Mickey's Bridge Celebration.

MICKEY HART: Grateful Gate Celebration

Grateful Dead drummer Mickey Hart was part of Sunday's 75th birthday celebration of San Francisco's Golden Gate Bridge. He created a 20-minute musical piece using vibratory information picked up by ultra-sensitive accelerometers from different parts of the span and unveiled it Sunday night at the culmination of the daylong event during a set by his band at nearby Crissy Field.

Hart says the bridge is "a mystery in its own way. It's a sound mark that needs to be heard. And since it is its birthday, I was thinking that instead of just composing a piece to it, or for it, I'd let it sing its own song. That was the first thought. Once I acquired the vibratory information from the bridge, I set in motion the composition... These things just come to me and then I see how far I can go with them."

He adds that he first got the idea notion of doing something using the sound of the bridge in the late '60s. He made two attempts to record the sounds of the bridge in the early '70s but was escorted off by the police. "Then, I went to the Bridge Authority and they laughed me out of the room: 'No, no, no; not on our watch!'"

As for how he did it this time, he says he approached the Geological Society, which has "sophisticated seismic information... the bridge is monitored 24 hours a day for stress. So I take those readings, sound design them and make music out of them." During the performance he triggered the sounds using a 23-foot stainless steel scale model of the bridge.