This is Throwback Thursday #310. In these, we look back into the past at ESCONI specifically and Earth Science in general. If you have any contributions, (science, pictures, stories, etc …), please send them to  esconi.info@gmail.com. Thanks!  email:esconi.info@gmail.com.

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Ran across this interesting episode of “It’s History” on Youtube…. “Why This Highway Runs Through Chicago’s Biggest Hole”. It’s about the Thornton Quarry and one of the founders of Chicago, Gurdon Saltonstall Hubbard, who is the namesake of Hubbard Street in Chicago.

Just south of Chicago sits a limestone quarry so massive it can be seen from space. Nearly 500 feet deep and over a mile wide, the Thornton Quarry is one of the largest excavations on Earth — and incredibly, a major highway runs directly through it. Drivers on I-294 pass sheer rock walls that drop hundreds of feet, while pilots use it as a visual landmark. But this giant pit isn’t just an industrial scar — it’s one of the most important engineering sites in America.

In this episode, we trace the story from Chicago founder Gurdon Saltonstall Hubbard’s early land speculation to the rise of industrial limestone mining, the construction of the Tri-State Tollway, and the creation of the Deep Tunnel Project. You’ll discover how this former quarry became a key part of Chicago’s flood control system, capable of holding billions of gallons of stormwater — and why its history stretches back 440 million years to a tropical sea and even a meteorite impact.