The western section of the bridge between San Francisco and Yerba Buena Island presented an enormous engineering challenge. The bay was up to deep in places and the soil required new foundation-laying techniques. A single main suspension span some in length was considered but rejected, as it would have required too much fill and reduced wharfage space at San Francisco, had less vertical clearance for shipping, and cost more than the design ultimately adopted. The solution was to construct a massive concrete anchorage halfway between San Francisco and the island, and to build a main suspension span on each side of this central anchorage.