Why This Highway Runs Through Chicago’s Biggest Hole

Just south of Chicago is a massive rock quarry, so huge that it can be seen from outer space. At a mile and a half across, and nearly 500 feet deep, this is one of the most significant excavations of its kind on earth. And yet the work has unfolded in a densely populated urban region. In fact, a major highway runs directly through the site. Pilots use it as a reference point because of its size and distinctiveness, and if you were to put the Statue of Liberty inside of this hole, the torch would still sit below the rim. Considering that, it's surprising that few people have ever heard of this place. So what's going on here? Why would anyone cut such a cavernous pit so close to one of America's largest cities? Why is there a highway going right through it? And is this whole situation dangerous? Stay tuned to find out as we uncover the history of Chicago's biggest hole. I'm your host Ryan Socash, and you're watching It's History. This story starts well over two centuries ago with the birth of Gordon Hubbard. According to most sources, Hubbard was a relentless New England teenager who hated school, skipped classes, and came from a once comfortable family that had lost its fortune and moved to Montreal in search of stability. Unfortunately, upon their arrival in Canada, it turned out that Gordon's father, breadwinner of the family, was unable to practice law there. And with that realization, the little stability the family had left disappeared almost immediately. With that in mind, Gordon chose not to follow in his father's footstep. Rather, he chased a life of adventure. At the initial opposition of friends and family, he pushed his way into the fur trade, signing on with the American Fur Company in 1818 for a grueling five-year contract at just $120 a year, roughly equivalent to low five-figure earnings today. Even so, anyone from Chicago likely knows that this guy now has a street named after him, so he went on to do amazing things despite such humble beginnings. You see, the decision to take that job sent him into the wild frontier of the Great Lakes, and ultimately, towards the region that became Chicago. Upon arrival, he quickly built connections with other founding figures such as John Kenzie, relationships that would go on to shape both his and the city's future. In the decades that followed, Chicago rose. Hubbard amassed wealth, political power, and enormous tracts of land. And some of this was thanks to his reportedly strong reputation among the Native American population. Allow me to explain. In addition to trading with the natives, he proved to be an ally for a few influential tribes. Reportedly, on one occasion, he walked about 75 miles to the town of Danville to warn a tribe of an incoming raid, which indeed was a gesture of courage. So as those ties grew closer, he was eventually given the nickname Swift Walker and eventually adopted into a tribe. From that point, he married his first wife, a Native American woman, and further built alliances, trade relationships, as well as cultural ties between communities. In the end, these relationships helped him secure several pieces of land, one of those being about 160 acres of Thornton, Illinois. Importantly here, Hubbard attempted to turn that tract of land into a rock quarry. This was a brilliant move in concept, since he saw the writing on the wall. He knew that with westward expansion, Chicago would become a major crossroads of America, and ultimately a global city in its own right, and that throughout the transformation, limestone would play a major role. Unfortunately, however, he was too early. The limestone boom hadn't happened yet, and the type of industrial technology needed to extract rock at the scale he envisioned wasn't perfected. Hence, this Chicago founder moved on to new horizons, yet little did he know that in many ways, Chicago would come to rise from a hole on the land he once possessed. By the 1870s, Hubbard had become so wealthy that he scaled his empire to other industries, and it was around this time that his fate turned a bit more grim. For example, he bought an ownership stake in a steamship that was rammed by a schooner, and sank in 1860 off the coast of present-day Winnetka, Illinois. As an interesting side note, that wreck was rediscovered in 1989, with over 130 artifacts still on board. Beyond that, Hubbard also invested in an insurance company, a venture that couldn't have come at a worse time, since the Chicago fire soon after reduced the city to a pile of rubble, and the resulting claims nearly left him bankrupt. The fire also consumed the only copy of his autobiography, an 800-page manuscript, so many of the details from his later life and the origins of this story were lost forever. In the end, Hubbard's health began to decline in the 1880s, and the accounts of what he went through were grueling. Hence, I can only hope that when he did pass on September 14, 1886, and was laid to rest at Graceland Cemetery, he would be at peace. Although, I don't think that was the case, and I mean this with the utmost respect, considering what an industrial force this founder was, he was probably rolling in his grave about a decade later, as indeed, Chicago's growth exploded, railroads changed everything, and the limestone quarry he once envisioned was finally on the verge