Many experts believed the 6,700 .ft (2,042 .m) strait could not be bridged. Swirling tides and currents, with icy water 500 .ft (150 .m) in depth at the center and ferocious winds and blinding fogs were seen as insurmountable obstacles for construction or operation of the bridge. In addition, the design elements were changed several times as engineers tried to find the best solution to bridge the gap from Marin County to San Francisco. Even now, retrofitting is ongoing, as it has been discovered that the bridge is not impervious to earthquakes. (Nolte 2007) It is, in fact, a very lucky set of circumstances that this bridge has shown none of the flaws of other constructions of its time, during which civil engineering and geological studies were just in their infancy. It was simply one of the best circumstances for bridging what appeared to be an unbridgeable gap.
Putting aside the amazing developments in engineering of the time, and the intuitive genius of its design which made this bridge possible, the geological and other environmental factors make this bridge a veritable miracle since they combine to make it possible. The depth of the channel opening into San Francisco Bay is naturally very deep to permit the entrance of deep-draft ships, but the shelf upon which the main supporting piers stand is very solid bedrock. In addition, the weather elements made construction quite dangerous, but a safety net saved 19 lives and would have saved more if a piece of the bridge had not broken the net at the same time as ten men fell to their deaths. The low number of fatalities for this construction was a new record for the time.
It is well known that this .region lies on a major geological fault system where two major tectonic plates are in constant stress, pushing against each other, sliding and causing massive earthquakes, often in excess of 6 on the Richter scale, and sometimes up to 8 points. .