What makes for the creation of a structural or architectural icon? Is it strictly a matter of design? Or do both design and engineering play a role? And what about the location or environment surrounding a given structure --- how might they be involved? We explore such questions with our guest, Donald MacDonald, the noted bridge architect. Born in Canada and based for many years in San Francisco, MacDonald has designed high-rise buildings, landmark homes, and even an earthquake-proof bed. But he and his firm (established in 1966) are best known for designing distinctive and elegant bridges. MacDonald, who earned a BA in Architecture at the University of Oklahoma before obtaining a Master's of Architecture at Columbia University, is the architect of the newly completed, soon-to-open East Span of the San Francisco-Oakland Bay Bridge. When it officially opens in September, the Bay Bridge will be the world's largest single-tower, self-anchored suspension bridge --- and, indeed, the bridge is already seen as something of an icon, much like the nearby San Francisco Golden Gate Bridge, for which MacDonald and his firm did seismic-rehabilitation work several years ago. MacDonald talks with us about the philosophy, research, history, and aesthetics that contributed to his design for the East Span of the Bay Bridge --- and also about his well-written, attractively illustrated new book on this topic: "Bay Bridge: History and Design of a New Icon" (Chronicle Books).