What Lies Beneath: Underground Secrets of San Francisco's Greatest Structures
The iconic Bay Bridge and the Golden Gate Bridge, two of San Francisco's most recognizable landmarks, tower majestically over the city and its busy waterways. However, what lies beneath these imposing structures is just as fascinating. In this article, we'll explore the hidden depths under the pylons of both bridges, uncovering surprising details about their foundations.
Under the Pylons: Bay Bridge and Golden Gate Bridge
Visitors to San Francisco often marvel at the towering pylons of the Bay Bridge and the Golden Gate Bridge. These magnificent structures not only serve as symbols of architectural achievement but also of the engineering prowess of their designers and builders. However, beneath these towering towers, there is a hidden world that is seldom talked about, and it is not always what one might expect.
The Bay Bridge's Foundation
The Bay Bridge, officially known as the San Francisco-Oakland Bay Bridge, consists of two main bridge spans along with a total of 54 east and west side spans. The largest section is the replacement eastern span, which is actually a suspension bridge supported by two massive main towers. However, what is usually overlooked is the foundation of these towers.
Under the pylons of the Bay Bridge, you will find bed rock in all cases, with one notable exception. The bedrock is the stable base that supports the towers, providing them with the necessary stability to withstand the strong winds and seismic forces that come with their location over the San Francisco Bay and the surrounding area.
Exception to the Rule: Mud and Pilings
However, it's different east of Yerba Buena Island. Here, the pylons are built on pilings driven into very old mud. This mud layer is a much softer and less stable foundation compared to the bedrock. The reason for this difference can be attributed to the fact that the east part of the Bay Bridge was not originally designed as a suspension bridge. Due to the softer base and the potential for sinking, the builders had to use a different approach to secure the pylons.
A Faunal DiscoveryInterestingly, there is an old story that adds a unique twist to this geological discovery. During the excavation work, workers reportedly found bones of Woolly Mammoths. These bones, while not directly linked to the current foundations, provide a chilling reminder of San Francisco's prehistoric past. The discovery suggests that the San Francisco Bay area was once home to these massive creatures, now long extinct. While the bones themselves cannot be seen by the public, the story reminds us that even in the modern city, there are remnants of a much more ancient world beneath our feet.
The Golden Gate Bridge's Foundation
Perhaps the most iconic span in San Francisco is the Golden Gate Bridge. Built from 1933 to 1937, the Golden Gate Bridge not only stands as a testament to the artful engineering of Joseph Strauss, but also as a bridge through time. One might assume that the pylons and supports of the Golden Gate Bridge share a similar foundation with the Bay Bridge. However, the reality is often more intriguing.
Under the pylons of the Golden Gate Bridge, just like the Bay Bridge, you will find the bedrock supporting the towers. This bedrock is not only a solid foundation but also a symbol of the bridge's strength and resilience. The pylons stand tall and proud, and the bedrock beneath them serves as a reminder of the geological stability of the land.
The Role of Engineering
The engineering of these bridges is a marvel to behold. The builders had to account for not just the existing bedrock but also the movement of the earth due to tectonic activity. The foundations of both bridges are designed to withstand the forces of nature and ensure that they remain safe and functional for generations to come.
Visiting the Foundations
While the foundations themselves are not open to the public, visitors can still experience the grandeur of these structures from above. The San Francisco-Oakland Bay Bridge offers guided tours that take visitors across the towers and through the channels of the bridge. Similarly, guided tours of the Golden Gate Bridge are available, allowing visitors to appreciate the engineering and beauty of the bridge even more.
Conclusion
From impressive aerial views to the intriguing geological secrets beneath the pylons, the Bay Bridge and the Golden Gate Bridge are more than just symbols of San Francisco. They are a testament to human ingenuity and a reminder of the natural forces that shape our world. Whether you're marveling at them from afar or exploring their hidden depths, there's always something new to discover about these iconic bridges.