Georgia O'Keeffe, the most famous woman artist of American modernism and a pioneer in abstract art, created a vision without precedent. She expressed the grandeur of her world in the Southwest, from the high desert mesas to the smallest flower, with fierce independence. And a separate world has risen up around her fame: from the photographic nudes of her by Alfred Stieglitz to the iconic images of her, years later, set in the stunning landscapes of...