Commissioned for SFMOMA's 75th anniversary in 2010, a site-specific installation by San Francisco-based sound art pioneer Bill Fontana explores both visible and invisible features of the museum building. Sonic Shadows reveals the internal resonance of structural elements like the fifth-floor pedestrian truss bridge and boiler room pipes, transforming them into musical instruments. This sound sculpture uses moving ultrasonic speakers and vibration sensors to transform the space below the dramatic circular skylight, surrounding the fifth-floor pedestrian bridge, into an acoustic drawing in real time. As visitors cross over the bridge, their footfalls contribute to real-time recordings of ambient sounds. While Fontana's past collaborations with SFMOMA relocated environmental sounds from the regional landscape, this new work creates a live composition generated by the building itself.