What 1915 series helped establish Georgia O'Keeffe's reputation as an abstract artist?

Georgia O'Keeffe's 1915 charcoal drawings helped establish her reputation as an abstract artist.

That year, she created a series of mostly abstract charcoal drawings using simple lines and shapes. Rather than depicting a recognizable object, the drawings explored movement, rhythm, and form. They became a turning point in her career because they showed an unusually personal approach to modern art.

O'Keeffe sent some of the drawings to her former classmate Anita Pollitzer, who showed them to Alfred Stieglitz in New York. Stieglitz exhibited them at his gallery, the 291, in 1916. This was the first public exhibition of her work in New York.

The series is sometimes described as paintings because O'Keeffe became famous for painting, but the works in question were charcoal drawings on paper. That distinction makes the canonical answer more specific.