Willa Cather published her first book of verses, April Twilights, in 1903. With O Pioneers! (1913) and My Ántonia (1918), which has frequently been seen as her finest achievement, she found her characteristic themes—the spirit and courage of the frontier she had known in her youth. One of Ours (1922), which won the Pulitzer Prize, and A Lost Lady (1923) mourned the passing of the pioneer spirit.

(http://www.biography.com/people/willa-cather-9241574#awesm=~oFNxj4hLw3YfYt)