Chicago Residents to Name Prehistoric O'Hare Boulder
The 50-ton dolostone formation unearthed at O'Hare Airport is now subject to a public naming contest.
Updated on Oct. 16, 2026 in Geology
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Chicago officials have selected six finalists for a naming contest involving a 50-ton dolostone boulder unearthed at O'Hare Airport. The public can vote on the final name until November 2, 2026.
Why it matters
The boulder provides a visible connection to the region's geological history, dating back 400 million years to the Silurian period. Its display at the O'Hare Multi-Modal Facility offers a rare opportunity for the public to engage with bedrock typically obscured by urban infrastructure.
The dolostone specimen measures 11.5 feet wide, 8 feet deep, and 7.5 feet tall, weighing 50 tons. It was recovered from a depth of 30 feet below the airfield surface during an expansion project.
The players
O'Hare Airport
A major international aviation hub in Chicago that oversees infrastructure expansion and site management.
The details
Dolostone is a sedimentary carbonate rock similar to limestone, composed primarily of the mineral dolomite. This specific specimen formed during the Silurian period, a time when the area now occupied by Chicago was covered by a shallow tropical sea. The boulder was moved to the surface by an excavator operator during airport construction in June.
Timeline
400 million years ago: The boulder formed during the Silurian period.
June 2026: The boulder was discovered during airport construction.
November 2, 2026: Public voting for the naming contest closes.
The Tech Race
This contest aligns with a broader municipal trend of leveraging public interest to humanize industrial infrastructure projects. It echoes past community engagement efforts in Chicago that sought to turn utilitarian city structures into recognizable local landmarks.
Residents can participate in the naming process through an online ballot open to the public. The winning name will eventually be featured as part of an official exhibit at the boulder's current location at 10255 W. Zemke Road.
The takeaway
This boulder serves as a massive, tangible artifact of the deep-time processes that shaped the Chicago basin. Readers should watch O'Hare social media channels for the announcement of the winning name following the November 2, 2026, closing of the polls.
Further reading
For more on the regional geological formations, visit Geology.
Source note: This article includes information reported by WTTW News.
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