of generating the kind of fortune even a king would envy. The real transformation of the quarry began around 1900, when steam-powered equipment and expanding rail connections suddenly made it possible to remove and transport enormous quantities of rock. Up to this point, smaller operations had still been attempting to extract what they could from the area. Enter Colonel Jefferson Hodgkins, with his Brownwell Improvement Company, a major 20th century force in mining, that began buying up the various properties of the surrounding land for consolidation. Chicago, meanwhile, was booming, growing into one of America's most important industrial cities, and it desperately needed limestone for everything. So, between the intense demand and the corporate consolidation, it's safe to say that this is where the operation entered a new era, shifting to industrial production. By the late 1910s, this acquired property turned into a modern powerhouse, further expanding operations, opening new quarry sections, and linking them with underground tunnels to allow the stone to be moved more efficiently across the entire site. This modernization transformed a patchwork of small pits into an industrial operation, setting the stage for the immense scale of extraction that would later come to supply Chicago's booming growth. And it was also around this time that the area's physical characteristics began to change. The Midwest now saw their most prominent rock producer. Though by the time of the Great Depression, construction nationwide slowed, but operations here didn't shut down. Public works projects and infrastructure programs still required aggregate material, keeping limestone demand alive even in hard economic times. And surprisingly, the constraints of the era also forced innovation, helping operators maintain output despite fluctuating markets. By the end of the 1930s, the site itself was already becoming visually striking from above, a geometric industrial scar near what would eventually emerge as a transportation route. Fast forward to World War II, and the site saw another wave of growth. During the 1940s, and then especially in the 1950s, post-war expansion reshaped the Chicago region. Suburbs spread rapidly, and the quarry supplied colossal quantities of crushed stone for that infrastructure. Methods also improved. Modern trucks and powerful blasting operations allowed stone removal on a scale that earlier generations couldn't have even imagined. These factors pushed the quarry even deeper into the bedrock, creating the steep walls that would later surprise drivers. And that brings us to the story of the highway. By the early 1950s, the Chicago region was changing fast. Post-war suburban growth was exploding, car ownership was rising, and planners were racing to build a modern expressway system that would reduce congestion by moving traffic around the city rather than through it. In particular, I-290 was designed as one of those bypass routes connecting Indiana to Chicago's suburbs and then on to Wisconsin. As for the route planners, they favored land that passed through heavily industrialized regions, They saw the quarry as an advantage, as industrial land was cheaper to route through than something like a dense neighborhood. And so the road was paved. But as the 1950s turned into the 60s, demand for crushed limestone surged once again. And somewhat ironically, it was needed for further highway construction. This is when history repeated itself. The pit grew aggressively to meet demand, and eventually approached the now heavily trafficked highway. By the 1970s, with such a rapid pace of digging, the contrast between one of Chicago's most trafficked toll roads and the sheer drop on either side of it became a novelty in its own right. At this point, you might be wondering about the safety of this paradox. Well, as it turns out, nothing unusually dangerous really happens here as far as road traffic is concerned. This is because even back in the 1950s, engineers already knew that the quarry would continue expanding. So safety measures were planned long before the pit reached its modern depth. In other words, the road didn't become dangerous later because it was designed to account for the quarry's growth from the start. With that in mind, by the end of the decade, the two systems of transportation and extraction were now permanently intertwined. Yet a third one, flood control, was about to join the mix. By the 1970s, Chicago was struggling with a major problem that dated back to its origins, flood control. You might remember from some of our previous videos on the topic that much of the region had originally been wet prairie and marshland, especially around the southern suburbs. This is where the problem emerged. As the city grew, the landscapes were just paved over with roads, parking lots, and neighborhoods. Meaning, the water that once soaked into wetlands, now rushed across concrete into sewers, where it found its way into Chicago's old plumbing system. This is where things got worse, since much of the network was what's called a combined sewer system, where stormwater and household waste runs through the same pipes. During heavy storms, those pipes filled up fast. When they overflowed, sewage backed up into basements, polluted natural waterways, and caused flooding. A major storm could overwhelm the city