Thornton Quarry, I-80’s Grand Canyon, an economic


THORNTON — Today, neighborhood kids frequent Walter Diekelman Park to clamber around the playground and rocket down the slide.

Families picnic under the shelter in the leafy patch of green in the south suburban village of Thornton. 

In the 1830s, the land speculator Gurdon Saltonstall Hubbard, who helped drive Chicago’s growth in the 19th century, dug Thornton’s first quarry on Kinzie Street at the site of what’s now Walter Diekelman Park. He found the stone was of too poor quality to be commercially mined, so he covered it up and the village eventually turned it into a public park.

It’s believed that many vintage cars were buried underneath as fill.

Stories abound about the Thornton Quarry, which has been dubbed the Midwest’s Grand Canyon and which thousands drive over daily as Interstate 80 spans the great gash that stretches 1.5 miles wide and cuts 450 feet deep into the earth. There’s a tale about a tour group that went down and loaded up the bus with so many prehistoric fossils that the tires blew and it had to be towed out.

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The Thornton Historical Society hosts twice-annual tours of the second-largest aggregate quarry in the world, which was once the largest. They sell punny T-shirts proclaiming that the “Thornton Quarry Rocks” and “Find the largest quarry in the USA and drop in.”

Busfulls of gawking sightseers recently descended again into the vast Thornton Quarry, which was originally dug at the current site in 1850. It was initially nine different quarries in the late 19th century that were combined into one huge quarry in 1890. Today, it’s partly used as a stormwater overflow reservoir and continues to be mined by Heidelberg Materials.

Video provided in partnership with The Times, JEDtv and WJOB. Sponsored by Strack & Van Til.

The German-based multinational Heidelberg Materials bought Lehigh Hanson in 2007, just a year after it acquired longtime quarry operator Material Services. After letting the subsidiary maintain a distinct identity for more than a decade, the parent company just rebranded Irving, Texas-based Lehigh Hanson as Heidelberg Materials earlier this year. It’s the largest aggregate producer in the world and the third largest by market share in North America.

“This is a major step change for our company, both globally and here in North America,” President and CEO Chris Ward said.

Visitors often joke about The Flintstones, but the Thornton Quarry is a lot older than that. It dates back 425 million years, 200 million years before dinosaurs walked the earth. It was covered by a warm tropical sea during the Silurian Period. Coral, crinoids, trilobites, sea lilies and other sea creatures proliferated in the Thornton Reef that rose from the shallow Silurian Sea that spanned Illinois and Wisconsin.

Cephalopods, horn corals and other fossils embedded in the rock walls in Thornton Quarry date back more than 400 million years.

The sea eventually dried up, glaciers carpeted the land, prairies took hold when it finally dethawed and the coral reef was buried deep under the surface. When it was first quarried, the stone was lifted by hand and put into carts pulled by mules. Geologists and petroleum engineers long studied the gigantic hole in the ground as it was believed to be the only place in the world where an ancient coral reef was laid bare.

The Thornton Quarry now gives six to 10 tours a year, mostly of student groups who are allowed to take home fossils from the ancient coral reef.

Miners have long blasted stone off the wall, which truckers haul to the crusher and then hundreds of feet back up to the surface. All the roads in the hot, chalky canyon are sprayed with a chemical dust depressor so clouds don’t rage into a giant dustbowl.

The trucks that rumble through Thornton Quarry haul loads of up to 85 tons of rock used to build everything from houses to infrastructure. The tires stand more than 6 feet tall, the cabs are only accessible by stairs and they’re so enormous that drivers could crush a Ford F-150 without even noticing.

It’s intensely hot down in the quarry, where dry heat radiates mercilessly off the imposing limestone walls.

The quarry produces more than 30 different products, including concrete for construction companies like Ozinga and Rieth-Riley and riprap that protects the Lake Michigan shoreline in Northwest Indiana from erosion. The stone has helped skyscrapers soar to the heavens, bridges span vast rivers and highways crisscross the country. The paving contractor Gallagher Asphalt Corporation uses so much stone from Thornton Quarry it has an operation right on site.

