Which Georgia O'Keeffe painting series uses a cow's pelvis against the sky?

Georgia O'Keeffe's Pelvis Series uses a cow's pelvis against the sky. She began the series in the 1940s, turning a large animal bone into a recurring frame for views of blue sky and clouds.

O'Keeffe collected bones in New Mexico and treated them as powerful, abstract shapes rather than simply as symbols of death. Their curves and openings allowed her to combine close-up natural forms with immense-looking spaces beyond them.

The series is sometimes mixed up with her skull paintings because both use bleached bones as central subjects. The pelvis works are specifically identified by the anatomical form and by the way the opening often reveals the sky. Pelvis Series—Red with Yellow is one related title.

These paintings also reflect O'Keeffe's broader practice of magnifying or cropping objects. By changing scale, she made a bone appear monumental and encouraged viewers to see familiar desert materials as formal structures.