Santa Fe Trail is a 1940 Michael Curtiz Western film starring Errol Flynn, Olivia de Havilland, Raymond Massey, Ronald Reagan, Alan Hale, Sr., Van Heflin and Gene Reynolds.
You can watch this one online:
TimeOut London says it's "spectacular enough to warrant a look, if only to see Reagan playing Custer. Now that was inspired casting." Variety calls it "a thrilling saga of hard bitten US army officers' fight to wipe out John Brown's marauding crew". The New York Times says, "We aren't saying that it lacks what is known as mass appeal.... Yet for any one who has the slightest regard for the spirit—not to mention the facts—of American history, it will prove exceedingly annoying." TCM has an overview.