Flatirons, Rock formations in Boulder County, United States.
The Flatirons are five massive sandstone slabs positioned on the eastern side of Green Mountain, rising steeply from the foothills. These rock formations sit parallel to each other and create a distinctive jagged profile that dominates the view above Boulder.
These rock formations developed roughly 300 million years ago from layers of sedimentary material that accumulated on an ancient seabed. When the Rocky Mountains formed, these layers were tilted at a steep angle, creating the angled slabs we see today.
The name "Flatirons" came from early 1900s residents who noticed how these rock slabs resembled the flat irons that pioneer women used for pressing clothes. This name has stayed with the formations and shapes how people talk about the place.
Multiple hiking trails of different difficulty levels start from the Chautauqua Trailhead, offering access to various vantage points of these rock formations. Bring plenty of water and wear sturdy footwear, as the trails can be rocky and slippery when conditions are wet.
University of Colorado students painted the letters "CU" on the Third Flatiron back in 1949, and the marking remains visible on the rock surface today. This bit of campus tradition has become an enduring feature of the formation.
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