Ocean tides flow through the Golden Gate four times a day -- twice coming in and twice going out. The quantity of salt water in motion between high and low tides averages 390 billion gallons.
Water depth at the Golden Gate is more than 300 feet, but San Francisco Bay waters are, on average, just 14 feet deep.
Thousands of animal species, including over 130 species of fish, call the bay home. Four distinct runs of Chinook salmon migrate through the bay on their way to spawn upstream.
San Francisco Bay is a drowned valley. At the end of the most recent Ice Age, 10,000 years ago, melting ice caused rising ocean levels. Water crept steadily through the Golden Gate and flooded the land beyond.
In October 1933, Civilian Convervation Corps workers arrived at Muir Woods National Monument, a protected old-growth redwood forest on the Marin headlands. They built revetments, bridges, buildings, benches, and an amphitheater -- anticipating a surge of new visitors to the majestic forest after the bridge opened.
In August 1933, a Portland-bound ship, the Sidney M. Hauptman, veered off course in a dense fog and crashed into a construction trestle, setting back the project by about a month.
"Hello -- Phone Service to Davy Jones' Locker," read a December 1934 headline in the San Francisco News. The accompanying photo showed bridge builders 107 feet down in an inspection well, calling to the surface to make their report.
Worker Albert "Frenchy" Gales was atop the unfinished south tower at the time of a June 1935 earthquake. He remembered, "the tower swayed 16 feet each way. There were 12 or 13 guys on top with no way to get down... The whole thing would sway toward the ocean, guys would say, 'here we go!' Then it would sway back toward the bay."
Days after a tragic accident that killed ten workers, searchers recovered the giant safety net that had also fallen from the bridge. Tides had carried it a mile out into the Pacific Ocean, and 500 feet beneath the surface. They found tangled in it the body of one of the victims, a carpenter named Arthur Anderson.
The bridge's original, two-tone fog horns functioned for almost half a century. In 1985, bridge officials replaced them with new air horns that only sound single tones.
The two main cables of the bridge weigh 11,000 tons apiece, and each main cable contains 25,572 separate wires.
The amount of concrete used on the bridge would be sufficient to build two 10-foot-wide sidewalks from Chicago to Omaha.
The initial car toll in 1937 was 50 cents (a whopping $6.25 in 2002 dollars). By 2004, the car toll had risen to $5.00, or $4.00 with an electronic transponder -- but tolls are only collected from vehicles heading south into San Francisco.
The month of December has historically brought the most dangerous winds. Officials have closed the bridge only three times due to wind, in the Decembers of 1951 (69 mph winds), 1982 (70 mph winds), and 1983 (75 mph winds). None of the gusts caused structural damage.
Engineered by William Barclay Parsons, the 21-mile, four-track route of the New York City Subway was the largest public works project in history.
Equipment failure, human error and bad luck led to the country's worst nuclear accident in 1979.
The Alaskan Highway stands today as one of the boldest homeland security initiatives ever undertaken.
The story of the polio crusade pays tribute to a time when Americans banded together to conquer a terrible disease.
Begun during the Civil War, the transcontinental railroad employed 20,000 men, mostly immigrants, who built the iron road with their bare hands.
The unusual life of David Vetter, who lived permanently inside a germ-free environment due to severe combined immunodeficiency.
The international race to develop biological weapons during the 20th century.
The contradictory history of a dam that became a statement of American power and prestige.