Filming started in May 1961 by John Ford in Paducah, Kentucky. Producer Smith said, "It is essential for our purposes that virtually the whole movie be shot outdoors. Throughout the movie, one of the basic themes is to show little people against a vast country – huge deserts, endless plains towering mountains, broad rivers. We want to capture the spirit of adventure, the restless spirit that led these men and women across the country in face of many difficulties and dangers."