From “Taliesin Drawings : Recent Architecture of Frank Lloyd Wright: Selected from his Drawings” by Wittenborn, Schultz, Inc., 1952: 

“When San Francisco began to consider duplicating its famous Bay Bridge, running the second alongside the first, Mr. Wright felt that something should be done to stop that. Something better suited to the times and their needs, to the superb scenery of the area, something more scientific, simpler, quieter could be designed.  In the summer of 1949 the drawings shown here were made after Mr. Wright was assured of the support of an internationally renowned engineer, J. J. Polivka, residing in San Francisco.

The bridge, all of reinforced concrete, rests upon a series of great hollow piers, penetrating the earth below the bay like spearheads, almond-shaped in section.  These are called “tap-roots” by Mr. Wright … Long, hollow, curved slabs like huge fans spring out and spread 80 feet on each side of a pier, supporting the roadway 70 feet wide, carrying six lanes of traffic and two pedestrian walks.  Over the main channel of the bay vast twin arches are flung across 2000 feet of water, leaving 200 feet clearance at the center.  Each arch carries traffic in one direction and the two are connected at their crowns by a garden, a pleasant relief and perhaps a stopping point for the traffic.”

Frank Lloyd Wright’s “Butterfly Wing Bridge” was originally intended as a southern crossing of the San Francisco Bay, connecting from its western terminus at approximately Army Street (now Chavez) and Third Street to its eastern terminus upon Bay Farm Island, just north of the Oakland Airport.

It was primarily a low, water-hugging viaduct of reinforced concrete until it reached the ship channel where it gradually rose up to become a graceful archway spanning 2,000 feet.  At the same time the opposing roadways divided and bowed out.  At the center of this arch and its highest point, a disk of reinforced concrete fans out from each roadway across the opening between and merge at their tangent.  This allows cars to pull out of traffic and park, and beyond, a lush, planted garden that individuals  can leave their cars to enjoy rest and pleasant views of the San Francisco Bay.

A large, table top model was built in Aaron Green’s 319 Grant office in 1951, where it became a focal point fixture for many years.  It was most recently displayed at the Oakland Museum in 1989, in an exhibition dedicated to Frank Lloyd Wright’s “Butterfly Wing Bridge.”