within hours, triggering a public health crisis in the process. So in the early 1970s, repeated floods forced engineers to admit that the old setup could not handle modern urban runoff. But they had a plan. They envisioned an entirely new way to store water during those storms. This brings us to one of the greatest civil engineering projects in American history, the Tunnel and Reservoir Plan, commonly called the Deep Tunnel Project. The idea was bold. Dig enormous tunnels deep underground to hold stormwater and sewage, temporarily preventing any overflows. Chicago acted. Crews began excavating miles of deep tunnels through bedrock, hundreds of feet below the city. You can think of the tunnels themselves as reservoirs. Instead of flooding the streets, excess water would drop into them until a treatment plant could process the load. But although the tunnels helped, they weren't enough. They needed giant storage basins. Enter Thornton Quarry, which was essentially a ready-made reservoir. Rather than digging a new basin, which might have cost billions, they could just repurpose part of the quarry itself. By connecting the quarry to the deep tunnel network, stormwater could be diverted into the enormous limestone pit during extreme rain. You might even say that the quarry functioned like a giant emergency bucket under a leaky roof. As the project developed through the 80s, 90s, and 2000s, Thornton became a key piece of a much wider network. Let me explain to you how it works. First, during heavy rain, combined sewers begin to overload. Then, the excess water is diverted into the deep underground tunnels, where it's carried across several portions of the Chicago region, and as far away as the suburbs. The failsafe happens when the tunnels fill to capacity. Water is sent into the vast reservoir system, places like Thornton. Finally, after the storm, pumps slowly move the water back to treatment plants, where it can be cleaned and then safely released. Tunnels stretch for dozens of miles, linking communities across Cook County and beyond, and they're a major pressure relief valve for the entire metro area. The result of this was so successful, that in the early 2000s, engineers expanded Thornton's role even further. These staggering construction projects carved additional sections and installed control structures, turning part of the complex into one of the largest storm reservoirs in the world. By 2015, Thornton Reservoir officially came online as a major component of the Deep Tunnel Project, and its scale is awe-inspiring. It's capable of holding over 7 billion gallons of water in an area big enough to fit six soldier fields. Now, it's here that we need to address an obvious question. If billions of gallons of stormwater, sewage, are stored here, why doesn't the entire area smell like a sewer? The answer is in the engineering. Remember, the reservoir isn't holding the sewage here indefinitely. It acts as a temporary holding basin during major storms, capturing overflow that would otherwise flood into streets and basements. Furthermore, much of what does end up here is highly diluted. Even so, parts of the reservoir use aeration and mixing methods to keep the water oxygenated and moving. The goal is to prevent stagnation, reduce odor, and improve the water quality to the extent possible before it's pumped back out to the treatment center. And thus, this once-industrial pit has proven its value, helping first to build Chicago itself, but then to protect it from its own waste. It should also be noted here that in its unfolding, some astonishing facts about Earth's history have been uncovered. For example, around 440 million years ago, this entire region sat near the equator and was covered by a warm, shallow, tropical sea. That's right. What's now a Chicago suburb was once a thriving coral reef ecosystem filled with ancient marine life, including a giant ancient relative, squid. A creature that was estimated to reach between 10 and 15 feet long. This torpedo-shaped shell crusher hunted the tropical sea, using its tentacles to grab prey and a powerful beak to then crush those it captured. So, I don't know about you, but as someone who grew up in Chicago myself, I have to admit I was rather shocked to learn that the land under a place I once called home was a tropical ocean. Especially since, you know, let's face it, Chicago is about as close to the opposite of that environment as you can get. Finally, scientists also discovered something here that literally came from outer space. In the 1990s, researchers identified evidence of an ancient impact structure. The object itself likely formed over 4 billion years ago before breaking off from its source and eventually colliding with Earth. That impact happened roughly 430 million years ago when the region was still a tropical sea. The strike blasted out a crater beneath the water, disrupting the reef environment and scattering debris across the seafloor. So, that's all to say that this land has always been interesting, far before the highway ever crossed this Grand Canyon-like scar. From a meteorite strike to wastewater management, that is the story of Chicago's biggest hole. I really hope you liked the show, and if you want more episodes like this one, please let me know by hitting that subscribe button. Otherwise, until next time, Brian Socash, signing off.