It’s ironic that the Flatirons were both formed by uplifting, and are in fact uplifting.

Symbol of Boulder, The Famous Flatirons.

We say it at least once a day. We blog about it, paint it, and it is part of our visual daily existence. But WHAT ARE THEY? What are the Flatirons?

The Boulder Flatirons are a series of striking, slanted, red sandstone formations located on the western edge of Boulder, Colorado. Towering over the city and the University of Colorado campus, these iconic landmarks are part of the Front Range of the Rocky Mountains and serve as a majestic backdrop that defines the city’s landscape. The name “Flatirons” was given due to their resemblance to flat, metal irons used for pressing clothes.

Geologically, the Flatirons were formed about 290 to 296 million years ago during the Paleozoic Era. The process of uplift and erosion that shaped these formations began around 300 million years ago when the ancestral Rocky Mountains were formed. Over millions of years, layers of sediment were deposited and then uplifted. This uplift, combined with the forces of erosion, sculpted the Flatirons into their present form. The tilted appearance of the Flatirons is the result of the uplift of the Rocky Mountains, where the once-horizontal layers of sedimentary rock were pushed upwards, creating the dramatic angles seen today.

The Flatirons are not only a symbol of Boulder but also a popular destination for hikers, rock climbers, and nature enthusiasts drawn by the area’s natural beauty, diverse ecosystems, and panoramic views. These formations capture the geological history of the region, standing as a testament to the Earth’s dynamic processes.

The Flatirons never look the same. No matter how many decades I’ve been watching them, they are constantly changing, and the show does not repeat!

Lenny Lensworth Frieling

Shared Knowledge is Power!

  • Senior Counsel Emeritus to the Boulder Law firm Dolan + Zimmerman LLP : (720)-610-0951
  • Former Judge
  • Photographer of the Year, AboutBoulder 2023
  • First Chair and Originator of the Colorado Bar Association’s Cannabis Law Committee, a National first.
  • Previous Chair, Boulder Criminal Defense Bar (8 years)
  • Twice chair Executive Counsel, Colorado Bar Association Criminal Law Section
  • NORML Distinguished Counsel Circle
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  • Life Member, Colorado Criminal Defense Bar
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  • Chair, Colorado NORML, 7 years including during the successful effort to legalize recreational pot in Colorado
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