Mother Nature set up one of the most formidable obstacles for the Golden Gate Bridge's builders. In January 1933, work began on the bridge's south tower, with foundations sunk deep into the ocean floor. Divers were hired to perform intricate procedures in the strait's violent currents, putting their equipment, skills and bravery to the test.

A diver prepares to work on the bridge's foundations

Tumultuous Currents
The narrow strait between Marin County and San Francisco is one of the world's most tumultuous bodies of water. Up to 335 feet deep and only a mile and a quarter wide, the Golden Gate is the largest California coastal opening -- a portal into which the Pacific Ocean surges. Powerful currents also flow in the opposite direction, as water from many of Northern California's freshwater rivers and streams rushes into San Francisco Bay. This freshwater flow collides with the incoming Pacific, creating complex and violent currents. At 2.3 million cubic feet per second, these currents pump one-sixth of the volume of the San Francisco Bay through the Gate and into the Pacific Ocean every day.

An Audacious Plan
To build the bridge, workers would have to erect a pier more than 1100 feet out in the middle of the Gate -- the first bridge support ever constructed in the open ocean. Chief engineer Joseph Strauss' bold plan called for workers to first build a giant fender to protect the pier from stray, fog-bound ships. The fender would enclose a football-field-sized area from which water would be pumped out. The concrete tower foundation would be laid inside. Once this was completed, water was to be pumped back into the 40-foot-thick concrete walls of the fender, in order to strengthen the fender against the current.

90 Feet Down
Divers were crucial to the plan. They guided beams, panels, blasting tubes and 40-ton steel forms into position and secured them, striving all the while to avoid being swept away in the current. Workers shot timed black powder bombs deep into bedrock through the blasting tubes, often with such power that dozens of fish would be thrown out of the water and onto the south shore. Divers sometimes ventured as deep as 90 feet below the surface to remove detonation debris. They smoothed the floor's surface using underwater hoses that exerted 500 pounds of hydraulic pressure. To add to the difficulty, divers worked blindly, forced to feel their way due to murky water, fast-changing currents and bulky diving suits.

Work inside the fender was the riskiest. At any moment, its walls could collapse from contact with a stray ship lost in the fog, or from the intense pressure exerted by the currents. "We were down damn near 50 feet, and every time you go down 29 feet you double your atmospheric pressure," recalled diver Bob Patching. "Well, that's strong enough it can hold you smack against a wall, and you can't move."

Divers had to wear extensive suits to withstand pressures up to 90 feet below the surface

Racing the Clock
The Gate's changing currents only afforded workers narrow windows of dive time. The men were restricted to submerging for four twenty-minute periods per day. With the construction team's tight schedule, divers were often forced to surface before having sufficient time to decompress, increasing the likelihood that they would develop caisson disease, a nitrogen deficiency also known as "the bends."

Lucrative Dives
Despite the danger, men flocked to the underwater work. In Depression-era America, any steady, well-paid job was a godsend.

A Solid Foundation
The divers' efforts ended in success. On December 3, 1934, chief diver Chris Hansen descended into an inspection well with the pier job superintendent, Jack Graham, and resident engineer Russell Cone. A hundred and seven feet down, they inspected the bedrock and the foundations, congratulating themselves on a job well done. A few days later, Berkeley geologist Andrew Lawson made the descent, and reported that "the rock of the entire area is compact, strong serpentine remarkably free from seams... When struck with a hammer, it rings like steel."

My American Experience

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From the Empire State Buiding to the carvings on Mount Rushmore, the Golden Gate Bridge, and the Space Needle, the U.S. has dozens of impressive, important, and iconic structures. Which ones have you been to? Which has had the biggest impact?