was fantastic. As I've come to read, his Westerns are among the best in the genre (think "3:10 to Yuma).
This, his fourth novel, was turned into a movie starring Tom Selleck.
Amazon sums up Last Stand at Saber River this way:
A quiet haunted man, Paul Cable walked away from a lost cause hoping to pick up where he left off. But things have changed in Arizona since he first rode out to go fight for the Confederacy. Two brothers—Union men—have claimed his spread and they're not about to give it back, leaving Cable and his family no place to settle in peace. It seems this war is not yet over for Paul Cable. But no one's going to take away his land and his future—not with their laws, their lies, or their guns.Amazonians gave it a 3.9 out of 5. The Haugenometer rated it a stellar 8- on the 10-point system.