The Boulder Flatirons

January 22, 2001


Provided by: Martin Ruzek, USRA
Summary authors & editors: Martin Ruzek

Boulder, Colorado is situated on the eastern front of the Rocky Mountains in the shadow of this spectacular outcrop known as the Flatirons. These rocks, part of the Fountain Formation, were laid down as coarse pink feldspar-rich sands that eroded from the Ancestral Rockies nearly 300 million years ago. Buried for eons under ocean sediments and desert dunes, the Fountain Formation was tilted steeply and thrust to the surface about 45 million years ago by processes which raised the current Rocky Mountains. Subsequent erosion sculpted this unique natural monument in Boulder's backyard.

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