The Flatirons are rock formations near Boulder, Colorado. There are five large, "numbered" Flatirons ranging from north to south (First through Fifth, respectively) along the east slope of Green Mountain, and the term "The Flatirons" sometimes refers to these five alone. Numerous additional "named" Flatirons are on the southern part of Green Mountain, Bear Peak, and among the surrounding foothills.

The Flatirons were named by pioneer women after the flat, metal irons used to press their clothes.


The Flatirons consist of conglomerate sandstone of the Fountain Formation. Geologists estimate the age of these rocks as 290-296 million years; they were lifted and tilted into their present orientation between 35 and 80 million years ago, during the Laramide Orogeny. The Flatirons were subsequently exposed by erosion. Other manifestations of the Fountain Formation can be found in many places along the Colorado Front Range, including Garden of the Gods near Colorado Springs, Roxborough State Park in Douglas County, and Red Rocks Amphitheatre near Morrison.


The Flatirons on Green Mountain are within the City of Boulder Mountain Parks. They are popular destinations for hikers and rock climbers, with rock grades ranging from easy (5.0) to world-class (5.14).

Graffiti on the Third Flatiron

On several occasions during the 1940s, 1950s and 1960s, students from the University of Colorado climbed the Third Flatiron on Green Mountain and wrote "CU" in giant white letters on it. On at least two occasions timed to coincide with athletic contests, students from rival schools modified the white letters to advertise a different institution: "DU" (University of Denver) and "OU" (University of Oklahoma). Each time, the Colorado students changed the letters back to "CU". In the 1970s, the City of Boulder painted over the illegal graffiti with a color very similar to the rock. Because the color match is not perfect, the disfiguring marks can be seen if examined closely.

A symbol of Boulder

Images of the numbered Flatirons on Green Mountain are a ubiquitous symbol of the city of Boulder. The area abounds with Flatirons photographs, drawings, paintings, and sculptures. The city government, the University of Colorado, and many businesses make use of this symbol. Many businesses also use the word "Flatirons" or "Flatiron" in their names.


* [http://www.summitpost.org/mountain/rock/154925/flatiron-rock-routes.html Climbing according to summitPost.org]
* [http://www.gravmag.com/fountain.html Geology]

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