Milestones Icon: The Flatirons

The jagged peaks run rampant on business cards, company signs and advertisements. They’re among the first things people notice when coming to Boulder and among the last things they see when leaving.

The Flatirons are Boulder.

Athletic clubs, car dealerships, banks, streets and malls are even named after the famous rock peaks.

While there are more, when people refer to the Flatirons they’re typically thinking about the five largest peaks numbered from north to south.

If a visitor wants to experience a Boulder hike – head to the Flatirons. If a climber wants a Boulder route – head to the Flatirons. If a photographer wants to capture a Boulder image – head to the Flatirons.

The conglomerate formation at Boulder’s edge of the Rocky Mountains was formed when river deposits were dropped there and continued to build up over time.

Said to be named after the metal irons pioneer women used to press their clothes, the tallest Flatiron (the “First Flatiron”) reaches to about 7,200 feet above sea level, according to Boulder Open Space and Mountain Parks.

The Flatirons are part of the Fountain Formation, which is the same formation to which the Garden of the Gods belongs, and likely formed between 280 million and 300 million years ago during the Paleozoic period.

Back then, the Boulder symbol was actually flat. It wasn’t until the Rocky Mountains formed – causing the flat-laying sediment of sand and pebbles to fold and push upwards – that the Flatirons became angled.

Eventually, erosion dominated the weaker rock and left the Flatirons tilting upwards at a roughly 80-degree angle.

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