The rock that comes out of the quarry can be sold for anywhere from an average price of $7 a ton to more than $30 a ton, said Bob Russell, who’s in charge of sales at the Thornton Quarry and led one of the Thornton Historical Society’s tours.

“We’ve had some inventory issues this year because of the light winter,” he said.

“Some of the piles aren’t as big,” he said. “We’re in panic mode because they need to grow.”

Thornton Quarry likely has about 200 more years of reserves left, Russell said. The quarry is producing 3.5 million to 4.1 million tons of stone a year. This year, it’s likely to produce 4.2 million tons of stone.

Competitors include US Aggregate and South Lake Stone in Lowell.

“We’ve got competitors all around,” he said.

More than three miles of conveyor belts run through the plant as the stone is moved through eight different crushers on different streams that crush the stone down for different end products like road base and limestone. 

Products that require more processing like manufactured sand and bridge deck cost more. 

“If you go in there, you have to wear earplugs,” he said. “If you don’t you will go deaf. It’s very, very loud.”

Piles of stone are dumped on top of crushers.

“Underground, there’s a crusher underneath. You’ll see that pile being sucked so it looks like a volcano where the edges are high and the center is low,” he said. “That looks like a big pile but it should be at least twice the size. Our main crusher was down three weeks and we lost 81,000 tons of production.”

It looks tiny from Interstate 80-294, where cars and semis whiz by 400 feet overhead, but the main crusher stands four stories high. 

“It’s big. The mill is more than 100 years old. But processes are evolving all the time,” he said.

The Thornton Quarry washes many of its finished products. The water runs into a sediment pond that reflects the towering and rough-hewn limestone walls. 

“You throw anything in there and you will never see it again,” he said. “There is so much sediment at the bottom it will sink an additional 10 to 15 feet when it reaches the bottom. The water’s not thick but the sediment below is.”

Thornton Quarry uses explosive chemicals to blow chunks off the walls three times a week: typically Mondays, Wednesdays and Fridays. Back when the quarry used dynamite, the explosions would rattle the surrounding village.

Now neighbors close by can only feel the blasts if know when to expect them.

“With all the heavy traffic in the Thornton area, it’s harder to feel,” he said.

It’s actually a few different quarries, connected by massive arched tunnels that make a school bus look as big as a Hot Wheels toy. The main quarry is where they do the crushing, the west quarry the blasting and the north quarry the wastewater retention. A water truck drives around nonstop spraying the roads to suppress dust. Trucks leaving have to pass by a washing station that rinses the tires so they don’t track mud, dirt or dust onto public streets.

The Thornton Quarry set production records during the coronavirus pandemic, which did not disrupt its operations. It’s stayed busy.

“We open at 4:30 a.m. in the morning. There could be 50 to 75 trucks waiting to move piles,” he said. “It is a huge rush. There’s 20 tons to 22 tons on a truck. We ship out 25,000 tons a day.”

Heidelberg Materials employs about 100 people at the site. Teenagers who occasionally sneak in are offered jobs as it’s sometimes challenging to recruit new truck drivers to keep moving stone at a time when more parents push their kids to college.

“A lot of the people who work here are of the older generation,” he said. “A lot worked here for 30 years, 20 years or a long time. They got a job after high school and stay here until they retire. They love it.”

They have a close-knit camaraderie.

“When you do a job for all intents and purposes people have died doing, you take it a little more seriously and value that person working next to you,” he said.

Thornton Quarry operates 24 hours a day, with two 12-hour shifts. 

“We crush stone 20 hours a day,” he said. “Depending on the product, we crush 800 to 900 stones an hour. In the past, it was a more volume-driven business but we’ve kind of taken a different direction and been more price-conscious over the last year and a half.”

While there are 200 years of rock left on the surface, the quarry could always keep digging further down.

“In 200 years, I assume they’re going to go underground because I assume there’s better rock 75 to 100 feet down,” he said. “This quarry’s going to be here for a long time.”

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