Since 2002, portions of the quarry have been used as a reservoir that's part of the Chicago Deep Tunnel, a public-works program commissioned in the 1970s and not scheduled to be completed until sometime later this decade. At its current depth, the quarry is revealing 450 million year old coral, yielding fossils of Silurian Age crustacean, squid, and octopus. In 1994, a 4.5 billion year old meteorite was uncovered that weighed nearly 1,000 lbs.
Truck drivers have a knack for giving clever names to the things they see on the road. These names are often colorful, and not always politically correct. For instance, a burning vehicle is a road-side barbecue. An ambulance is a meat wagon or a band-aid buggy. San Francisco is "Gay Bay" and some of the old timers still call Chicago "The Mistake on the Lake". That seems to be the protocol in trucker slang when it comes to naming geographical locations, usually it's something distinctive about the city. Chicago is famous for its Polish population, boasting the largest in the country.
Which is what lead to the Thornton Quarry receiving its trucker name, "The Polish Grand Canyon".
The first Polish joke I learned (after the light bulb joke) was about a Polish man sitting on a hillside watching his house burn to the ground, just laughing his head off. A neighbor came up and asked, "Why are you laughing? Your house has been completely destroyed!" After catching his breath, the Pole responded, "I've got enough lumber in the attic to build another."
Two Polish truck drivers are barreling along when they come up to an overpass. A sign says, "Clearance: 11"2'." So they get out, measure their truck, and realize that it's 11"6'. So the first man looks at his friend and says, "I don't see any police around... let's go for it!"
I've just always like the Polish Grand Canyon thing, 'cause it's kinda like the punchline to a Polish joke with a setup that needs to be seen and not heard.