By Levi Clancy for לוי on
An ancient river cut a canyon, forming the Golden Gate Strait.
During the Ice Age (until 10,000 years ago) the sea level was over 100 meters (300 feet) lower than today. The Golden Gate Strait was filled by just a river. When the Ice Age concluded, the sea level rose and flooded an interior valley to form the San Francisco Bay, which was connected to the Pacific Ocean via the Golden Gate Strait.
Sixty percent of all rain and snow the falls on California still drains through the Strait. It is exposed to enormous tides, wind, fog and salt air. Also, the San Andreas Fault is just 7 miles offshore.
Americans living in San Francisco Bay saw their first recorded European exploration in 1775, when the Spanish ship San Carlos entered the Bay through the Golden Gate Strait.
In 1776, Spain established the settlement Yerba Buena, later re-named San Francisco (Saint Francis). In 1848, the popuplation of the city was less than 500. But the Gold Rush meant that just a year later, in 1849, the population grew ten-fold.
The emerging metropolis needed a bridge across the Strait.
Soon after 1900, the San Francisco Bay's regional population had reached one million. To support this population, California's major north-south highway, Hwy 101, needed a bridge across the Strait. However, the Strait posed enormous natural challenges -- and the bridge would require the longest span in the world.
Early 20th century engineering developments made the Golden Gate Bridge a challenging possibility. Against natural, engineering, political and fiscal challenges, "the bridge that couldn't be built" began construction in the midst of the Great Depression.