For his groundbreaking 1948 LIFE magazine photo essay, “Country Doctor” — seen here, in its entirety, followed by several unpublished photographs from the shoot — photographer W. Eugene Smith spent 23 days in Kremmling, Colo., chronicling the day-to-day challenges faced by an indefatigable general practitioner named Dr. Ernest Ceriani.

Six decades later, Smith’s images from those three weeks remain as fresh as they were the moment he took them, and as revelatory as they surely felt to millions of LIFE’s readers as they encountered Dr. Ceriani, his patients and his fellow tough, uncompromising Coloradans.

Born on a sheep ranch in Wyoming, Dr. Ceriani attended Chicago’s Loyola School of Medicine but opted not to pursue a medical career in the big city. In 1946, after a stint in the Navy, he was recruited by the hospital in Kremmling, and he and wife Bernetha, who was born in Colorado, settled into the rural town. Dr. Ceriani was the sole physician for an area of about 400 square miles, inhabited by some 2,000 people.

Eugene Smith’s at-times almost unsettlingly intimate pictures illustrate in poignant detail the challenges faced by a modest, tireless rural physician — and gradually reveal the inner workings and the outer trappings of what is clearly a uniquely rewarding life.

“Country Doctor” was an instant classic when first published, establishing Smith as a master of the uniquely commanding young art form of the photo essay, and solidifying his stature as one of the most passionate and influential photojournalists of the 20th century. In 1979, the W. Eugene Smith Memorial Fund was founded to support those working in the profoundly humanistic style of photography to which Smith dedicated his life and his art.